# Coming talks

## Historique de Main.GT

18 mars 2018 à 21h00 par 93.6.71.19 -
Lignes 19-25 modifiées:
en:

Lundi 23 avril 2018 : Whac-A-Mole: Smart node positioning in clone attack in wireless sensor networks Akka Zemmari
Résumé : Wireless sensor networks are often deployed in unattended environments and, thus, an adversary can physically capture some of the sensors, build clones with the same identity as the captured sensors, and place these clones at strategic positions in the network for further malicious activities. Such attacks, called clone attacks, are a very serious threat against the usefulness of wireless networks. Researchers proposed different techniques to detect such attacks. The most promising detection techniques are the distributed ones that scale for large networks and distribute the task of detecting the presence of clones among all sensors, thus, making it hard for a smart attacker to position the clones in such a way as to disrupt the detection process. However, even when the distributed algorithms work normally, their ability to discover an attack may vary greatly with the position of the clones. We believe this aspect has been greatly underestimated in the literature. In this paper, we present a thorough and novel study of the relation between the position of clones and the probability that the clones are detected. To the best of our knowledge, this is the first such study. In particular, we consider four algorithms that are re- presentatives of the distributed approach. We evaluate for them whether their capability of detecting clone attacks is influenced by the positions of the clones. Since wireless sensor networks may be deployed in different situations, our study considers several possible scenarios: a uniform scenario in which the sensors are deployed uniformly, and also not uniform scenarios, in which there are one or more large areas with no sensor (we call such areas “holes”) that force communications to flow around these areas. We show that the different scenarios greatly influence the performance of the algorithms. For instance, we show that, when holes are present, there are some clone positions that make the attacks much harder to be detected. We believe that our work is key to better understand the actual security risk of the clone attack in the presence of a smart adversary and also with respect to different deployment scenarios. Moreover, our work suggests, for the different scenarios, effective clone detection solutions even when a smart adversary is part of the game.

08 mars 2018 à 01h55 par 87.231.50.68 -
Ligne 33 modifiée:

Lundi 12 mars 2018 : TBA Akka Zemmari \\

en:

Lundi 12 mars 2018 : TBA Akka Zemmari REPORTÉ \\

08 mars 2018 à 01h52 par 87.231.50.68 -
Lignes 23-25 modifiées:

Lundi 26 mars 2018 : Distributed coloring with fewer colors Marthe Bonamy
Résumé :

en:

Lundi 26 mars 2018 : Distributed coloring in sparse graphs with fewer colors Marthe Bonamy
Résumé : We are concerned with efficiently coloring sparse graphs in the distributed setting with as few colors as possible. According to the celebrated Four Color Theorem, planar graphs can be colored with at most 4 colors, and the proof gives a (sequential) quadratic algorithm finding such a coloring. A natural problem is to improve this complexity in the distributed setting. Using the fact that planar graphs contain linearly many vertices of degree at most 6, Goldberg, Plotkin, and Shannon obtained a deterministic distributed algorithm coloring n-vertex planar graphs with 7 colors in O(logn) rounds. Here, we show how to color planar graphs with 6 colors in polylog(n) rounds. Our algorithm indeed works more generally in the list-coloring setting and for sparse graphs (for such graphs we improve by at least one the number of colors resulting from an efficient algorithm of Barenboim and Elkin, at the expense of a slightly worst complexity). Our bounds on the number of colors turn out to be quite sharp in general. Among other results, we show that no distributed algorithm can color every n-vertex planar graph with 4 colors in o(n) rounds. This is joint work with Pierre Aboulker, Nicolas Bousquet and Louis Esperet.

25 février 2018 à 23h04 par 87.231.50.68 -
Ligne 65 modifiée:

Lundi 26 février 2018 : TBA Nicolas Hanusse \\

en:

Lundi 26 février 2018 : TBA Nicolas Hanusse REPORTÉ \\

19 février 2018 à 18h11 par 92.136.92.43 -
Lignes 43-65 modifiées:

Self-stabilization is a property that allows distributed algorithms

    to withstand transient faults and recover a correct behavior within
finite time. It has been introduced by Dijkstra in 1974. Over the
last decades, progress in self-stabilization has led to consider
more and more adversarial environments. This make the design, proof
for correctness and complexity analysis of self-stabilizing
solutions more and more intricate.

However, those proofs are commonly written by hand, based on
informal reasoning. In this work, we propose instead to use a proof
assistant, a tool which allows to develop certified proofs
interactively and check them mechanically. We present the PADEC
framework, a Coq library dedicated to building certified proofs of
self-stabilizing algorithms.

We first define in Coq the computational model which is the most
commonly used in the self-stabilizing area, and its semantics. We
propose several tools for proving convergence of algorithms and for
counting elements.  We illustrate the use of our framework by:
- certifying a non-trivial part of an existing self-stabilizing
algorithm;
- certifying a commonly-used composition operation for
self-stabilizing algorithms.

en:

Self-stabilization is a property that allows distributed algorithms to withstand transient faults and recover a correct behavior within finite time. It has been introduced by Dijkstra in 1974. Over the last decades, progress in self-stabilization has led to consider more and more adversarial environments. This make the design, proof for correctness and complexity analysis of self-stabilizing solutions more and more intricate.

However, those proofs are commonly written by hand, based on informal reasoning. In this work, we propose instead to use a proof assistant, a tool which allows to develop certified proofs interactively and check them mechanically. We present the PADEC framework, a Coq library dedicated to building certified proofs of self-stabilizing algorithms.

We first define in Coq the computational model which is the most commonly used in the self-stabilizing area, and its semantics. We propose several tools for proving convergence of algorithms and for counting elements. We illustrate the use of our framework by: - certifying a non-trivial part of an existing self-stabilizing algorithm; - certifying a commonly-used composition operation for self-stabilizing algorithms.

19 février 2018 à 17h40 par 92.136.92.43 -
19 février 2018 à 17h40 par 92.136.92.43 -
Lignes 38-40 modifiées:

Lundi 5 mars 2018 : ' PADEC: A Framework for Certified Self-Stabilization ' Karine Altisen, Verimag

en:

Lundi 5 mars 2018 : ' PADEC: A Framework for Certified Self-Stabilization ' Karine Altisen, Verimag

Lignes 43-44 modifiées:
    Self-stabilization is a property that allows distributed algorithms

en:

Self-stabilization is a property that allows distributed algorithms

19 février 2018 à 17h35 par 92.136.92.43 -
Lignes 38-40 modifiées:

Lundi 5 mars 2018 : TBA Karine Altisen, Verimag
Résumé :

en:

Lundi 5 mars 2018 : ' PADEC: A Framework for Certified Self-Stabilization ' Karine Altisen, Verimag
Résumé : Joint work with Pierre Corbineau and Stéphane Devismes

    Self-stabilization is a property that allows distributed algorithms
to withstand transient faults and recover a correct behavior within
finite time. It has been introduced by Dijkstra in 1974. Over the
last decades, progress in self-stabilization has led to consider
more and more adversarial environments. This make the design, proof
for correctness and complexity analysis of self-stabilizing
solutions more and more intricate.

However, those proofs are commonly written by hand, based on
informal reasoning. In this work, we propose instead to use a proof
assistant, a tool which allows to develop certified proofs
interactively and check them mechanically. We present the PADEC
framework, a Coq library dedicated to building certified proofs of
self-stabilizing algorithms.

We first define in Coq the computational model which is the most
commonly used in the self-stabilizing area, and its semantics. We
propose several tools for proving convergence of algorithms and for
counting elements.  We illustrate the use of our framework by:
- certifying a non-trivial part of an existing self-stabilizing
algorithm;
- certifying a commonly-used composition operation for
self-stabilizing algorithms.

12 février 2018 à 09h32 par 147.210.204.186 -
Lignes 6-7 ajoutées:

Pour s'inscrire à la liste de diffusion, envoyer un courrier électronique à sympa@diff.u-bordeaux.fr avec comme sujet "subscribe labri.algodist-gt votre_nom votre_prénom". Pour se désabonner, il suffit d'envoyer à sympa@diff.u-bordeaux.fr un message dont le sujet est "unsubscribe labri.algodist-gt"

Ligne 14 modifiée:
en:

To unsubscribe, send email to sympa@diff.u-bordeaux.fr with subject "unsubscribe labri.algodist-gt".

12 février 2018 à 09h25 par 147.210.204.186 -
Lignes 10-13 ajoutées:

To subscribe to the mailing list, send an email to sympa@diff.u-bordeaux.fr with subject "subscribe labri.algodist-gt your_name your_surname".

24 janvier 2018 à 16h44 par 147.210.204.186 -
Lignes 28-32 ajoutées:

Résumé :

Lundi 5 mars 2018 : TBA Karine Altisen, Verimag \\

23 janvier 2018 à 16h15 par 147.210.204.186 -
Lignes 16-19 ajoutées:

Lundi 26 mars 2018 : Distributed coloring with fewer colors Marthe Bonamy
Résumé :

23 janvier 2018 à 09h46 par 2001:660:6101:402:bc1d:f305:a474:c7a1 -
Ligne 18 modifiée:

Lundi 12 mars 2018 : Simple Consensus Protocols Frederik Mallmann-Trenn, MIT \\

en:

Lundi 19 mars 2018 : Simple Consensus Protocols Frederik Mallmann-Trenn, MIT \\

23 janvier 2018 à 09h45 par 2001:660:6101:402:bc1d:f305:a474:c7a1 -
Lignes 16-21 ajoutées:

Lundi 12 mars 2018 : Simple Consensus Protocols Frederik Mallmann-Trenn, MIT
Résumé : We study consensus processes on the complete graph of n nodes. Initially, each node supports one from up to n different opinions. Nodes randomly and in parallel sample the opinions of constant many nodes. Based on these samples, they use an update rule to change their own opinion. The goal is to reach consensus, a configuration where all nodes support the same opinion. In particular, we consider the Voter process, 3-Majority, and 2-Choices.

23 janvier 2018 à 09h44 par 2001:660:6101:402:bc1d:f305:a474:c7a1 -
Lignes 34-40 ajoutées:

Lundi 5 février 2018 : Refinement-Based Composition for Computing Snapshots in Distributed Anonymous Networks Maha Boussabbeh

Résumé : Recording a global state of a distributed computation is one of the most important paradigm that finds applications in several aspects of a distributed system design. Algorithms recording such global states are called snapshot algorithms. Most of them assume that the network is not anonymous or there exists a distinguished process. We explore the correct-by-construction process to formalize snapshot computations in an anonymous network. Based on recent studies, we investigate existing algorithms to highlight how they can be composed and specified in a top/down approach in order to obtain a global view anonymously. This approach is supported by an incremental process controlled by model refinements.

17 janvier 2018 à 11h13 par 147.210.204.186 -
Lignes 17-18 modifiées:

Lundi 12 mars 2018 : On the simplification of temporal cliques Arnaud Casteigts

en:

Lundi 12 mars 2018 : TBA Akka Zemmari
Résumé :

Lundi 26 février 2018 : TBA Nicolas Hanusse

Lundi 12 février 2018 : Distributed Recoloring: the addition of colors Mikaël Rabie, Aalto University

Résumé : Given two colorings of a graph, we consider the following question: can we re-color the graph from one coloring to the other through a series of elementary changes? Here, an elementary change, or step, consists in selecting an independent set and changing the color of each vertex to another also compatible with the colors of its neighbors. The answer is not always positive, and it is in fact a PSPACE-complete decision problem. In this talk, we try to quantify how considering a stable set at each step instead of a single vertex impacts the number of steps necessary for a re-coloring, and how much communication is needed in the LOCAL model (at each round, a vertex can only communicate with its neighbors, with no limitation as to the size of the messages nor the computation power of the vertex) to compute the re-coloring or decide there is none. We also consider the question of how many extra colors are needed to make the problem always feasible, and beyond that, how the number of necessary steps decreases with the addition of colors. The case of trees is of special interest. I will provide a collection of both positive and negative results around those questions. This a joint work with Marthe Bonamy, Paul Ouvrard, Jukka Suomela and Jara Uitto.

Lundi 22 janvier 2018 : On the simplification of temporal cliques Arnaud Casteigts

Lignes 54-69 supprimées:

Lundi 26 février 2018 : TBA Nicolas Hanusse

Lundi 12 février 2018 : Distributed Recoloring: the addition of colors Mikaël Rabie, Aalto University

Résumé : Given two colorings of a graph, we consider the following question: can we re-color the graph from one coloring to the other through a series of elementary changes? Here, an elementary change, or step, consists in selecting an independent set and changing the color of each vertex to another also compatible with the colors of its neighbors. The answer is not always positive, and it is in fact a PSPACE-complete decision problem. In this talk, we try to quantify how considering a stable set at each step instead of a single vertex impacts the number of steps necessary for a re-coloring, and how much communication is needed in the LOCAL model (at each round, a vertex can only communicate with its neighbors, with no limitation as to the size of the messages nor the computation power of the vertex) to compute the re-coloring or decide there is none. We also consider the question of how many extra colors are needed to make the problem always feasible, and beyond that, how the number of necessary steps decreases with the addition of colors. The case of trees is of special interest. I will provide a collection of both positive and negative results around those questions. This a joint work with Marthe Bonamy, Paul Ouvrard, Jukka Suomela and Jara Uitto.

16 janvier 2018 à 13h14 par 147.210.204.156 -
Lignes 17-18 modifiées:

Lundi 12 mars 2018 : 'On the simplification of temporal cliques

 '  Arnaud Casteigts  \\

en:

Lundi 12 mars 2018 : On the simplification of temporal cliques Arnaud Casteigts \\

16 janvier 2018 à 13h13 par 147.210.204.156 -
Lignes 17-18 modifiées:

Lundi 12 mars 2018 : TBA Arnaud Casteigts \\

en:

Lundi 12 mars 2018 : 'On the simplification of temporal cliques

 '  Arnaud Casteigts  \\

16 janvier 2018 à 13h13 par 147.210.204.156 -
Lignes 19-35 ajoutées:

Résumé : In the context of this talk, a temporal clique is a complete graph with a unique integer label on every edge. This number can be thought of as the only date at which both endpoints interact. In a recent article, Akrida, Gasieniek, Mertzios, and Spirakis show that n/4 well chosen edges can be removed in such a graph without breaking temporal connectivity (i.e. maintaining increasing paths (journeys) between every pair of nodes, in both directions). In this talk, I will present a three-steps proof which gradually improves upon this result. The first step shows that (n^2)/8 edges (i.e. one quarter of the edges) can be removed; the second step, building upon the first, shows that half of the edges can actually be removed; then the third step, building upon the other two, shows that all edges but O(n) can actually be removed. This is obviously tight (up to a constant factor). Characterizing the exact factor that our proof yields is still work in progress. On the other hand, we give a conjecture as to the exact number of edges which can be removed (à un près), supported by extensive simulations.

12 janvier 2018 à 13h39 par 2001:660:6101:402:bc1d:f305:a474:c7a1 -
Lignes 19-21 ajoutées:

Lundi 26 février 2018 : TBA Nicolas Hanusse \\

11 janvier 2018 à 14h34 par 194.254.61.45 -
Lignes 16-17 ajoutées:

Lundi 12 mars 2018 : TBA Arnaud Casteigts \\

08 janvier 2018 à 21h51 par 87.231.47.3 -
08 janvier 2018 à 21h51 par 87.231.47.3 -
Lignes 16-29 ajoutées:

Lundi 12 février 2018 : Distributed Recoloring: the addition of colors Mikaël Rabie, Aalto University

Résumé : Given two colorings of a graph, we consider the following question: can we re-color the graph from one coloring to the other through a series of elementary changes? Here, an elementary change, or step, consists in selecting an independent set and changing the color of each vertex to another also compatible with the colors of its neighbors. The answer is not always positive, and it is in fact a PSPACE-complete decision problem. In this talk, we try to quantify how considering a stable set at each step instead of a single vertex impacts the number of steps necessary for a re-coloring, and how much communication is needed in the LOCAL model (at each round, a vertex can only communicate with its neighbors, with no limitation as to the size of the messages nor the computation power of the vertex) to compute the re-coloring or decide there is none. We also consider the question of how many extra colors are needed to make the problem always feasible, and beyond that, how the number of necessary steps decreases with the addition of colors. The case of trees is of special interest. I will provide a collection of both positive and negative results around those questions. This a joint work with Marthe Bonamy, Paul Ouvrard, Jukka Suomela and Jara Uitto.

30 novembre 2017 à 09h54 par 147.210.204.173 -
Ligne 55 modifiée:

Lundi 11 décembre 2017 : Présentation des travaux du thème \\

en:

Lundi 11 décembre 2017 : Présentation de l'activité du thème \\

30 novembre 2017 à 09h53 par 147.210.204.173 -
Ligne 27 modifiée:
        A natural extension of the firing squad problem, introduced in this paper, allows each node to postpone

en:

A natural extension of the firing squad problem, introduced in this paper, allows each node to postpone

Ligne 32 modifiée:
        The main goal of this paper is to study  the above variant of the firing squad problem under the assumptions

en:

The main goal of this paper is to study the above variant of the firing squad problem under the assumptions

Ligne 37 modifiée:
        Our main result  is an exact characterization of the dynamic graphs for which the firing squad problem can be solved.

en:

Our main result is an exact characterization of the dynamic graphs for which the firing squad problem can be solved.

30 novembre 2017 à 09h52 par 147.210.204.173 -
Lignes 18-46 ajoutées:

Lundi 15 janvier 2018 : The Firing Squad Problem Revisited Bernadette Charron-Bost, LIX

Résumé : In the classical firing squad problem, an unknown number of nodes represented by identical finite states machines is arranged on a line and in each time unit each node may change its state according to its neighbors' states. Initially all nodes are passive, except one specific node located at an end of the line, which issues a fire command. This command needs to be propagated to all other nodes, so that eventually all nodes simultaneously enter some designated “firing" state.

        A natural extension of the firing squad problem, introduced in this paper, allows each node to postpone


its participation in the squad for an arbitrary time, possibly forever, and firing is allowed only after all nodes decided to participate. This variant is highly relevant in the context of decentralized distributed computing, where processes have to coordinate for initiating various tasks simultaneously.

        The main goal of this paper is to study  the above variant of the firing squad problem under the assumptions


that the nodes are infinite state machines, have full computational capabilities, and that the inter-node communication links can be changed arbitrarily in each time unit, i.e., are defined by a dynamic graph. In this setting, we study the following fundamental question: what connectivity requirements enable a solution to the firing squad problem?

        Our main result  is an exact characterization of the dynamic graphs for which the firing squad problem can be solved.


When restricted to static directed graphs, this characterization implies that the problem can be solved if and only if the graph is strongly connected. We also discuss how information on the number of nodes or on the diameter of the network, and the use of randomization, can improve the solutions to the problem.

Joint work with Shlomo Moran (Technion)

Ligne 53 ajoutée:
Lignes 55-59 modifiées:

Lundi 11 décembre 2017 : ??? xxx

Résumé :

en:

Lundi 11 décembre 2017 : Présentation des travaux du thème

Résumé : Présentation informelle de l'activité du thème. Chacun est invité à présenter en quelques slides ou directement au tableau ses préoccupations actuelles au sens large (travail en cours, problème ouvert, problème intéressant, ou collaborations, projets, etc.)

Lignes 67-70 modifiées:

Lundi 27 novembre 2017 : ??? xxx

Résumé :

en:

Lundi 27 novembre 2017 : Pas de GT

Résumé : On pourra par contre aller voir une soutenance de thèse.

09 novembre 2017 à 16h07 par 147.210.204.173 -
Lignes 18-22 modifiées:

Lundi 4 décembre 2017 : Error-sensitive proof-labeling schemes Laurent Feuilloley, IRIF.

Résumé : Proof-labeling schemes are known mechanisms providing nodes of networks with certificates that can be verified locally by distributed algorithms. Given a boolean predicate on network states, such schemes enable to check whether the predicate is satisfied by the actual state of the network, by having nodes interacting with their neighbors only. Proof-labeling schemes are typically designed for enforcing fault-tolerance, by making sure that if the current state of the network is illegal with respect to some given predicate, then at least one node will detect it. Such a node can raise an alarm, or launch a recovery procedure enabling the system to return to a legal state. In this paper, we introduce error-sensitive proof-labeling schemes. These are proof-labeling schemes which guarantee that the number of nodes detecting illegal states is linearly proportional to the edit-distance between the current state and the set of legal states. By using error-sensitive proof-labeling schemes, states which are far from satisfying the predicate will be detected by many nodes, enabling fast return to legality. We provide a structural characterization of the set of boolean predicates on network states for which there exist error-sensitive proof-labeling schemes. This characterization allows us to show that classical predicates such as, e.g., acyclicity, and leader admit error-sensitive proof-labeling schemes, while others like regular subgraphs don't. We also focus on compact error-sensitive proof-labeling schemes. In particular, we show that the known proof-labeling schemes for spanning tree and minimum spanning tree, using certificates on O(logn) bits, and on O(log2n) bits, respectively, are error-sensitive, as long as the trees are locally represented by adjacency lists, and not just by parent pointers.

en:

Lundi 18 décembre 2017 : fête du LaBRI

Résumé : moment qui se veut convivial et festif

Lundi 11 décembre 2017 : ??? xxx

Résumé :

Lundi 4 décembre 2017 : Error-sensitive proof-labeling schemes Laurent Feuilloley, IRIF.

Résumé : Proof-labeling schemes are known mechanisms providing nodes of networks with certificates that can be verified locally by distributed algorithms. Given a boolean predicate on network states, such schemes enable to check whether the predicate is satisfied by the actual state of the network, by having nodes interacting with their neighbors only. Proof-labeling schemes are typically designed for enforcing fault-tolerance, by making sure that if the current state of the network is illegal with respect to some given predicate, then at least one node will detect it. Such a node can raise an alarm, or launch a recovery procedure enabling the system to return to a legal state. In this paper, we introduce error-sensitive proof-labeling schemes. These are proof-labeling schemes which guarantee that the number of nodes detecting illegal states is linearly proportional to the edit-distance between the current state and the set of legal states. By using error-sensitive proof-labeling schemes, states which are far from satisfying the predicate will be detected by many nodes, enabling fast return to legality. We provide a structural characterization of the set of boolean predicates on network states for which there exist error-sensitive proof-labeling schemes. This characterization allows us to show that classical predicates such as, e.g., acyclicity, and leader admit error-sensitive proof-labeling schemes, while others like regular subgraphs don't. We also focus on compact error-sensitive proof-labeling schemes. In particular, we show that the known proof-labeling schemes for spanning tree and minimum spanning tree, using certificates on O(logn) bits, and on O(log2n) bits, respectively, are error-sensitive, as long as the trees are locally represented by adjacency lists, and not just by parent pointers.

Lundi 27 novembre 2017 : ??? xxx

Résumé :

09 novembre 2017 à 15h55 par 147.210.204.173 -
Lignes 24-27 modifiées:

Lundi 20 novembre 2017 : TBA Juho Hirvonen, IRIF.

Résumé :

en:

Lundi 20 novembre 2017 : Proving lower bounds in the LOCAL model Juho Hirvonen, IRIF.

Résumé : Locality of distributed computing is the study of how far information has to propagate in distributed systems. In the last few years, we have seen the emergence of a complexity theory of locality for a large class of natural problems, the locally checkable labelings. I will present some of the new lower bound techniques that have contributed to this theory. These techniques are based on simulation, providing elegant and simple proofs.

The sinkless orientation problem has played a key role a key role in this new theory. We gave a randomized lower bound of Ω(log log n) for this problem (Brandt et al., STOC 2016), establishing it as the first problem with provably "intermediate" complexity. Our lower bound was later lifted to an Ω(log n) deterministic lower bound by Chang et al. (FOCS 2016). This, along with the matching algorithms of Ghaffari and Su (SODA 2017), show that this problem exhibits an exponential separation between deterministic and randomized complexities.

I will show a simpler lower bound proof for this problem, using elements from different proofs. I will try to highlight the effectiveness of simulation as a proof technique, and try to showcase how complexity theoretic results can be used as black boxes in order to aid these proofs.

09 novembre 2017 à 14h33 par 147.210.204.173 -
Lignes 30-33 modifiées:

Lundi 13 novembre 2017 : TBA Damien Imbs, LIF, U. Marseille.

Résumé :

en:

Lundi 13 novembre 2017 : Model Equivalences through Simulations Damien Imbs, LIF, U. Marseille.

Résumé : Simulations are powerful tools in the study of the computability power of a distributed system. A simulation takes as input an algorithm that solves an instance of a given class of problems in a given model and produces as output another algorithm that executes correctly in another model.

This talk will first present the BG simulation, that shows that in a crash-prone asynchronous shared memory model, the important parameter regarding computability is the number of possible crashes, not the total number of processes. It will then present a more recent simulation that shows that, under certain conditions, Byzantine failure-prone systems can solve the same class of problems as crash-prone ones.

08 novembre 2017 à 09h34 par 147.210.204.186 -
Lignes 16-22 ajoutées:

Lundi 4 décembre 2017 : Error-sensitive proof-labeling schemes Laurent Feuilloley, IRIF.

Résumé : Proof-labeling schemes are known mechanisms providing nodes of networks with certificates that can be verified locally by distributed algorithms. Given a boolean predicate on network states, such schemes enable to check whether the predicate is satisfied by the actual state of the network, by having nodes interacting with their neighbors only. Proof-labeling schemes are typically designed for enforcing fault-tolerance, by making sure that if the current state of the network is illegal with respect to some given predicate, then at least one node will detect it. Such a node can raise an alarm, or launch a recovery procedure enabling the system to return to a legal state. In this paper, we introduce error-sensitive proof-labeling schemes. These are proof-labeling schemes which guarantee that the number of nodes detecting illegal states is linearly proportional to the edit-distance between the current state and the set of legal states. By using error-sensitive proof-labeling schemes, states which are far from satisfying the predicate will be detected by many nodes, enabling fast return to legality. We provide a structural characterization of the set of boolean predicates on network states for which there exist error-sensitive proof-labeling schemes. This characterization allows us to show that classical predicates such as, e.g., acyclicity, and leader admit error-sensitive proof-labeling schemes, while others like regular subgraphs don't. We also focus on compact error-sensitive proof-labeling schemes. In particular, we show that the known proof-labeling schemes for spanning tree and minimum spanning tree, using certificates on O(logn) bits, and on O(log2n) bits, respectively, are error-sensitive, as long as the trees are locally represented by adjacency lists, and not just by parent pointers.

19 octobre 2017 à 09h56 par 87.231.48.130 -
Lignes 16-20 ajoutées:

Lundi 20 novembre 2017 : TBA Juho Hirvonen, IRIF.

Résumé :

13 octobre 2017 à 09h35 par 87.231.48.130 -
Ligne 16 supprimée:
Lignes 18-25 modifiées:

Lundi 6 novembre 2017 : Fast Asymptotic and Approximate Consensus in Highly Dynamic Networks. Matthias Fuegger. \\

en:

Lundi 13 novembre 2017 : TBA Damien Imbs, LIF, U. Marseille.

Résumé :

Lundi 6 novembre 2017 : Fast Asymptotic and Approximate Consensus in Highly Dynamic Networks. Matthias Fuegger, LSV. \\

17 septembre 2017 à 22h39 par 87.231.48.130 -
Lignes 51-54 modifiées:

Lundi 25 septembre 2017 : TBA Loïg Jézéquel, IRCCyN, Université de Nantes.

Résumé : TBA

en:

Lundi 25 septembre 2017 : Message-Passing Algorithms for the Verification of Distributed Protocols Loïg Jézéquel, IRCCyN, Université de Nantes.

Résumé : Message-passing algorithms (MPAs) are an algorithmic paradigm for the following generic problem: given a system consisting of several interacting components, compute a new version of each component representing its behaviour inside the system. MPAs avoid computing the full state space by propagating messages along the edges of the system interaction graph. We present an MPA for verifying local properties of distributed protocols with a tree communication structure. We report on an implementation, and validate it by means of two case studies, including an analysis of the PGM protocol.

13 septembre 2017 à 22h00 par 87.231.48.130 -
Lignes 33-37 ajoutées:

16-20 octobre 2017 : DISC

Résumé : 31ème édition, à Vienne.

13 septembre 2017 à 21h58 par 87.231.48.130 -
Ligne 19 modifiée:

Date à définir : Fast Asymptotic and Approximate Consensus in Highly Dynamic Networks. Matthias Fuegger. \\

en:

Lundi 6 novembre 2017 : Fast Asymptotic and Approximate Consensus in Highly Dynamic Networks. Matthias Fuegger. \\

13 septembre 2017 à 11h54 par 147.210.179.67 -
Lignes 16-50 ajoutées:

Date à définir : Fast Asymptotic and Approximate Consensus in Highly Dynamic Networks. Matthias Fuegger.

Résumé : Reaching consensus on a common value in a distributed system is a well-studied central problem in distributed computing. Unfortunately, even modest network dynamics prohibit solvability. For many problems, such as, distributed control, clock synchronization, etc., it is however sufficient to asymptotically converge to the same value, or decide on values not too far from each other. We study solvability of these consensus variants in highly dynamic networks, provide time complexity results, and present fast algorithms. The talk finishes with an outlook on current research in biology.

The talk is on previous and current research with Bernadette Charron-Bost (LIX) and Thomas Nowak (LRI).

Lundi 9 octobre 2017 : Relationships between various communication models of shared memory paradigm for fault-tolerant distributed computing Colette Johnen.

Résumé : There is a proliferation of communication models for distributed computing, in shared memory paradigm. Since subtle changes in the communication model can result in significant changes to the solvability/unsolvability or to the complexity of various problems, it becomes imperative to understand the relationships between the many models The situation becomes even more complicated when additional requirements such as fault-tolerance are added to the mix. This motivates us to study under what circumstances a program designed for one model and delivering some set of additional guarantees can be converted into an equivalent'' programs for a different model while delivering comparable guarantees.

Du 2 au 4 octobre 2017 : Réunion ANR Descartes

Résumé : Dans un château pas loin de Poitiers

Lundi 25 septembre 2017 : TBA Loïg Jézéquel, IRCCyN, Université de Nantes.

Résumé : TBA

20 juillet 2017 à 10h26 par 2a01:e0a:9:2030:12ba:802a:a3ee:6c1a -
Lignes 18-21 modifiées:

Lundi 11 septembre 2017 : Conférence "Fundamentals of Computation Theory" (Amphi du LaBRI)

Les exposés "distribués" ont été planifiés le lundi. Vous pouvez trouver le programme sur https://fct2017.labri.fr

en:

Du 11 au 13 septembre 2017 : Conférence "Fundamentals of Computation Theory" (Amphi du LaBRI)

Les exposés "distribués" ont été planifiés le mercredi. Vous pouvez trouver le programme sur https://fct2017.labri.fr

18 juillet 2017 à 10h12 par 2a01:e0a:9:2030:12ba:802a:a3ee:6c1a -
Lignes 16-21 ajoutées:

Lundi 11 septembre 2017 : Conférence "Fundamentals of Computation Theory" (Amphi du LaBRI)

Les exposés "distribués" ont été planifiés le lundi. Vous pouvez trouver le programme sur https://fct2017.labri.fr

14 juin 2017 à 09h35 par 2001:660:6101:403::1:a -
Lignes 17-21 ajoutées:

Lundi 26 juin 2017 : Exploration de graphes par des robots amnésiques David Ilcinkas

Résumé : Je présenterai un panorama général des résultats et techniques habituelles concernant l'exploration de graphes par des robots amnésiques mais doués de vision globale.

07 juin 2017 à 23h02 par 93.21.74.30 -
Ligne 28 modifiée:

Lundi 12 juin 2017 : Orientation de graphe dans un environnement asynchrone et avec pannes Noël Gillet \\

en:

Lundi 12 juin 2017 : Orientation de graphes dans un environnement asynchrone et avec pannes Noël Gillet \\

07 juin 2017 à 22h56 par 93.21.74.30 -
Lignes 28-29 modifiées:

Lundi 12 juin 2017 : ' Orientation de graphe dans un environnement asynchrone et avec

    pannes.' Noël Gillet  \\

en:

Lundi 12 juin 2017 : Orientation de graphe dans un environnement asynchrone et avec pannes Noël Gillet \\

07 juin 2017 à 22h55 par 93.21.74.30 -
Lignes 19-21 modifiées:

Lundi 22 mai 2017 : Jointure en Map-Reduce Sofian Maabout

en:

Lundi 24 avril 22 mai 19 juin 2017 : Jointure en Map-Reduce Sofian Maabout

Lignes 25-35 ajoutées:

Lundi 12 juin 2017 : ' Orientation de graphe dans un environnement asynchrone et avec

    pannes.' Noël Gillet


Résumé : Dans cette présentation, nous nous intéressons à l'orientation de graphe de manière distribuée. Plus précisément, nous cherchons à calculer une orientation minimum, c'est-à-dire à minimiser le degré sortant maximum d'un nœud du graphe. Ce problème d'orientation est notamment une modélisation naturelle pour des problèmes d'allocation de ressources. Nous présentons l'algorithme AvgDegAsync qui fonctionne dans un environnement distribué où les communications sont asynchrones et où les nœuds peuvent être en panne. Notre algorithme garantit une $2(2+\epsilon)$-approximation de l'orientation optimale en utilisant un nombre logarithmique de rondes asynchrones. De plus, il ne nécessite pas de connaissance sur le graphe comme le nombre de nœuds ou encore sa densité.

Ce travail a été réalisé avec Nicolas Hanusse et une présentation a été donnée à AlgoTel 2017

19 mai 2017 à 10h04 par 78.250.143.229 -
Ligne 17 ajoutée:
Lignes 19-27 ajoutées:

Lundi 22 mai 2017 : Jointure en Map-Reduce Sofian Maabout

Résumé : Joindre deux tables revient à concaténer leurs enregistrements qui partagent la même valeur sur certains attributs. Nous passons en revue quelques techniques de mise en œuvre de cette opération dans le paradigme Map-Reduce avec étude de leurs complexités.

Lignes 30-31 modifiées:

Abstract:' Dans cette thèse, nous nous intéressons aux modèles de calculs dans les réseaux d'objets à capacités restreintes, tels que les réseaux de capteurs sans fil. Nous nous focalisons sur les protocoles de population proposés par Angluin et al. Dans ce modèle, les objets sont représentés par des agents à états finis, passivement mobiles, communiquant entre paires et formant un réseau asynchrone et anonyme. Nous présentons deux études comparatives qui nous permettent par la suite de proposer une approche établissant le lien des protocoles de population avec deux autres modèles : le modèle des tâches avec les systèmes de réécritures de graphes, et le modèle asynchrone et anonyme d'échange de messages.

en:

Résumé : ' Dans cette thèse, nous nous intéressons aux modèles de calculs dans les réseaux d'objets à capacités restreintes, tels que les réseaux de capteurs sans fil. Nous nous focalisons sur les protocoles de population proposés par Angluin et al. Dans ce modèle, les objets sont représentés par des agents à états finis, passivement mobiles, communiquant entre paires et formant un réseau asynchrone et anonyme. Nous présentons deux études comparatives qui nous permettent par la suite de proposer une approche établissant le lien des protocoles de population avec deux autres modèles : le modèle des tâches avec les systèmes de réécritures de graphes, et le modèle asynchrone et anonyme d'échange de messages.

Ligne 33 ajoutée:
Lignes 49-55 supprimées:

Lundi 24 avril 2017 : Jointure en Map-Reduce Sofian Maabout
REPORTE Abstract: Joindre deux tables revient à concaténer leurs enregistrements qui partagent la même valeur sur certains attributs. Nous passons en revue quelques techniques de mise en œuvre de cette opération dans le paradigme Map-Reduce avec étude de leurs complexités.

18 mai 2017 à 20h56 par 93.21.74.30 -
Lignes 20-22 ajoutées:

Abstract:' Dans cette thèse, nous nous intéressons aux modèles de calculs dans les réseaux d'objets à capacités restreintes, tels que les réseaux de capteurs sans fil. Nous nous focalisons sur les protocoles de population proposés par Angluin et al. Dans ce modèle, les objets sont représentés par des agents à états finis, passivement mobiles, communiquant entre paires et formant un réseau asynchrone et anonyme. Nous présentons deux études comparatives qui nous permettent par la suite de proposer une approche établissant le lien des protocoles de population avec deux autres modèles : le modèle des tâches avec les systèmes de réécritures de graphes, et le modèle asynchrone et anonyme d'échange de messages.

Nous passons ensuite au problème d'ordonnancement dans les protocoles de population. Nous proposons un nouvel ordonnanceur probabiliste, 1-central, basé sur les rendez-vous randomisés et appelé HS Scheduler. Contrairement aux autres ordonnanceurs, il est permet à plus d'une paire de communiquer à la fois. Nous prouvons qu'il est équitable avec probabilité 1. Nous analysons par la suite le temps de stabilisation de certains protocoles s'exécutant sous le Random Scheduler (proposé par Angluin et al.) ou le HS Scheduler et sur différentes topologies du graphe d'interaction. Nous prouvons que le HS Scheduler est équivalent en temps au Random Scheduler quand le graphe d'interaction est complet mais qu'il permet une stabilisation plus rapide quand le graphe est aléatoire. Par la suite, nous proposons un autre ordonnanceur qui prend en considération les états des agents et permet d'introduire la terminaison à certains protocoles : le Prorotol Aware HS Scheduler. Nous prouvons qu'il est équitable avec probabilité 1. Nous faisons l'analyse du temps de stabilisation de certains protocoles s'exécutant sous cet ordonnanceur en considérant différentes topologies du graphe d'interaction. Nous prouvons que cet ordonnanceur permet une stabilisation plus rapide pour ces protocoles. Finalement, nous implémentons et simulons sur ViSiDiA l'ensemble des scénarios étudiés et validons les bornes théoriques que nous avons établies.

Ligne 42 modifiée:
en:

REPORTE

11 mai 2017 à 15h21 par 147.210.245.180 -
Ligne 18 modifiée:

Lundi 22 mai 2017 : Soutenance de la thèse de Nesrine Ouled Abdallah \\

en:

Lundi 22 mai 2017 : Soutenance de la thèse de Nesrine Ouled Abdallah Attention ! Lieu : Amphi du LaBRI et horaire : 10h30. \\

11 mai 2017 à 15h20 par 147.210.245.180 -
Ligne 19 ajoutée:
11 mai 2017 à 15h20 par 147.210.245.180 -
Lignes 17-18 modifiées:
en:

Lundi 22 mai 2017 : Soutenance de la thèse de Nesrine Ouled Abdallah \\

12 avril 2017 à 09h46 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
Lignes 35-38 modifiées:

Lundi 24 avril 2017 : TBA Sofian Maabout

Abstract: TBA

en:

Lundi 24 avril 2017 : Jointure en Map-Reduce Sofian Maabout

Abstract: Joindre deux tables revient à concaténer leurs enregistrements qui partagent la même valeur sur certains attributs. Nous passons en revue quelques techniques de mise en œuvre de cette opération dans le paradigme Map-Reduce avec étude de leurs complexités.

12 avril 2017 à 09h41 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
Lignes 35-38 modifiées:

Lundi 24 avril 2017 : TBA

Abstract:

en:

Lundi 24 avril 2017 : TBA Sofian Maabout

Abstract: TBA

28 mars 2017 à 10h51 par 147.210.204.156 -
Lignes 65-68 modifiées:

Lundi 3 avril 2017 : TBA Sergio Rajsbaum (UNAM, Mexico)

Abstract:

en:

Lundi 3 avril 2017 : Modelling Distributed Computing Task Computability with Dynamic Epistemic Logic Sergio Rajsbaum (UNAM, Mexico)

Abstract: The usual epistemic S5 model for multi-agent systems is a Kripke graph, whose edges are labeled with the agents that do not distinguish between two states. We propose to uncover the higher dimensional information implicit in the Kripke graph, by using as a model its dual, a chromatic simplicial complex. For each state of the Kripke model there is a facet in the complex, with one vertex per agent. If an edge (u,v) is labeled with a set of agents S, the facets corresponding to u and v intersect in a simplex consisting of one vertex for each agent of S. Then we use dynamic epistemic logic to study how the simplicial complex epistemic model changes after the agents communicate with each other. There are topological invariants preserved from the initial epistemic complex to the epistemic complex after an action model is applied, that depend on how reliable the communication is. In turn these topological properties determine the knowledge that the agents may gain after the communication happens, to solve a given distributed task, also modelled using dynamic epistemic logic.

20 mars 2017 à 09h28 par 2001:660:6101:403::1:139 -
Ligne 65 modifiée:

Lundi 10 avril 2017 : TBA Sergio Rajsbaum (UNAM, Mexico) \\

en:

Lundi 3 avril 2017 : TBA Sergio Rajsbaum (UNAM, Mexico) \\

16 mars 2017 à 21h13 par 93.21.74.30 -
Lignes 73-76 modifiées:

Lundi 27 mars 2017 : TBA Ralf Klasing

Abstract:

en:

Lundi 27 mars 2017 : Bamboo Garden Trimming Problem (Perpetual maintenance of machines with different attendance urgency factors) Ralf Klasing

Abstract: A garden G is populated by n > 1 bamboos b_1, b_2, ..., b_n with the respective daily growth rates h_1, h_2, ... h_n. It is assumed that the initial heights of bamboos are zero. The robotic gardener or simply a robot maintaining the bamboo garden is attending bamboos and trimming them to height zero according to some schedule.

The Bamboo Garden Trimming Problem, or simply BGT, is to design a perpetual schedule of cuts to maintain the elevation of bamboo garden as low as possible. The bamboo garden is a metaphor for a collection of machines which have to be serviced with different frequencies, by a robot which can service only one machine during a visit. The objective is to design a perpetual schedule of servicing the machines which minimizes the maximum (weighted) waiting time for servicing. We consider two variants of BGT.

In discrete BGT the robot is allowed to trim only one bamboo at the end of each day. In continuous BGT the bamboos can be cut at any time, however, the robot needs time to move from one bamboo to the next one and this time is defined by a weighted network of connections.

For discrete BGT, we show a simple 4-approximation algorithm and, by exploiting relationship between BGT and the classical Pinwheel Scheduling Problem, we obtain also a 2-approximation and even a closer approximation for more balanced growth rates. For continuous BGT, we propose approximation algorithms which achieve approximation ratios O(log(h_1/h_n)) and O(log n).

This is a joint work with L. Gasieniec, Ch. Levcopoulos, A. Lingas, J. Min, and T. Radzik.

16 mars 2017 à 14h55 par 2001:660:6101:403::1:139 -
Lignes 81-84 modifiées:

Lundi 20 mars 2017 : TBA David Ilcinkas

Abstract:

en:

Lundi 20 mars 2017 : Self-Stabilizing Disconnected Components Detection and Rooted Shortest-Path Tree Maintenance in Polynomial Steps David Ilcinkas

Abstract: We deal with the problem of maintaining a shortest-path tree rooted at some process r in a network that may be disconnected after topological changes. The goal is then to maintain a shortest-path tree rooted at r in its connected component, V_r, and make all processes of other components detecting that r is not part of their connected component. We propose, in the composite atomicity model, a silent self-stabilizing algorithm for this problem working in semi-anonymous networks under the distributed unfair daemon (the most general daemon) without requiring any a priori knowledge about global parameters of the network. This is the first algorithm for this problem that is proven to achieve a polynomial stabilization time in steps. Namely, we exhibit a bound in O(\maxi \nmax^3 n), where \maxi is the maximum weight of an edge, \nmax is the maximum number of non-root processes in a connected component, and n is the number of processes. The stabilization time in rounds is at most 3\nmax+D, where D is the hop-diameter of V_r.

08 mars 2017 à 11h16 par 147.210.204.156 -
Lignes 49-50 ajoutées:
Lignes 53-63 modifiées:

Lundi 10 avril 2017 : TBA

Abstract:

Lundi 3 avril 2017 : Robustness in Highly Dynamic Networks Arnaud Casteigts

en:

Lundi 10 avril 2017 : Robustness in Highly Dynamic Networks Arnaud Casteigts

Lignes 59-68 ajoutées:

Lundi 10 avril 2017 : TBA Sergio Rajsbaum (UNAM, Mexico)

Abstract:

28 février 2017 à 09h54 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
27 février 2017 à 14h06 par 147.210.128.218 -
Lignes 85-88 modifiées:

Lundi 13 mars 2017 : TBA Colette Johnen

Abstract:

en:

Lundi 13 mars 2017 : On the Space Complexity of Conflict Detector Objects and Related Objects Colette Johnen

Abstract: We study 3 objects in shared-memory model: conflict detector, adopt-commit and value splitter. We design for each of these objects an implementation that is wait-free, anonymous, input-oblivious and only uses two register primitive operations: read and write. Each of these implementations requires $O(\sqrt(n))$ atomic registers where $n$ is the number of processes. We conclude, by establishing a lower bound for each of these implementations matching the upper bounds derived from the proposed implementations.

Joint work with Claire Capdevielle and Alessia Milani

23 février 2017 à 22h24 par 2a01:e0a:9:2030:b8ad:6526:192f:4e85 -
Ligne 62 modifiée:

Abstract: We investigate a special case of hereditary property that we refer to as {\em robustness}. A property is {\em robust} in a given graph if it is inherited by all connected spanning subgraphs of this graph. We motivate this definition in different contexts, showing that it plays a central role in highly dynamic networks, although the problem is defined in terms of classical (static) graph theory. In this paper, we focus on the robustness of {\em maximal independent sets} (MIS). Following the above definition, a MIS is said to be robust (RMIS) if it remains a valid MIS in all connected spanning subgraphs of the original graph. We characterize the class of graphs in which {\em all} possible MISs are robust. We show that, in these particular graphs, the problem of finding a robust MIS is {\em local}; that is, we present an RMIS algorithm using only a sublogarithmic number of rounds (in the number of nodes n) in the LOCAL model. On the negative side, we show that, in general graphs, the problem is not local. Precisely, we prove a $\Omega(n)$ lower bound on the number of rounds required for the nodes to decide consistently in some graphs. This result implies a separation between the RMIS problem and the MIS problem in general graphs. It also implies that any strategy in this case is asymptotically (in order) as bad as collecting all the network information at one node and solving the problem in a centralized manner. Motivated by this observation, we present a centralized algorithm that computes a robust MIS in a given graph, if one exists, and rejects otherwise. Significantly, this algorithm requires only a polynomial amount of local computation time, despite the fact that exponentially many MISs and exponentially many connected spanning subgraphs may exist.

en:

Abstract: We investigate a special case of hereditary property that we refer to as {\em robustness}. A property is robust in a given graph if it is inherited by all connected spanning subgraphs of this graph. We motivate this definition in different contexts, showing that it plays a central role in highly dynamic networks, although the problem is defined in terms of classical (static) graph theory. In this paper, we focus on the robustness of {\em maximal independent sets} (MIS). Following the above definition, a MIS is said to be robust (RMIS) if it remains a valid MIS in all connected spanning subgraphs of the original graph. We characterize the class of graphs in which all possible MISs are robust. We show that, in these particular graphs, the problem of finding a robust MIS is local; that is, we present an RMIS algorithm using only a sublogarithmic number of rounds (in the number of nodes n) in the LOCAL model. On the negative side, we show that, in general graphs, the problem is not local. Precisely, we prove a $\Omega(n)$ lower bound on the number of rounds required for the nodes to decide consistently in some graphs. This result implies a separation between the RMIS problem and the MIS problem in general graphs. It also implies that any strategy in this case is asymptotically (in order) as bad as collecting all the network information at one node and solving the problem in a centralized manner. Motivated by this observation, we present a centralized algorithm that computes a robust MIS in a given graph, if one exists, and rejects otherwise. Significantly, this algorithm requires only a polynomial amount of local computation time, despite the fact that exponentially many MISs and exponentially many connected spanning subgraphs may exist.

23 février 2017 à 22h21 par 2a01:e0a:9:2030:b8ad:6526:192f:4e85 -
Ligne 62 modifiée:

Abstract: We investigate a special case of hereditary property that we refer to as {\em robustness}. A property is {\em robust} in a given graph if it is inherited by all connected spanning subgraphs of this graph. We motivate this definition in different contexts, showing that it plays a central role in highly dynamic networks, although the problem is defined in terms of classical (static) graph theory. In this paper, we focus on the robustness of {\em maximal independent sets} (MIS). Following the above definition, a MIS is said to be {\em robust} (RMIS) it is remains a valid MIS in all connected spanning subgraphs of the original graph. We characterize the class of graphs in which {\em all} possible MISs are robust. We show that, in these particular graphs, the problem of finding a robust MIS is {\em local}; that is, we present an RMIS algorithm using only a sublogarithmic number of rounds (in the number of nodes n) in the LOCAL model. On the negative side, we show that, in general graphs, the problem is not local. Precisely, we prove a $\Omega(n)$ lower bound on the number of rounds required for the nodes to decide consistently in some graphs. This result implies a separation between the RMIS problem and the MIS problem in general graphs. It also implies that any strategy in this case is asymptotically (in order) as bad as collecting all the network information at one node and solving the problem in a centralized manner. Motivated by this observation, we present a centralized algorithm that computes a robust MIS in a given graph, if one exists, and rejects otherwise. Significantly, this algorithm requires only a polynomial amount of local computation time, despite the fact that exponentially many MISs and exponentially many connected spanning subgraphs may exist.

en:

Abstract: We investigate a special case of hereditary property that we refer to as {\em robustness}. A property is {\em robust} in a given graph if it is inherited by all connected spanning subgraphs of this graph. We motivate this definition in different contexts, showing that it plays a central role in highly dynamic networks, although the problem is defined in terms of classical (static) graph theory. In this paper, we focus on the robustness of {\em maximal independent sets} (MIS). Following the above definition, a MIS is said to be robust (RMIS) if it remains a valid MIS in all connected spanning subgraphs of the original graph. We characterize the class of graphs in which {\em all} possible MISs are robust. We show that, in these particular graphs, the problem of finding a robust MIS is {\em local}; that is, we present an RMIS algorithm using only a sublogarithmic number of rounds (in the number of nodes n) in the LOCAL model. On the negative side, we show that, in general graphs, the problem is not local. Precisely, we prove a $\Omega(n)$ lower bound on the number of rounds required for the nodes to decide consistently in some graphs. This result implies a separation between the RMIS problem and the MIS problem in general graphs. It also implies that any strategy in this case is asymptotically (in order) as bad as collecting all the network information at one node and solving the problem in a centralized manner. Motivated by this observation, we present a centralized algorithm that computes a robust MIS in a given graph, if one exists, and rejects otherwise. Significantly, this algorithm requires only a polynomial amount of local computation time, despite the fact that exponentially many MISs and exponentially many connected spanning subgraphs may exist.

23 février 2017 à 22h20 par 2a01:e0a:9:2030:b8ad:6526:192f:4e85 -
Lignes 59-62 modifiées:

Lundi 3 avril 2017 : Robustesse dans les graphes dynamiques (work in progress...) Arnaud Casteigts

Abstract:

en:

Lundi 3 avril 2017 : Robustness in Highly Dynamic Networks Arnaud Casteigts

Abstract: We investigate a special case of hereditary property that we refer to as {\em robustness}. A property is {\em robust} in a given graph if it is inherited by all connected spanning subgraphs of this graph. We motivate this definition in different contexts, showing that it plays a central role in highly dynamic networks, although the problem is defined in terms of classical (static) graph theory. In this paper, we focus on the robustness of {\em maximal independent sets} (MIS). Following the above definition, a MIS is said to be {\em robust} (RMIS) it is remains a valid MIS in all connected spanning subgraphs of the original graph. We characterize the class of graphs in which {\em all} possible MISs are robust. We show that, in these particular graphs, the problem of finding a robust MIS is {\em local}; that is, we present an RMIS algorithm using only a sublogarithmic number of rounds (in the number of nodes n) in the LOCAL model. On the negative side, we show that, in general graphs, the problem is not local. Precisely, we prove a $\Omega(n)$ lower bound on the number of rounds required for the nodes to decide consistently in some graphs. This result implies a separation between the RMIS problem and the MIS problem in general graphs. It also implies that any strategy in this case is asymptotically (in order) as bad as collecting all the network information at one node and solving the problem in a centralized manner. Motivated by this observation, we present a centralized algorithm that computes a robust MIS in a given graph, if one exists, and rejects otherwise. Significantly, this algorithm requires only a polynomial amount of local computation time, despite the fact that exponentially many MISs and exponentially many connected spanning subgraphs may exist.

23 février 2017 à 16h58 par 213.209.187.14 -
Lignes 103-106 modifiées:

Lundi 27 février 2017 : TBA Thomas Lambert

Abstract: TBA

en:

Lundi 27 février 2017 : Stratégies d’assignation basées sur des couplages pour améliorer la localité dans les opérations de type Map/Reduce Thomas Lambert

Abstract: Map/Reduce est un paradigme d'algorithme parallèle qui cherche à séparer une tâche en plusieurs sous-tâches de tailles plus réduites afin de les traiter indépendamment et d'agréger ensuite les résultats. Dans cet exposé nous nous intéresserons à la première phase, la phase dite de "Map", c'est à dire le placement de plusieurs tâches indépendantes sur un ensemble de machines. Lors de cette phase, les fichiers d'entrées sont répliqués et pré-placés sur plusieurs processeurs de manière aléatoire afin d'augmenter le nombre de machines susceptible d'exécuter une tâche. Nous voulons ici essayer d'utiliser au mieux cette distribution initiale des fichiers afin de finir l'ensemble des tâches au plus vite (minimisation du makespan). Pour cela nous nous restreignons au cas des tâches homogènes et proposons une modélisation basée sur les graphes bipartis (les arêtes représentent les placement initiaux des fichiers d'entrées). Grâce à un algorithme inspiré des algorithmes de couplage nous montrerons qu'il est possible d’obtenir la solution optimale du problème en temps polynomial. Nous analyserons ensuite la qualité de cette solution en montrons qu'avec forte probabilité elle est au moins quasi-parfaite, c'est à dire égale à l'optimal théorique plus un. Enfin nous conclurons l'exposé sur différents résultats de simulations permettant une analyse du cas où l'on autorise le déplacement des fichiers d'entrées et où l'on cherche à minimiser ces déplacements.

05 février 2017 à 15h28 par 92.95.243.199 -
Ligne 136 modifiée:

Lundi 6 février 2017 : Calcul de routes et Projets en cours chez Mappy *11h Amphi du Labri Yvan Montalieu - (Mappy)\\

en:

Lundi 6 février 2017 : Calcul de routes et Projets en cours chez Mappy 11h Amphi du Labri Yvan Montalieu - (Mappy)\\

05 février 2017 à 15h27 par 92.95.243.199 -
Lignes 124-125 supprimées:
Lignes 127-133 modifiées:

Lundi 6 février 2017 : TBA Yvan Montalieu - (Mappy)

Abstract: à venir. L'exposé portera essentiellement sur le calcul d'itinéraires.

en:

Lundi 6 février 2017 : Petite école du distribué : Analyse des algorithmes distribués probabilistes 3/2 Akka Zemmari

Résumé : Le but de ce cours est de présenter quelques inégalités de concentration utilisées en analyse d’algorithmes distribuées probabilistes. Après quelques rappels et quelques définitions, nous verrons les inégalités utiles et comment les utiliser pour prouver des bornes (supérieures) sur la complexité des algorithmes. Ces bornes étant vraie avec forte probabilité. Nous illustrerons toutes ces méthodes au travers d’un exemple classique en algorithmique distribuée : le calcul d’un ensemble indépendant maximal (MIS).

Remarque : il y a bien deux exposé ce lundi 6 février !

Lundi 6 février 2017 : Calcul de routes et Projets en cours chez Mappy *11h Amphi du Labri Yvan Montalieu - (Mappy)

Abstract: Ce séminaire de présentation des projets en cours chez mappy, entreprise spécialiste du calcul d’itinéraires et des services de cartographie.

Il est ouvert à tous (étudiants master inclus) et devrait intéresser principalement les chercheurs en:

• algorithmique de "grands" graphes
• analyse d'image et apprentissage
30 janvier 2017 à 14h02 par 147.210.245.180 -
Lignes 103-106 modifiées:

Lundi 27 février 2017 : TBA

Abstract:

en:

Lundi 27 février 2017 : TBA Thomas Lambert

Abstract: TBA

20 janvier 2017 à 13h21 par 2001:660:6101:402:849c:3f32:ef6d:8dae -
Lignes 20-22 modifiées:

15 - 19 mai : EPIT

en:

15 - 19 mai 2017 : EPIT

Lignes 29-31 modifiées:

Lundi 1/8 mai : relâche

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Lundi 1/8 mai 2017 : relâche

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Lundi 24 avril : TBA

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Lundi 24 avril 2017 : TBA

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Lundi 17 avril : relâche

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Lundi 17 avril 2017 : relâche

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Lundi 10 avril : TBA

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Lundi 10 avril 2017 : TBA

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Lundi 3 avril : Robustesse dans les graphes dynamiques (work in progress...) Arnaud Casteigts

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Lundi 3 avril 2017 : Robustesse dans les graphes dynamiques (work in progress...) Arnaud Casteigts

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Lundi 27 mars : TBA Ralf Klasing

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Lundi 27 mars 2017 : TBA Ralf Klasing

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Lundi 20 mars : TBA David Ilcinkas

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Lundi 20 mars 2017 : TBA David Ilcinkas

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Lundi 13 mars : TBA Colette Johnen

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Lundi 13 mars 2017 : TBA Colette Johnen

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Lundi 6 mars : L’agrégation de données dans les graphes dynamiques Quentin Bramas

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Lundi 6 mars 2017 : L’agrégation de données dans les graphes dynamiques Quentin Bramas

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Lundi 27 février : TBA

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Lundi 27 février 2017 : TBA

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Lundi 20 février : relâche

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Lundi 20 février 2017 : relâche

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Lundi 13 février : TBA Nicolas Hanusse

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Lundi 13 février 2017 : TBA Nicolas Hanusse

Lignes 129-131 modifiées:

Lundi 6 février : TBA Yvan Montalieu - (Mappy)

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Lundi 6 février 2017 : TBA Yvan Montalieu - (Mappy)

Lignes 138-140 modifiées:

Lundi 30 janvier : Petite école du distribué : Analyse des algorithmes distribués probabilistes 2/2 Akka Zemmari

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Lundi 30 janvier 2017 : Petite école du distribué : Analyse des algorithmes distribués probabilistes 2/2 Akka Zemmari

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Lundi 23 janvier : Petite école du distribué : Analyse des algorithmes distribués probabilistes 1/2 Akka Zemmari

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Lundi 23 janvier 2017 : Petite école du distribué : Analyse des algorithmes distribués probabilistes 1/2 Akka Zemmari

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28-29 novembre : GDR CoA \\

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28-29 novembre 2016 : GDR CoA \\

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Lundi 3 avril : TBA Arnaud Casteigts \\

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Lundi 3 avril : Robustesse dans les graphes dynamiques (work in progress...) Arnaud Casteigts \\

10 janvier 2017 à 09h07 par 2001:660:6101:402:3cae:17ed:febf:8b17 -
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Lundi 6 mars : TBA Quentin Bramas

Abstract:

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Lundi 6 mars : L’agrégation de données dans les graphes dynamiques Quentin Bramas

Résumé : Les graphes dynamiques, aussi appelés graphes évolutifs, graphes temporels ou graphes variant dans le temps, ont gagné en popularité car il permettent de modéliser un grand nombre de phénomènes, et plus particulièrement les interactions dans les réseaux dont la topologie évolue rapidement, comme les réseaux de capteurs sans fil, les protocoles de population, ou bien les réseaux sociaux. Dans un graphe dynamique, les noeuds et les arrêtes apparaissent et disparaissent au fil du temps, et ces changements ne sont pas vus comme des fautes mais bien comme une caractéristique à part entière du graphe. Dans cette présentation, je vais montrer plusieurs manières de définir les graphes dynamiques et quelles sont leurs propriétés. Enfin, je présenterai à titre d’exemple mes contributions sur le problème de l’agrégation de données dans les graphes dynamiques, d’un point de vue centralisé ou distribué, avec connaissance du futur ou non.

09 janvier 2017 à 16h07 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
Lignes 35-40 modifiées:

Lundi 24 avril : relâche

Abstract: lundi de pââââââques

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Lundi 24 avril : TBA

Abstract:

Lignes 59-61 modifiées:

Lundi 3 avril : TBA

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Lundi 3 avril : TBA Arnaud Casteigts

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Lundi 27 mars : TBA

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Lundi 27 mars : TBA Ralf Klasing

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Lundi 20 mars : TBA

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Lundi 20 mars : TBA David Ilcinkas

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Lundi 13 mars : TBA

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Lundi 13 mars : TBA Colette Johnen

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Lundi 6 mars : TBA

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Lundi 6 mars : TBA Quentin Bramas

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Lundi 13 février : TBA

Abstract:

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Lundi 13 février : TBA Nicolas Hanusse

Abstract: Un exposé pas très long

09 janvier 2017 à 15h51 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
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Lundi 6 février : TBA Yvan Montalieu - (Mappy)

Abstract: à venir. L'exposé portera essentiellement sur le calcul d'itinéraires.

en:

15 - 19 mai : EPIT

Abstract: Ecole de Printemps en Informatique Théorique à porquerolles. Le thème cette année est le calcul distribué. Venez nombreux ! http://epit2017.labri.fr/fr/

Lignes 27-33 modifiées:

Lundi 30 janvier : Petite école du distribué Analyse des algorithmes distribués probabilistes Akka Zemmari

Résumé : Le but de ce cours est de présenter quelques inégalités de concentration utilisées en analyse d’algorithmes distribuées probabilistes. Après quelques rappels et quelques définitions, nous verrons les inégalités utiles et comment les utiliser pour prouver des bornes (supérieures) sur la complexité des algorithmes. Ces bornes étant vraie avec forte probabilité. Nous illustrerons toutes ces méthodes au travers d’un exemple classique en algorithmique distribuée : le calcul d’un ensemble indépendant maximal (MIS).

en:

Lundi 1/8 mai : relâche

Abstract: jours fériés

Lundi 24 avril : relâche

Abstract: lundi de pââââââques

Lundi 17 avril : relâche

Abstract: lundi de pââââââques

Lundi 10 avril : TBA

Abstract:

Lundi 3 avril : TBA

Abstract:

Lundi 27 mars : TBA

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Lundi 20 mars : TBA

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Lundi 13 mars : TBA

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Lundi 6 mars : TBA

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Lundi 27 février : TBA

Abstract:

Lundi 20 février : relâche

Abstract: vacaaaaances

Lundi 13 février : TBA

Abstract:

Lundi 6 février : TBA Yvan Montalieu - (Mappy)

Abstract: à venir. L'exposé portera essentiellement sur le calcul d'itinéraires.

Lundi 30 janvier : Petite école du distribué : Analyse des algorithmes distribués probabilistes 2/2 Akka Zemmari

Résumé : Le but de ce cours est de présenter quelques inégalités de concentration utilisées en analyse d’algorithmes distribuées probabilistes. Après quelques rappels et quelques définitions, nous verrons les inégalités utiles et comment les utiliser pour prouver des bornes (supérieures) sur la complexité des algorithmes. Ces bornes étant vraie avec forte probabilité. Nous illustrerons toutes ces méthodes au travers d’un exemple classique en algorithmique distribuée : le calcul d’un ensemble indépendant maximal (MIS).

Lundi 23 janvier : Petite école du distribué : Analyse des algorithmes distribués probabilistes 1/2 Akka Zemmari \\

09 janvier 2017 à 13h55 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
Lignes 19-27 ajoutées:

Lundi 6 février : TBA Yvan Montalieu - (Mappy)

Abstract: à venir. L'exposé portera essentiellement sur le calcul d'itinéraires.

Lignes 33-39 supprimées:

Lundi 23 janvier : TBA Yvan Montalieu - (Mappy)

Abstract: à venir. L'exposé portera essentiellement sur le calcul d'itinéraires.

09 janvier 2017 à 13h55 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
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09 janvier 2017 à 13h54 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
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Lundi 30 janvier : TBA Akka Zemmari

Abstract: à venir. Exposé dans le cadre de la petite école du distribué

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Lundi 30 janvier : Petite école du distribué Analyse des algorithmes distribués probabilistes Akka Zemmari

Résumé : Le but de ce cours est de présenter quelques inégalités de concentration utilisées en analyse d’algorithmes distribuées probabilistes. Après quelques rappels et quelques définitions, nous verrons les inégalités utiles et comment les utiliser pour prouver des bornes (supérieures) sur la complexité des algorithmes. Ces bornes étant vraie avec forte probabilité. Nous illustrerons toutes ces méthodes au travers d’un exemple classique en algorithmique distribuée : le calcul d’un ensemble indépendant maximal (MIS).

04 janvier 2017 à 11h47 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
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Lundi 30 janvier : TBA Akka Zemmari

Abstract: à venir. Exposé dans le cadre de la petite école du distribué

13 décembre 2016 à 09h47 par 2001:660:6101:402:9277:f9a7:6e64:a00b -
Lignes 17-23 ajoutées:

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Lundi 23 janvier : TBA Yvan Montalieu - (Mappy)

Abstract: à venir. L'exposé portera essentiellement sur le calcul d'itinéraires.

14 novembre 2016 à 15h01 par 147.210.245.180 -
Lignes 23-33 ajoutées:

21 novembre : Petite école du distribué (3/2) Le model LOCAL et la coloration de graphes, Cyril Gavoille
Abstract: - La fin de la borne inférieure sur la coloration des cycles (Linial) - Preuve alternative fondé sur le théorème de Ramsey

03 novembre 2016 à 16h06 par 2001:660:6101:403::1:116 -
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- Coloration rapide des cycles - Borne inférieure en log* sur la coloration des cycles - Etat de l'art

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Le modèle LOCAL - Le problème de la coloration - Coloration des 1-orientations en 6 couleurs - De 6 à 3 couleurs - Cas des graphes arbitraires

03 novembre 2016 à 16h05 par 2001:660:6101:403::1:116 -
Lignes 27-28 modifiées:

14 novembre : Petite école du distribué (2/2) titre et orateur à définir

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14 novembre : Petite école du distribué (2/2) Le model LOCAL et la coloration de graphes, Cyril Gavoille

Ligne 34 modifiée:

7 novembre : Petite école du distribué (1/2) titre et orateur à définir \\

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7 novembre : Petite école du distribué (1/2) Le model LOCAL et la coloration de graphes, Cyril Gavoille \\

17 octobre 2016 à 11h16 par 2001:660:6101:402:223:24ff:fe07:ab60 -
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failures prone and asynchronous shared memory systems is investigated. A

 new class of failure detectors, called

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failures prone and asynchronous shared memory systems is investigated. A new class of failure detectors, called

17 octobre 2016 à 11h16 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 61-64 modifiées:

Lundi 17 octobre : titre à définir Ahmed Wade - (???)

Abstract:

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Lundi 17 octobre : Anonymity Preserving Failure Detector Corentin Travers - (Université de Bordeaux)

Abstract: The consensus problem in anonymous, failures prone and asynchronous shared memory systems is investigated. A

 new class of failure detectors, called


anonymity-preserving failure detectors suited to anonymous systems is introduced. As its name indicates, a failure detector in this class cannot be relied upon to break anonymity. For example, the anonymous perfect detector AP , which gives at each process an estimation of the number of processes that have failed belongs to this class. The weakest failure detector among this class for consensus is then determined. This failure detector, called C, may be seen as a loose failures counter: (1) after a failure occurs, the counter is eventually incremented, and (2) if two or more processes are non-faulty, it eventually stabilizes.

13 octobre 2016 à 10h48 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 35-40 ajoutées:

Abstract:

3 novembre : Soutenance de thèse de Claire Capdevielle \\

03 octobre 2016 à 13h50 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 61-64 modifiées:

Lundi 10 octobre : titre à définir Lamine Lamali - (Université de Bordeaux)

Abstract:

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Lundi 10 octobre : Calcul de chemins dans les réseaux multicouches : une approche par la théorie des langages Lamine Lamali - (Université de Bordeaux)

Abstract: Les réseaux multicouches sont des réseaux où plusieurs protocoles coexistent sur différentes couches. Néanmoins, plusieurs architectures réseaux définissent des fonctions de conversion, encapsulation et désencapsulation de protocoles pour pallier cette hétérogénéité. Les algorithmes classiques de calcul de chemins dans les graphes ne peuvent être appliqués dans ce contexte car ils ne prennent pas en compte ces (dés)encapsulations. De plus, les plus courts chemins dans ce type de réseaux ont des caractéristiques non triviales : ils peuvent comporter des boucles et n’ont pas de sous-structure optimale.

Après avoir constaté que les séquences de protocoles associées à un chemin dans un réseau multicouche forment un langage à contexte libre, nous proposons un nouveau modèle de réseau basé sur les automates à pile, ainsi que des algorithmes issus de la théorie des langages pour calculer le(s) plus court(s) chemin(s) dans ce type de réseaux. Nous montrons également que sous contrainte de bande passante, le calcul de chemins devient NP-complet, même dans un réseau symétrique et avec seulement deux protocoles."

19 septembre 2016 à 15h40 par 2001:660:6101:402:223:24ff:fe07:ab60 -
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Lundi 17 octobre : titre à définir Ahmed Wade - (???)

Abstract:

12 septembre 2016 à 14h44 par 147.210.245.180 -
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12 septembre 2016 à 14h43 par 147.210.245.180 -
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Lundi 10 octobre : '' titre à définir ' Lamine Lamali - (Université de Bordeaux)\\

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Lundi 10 octobre : titre à définir Lamine Lamali - (Université de Bordeaux)\\

12 septembre 2016 à 14h42 par 147.210.245.180 -
Ligne 56 modifiée:

Lundi 10 octobre : '' titre à définir' Lamine Lamali - (Université de Bordeaux)\\

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Lundi 10 octobre : '' titre à définir ' Lamine Lamali - (Université de Bordeaux)\\

12 septembre 2016 à 14h42 par 147.210.245.180 -
Ligne 17 ajoutée:
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28-29 novembre : GDR CoA

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28-29 novembre : GDR CoA

Lignes 27-33 modifiées:

lundi 31 octobre : relâche
Abstract: C'est les vacances

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14 novembre : Petite école du distribué (2/2) titre et orateur à définir
Abstract:

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Lundi 24 octobre : Soutenance de thèse de Yessin M. Neggaz - (Université de Bordeaux) \\

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7 novembre : Petite école du distribué (1/2) titre et orateur à définir
Abstract:

lundi 31 octobre : relâche \\

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Abstract:

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Abstract: C'est les vacances

Lundi 24 octobre : Soutenance de thèse de Yessin M. Neggaz - (Université de Bordeaux)
Abstract:

Lundi 10 octobre : '' titre à définir' Lamine Lamali - (Université de Bordeaux)

Abstract:

12 septembre 2016 à 11h52 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 16-30 ajoutées:

28-29 novembre : GDR CoA
Abstract: Programme à venir par ici https://www.irif.univ-paris-diderot.fr/~nschaban/GT-COA/

lundi 31 octobre : relâche
Abstract: C'est les vacances

12 septembre 2016 à 11h43 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 27 modifiée:

Lundi 3 octobre : TBA Marthe Bonamy- (Université de Bordeaux) \\

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Lundi 3 octobre : An overview of discharging methods Marthe Bonamy- (Université de Bordeaux) \\

Lignes 29-32 modifiées:

Abstract:

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Abstract: Discharging methods are used in order to obtain structural lemmas in graph theory. In general, the point is to prove by contradiction that a graph with some properties (planarity, bounded density...) must contain an element of a given list as a subgraph. The idea of this proof technique is as follows: (1) weights are assigned to some elements of the graph (vertices, edges, faces...), (2) a discharging phase allows to redistribute the weights over the graph, (3) using the hypothesis that some subgraphs do not appear in the graph, a weight assessment shows that the total weight is in contradiction with the density/planarity assumptions. In short, it is a counting argument that takes strong advantage of the graph structure. Though the proofs are easier to handle as such for humans, they can be straightforwardly translated into linear programs for the sake of computers.

The existence of a subgraph from this given list can then be used for example for coloring purpose. In particular, this proof technique is decisive for the Four Colour Theorem. During step (2), the weight redistribution is typically local (the weight travels to close elements only). In 2005, Borodin made this technique evolve by introducing global discharging rules (the weight can travel arbitrarily far away). To this day, global discharging methods are still under-developed, but look promising. This talk is meant as an overview of different discharging techniques, through coloring problems they helped answer to. We will also mention their algorithmic appeal, as efficient coloring algorithms as well as tools toward more refined bounds of Fixed Parameter Tractability kernels.

12 septembre 2016 à 11h41 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 31-470 supprimées:

Lundi 20 juin : Gabriel Triangulations and Angle-Monotone Graphs: Local Routing and Recognition Nicolas Bonichon - (Université de Bordeaux)
Abstract: A geometric graph is \emph{angle-monotone} if every pair of vertices has a path between them that---after some rotation---is $x$- and $y$-monotone. Angle-monotone graphs are $\sqrt 2$-spanners and they are increasing\hyp chord graphs. Dehkordi, Frati, and Gudmundsson introduced angle-monotone graphs in 2014 and proved that Gabriel triangulations are angle\hyp monotone graphs. We give a polynomial time algorithm to recognize angle-monotone geometric graphs. We prove that every point set has a plane geometric graph that is \emph{generalized angle-monotone}---specifically, we prove that the \hts is generalized angle-monotone. We give a local routing algorithm for Gabriel triangulations that finds a path from any vertex $s$ to any vertex $t$ whose length is within $1 + \sqrt 2$ times the Euclidean distance from $s$ to $t$. Finally, we prove some lower bounds and limits on local routing algorithms on Gabriel triangulations.

Lundi 30 mai : Randomized Distributed MIS and Colouring Algorithms for Rings with Oriented Edges in O(\sqrt{log n}) bit rounds Akka Zemmari - (Université de Bordeaux)
Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a colouring for anonymous rings with an arbitrary orientation of the edges; their bit complexity and time complexity are O(\sqrt{log n}) with high probability. These algorithms are optimal modulo a multiplicative constant.

Joint work with Yves Métivier and Mike Robson

Lundi 23 mai : Relâche
Abstract: On peut éventuellement aller à Algotel qui débute le lendemain https://algotel2016.labri.fr/

Lundi 16 mai : Relâche
Abstract: Lundi de Pentecôte

Lundi 9 mai : Majority population protocols Leszek Gasieniec (University of Liverpool)
Abstract: We start with the review of literature on majority population protocols. In the considered problem a large group of simple asynchronous entities, each associated with one of the two basic colours, is asked to decide which colour is attributed to the majority. Later we present some extensions of such protocols to different models and tasks. We also show how to amend majority protocols to report equality if neither of the original colours dominates the other in the population. Finally we consider populations with elevated diversity (with larger number of colours) and provide space efficient solutions to the absolute and relative majority problems.

Lundi 2 mai : A General Framework for Reusing Proofs of Termination Detection by Refinement-Based Compositions Maha Boussabbeh - (Université de Bordeaux)
Abstract: We propose a formal framework enhancing the termination detection property of distributed algorithms and reusing their specifications as well as their proofs. By relying on refinement and composition, we show that an algorithm specified with local termination detection, can be reused in order to compute the same algorithm with global termination detection. The main idea relies upon the development of distributed algorithms following a top/down approach and the integration of additional computation steps developed in a pre-defined module. This module is specified in a generic and scalable way in order to be composed with particular developments. Once the composition link is proven, the global termination emerges automatically. This work is done within the DAMPAS project.

Lundi 25 avril : A Faster Counting Protocol for Anonymous Dynamic Networks Alessia Milani - (Université de Bordeaux)
Abstract: We study the problem of counting the number of nodes in a slotted-time communication network, under the challenging assumption that nodes do not have identifiers and the network topology changes frequently. That is, for each time slot links among nodes can change arbitrarily provided that the network is always connected. This network model has been motivated by the ongoing development of new communication technologies that en- able the deployment of a massive number of devices with highly dynamic connectivity patterns. Tolerating dynamic topologies is clearly crucial in face of mobility and unreliable communication. Current communication networks do have node identifiers though. Nevertheless, even if identifiers may be still available in future massive networks, it might be convenient to ignore them if neighboring nodes change all the time. Consequently, knowing what is the cost of anonymity is of paramount importance to understand what is feasible or not for future generations of Dynamic Networks.

Counting is a fundamental task in distributed computing since knowing the size of the system often facilitates the desing of solutions for more complex problems. Also, the size of the system is usually used to decide termination in distributed algorithms. Currently, the best upper bound proved on the running time to compute the exact network size is double-exponential. However, only linear complexity lower bounds are known, leaving open the question of whether efficient Counting protocols for Anonymous Dynamic Networks exist or not.

In this paper we make a significant step towards answering this question by presenting a distributed Counting protocol for Anonymous Dynamic Networks which has exponential time complexity. Our algorithm ensures that eventually every node knows the exact size of the system and stops executing the algorithm. Previous Counting protocols have either double-exponential time complexity, or they are exponential but do not terminate, or terminate but do not provide running-time guarantees, or guarantee only an exponential upper bound on the network size. Other protocols are heuristic and do not guarantee the correct count.

Joint work with Miguel Mosteiro,

Lundi 18 avril : Relâche
Abstract: C'est les vaacaaaannnnces

Lundi 11 avril : Jeux sur les graphes Clément Charpentier - (Université de Lyon)
Abstract: Nous présentons deux jeux sur les graphes, le jeu de coloration et le jeu de poursuite, ainsi que les principales stratégies utilisées pour l'étude de ces jeux. Le premier est une version à deux joueurs du problème de coloration de graphes, l'autre est un jeu de type "gendarmes et voleur" sur les sommets d'un graphe. Nous discutons enfin des variantes distribuées de ces jeux et des possibilités d'étude qu'elles offrent. Candidat MCF

Lundi 4 avril : Le point de vue théorie de l'information et aléatoire sur l'élection de leader -- seconde partie (d'après Beauquier, Blanchard, Burman et Guerraoui) Philippe Duchon - (Université de Bordeaux)
Abstract: La suite de l'exposé de l'exposé du 29 février

Lundi 28 mars : Relâche
Abstract: C'est pââââââques

Lundi 21 mars : Deterministic Leader Election in O(D+ log n) Rounds with Messages of size O(1) Yves Métivier - (Bordeaux INP)
Abstract: We present a distributed algorithm for electing deterministically a leader in a general network where each processor has a unique identifier of size O(log n) (n is the number of nodes in the network). It elects a leader in O(D + log n) rounds (D is the diameter of the network) with messages of size O(1), thus it has a bit complexity of O(D + log n). This substantially improves upon the best known algorithm whose bit complexity is O(D log n). In fact, using the lower bound by Kutten et al. and a result of Dinitz and Solomon, we show that the bit complexity is optimal (up to a multiplicative constant). Furthermore, this algorithm requires no knowledge on the graph, such as n or D. (Travail réalisé avec : A. Casteigts, J.M. Robson, and A. Zemmari)

Lundi 14 mars : Time and Homonyms Considerations over Community Protocols Mikaël Rabie - (LAMSADE, U. Paris Dauphine)
Abstract: Guerraoui and Ruppert introduced the model of Community Protocols. This Distributed System works with agents having a finite memory and unique identifiers (the set of identifiers being ordered). Each agent can store a finite number of identifiers they heard about. The interactions are asynchronous and pairwise, following a fair scheduler. The computation power of this model is fully characterized: it corresponds exactly to what non deterministic Turing Machines can compute on a space O(n\log n). In this talk, I will focus on two restrictions of the model: The first is what happens when agents may share identifiers, the population admitting homonyms. I will introduce a hierarchy, with characterizations depending on the rate of unique identifiers present in the population. The main result is that with log n identifiers, a Turing Machine with a polylogarithmic space can be simulated. The second consider the following time restriction: what can be computed in a polylogarithmic number of parallel interactions. This version is not yet characterized, but I will provide some impossibility results, some computable protocols, and I will give the tighter bound we found.

Lundi 7 mars : Time vs. Information Tradeoffs for Leader Election in Anonymous Trees Christian Glacet - (CNR - IEIIT, Torino, Italy)
Abstract: Dans cette présentation je donnerai des résultats concernant l'élection de leader dans des arbres anonymes.

Dans le modèle utilisé, l'ensemble des nœuds doivent produire en sortie un chemin simple vers l'un d'entre eux, ce dernier sera alors qualifié de leader. Le cas particulier étudié est celui de l'élection lorsque le temps alloué est inférieur au diamètre de l'arbre considéré.

Si aucune information supplémentaire n'est accessible, les nœuds ne pouvant pas avoir une vision complète du réseau, l'élection est impossible et ce quel que soit l'algorithme utilisé. L'étude proposée concerne donc le compromis entre la quantité d'information initialement requise par les nœuds et le temps leur étant alloué pour réaliser l'élection. Le modèle utilisé est celui des algorithmes avec conseil dans lequel un oracle ayant une connaissance complète du réseau, fournit un conseil unique sous forme d'une chaîne binaire, à l'ensemble des nœuds avant que ceux-ci n'initient leurs calculs.

Pour la majorité des valeurs de temps nos bornes inférieures et supérieures sont proches à un facteur multiplicatif près, ou diffèrent seulement d'un facteur logarithmique. Je présenterai le détail des résultats ainsi que les outils utilisés pour l'établissement de deux bornes me paraissant représentatives de cette étude.

Lundi 29 février : Le point de vue théorie de l'information et aléatoire sur l'élection de leader (d'après Beauquier, Blanchard, Burman et Guerraoui) Philippe Duchon - (Université de Bordeaux)
Abstract: Dans un papier récent, Beauquier et al. décrivent des conditions sur l'ordonnancement d'un système distribué (totalement asynchrone), de type théorie de l'information et aléa algorithmique ("algorithmic randomness"), qui permettent d'assurer que tel ou tel problème peut être résolu pour *tout* ordonnancement respectant ces conditions. Les conditions sont du type "la séquence d'actions est T-aléatoire", ce qui signifie qu'un programme générant un n-préfixe de la séquence doit être de taille au moins T.n (le cas T=1 correspond à une séquence aléatoire au sens de Kolmogorov). En particulier, ils montrent que lorsque T=1 est suffisant pour résoudre un problème, il n'est jamais nécessaire - il existe toujours une constante T'<1 qui suffit.

Je n'ai aucun résultat original sur le sujet; je me contenterai de présenter ce que j'en ai compris.

Lundi 22 février : Relâche
Abstract: C'est les vaaaaaaacaaaaances

Lundi 15 février : k-Set Agreement with n − k + 1 Atomic Read/Write Registers Zohir Bouzid - (Université de Bordeaux)
Abstract: The k-set agreement problem is a generalization of the consensus problem. Namely, assuming that each process proposes a value, every non-faulty process should decide one of the proposed values, and no more than k different values should be decided. This is a hard problem in the sense that we cannot solve it in an asynchronous system, as soon as k or more processes may crash. One way to sidestep this impossibility result consists in weakening the termination property, requiring that a process must decide a value only if it executes alone during a long enough period of time.

This is the well-known obstruction-freedom progress condition.

Consider a system of n anonymous asynchronous processes that communicate through atomic read/write registers, and such that any number of them may crash. In this paper, we address and solve the challenging open problem of designing an obstruction-free k-set agreement algorithm using only (n − k + 1) atomic registers. From a shared memory cost point of view, our algorithm is the best algorithm known so far, thereby establishing a new upper bound on the number of registers needed to solve the problem, and in comparison to the previous upper bound, its gain is (n−k) registers.

Joint work with M. Raynal and P. Sutra

Lundi 8 février : Impact de la réplication pour les bases de données distribuées Noël Gillet - (Université Bordeaux )
Abstract: Les bases de données distribuées, massivement utilisées dans le contexte actuel du Big Data, doivent traiter de très grande quantité de requêtes sur les données qu'elles stockent. Une des problématique majeure est donc de minimiser le temps de traitement de ces requêtes. La réplication de données est classiquement utilisée à des fins de robustesse mais rarement pour la performance. Nous proposons un algorithme de gestion de copies qui va adapter le nombre de répliquas de chaque donnée afin de mieux répartir la charge des requêtes entre les différents noeuds stockant ces copies. Nous présentons une évaluation expérimentale de notre algorithme pour la base de données distribuée Apache Cassandra. Nous comparons notamment différents algorithmes d'affectation de requêtes et montrons le gain réel sur le temps de complétion grâce à notre gestion de copies.

Travail en commun avec Nicolas Hanusse et Frédéric Lalanne

Lundi 1 février : Incentives in distributed systems Paolo Penna - (ETH Zurich)
Abstract: In this talk I will give an overview of the role of "incentives" in distributed systems, and how game-theoretic considerations can be used for the analysis of a (distributed) protocol. Roughly speaking, the "participants" of the protocol may deviate from the prescribed "actions" whenever this is convenient for themselves (possibly creating trouble to the overall system).

I will present several applications and examples showing how much incentives can affect the "system performance" and how to cope with that. Along the way, I will discuss how certain "classical" approaches and methods in game theory underly some assumption on distributed system (e.g., synchronization, use of randomness, etc.) and highlight some open questions in this field.

Lundi 25 janvier : Pré-calcul distribué pour la visualisation interactive de densité pour de grands nuages de points Alexandre Perrot - (LaBRI, MaBIOVIS, Université de Bordeaux)
Abstract: Arriver à naviguer en temps réel dans des cartes représentant des milliards de points nécessite de faire des pré-calcul de structures de données distribués. Nous montrerons dans cet exposé un algorithme de calcul distribué d'aggrégation de valeurs ainsi que son implémentation dans un environnement Hadoop dans le cadre d'un système de visualisation pour l'exploration de cartes de chaleur.

Lundi 18 janvier : The read/write protocol complex is collapsible Fernando Benavides - (Instituto de Matematicas, UNAM)
Abstract: The celebrated asynchronous computability theorem provides a characterization of the class of decision tasks that can be solved in a wait-free manner by asynchronous processes that communicate by writing and taking atomic snapshots of a shared memory. Several variations of the model have been proposed (immediate snapshots and iterated immediate snapshots), all equivalent for wait-free solution of decision tasks, in spite of the fact that the protocol complexes that arise from the different models are structurally distinct. The topological and combinatorial properties of these snapshot protocol complexes have been studied in detail, providing explanations for why the asynchronous computability theorem holds in all the models.

In reality concurrent systems do not provide processes with snapshot operations. Instead, snapshots are implemented (by a wait-free protocol) using operations that write and read individual shared memory locations.

Thus, read/write protocols are also computationally equivalent to snapshot protocols. However, the structure of the read/write protocol complex has not been studied. In this paper we show that the read/write iterated protocol complex is collapsible (and hence contractible). Furthermore, we show that a distributed protocol that wait-free implements atomic snapshots in effect is performing the collapses.

This is a joint work with Sergio Rajsbaum.

Lundi 14 décembre : Beachcombing on Strips and Islands David Ilcinkas - (LaBRI, Université de Bordeaux)
Abstract: A group of mobile robots (beachcombers) have to search collectively every point of a given domain. At any given moment, each robot can be in walking mode or in searching mode. It is assumed that each robot's maximum allowed searching speed is strictly smaller than its maximum allowed walking speed. A point of the domain is searched if at least one of the robots visits it in searching mode. The Beachcombers' Problem consists in developing efficient schedules (algorithms) for the robots which collectively search all the points of the given domain as fast as possible. In this talk, I will present recent results on this topic.

Lundi 7 décembre : Rendezvous of Heterogeneous Mobile Agents in Edge-weighted Networks. Ralf Klasing - (LaBRI, Université de Bordeaux)

Abstract: We introduce a variant of the deterministic rendezvous problem for a pair of heterogeneous agents operating in an undirected graph, which differ in the time they require to traverse particular edges of the graph. Each agent knows the complete topology of the graph and the initial positions of both agents. The agent also knows its own traversal times for all of the edges of the graph, but is unaware of the corresponding traversal times for the other agent. The goal of the agents is to meet on an edge or a node of the graph. In this scenario, we study the time required by the agents to meet, compared to the meeting time T_OPT in the offline scenario in which the agents have complete knowledge about each others speed characteristics. When no additional assumptions are made, we show that rendezvous in our model can be achieved after time O(n T_OPT) in a n-node graph, and that such time is essentially in some cases the best possible. However, we prove that the rendezvous time can be reduced to Θ(T_OPT) when the agents are allowed to exchange Θ(n) bits of information at the start of the rendezvous process. We then show that under some natural assumption about the traversal times of edges, the hardness of the heterogeneous rendezvous problem can be substantially decreased, both in terms of time required for rendezvous without communication, and the communication complexity of achieving rendezvous in time Θ(T_OPT).

Lundi 30 novembre : Machine Learning Approach for Android Apps Analysis Akka Zemmari - (LaBRI, Université de Bordeaux)

Abstract: Android being the most popular open source mobile operating system, attracts a plethora of app developers. Millions of applications are developed for Android platform with a great extent of behavioral diversities and are available on Play Store as well as on many third party app stores. Due to its open nature, Android Platform has been targeted by many malware writers. The conventional way of signature-based detection methods for detecting malware on a device are no longer promising due to an exponential increase in the number of variants of the same application with different signatures. In this talk, we present a machine learning approach for malware detection in Android Apps.

Mardi 24 novembre (après-midi): Soutenance de thèse de David Bonnin

Abstract: 14h dans amphi du LaBRI.

Lundi 23 novembre et Mardi 24 novembre (matin): Journées du GT CoA

Abstract: Programme et inscription ici http://5.135.166.57/COA/index.php/welcome/pagePresentation

Lundi 16 novembre : Réunion du thème
Abstract: Réunion du thème Algo Dist

Lundi 9 novembre : Classification automatique de graphes dynamique Yessin Neggaz - (LaBRI, Université de Bordeaux) /!\ SALLE 75 /!\
Abstract: Étant donné un graphe dynamique, donné sous la forme d’une séquence de graphes statiques ou bien comme une succession d’évènements topologiques (apparitions/disparitions de liens de communication), on s’intéresse à tester automatiquement certaines propriétés temporelles sur le graphe. Les propriétés qui nous intéressent correspondent à des conditions nécessaires et/ou suffisantes pour la réalisation de tâches distribuées classiques (élection, diffusion, comptage, etc.) Nous avons répertorié à ce jour une vingtaine de propriétés. Par exemple, le réseau est-il temporellement connexe ? (existence d’un trajet, i.e. d’une succession d’arêtes dont les dates d’existence sont temporellement croissantes, depuis chaque sommet vers chaque autre sommet) ; certaines arêtes réapparaissent-elles dans un temps borné ou de manière périodique ? Leur ensemble vérifie-t-il certaines propriétés ? Être capable de vérifier ce type de propriété automatiquement nous permettrait de déterminer dans un contexte de mobilité donné (p. ex. drones, robots, voitures, dont on peut obtenir ou générer des traces de connexité), les tâches réalisables par l’ensemble des entités.

Lundi 2 novembre : On the Uncontended Complexity of Anonymous Consensus Claire Capdevielle - (LaBRI, Université de Bordeaux)

Abstract: We study on uncontended complexity of anonymous algorithms, counting the number of distinct memory accesses in operations that encounter no contention. We assume that contention-free operations on a concurrent object perform “fast” reads and writes, and resort to more expensive synchronization primitives, such as CAS, only when contention is detected. We call such concurrent implementations interval-solo-fast and derive tight lower bounds on time and space complexity of anonymous interval-solo-fast consensus.

Lundi 26 octobre : Pas d'exposé
On pourra cependant assister le matin à la soutenace de thèse de Vincent Autefage dans l' amphi du LaBRI à 10h dont le titre et le résumé suivent :

''Découverte de services et collaboration au sein d’une flotte hétérogène et hautement dynamique d’objets mobiles communicants autonomes', Vincent Autefage
Résumé: Les systèmes autonomes sont des objets mobiles communicants capables de réaliser un certain nombre de tâches sans intervention humaine. Le coût (e.g. argent, poids, éner- gie) de la charge utile requise pour effectuer certaines missions est parfois trop important pour permettre aux engins d’embarquer la totalité des capacités nécessaires (i.e. capteurs et actionneurs). Répartir ces capacités sur plusieurs entités est une solution naturelle à ce problème. Un tel groupe d’entités constitue une flotte à laquelle devient nécessaire de fournir un mécanisme de découverte permettant aux différents engins de partager leurs capacités respectives afin de résoudre une mission globale de façon collaborative. Ce mé- canisme, outre l’affectation des tâches, doit gérer les conflits et les pannes potentielles qui peuvent survenir à tout moment sur tout engin de la flotte. Fort de ces constations, nous proposons un nouveau mécanisme collaboratif nommé AMiRALE qui apporte une solution aux problèmes ci-dessus pour les flottes hétérogènes d’engins mobiles autonomes. Notre système est entièrement distribué et repose uniquement sur des communications asyn- chrones. Nous proposons également un nouvel outil nommé NEmu permettant de créer des réseaux virtuels mobiles avec un contrôle important sur les propriétés de la topologie du réseau ainsi que sur la configuration des nœuds et des inter-connexions. Cet outil per- met la réalisation d’expérimentations réalistes sur des prototypes d’applications réseaux. Enfin, nous proposons une évaluation de notre système collaboratif AMiRALE au travers d’un scénario de nettoyage de parc utilisant une flotte autonome de drones et de robots terrestres spécialisés.

Lundi 19 octobre : Algorithmes auto-stabilisants pour des paramètres de décomposition et de domination dans les graphes Mohammed Haddad - (Université de Lyon 1)

Abstract: Un système distribué est dit auto-stabilisant s’il peut reprendre un comportement correct en un temps fini après l’occurrence de fautes et ce sans intervention extérieure. De ce fait, l’auto-stabilisation est une approche optimiste pour la tolérance aux fautes dans le sens où elle protège le système des fautes transitoires. Un algorithme auto-stabilisant peut être défini selon différents modèles de communication ainsi que différents modèles de calcul. En effet, prouver la convergence d'un algorithme auto-stabilisant se doit dêtre faite selon un démon/scheduler qui peut être centralisé ou distribué, équitable ou non. De de plus, la complexité de ces algorithmes peut se calculer selon différentes mesures : moves, steps ou rounds, chacune d'entre elles apportant une connaissance propre sur l'algorithme proposé. Cependant, réussir à borner l'ensemble de ces mesures n'est pas toujours trivial, en particulier pour les cas les plus généraux de démons. La littérature des algorithmes auto-stabilisants est très riches. Cependant, nous allons nous intéresser dans cet exposé aux algorithmes auto-stabilisants pour quelques paramètres de théorie des graphes. En particulier, nous nous focaliserons dans un premier temps sur des décompositions particulières des graphes : en triangles et en étoiles uniformes ainsi que des paramètres de domination. Nous nous attarderons par la suite sur les techniques de preuve de convergence utilisées pour ces algorithmes.

Lundi 12 octobre : On Distinguishing Views in Symmetric Networks. Dominik Pająk - (University of Cambridge)
Abstract: The view of a node in a port-labeled network is an infinite tree encoding all walks in the network originating from this node. It is an important concept in the context of symmetry breaking in distributed systems. For example a deterministic rendezvous is infeasible if the agents start from positions with the same views. We want to decide if two views are identical but we would like to compare the infinite trees truncated to certain depth d. We are looking for such d that if the views truncated to depth d are equal then the whole infinite trees are also equal and there are some nodes whose views differ only at depth d. It turns out that truncating to depth Theta(D*log(n/D)) (where D is the diameter and n is the number of nodes) is always sufficient and sometimes necessary to distinguish the views.

The talk will be based on two papers:

Views in a graph: to which depth must equality be checked? Julien M. Hendrickx

Distinguishing Views in Symmetric Networks: A Tight Lower Bound Dariusz Dereniowski, Adrian Kosowski, Dominik Pająk

Lundi 5 octobre : Silent Self-stabilizing BFS Tree Algorithms Revised Colette Johnen - (LaBRI, Université de Bordeaux)
Abstract: Analysis of two fundamental results of the self-stabilizing literature about silent BFS spanning tree constructions: the Dolev et al algorithm and the Huang and Chen's algorithm. More precisely, we propose in the composite atomicity model three straightforward adaptations inspired from those algorithms. We then present a deep study of these three algorithms. Our results are related to both correctness (convergence and closure, assuming a distributed unfair daemon) and complexity (analysis of the stabilization time in terms of rounds and steps).

(joint work with with Stéphane Devismes - VERIMAG)

Lundi 28 septembre : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

Abstract: La suite de l'exposé du 18 mai. JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

Lundi 21 septembre : Bridging the Gap between Performance and Bounds of Cholesky Factorization on Heterogeneous Platforms / Planar graphs and power domination + réunion de rentrée du thème Suraj Kumar/Claire Pennarun - (LaBRI, Université de Bordeaux)

Abstract: Nous écouterons Claire et Suraj nous exposer brièvement leur sujet de thèse et leur premiers résultats. Les exposés seront suivi de la réunion de rentrée du thème.

Suraj Kumar: Bridging the Gap between Performance and Bounds of Cholesky Factorization on Heterogeneous Platforms

Abstract: We consider the scheduling problem of Cholesky factorization on heterogeneous system. In this context we investigate how to adding static information based on an offline analysis to the scheduler improve their performance. We are comparing simulated performance with different theoretical bounds which we introduce.

Claire Pennarun: Planar graphs and power domination

12 juillet 2016 à 18h05 par 88.122.54.83 -
Ligne 20 modifiée:

Lundi 3 octobre : TBA Marthe Bonamy- (Université de Bordeaux) \\

en:

Lundi 24 octobre : Soutenance de thèse de Yessin M. Neggaz - (Université de Bordeaux) \\

Ligne 27 modifiée:

Lundi 24 septembre : Soutenance de thèse de Yessin M. Neggaz - (Université de Bordeaux) \\

en:

Lundi 3 octobre : TBA Marthe Bonamy- (Université de Bordeaux) \\

12 juillet 2016 à 18h04 par 88.122.54.83 -
Lignes 21-27 ajoutées:

Abstract:

Lundi 24 septembre : Soutenance de thèse de Yessin M. Neggaz - (Université de Bordeaux) \\

16 juin 2016 à 18h30 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 17 ajoutée:
Ligne 20 modifiée:

Lundi 20 juin : TBA Nicolas Bonichon - (Université de Bordeaux) \\

en:

Lundi 3 octobre : TBA Marthe Bonamy- (Université de Bordeaux) \\

Lignes 23-36 ajoutées:

Lundi 20 juin : Gabriel Triangulations and Angle-Monotone Graphs: Local Routing and Recognition Nicolas Bonichon - (Université de Bordeaux)
Abstract: A geometric graph is \emph{angle-monotone} if every pair of vertices has a path between them that---after some rotation---is $x$- and $y$-monotone. Angle-monotone graphs are $\sqrt 2$-spanners and they are increasing\hyp chord graphs. Dehkordi, Frati, and Gudmundsson introduced angle-monotone graphs in 2014 and proved that Gabriel triangulations are angle\hyp monotone graphs. We give a polynomial time algorithm to recognize angle-monotone geometric graphs. We prove that every point set has a plane geometric graph that is \emph{generalized angle-monotone}---specifically, we prove that the \hts is generalized angle-monotone. We give a local routing algorithm for Gabriel triangulations that finds a path from any vertex $s$ to any vertex $t$ whose length is within $1 + \sqrt 2$ times the Euclidean distance from $s$ to $t$. Finally, we prove some lower bounds and limits on local routing algorithms on Gabriel triangulations.

30 mai 2016 à 14h07 par 2001:660:6101:403::1:159 -
Lignes 16-21 ajoutées:

Lundi 20 juin : TBA Nicolas Bonichon - (Université de Bordeaux)
Abstract:

08 mai 2016 à 17h41 par 92.89.74.148 -
Lignes 17-18 modifiées:
en:

Ligne 23 modifiée:
 Joint work with Yves Métivier and Mike Robson

en:

Joint work with Yves Métivier and Mike Robson

08 mai 2016 à 17h41 par 92.89.74.148 -
Ligne 18 modifiée:

Lundi 30 mai : TBA Akka Zemmari - (Université de Bordeaux) \\

en:

Lundi 30 mai : Randomized Distributed MIS and Colouring Algorithms for Rings with Oriented Edges in O(\sqrt{log n}) bit rounds Akka Zemmari - (Université de Bordeaux) \\

Lignes 20-24 modifiées:

Abstract:

en:

Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a colouring for anonymous rings with an arbitrary orientation of the edges; their bit complexity and time complexity are O(\sqrt{log n}) with high probability. These algorithms are optimal modulo a multiplicative constant.

 Joint work with Yves Métivier and Mike Robson


03 mai 2016 à 15h17 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 16-46 ajoutées:

Lundi 30 mai : TBA Akka Zemmari - (Université de Bordeaux)
Abstract:

Lundi 23 mai : Relâche
Abstract: On peut éventuellement aller à Algotel qui débute le lendemain https://algotel2016.labri.fr/

Lundi 16 mai : Relâche
Abstract: Lundi de Pentecôte

Lundi 9 mai : Majority population protocols Leszek Gasieniec (University of Liverpool)
Abstract: We start with the review of literature on majority population protocols. In the considered problem a large group of simple asynchronous entities, each associated with one of the two basic colours, is asked to decide which colour is attributed to the majority. Later we present some extensions of such protocols to different models and tasks. We also show how to amend majority protocols to report equality if neither of the original colours dominates the other in the population. Finally we consider populations with elevated diversity (with larger number of colours) and provide space efficient solutions to the absolute and relative majority problems.

10 avril 2016 à 19h52 par 92.89.74.148 -
Lignes 67-69 modifiées:

Lundi 11 avril : TBA Clément Charpentier - (Université de Lyon)
Abstract: à venir

en:

Lundi 11 avril : Jeux sur les graphes Clément Charpentier - (Université de Lyon)
Abstract: Nous présentons deux jeux sur les graphes, le jeu de coloration et le jeu de poursuite, ainsi que les principales stratégies utilisées pour l'étude de ces jeux. Le premier est une version à deux joueurs du problème de coloration de graphes, l'autre est un jeu de type "gendarmes et voleur" sur les sommets d'un graphe. Nous discutons enfin des variantes distribuées de ces jeux et des possibilités d'étude qu'elles offrent.

21 mars 2016 à 15h20 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 16-24 ajoutées:

Lundi 2 mai : A General Framework for Reusing Proofs of Termination Detection by Refinement-Based Compositions Maha Boussabbeh - (Université de Bordeaux)
Abstract: We propose a formal framework enhancing the termination detection property of distributed algorithms and reusing their specifications as well as their proofs. By relying on refinement and composition, we show that an algorithm specified with local termination detection, can be reused in order to compute the same algorithm with global termination detection. The main idea relies upon the development of distributed algorithms following a top/down approach and the integration of additional computation steps developed in a pre-defined module. This module is specified in a generic and scalable way in order to be composed with particular developments. Once the composition link is proven, the global termination emerges automatically. This work is done within the DAMPAS project.

10 mars 2016 à 10h29 par 2001:660:6101:402:224:e8ff:fefb:d350 -
Ligne 80 modifiée:

Abstract: We present a distributed algorithm for electing deterministically a leader in a general network where each processor has a unique identifier of size O(log n) (n is the number of nodes in the network). It elects a leader in O(D +log n) rounds (D is the diameter of the network) with messages of size O(1), thus it has a bit complexity of O(D + log n). This substantially improves upon the best known algorithm whose bit complexity is O(D\log n). In fact, using the lower bound by Kutten et al. and a result of Dinitz and Solomon, we show that the bit complexity is optimal (up to a multiplicative constant). Furthermore, this algorithm requires no knowledge on the graph, such as n or D.

en:

Abstract: We present a distributed algorithm for electing deterministically a leader in a general network where each processor has a unique identifier of size O(log n) (n is the number of nodes in the network). It elects a leader in O(D + log n) rounds (D is the diameter of the network) with messages of size O(1), thus it has a bit complexity of O(D + log n). This substantially improves upon the best known algorithm whose bit complexity is O(D log n). In fact, using the lower bound by Kutten et al. and a result of Dinitz and Solomon, we show that the bit complexity is optimal (up to a multiplicative constant). Furthermore, this algorithm requires no knowledge on the graph, such as n or D.

10 mars 2016 à 10h28 par 2001:660:6101:402:224:e8ff:fefb:d350 -
Lignes 80-82 modifiées:

Abstract: We present a distributed algorithm for electing deterministically a leader in a general network where each processor has a unique identifier of size O(log n) (n is the number of nodes in the network). It elects a leader in O(D +log n) rounds (D is the diameter of the network) with messages of size O(1), thus it has a bit complexity of O(D + log n). This substantially improves upon the best known algorithm whose bit

  complexity is O(D\log n). In fact, using the lower bound by Kutten et al. and a result of Dinitz and Solomon, we show that the bit complexity
is optimal (up to a multiplicative constant). Furthermore, this algorithm requires no knowledge on the graph, such as n or D.

en:

Abstract: We present a distributed algorithm for electing deterministically a leader in a general network where each processor has a unique identifier of size O(log n) (n is the number of nodes in the network). It elects a leader in O(D +log n) rounds (D is the diameter of the network) with messages of size O(1), thus it has a bit complexity of O(D + log n). This substantially improves upon the best known algorithm whose bit complexity is O(D\log n). In fact, using the lower bound by Kutten et al. and a result of Dinitz and Solomon, we show that the bit complexity is optimal (up to a multiplicative constant). Furthermore, this algorithm requires no knowledge on the graph, such as n or D.

10 mars 2016 à 10h27 par 2001:660:6101:402:224:e8ff:fefb:d350 -
Lignes 80-92 modifiées:

Abstract: We present a distributed algorithm for

  electing deterministically a leader in a general network where each
processor has a unique identifier of size O(log n)  (n is the
number of nodes in the network). It elects a leader in O(D +log
n) rounds (D is the diameter of the network) with messages of
size O(1), thus it has a bit complexity of O(D + log n). This
substantially improves upon the best known algorithm whose bit
complexity is O(D\log n). In fact, using the lower bound by Kutten
et al. and a result of Dinitz and
Solomon, we show that the bit complexity
is optimal (up to a multiplicative constant). Furthermore,
this algorithm requires no knowledge on the graph, such as n or
D.

en:

Abstract: We present a distributed algorithm for electing deterministically a leader in a general network where each processor has a unique identifier of size O(log n) (n is the number of nodes in the network). It elects a leader in O(D +log n) rounds (D is the diameter of the network) with messages of size O(1), thus it has a bit complexity of O(D + log n). This substantially improves upon the best known algorithm whose bit

  complexity is O(D\log n). In fact, using the lower bound by Kutten et al. and a result of Dinitz and Solomon, we show that the bit complexity
is optimal (up to a multiplicative constant). Furthermore, this algorithm requires no knowledge on the graph, such as n or D.

10 mars 2016 à 10h24 par 2001:660:6101:402:224:e8ff:fefb:d350 -
Lignes 79-81 modifiées:

Lundi 21 mars : Deterministic Leader Election in O(D+\log n) Rounds with Messages of size O(1) Yves Métivier - (Bordeaux INP)
Abstract:

  We  present a distributed algorithm for

en:

Lundi 21 mars : Deterministic Leader Election in O(D+ log n) Rounds with Messages of size O(1) Yves Métivier - (Bordeaux INP)
Abstract: We present a distributed algorithm for

Ligne 92 modifiée:
  D$.  en:  D.  10 mars 2016 à 10h23 par 2001:660:6101:402:224:e8ff:fefb:d350 - Lignes 83-86 modifiées:  processor has a unique identifier of size$O(\log n)$($n$is the number of nodes in the network). It elects a leader in$O(D +\log
n)$rounds ($D$is the diameter of the network) with messages of size$O(1)$, thus it has a bit complexity of$O(D +\log n)$. This  en:  processor has a unique identifier of size O(log n) (n is the number of nodes in the network). It elects a leader in O(D +log n) rounds (D is the diameter of the network) with messages of size O(1), thus it has a bit complexity of O(D + log n). This  Lignes 88-95 modifiées:  complexity is$O(D\log n)$. In fact, using the lower bound by Kutten et al.~\cite{KPPRT15} and a result of Dinitz and Solomon~\cite{DS07}, we show that the bit complexity  %(as defined in \cite{KOSS})  of \STT is optimal (up to a multiplicative constant). Furthermore, this algorithm requires no knowledge on the graph, such as$n$or$D$.  Abstract: en:  complexity is O(D\log n). In fact, using the lower bound by Kutten et al. and a result of Dinitz and Solomon, we show that the bit complexity is optimal (up to a multiplicative constant). Furthermore, this algorithm requires no knowledge on the graph, such as n or D$.

10 mars 2016 à 10h19 par 2001:660:6101:402:224:e8ff:fefb:d350 -
Lignes 79-80 modifiées:

Lundi 21 mars : Deterministic Leader Election in O(D+\log n) Rounds with Messages of size O(1) Yves Métivier - (Université de Bordeaux) \\

en:

Lundi 21 mars : Deterministic Leader Election in O(D+\log n) Rounds with Messages of size O(1) Yves Métivier - (Bordeaux INP)
Abstract:

10 mars 2016 à 10h18 par 2001:660:6101:402:224:e8ff:fefb:d350 -
Ligne 80 modifiée:
  We  present a distributed algorithm, called \STT, for

en:
  We  present a distributed algorithm for

10 mars 2016 à 10h16 par 2001:660:6101:402:224:e8ff:fefb:d350 -
Lignes 80-88 modifiées:

Abstract: We present a bit complexity optimal (modulo a multiplicative constant) distributed algorithm for electing deterministically a leader in a general network where each processor has a unique identifier of size $O(\log n)$ ($n$ is the size of the network). It elects a leader in $O(D +\log n)$ rounds ($D$ is the diameter of the network) with messages of size $O(1)$ thus its bit complexity is also $O(D +\log n)$. This algorithm needs no knowledge on the graph as the size or the diameter.

en:
  We  present a distributed algorithm, called \STT, for
electing deterministically a leader in a general network where each
processor has a unique identifier of size $O(\log n)$ ($n$ is the
number of nodes in the network). It elects a leader in $O(D +\log n)$ rounds ($D$ is the diameter of the network) with messages of
size $O(1)$, thus it has a bit complexity of $O(D +\log n)$. This
substantially improves upon the best known algorithm whose bit
complexity is $O(D\log n)$. In fact, using the lower bound by Kutten
et al.~\cite{KPPRT15} and a result of Dinitz and
Solomon~\cite{DS07}, we show that the bit complexity


%(as defined in \cite{KOSS})

  of \STT is optimal (up to a multiplicative constant). Furthermore,
this algorithm requires no knowledge on the graph, such as $n$ or
$D$.


Abstract:

08 mars 2016 à 16h20 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 18 modifiée:

Lundi 28 mars : Relâche \\

en:

Lundi 25 avril : A Faster Counting Protocol for Anonymous Dynamic Networks Alessia Milani - (Université de Bordeaux) \\

Lignes 20-50 ajoutées:

Abstract: We study the problem of counting the number of nodes in a slotted-time communication network, under the challenging assumption that nodes do not have identifiers and the network topology changes frequently. That is, for each time slot links among nodes can change arbitrarily provided that the network is always connected. This network model has been motivated by the ongoing development of new communication technologies that en- able the deployment of a massive number of devices with highly dynamic connectivity patterns. Tolerating dynamic topologies is clearly crucial in face of mobility and unreliable communication. Current communication networks do have node identifiers though. Nevertheless, even if identifiers may be still available in future massive networks, it might be convenient to ignore them if neighboring nodes change all the time. Consequently, knowing what is the cost of anonymity is of paramount importance to understand what is feasible or not for future generations of Dynamic Networks.

Counting is a fundamental task in distributed computing since knowing the size of the system often facilitates the desing of solutions for more complex problems. Also, the size of the system is usually used to decide termination in distributed algorithms. Currently, the best upper bound proved on the running time to compute the exact network size is double-exponential. However, only linear complexity lower bounds are known, leaving open the question of whether efficient Counting protocols for Anonymous Dynamic Networks exist or not.

In this paper we make a significant step towards answering this question by presenting a distributed Counting protocol for Anonymous Dynamic Networks which has exponential time complexity. Our algorithm ensures that eventually every node knows the exact size of the system and stops executing the algorithm. Previous Counting protocols have either double-exponential time complexity, or they are exponential but do not terminate, or terminate but do not provide running-time guarantees, or guarantee only an exponential upper bound on the network size. Other protocols are heuristic and do not guarantee the correct count.

Joint work with Miguel Mosteiro,

Lundi 18 avril : Relâche

Ligne 52 modifiée:

C'est pââââââques

en:

C'est les vaacaaaannnnces

08 mars 2016 à 16h11 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 16-37 ajoutées:

Lundi 28 mars : Relâche
Abstract: C'est pââââââques

Lundi 11 avril : TBA Clément Charpentier - (Université de Lyon)
Abstract: à venir Candidat MCF

Lundi 4 avril : Le point de vue théorie de l'information et aléatoire sur l'élection de leader -- seconde partie (d'après Beauquier, Blanchard, Burman et Guerraoui) Philippe Duchon - (Université de Bordeaux)
Abstract: La suite de l'exposé de l'exposé du 29 février

27 février 2016 à 22h05 par 92.89.74.148 -
Lignes 66-67 modifiées:

Lundi 29 février : ' Le point de vue "théorie de l'information et aléatoire" sur l'élection de leader (d'après Beauquier, Blanchard, Burman et Guerraoui) ' Philippe Duchon - (Université de Bordeaux) \\

en:

Lundi 29 février : Le point de vue théorie de l'information et aléatoire sur l'élection de leader (d'après Beauquier, Blanchard, Burman et Guerraoui) Philippe Duchon - (Université de Bordeaux) \\

27 février 2016 à 22h04 par 92.89.74.148 -
Lignes 66-67 modifiées:

Lundi 29 février : TBA Philippe Duchon - (Université de Bordeaux) \\

en:

Lundi 29 février : ' Le point de vue "théorie de l'information et aléatoire" sur l'élection de leader (d'après Beauquier, Blanchard, Burman et Guerraoui) ' Philippe Duchon - (Université de Bordeaux) \\

Lignes 69-72 modifiées:

Abstract:

en:

Abstract: Dans un papier récent, Beauquier et al. décrivent des conditions sur l'ordonnancement d'un système distribué (totalement asynchrone), de type théorie de l'information et aléa algorithmique ("algorithmic randomness"), qui permettent d'assurer que tel ou tel problème peut être résolu pour *tout* ordonnancement respectant ces conditions. Les conditions sont du type "la séquence d'actions est T-aléatoire", ce qui signifie qu'un programme générant un n-préfixe de la séquence doit être de taille au moins T.n (le cas T=1 correspond à une séquence aléatoire au sens de Kolmogorov). En particulier, ils montrent que lorsque T=1 est suffisant pour résoudre un problème, il n'est jamais nécessaire - il existe toujours une constante T'<1 qui suffit.

Je n'ai aucun résultat original sur le sujet; je me contenterai de présenter ce que j'en ai compris.

11 février 2016 à 11h00 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 81 modifiée:

Lundi 15 février : A définir Zohir Bouzid - (Université de Bordeaux) \\

en:

Lundi 15 février : k-Set Agreement with n − k + 1 Atomic Read/Write Registers Zohir Bouzid - (Université de Bordeaux) \\

Lignes 83-85 modifiées:

Abstract: TBA

en:

Abstract: The k-set agreement problem is a generalization of the consensus problem. Namely, assuming that each process proposes a value, every non-faulty process should decide one of the proposed values, and no more than k different values should be decided. This is a hard problem in the sense that we cannot solve it in an asynchronous system, as soon as k or more processes may crash. One way to sidestep this impossibility result consists in weakening the termination property, requiring that a process must decide a value only if it executes alone during a long enough period of time.

This is the well-known obstruction-freedom progress condition.

Consider a system of n anonymous asynchronous processes that communicate through atomic read/write registers, and such that any number of them may crash. In this paper, we address and solve the challenging open problem of designing an obstruction-free k-set agreement algorithm using only (n − k + 1) atomic registers. From a shared memory cost point of view, our algorithm is the best algorithm known so far, thereby establishing a new upper bound on the number of registers needed to solve the problem, and in comparison to the previous upper bound, its gain is (n−k) registers.

Joint work with M. Raynal and P. Sutra

09 février 2016 à 14h52 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 26-27 modifiées:

Lundi 21 mars : ' Deterministic Leader Election in O(D+\log n) Rounds with Messages of size O(1) ' Yves Métivier - (Université de Bordeaux) \\

en:

Lundi 21 mars : Deterministic Leader Election in O(D+\log n) Rounds with Messages of size O(1) Yves Métivier - (Université de Bordeaux) \\

09 février 2016 à 14h52 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 26 modifiée:

Lundi 21 mars : ' Deterministic Leader Election in O(D+\log n) Rounds

en:

Lundi 21 mars : ' Deterministic Leader Election in O(D+\log n) Rounds

Lignes 29-30 modifiées:

Abstract:

 We present a bit complexity optimal (modulo a multiplicative constant)

en:

Abstract: We present a bit complexity optimal (modulo a multiplicative constant)

09 février 2016 à 14h51 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 26-27 modifiées:

Lundi 21 mars : TBA Yves Métivier - (Université de Bordeaux) \\

en:

Lundi 21 mars : ' Deterministic Leader Election in O(D+\log n) Rounds with Messages of size O(1) ' Yves Métivier - (Université de Bordeaux) \\

Lignes 30-38 modifiées:
en:
 We present a bit complexity optimal (modulo a multiplicative constant)


distributed algorithm for electing deterministically a leader in a general network where each processor has a unique identifier of size $O(\log n)$ ($n$ is the size of the network). It elects a leader in $O(D +\log n)$ rounds ($D$ is the diameter of the network) with messages of size $O(1)$ thus its bit complexity is also $O(D +\log n)$. This algorithm needs no knowledge on the graph as the size or the diameter. (Travail réalisé avec : A. Casteigts, J.M. Robson, and A. Zemmari)

09 février 2016 à 10h39 par 92.95.247.235 -
Lignes 23-28 ajoutées:

Lundi 21 mars : TBA Yves Métivier - (Université de Bordeaux)
Abstract:

09 février 2016 à 09h28 par 92.95.247.235 -
Lignes 16-24 ajoutées:

Lundi 28 mars : Relâche
Abstract: C'est pââââââques

07 février 2016 à 22h15 par 92.95.247.235 -
Ligne 71 ajoutée:

Travail en commun avec Nicolas Hanusse et Frédéric Lalanne

07 février 2016 à 22h14 par 92.95.247.235 -
Ligne 67 modifiée:

Lundi 8 février : Algorithme distribué d'orientation de graphes dans un environnement asynchrone et avec pannes Noël Gillet - (Université Bordeaux ) \\

en:

Lundi 8 février : Impact de la réplication pour les bases de données distribuées Noël Gillet - (Université Bordeaux ) \\

Lignes 69-84 modifiées:

Abstract: Soit G un graphe non orienté, trouver l'orientation de G afin de minimiser le degré sortant est un problème bien connu en théorie des graphes. Parmi les applications qui en découlent, on peut notamment citer l'équilibrage de charge ou le stockage compact de graphes. Soit \Delta le minimum des degrés entrants maximaux parmi l'ensemble des orientations. Concevoir un algorithme distribué efficace tant du point de vue du temps ou de la mémoire et fonctionnant dans un environnement avec pannes reste un problème ouvert. Nous montrons tout d'abord qu'il n'existe pas d'algorithme d'orientation (2-\epsilon)-approché utilisant moins de D rondes de communication, où D correspond au diamètre du graphe.

Nous proposons ensuite un algorithme purement asynchrone dans le modèle par passage de message et qui fonctionne avec des pannes. L'algorithme effectue un nombre logarithmique de diffusion dans le graphe et produit une \max((4+2\epsilon)\Delta,\Delta+2f/\epsilon)-orientation avec \Delta le paramètre d'orientation optimal et f le nombre de pannes.

en:

Abstract: Les bases de données distribuées, massivement utilisées dans le contexte actuel du Big Data, doivent traiter de très grande quantité de requêtes sur les données qu'elles stockent. Une des problématique majeure est donc de minimiser le temps de traitement de ces requêtes. La réplication de données est classiquement utilisée à des fins de robustesse mais rarement pour la performance. Nous proposons un algorithme de gestion de copies qui va adapter le nombre de répliquas de chaque donnée afin de mieux répartir la charge des requêtes entre les différents noeuds stockant ces copies. Nous présentons une évaluation expérimentale de notre algorithme pour la base de données distribuée Apache Cassandra. Nous comparons notamment différents algorithmes d'affectation de requêtes et montrons le gain réel sur le temps de complétion grâce à notre gestion de copies.

04 février 2016 à 13h41 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 67-68 modifiées:

Lundi 8 février : ' Algorithme distribué d'orientation de graphes dans un environnement asynchrone et avec pannes ' Noël Gillet - (Université Bordeaux ) \\

en:

Lundi 8 février : Algorithme distribué d'orientation de graphes dans un environnement asynchrone et avec pannes Noël Gillet - (Université Bordeaux ) \\

Ligne 83 modifiée:

paramètre d'orientation optimal et f le nombre de pannes."

en:

paramètre d'orientation optimal et f le nombre de pannes.

04 février 2016 à 13h37 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 67-68 modifiées:

Lundi 8 février : A définir Noël Gillet - (Université Bordeaux ) \\

en:

Lundi 8 février : ' Algorithme distribué d'orientation de graphes dans un environnement asynchrone et avec pannes ' Noël Gillet - (Université Bordeaux ) \\

Lignes 70-71 modifiées:

Abstract: TBA

en:

Abstract: Soit G un graphe non orienté, trouver l'orientation de G afin de minimiser le degré sortant est un problème bien connu en théorie des graphes. Parmi les applications qui en découlent, on peut notamment citer l'équilibrage de charge ou le stockage compact de graphes. Soit \Delta le minimum des degrés entrants maximaux parmi l'ensemble des orientations. Concevoir un algorithme distribué efficace tant du point de vue du temps ou de la mémoire et fonctionnant dans un environnement avec pannes reste un problème ouvert. Nous montrons tout d'abord qu'il n'existe pas d'algorithme d'orientation (2-\epsilon)-approché utilisant moins de D rondes de communication, où D correspond au diamètre du graphe.

Nous proposons ensuite un algorithme purement asynchrone dans le modèle par passage de message et qui fonctionne avec des pannes. L'algorithme effectue un nombre logarithmique de diffusion dans le graphe et produit une \max((4+2\epsilon)\Delta,\Delta+2f/\epsilon)-orientation avec \Delta le paramètre d'orientation optimal et f le nombre de pannes."

01 février 2016 à 16h58 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 29-40 modifiées:
en:

Lundi 7 mars : Time vs. Information Tradeoffs for Leader Election in Anonymous Trees Christian Glacet - (CNR - IEIIT, Torino, Italy)
Abstract: Dans cette présentation je donnerai des résultats concernant l'élection de leader dans des arbres anonymes.

Dans le modèle utilisé, l'ensemble des nœuds doivent produire en sortie un chemin simple vers l'un d'entre eux, ce dernier sera alors qualifié de leader. Le cas particulier étudié est celui de l'élection lorsque le temps alloué est inférieur au diamètre de l'arbre considéré.

Si aucune information supplémentaire n'est accessible, les nœuds ne pouvant pas avoir une vision complète du réseau, l'élection est impossible et ce quel que soit l'algorithme utilisé. L'étude proposée concerne donc le compromis entre la quantité d'information initialement requise par les nœuds et le temps leur étant alloué pour réaliser l'élection. Le modèle utilisé est celui des algorithmes avec conseil dans lequel un oracle ayant une connaissance complète du réseau, fournit un conseil unique sous forme d'une chaîne binaire, à l'ensemble des nœuds avant que ceux-ci n'initient leurs calculs.

Pour la majorité des valeurs de temps nos bornes inférieures et supérieures sont proches à un facteur multiplicatif près, ou diffèrent seulement d'un facteur logarithmique. Je présenterai le détail des résultats ainsi que les outils utilisés pour l'établissement de deux bornes me paraissant représentatives de cette étude.

28 janvier 2016 à 10h08 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 18 modifiée:

Lundi 14 mars : TBA Mikaël Rabie - (LAMSADE, U. Paris Dauphine) \\

en:

Lundi 14 mars : Time and Homonyms Considerations over Community Protocols Mikaël Rabie - (LAMSADE, U. Paris Dauphine) \\

Lignes 20-25 modifiées:

Abstract:

en:

Abstract: Guerraoui and Ruppert introduced the model of Community Protocols. This Distributed System works with agents having a finite memory and unique identifiers (the set of identifiers being ordered). Each agent can store a finite number of identifiers they heard about. The interactions are asynchronous and pairwise, following a fair scheduler. The computation power of this model is fully characterized: it corresponds exactly to what non deterministic Turing Machines can compute on a space O(n\log n). In this talk, I will focus on two restrictions of the model: The first is what happens when agents may share identifiers, the population admitting homonyms. I will introduce a hierarchy, with characterizations depending on the rate of unique identifiers present in the population. The main result is that with log n identifiers, a Turing Machine with a polylogarithmic space can be simulated. The second consider the following time restriction: what can be computed in a polylogarithmic number of parallel interactions. This version is not yet characterized, but I will provide some impossibility results, some computable protocols, and I will give the tighter bound we found.

25 janvier 2016 à 11h10 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 18 modifiée:

Lundi 14 mars : TBA Mikaël Rabie - (LIX) \\

en:

Lundi 14 mars : TBA Mikaël Rabie - (LAMSADE, U. Paris Dauphine) \\

21 janvier 2016 à 11h26 par 2001:660:6101:402:223:24ff:fe07:ab60 -
21 janvier 2016 à 11h26 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 59-60 modifiées:

Lundi 1 février : ' Incentives in distributed systems

 ' Paolo Penna  - (ETH Zurich)  \\

en:

Lundi 1 février : Incentives in distributed systems Paolo Penna - (ETH Zurich) \\

21 janvier 2016 à 11h19 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 59-60 modifiées:

Lundi 1 février : A définir Paolo Penna ??? - (Université Paris-Diderot) \\

en:

Lundi 1 février : ' Incentives in distributed systems

 ' Paolo Penna  - (ETH Zurich)  \\

Lignes 62-66 modifiées:

Abstract:

en:

Abstract: In this talk I will give an overview of the role of "incentives" in distributed systems, and how game-theoretic considerations can be used for the analysis of a (distributed) protocol. Roughly speaking, the "participants" of the protocol may deviate from the prescribed "actions" whenever this is convenient for themselves (possibly creating trouble to the overall system).

I will present several applications and examples showing how much incentives can affect the "system performance" and how to cope with that. Along the way, I will discuss how certain "classical" approaches and methods in game theory underly some assumption on distributed system (e.g., synchronization, use of randomness, etc.) and highlight some open questions in this field.

20 janvier 2016 à 16h11 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 16-24 ajoutées:

Lundi 14 mars : TBA Mikaël Rabie - (LIX)
Abstract:

14 janvier 2016 à 10h29 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 34 modifiée:

Lundi 15 février : A définir ??? - (Université ) \\

en:

Lundi 15 février : A définir Zohir Bouzid - (Université de Bordeaux) \\

Lignes 36-39 modifiées:

Abstract:

en:

Abstract: TBA

Ligne 42 modifiée:

Lundi 8 février : A définir ??? - (Université ) \\

en:

Lundi 8 février : A définir Noël Gillet - (Université Bordeaux ) \\

Lignes 44-51 ajoutées:

Abstract: TBA

Lundi 1 février : A définir Paolo Penna ??? - (Université Paris-Diderot)

Ligne 54 supprimée:
Ligne 57 modifiée:

Lundi 1 février : A définir Paolo Penna ??? - (Université Paris-Diderot) \\

en:

Lundi 25 janvier : Pré-calcul distribué pour la visualisation interactive de densité pour de grands nuages de points Alexandre Perrot - (LaBRI, MaBIOVIS, Université de Bordeaux) \\

Lignes 60-67 modifiées:

Lundi 25 janvier : Pré-calcul distribué pour la visualisation interactive de densité pour de grands nuages de points Alexandre Perrot - (LaBRI, MaBIOVIS, Université de Bordeaux)
Abstract: Arriver à naviguer en temps réel dans des cartes représentant des milliards de points nécessite de faire des pré-calcul de structures de données distribués. Nous montrerons dans cet exposé un algorithme de calcul distribué d'aggrégation de valeurs, son implémentation dans un environnement Hadoop et une démonstration pour l'exploration de cartes de chaleur.

en:

Arriver à naviguer en temps réel dans des cartes représentant des milliards de points nécessite de faire des pré-calcul de structures de données distribués. Nous montrerons dans cet exposé un algorithme de calcul distribué d'aggrégation de valeurs ainsi que son implémentation dans un environnement Hadoop dans le cadre d'un système de visualisation pour l'exploration de cartes de chaleur.

11 janvier 2016 à 17h27 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 16 ajoutée:
Lignes 18-85 ajoutées:

Lundi 29 février : TBA Philippe Duchon - (Université de Bordeaux)
Abstract:

Lundi 22 février : Relâche
Abstract: C'est les vaaaaaaacaaaaances

Lundi 15 février : A définir ??? - (Université )
Abstract:

Lundi 8 février : A définir ??? - (Université )
Abstract:

Lundi 1 février : A définir Paolo Penna ??? - (Université Paris-Diderot)
Abstract:

Lundi 25 janvier : Pré-calcul distribué pour la visualisation interactive de densité pour de grands nuages de points Alexandre Perrot - (LaBRI, MaBIOVIS, Université de Bordeaux)
Abstract: Arriver à naviguer en temps réel dans des cartes représentant des milliards de points nécessite de faire des pré-calcul de structures de données distribués. Nous montrerons dans cet exposé un algorithme de calcul distribué d'aggrégation de valeurs, son implémentation dans un environnement Hadoop et une démonstration pour l'exploration de cartes de chaleur.

Lundi 18 janvier : The read/write protocol complex is collapsible Fernando Benavides - (Instituto de Matematicas, UNAM)
Abstract: The celebrated asynchronous computability theorem provides a characterization of the class of decision tasks that can be solved in a wait-free manner by asynchronous processes that communicate by writing and taking atomic snapshots of a shared memory. Several variations of the model have been proposed (immediate snapshots and iterated immediate snapshots), all equivalent for wait-free solution of decision tasks, in spite of the fact that the protocol complexes that arise from the different models are structurally distinct. The topological and combinatorial properties of these snapshot protocol complexes have been studied in detail, providing explanations for why the asynchronous computability theorem holds in all the models.

In reality concurrent systems do not provide processes with snapshot operations. Instead, snapshots are implemented (by a wait-free protocol) using operations that write and read individual shared memory locations.

Thus, read/write protocols are also computationally equivalent to snapshot protocols. However, the structure of the read/write protocol complex has not been studied. In this paper we show that the read/write iterated protocol complex is collapsible (and hence contractible). Furthermore, we show that a distributed protocol that wait-free implements atomic snapshots in effect is performing the collapses.

This is a joint work with Sergio Rajsbaum.

08 janvier 2016 à 13h40 par 147.210.245.180 -
Ligne 15 modifiée:

en:

08 janvier 2016 à 13h28 par 147.210.245.180 -
Ligne 15 modifiée:
en:

03 décembre 2015 à 04h52 par 189.134.19.207 -
Lignes 27-28 modifiées:

Lundi 7 décembre : ' Rendezvous of Heterogeneous Mobile Agents in Edge-weighted Networks.

 ' Ralf Klasing - (LaBRI, Université de Bordeaux)  \\

en:

Lundi 7 décembre : Rendezvous of Heterogeneous Mobile Agents in Edge-weighted Networks. Ralf Klasing - (LaBRI, Université de Bordeaux) \\

03 décembre 2015 à 04h52 par 189.134.19.207 -
Lignes 27-30 modifiées:

Lundi 7 décembre : titre à définir Ralf Klasing - (LaBRI, Université de Bordeaux)

Abstract:

en:

Lundi 7 décembre : ' Rendezvous of Heterogeneous Mobile Agents in Edge-weighted Networks.

 ' Ralf Klasing - (LaBRI, Université de Bordeaux)


Abstract: We introduce a variant of the deterministic rendezvous problem for a pair of heterogeneous agents operating in an undirected graph, which differ in the time they require to traverse particular edges of the graph. Each agent knows the complete topology of the graph and the initial positions of both agents. The agent also knows its own traversal times for all of the edges of the graph, but is unaware of the corresponding traversal times for the other agent. The goal of the agents is to meet on an edge or a node of the graph. In this scenario, we study the time required by the agents to meet, compared to the meeting time T_OPT in the offline scenario in which the agents have complete knowledge about each others speed characteristics. When no additional assumptions are made, we show that rendezvous in our model can be achieved after time O(n T_OPT) in a n-node graph, and that such time is essentially in some cases the best possible. However, we prove that the rendezvous time can be reduced to Θ(T_OPT) when the agents are allowed to exchange Θ(n) bits of information at the start of the rendezvous process. We then show that under some natural assumption about the traversal times of edges, the hardness of the heterogeneous rendezvous problem can be substantially decreased, both in terms of time required for rendezvous without communication, and the communication complexity of achieving rendezvous in time Θ(T_OPT).

26 novembre 2015 à 10h45 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 37-40 modifiées:

Lundi 30 novembre : titre à définir Akka Zemmari - (LaBRI, Université de Bordeaux) /!\ Salle 75 /!\

Abstract:

en:

Lundi 30 novembre : Machine Learning Approach for Android Apps Analysis Akka Zemmari - (LaBRI, Université de Bordeaux)

Abstract: Android being the most popular open source mobile operating system, attracts a plethora of app developers. Millions of applications are developed for Android platform with a great extent of behavioral diversities and are available on Play Store as well as on many third party app stores. Due to its open nature, Android Platform has been targeted by many malware writers. The conventional way of signature-based detection methods for detecting malware on a device are no longer promising due to an exponential increase in the number of variants of the same application with different signatures. In this talk, we present a machine learning approach for malware detection in Android Apps.

13 novembre 2015 à 17h21 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 18-21 modifiées:

Lundi 14 décembre : titre à définir Philippe Duchon - (LaBRI, Université de Bordeaux)

en:

Lundi 14 décembre : Beachcombing on Strips and Islands David Ilcinkas - (LaBRI, Université de Bordeaux)

Lignes 21-22 modifiées:
en:

A group of mobile robots (beachcombers) have to search collectively every point of a given domain. At any given moment, each robot can be in walking mode or in searching mode. It is assumed that each robot's maximum allowed searching speed is strictly smaller than its maximum allowed walking speed. A point of the domain is searched if at least one of the robots visits it in searching mode. The Beachcombers' Problem consists in developing efficient schedules (algorithms) for the robots which collectively search all the points of the given domain as fast as possible. In this talk, I will present recent results on this topic.

Ligne 70 modifiée:

Lundi 16 novembre : Beachcombing on Strips and Islands David Ilcinkas - (LaBRI, Université de Bordeaux) \\

en:

Lundi 16 novembre : Réunion du thème \\

Lignes 73-74 modifiées:

A group of mobile robots (beachcombers) have to search collectively every point of a given domain. At any given moment, each robot can be in walking mode or in searching mode. It is assumed that each robot's maximum allowed searching speed is strictly smaller than its maximum allowed walking speed. A point of the domain is searched if at least one of the robots visits it in searching mode. The Beachcombers' Problem consists in developing efficient schedules (algorithms) for the robots which collectively search all the points of the given domain as fast as possible. In this talk, I will present recent results on this topic.

en:

Réunion du thème Algo Dist

19 octobre 2015 à 16h13 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 117-119 modifiées:

On pourra cependant assister à la soutenace de thèse de Vincent Autefage dont le titre et le résumé suivent :

Découverte de services et collaboration au sein d’une flotte hétérogène et hautement dynamique d’objets mobiles communicants autonomes

en:

On pourra cependant assister le matin à la soutenace de thèse de Vincent Autefage dans l' amphi du LaBRI à 10h dont le titre et le résumé suivent :

''Découverte de services et collaboration au sein d’une flotte hétérogène et hautement dynamique d’objets mobiles communicants autonomes', Vincent Autefage\\

19 octobre 2015 à 16h11 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 117-118 modifiées:

Abstract: c'est les vacances

en:

On pourra cependant assister à la soutenace de thèse de Vincent Autefage dont le titre et le résumé suivent :

Découverte de services et collaboration au sein d’une flotte hétérogène et hautement dynamique d’objets mobiles communicants autonomes

Résumé: Les systèmes autonomes sont des objets mobiles communicants capables de réaliser un certain nombre de tâches sans intervention humaine. Le coût (e.g. argent, poids, éner- gie) de la charge utile requise pour effectuer certaines missions est parfois trop important pour permettre aux engins d’embarquer la totalité des capacités nécessaires (i.e. capteurs et actionneurs). Répartir ces capacités sur plusieurs entités est une solution naturelle à ce problème. Un tel groupe d’entités constitue une flotte à laquelle devient nécessaire de fournir un mécanisme de découverte permettant aux différents engins de partager leurs capacités respectives afin de résoudre une mission globale de façon collaborative. Ce mé- canisme, outre l’affectation des tâches, doit gérer les conflits et les pannes potentielles qui peuvent survenir à tout moment sur tout engin de la flotte. Fort de ces constations, nous proposons un nouveau mécanisme collaboratif nommé AMiRALE qui apporte une solution aux problèmes ci-dessus pour les flottes hétérogènes d’engins mobiles autonomes. Notre système est entièrement distribué et repose uniquement sur des communications asyn- chrones. Nous proposons également un nouvel outil nommé NEmu permettant de créer des réseaux virtuels mobiles avec un contrôle important sur les propriétés de la topologie du réseau ainsi que sur la configuration des nœuds et des inter-connexions. Cet outil per- met la réalisation d’expérimentations réalistes sur des prototypes d’applications réseaux. Enfin, nous proposons une évaluation de notre système collaboratif AMiRALE au travers d’un scénario de nettoyage de parc utilisant une flotte autonome de drones et de robots terrestres spécialisés.

19 octobre 2015 à 16h07 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 105-108 modifiées:

Lundi 2 novembre : titre à définir Claire Capdevielle - (LaBRI, Université de Bordeaux)

Abstract:

en:

Lundi 2 novembre : On the Uncontended Complexity of Anonymous Consensus Claire Capdevielle - (LaBRI, Université de Bordeaux)

Abstract: We study on uncontended complexity of anonymous algorithms, counting the number of distinct memory accesses in operations that encounter no contention. We assume that contention-free operations on a concurrent object perform “fast” reads and writes, and resort to more expensive synchronization primitives, such as CAS, only when contention is detected. We call such concurrent implementations interval-solo-fast and derive tight lower bounds on time and space complexity of anonymous interval-solo-fast consensus.

14 octobre 2015 à 18h12 par 180.9.247.71 -
Ligne 71 modifiée:

Lundi 16 novembre : Titre à définir David Ilcinkas - (LaBRI, Université de Bordeaux) \\

en:

Lundi 16 novembre : Beachcombing on Strips and Islands David Ilcinkas - (LaBRI, Université de Bordeaux) \\

Ligne 74 ajoutée:

A group of mobile robots (beachcombers) have to search collectively every point of a given domain. At any given moment, each robot can be in walking mode or in searching mode. It is assumed that each robot's maximum allowed searching speed is strictly smaller than its maximum allowed walking speed. A point of the domain is searched if at least one of the robots visits it in searching mode. The Beachcombers' Problem consists in developing efficient schedules (algorithms) for the robots which collectively search all the points of the given domain as fast as possible. In this talk, I will present recent results on this topic.

13 octobre 2015 à 19h12 par 180.9.247.71 -
Lignes 19-21 modifiées:

Lundi 14 décembre : titre à définir Philippe Duchon - (Université de Bordeaux)

en:

Lundi 14 décembre : titre à définir Philippe Duchon - (LaBRI, Université de Bordeaux)

Lignes 28-30 modifiées:

Lundi 7 décembre : titre à définir Ralf Klasing - (Université de Bordeaux)

en:

Lundi 7 décembre : titre à définir Ralf Klasing - (LaBRI, Université de Bordeaux)

Ligne 38 modifiée:

Lundi 30 novembre : titre à définir Akka Zemmari - (Université de Bordeaux) /!\ Salle 75 /!\ \\

en:

Lundi 30 novembre : titre à définir Akka Zemmari - (LaBRI, Université de Bordeaux) /!\ Salle 75 /!\ \\

13 octobre 2015 à 19h10 par 180.9.247.71 -
Lignes 19-21 modifiées:

Lundi 30 novembre : titre à définir Akka Zemmari - (Université de Bordeaux) /!\ Salle 75 /!\

en:

Lundi 14 décembre : titre à définir Philippe Duchon - (Université de Bordeaux)

Lignes 24-25 supprimées:
Lignes 28-35 modifiées:

Lundi 23 novembre : Pas d'exposé

Abstract: On pourra cependant assister à la soutenance de thèse de David Bonnin le 24 novembre à 14h dans l'amphi du LaBRI.

en:

Lundi 7 décembre : titre à définir Ralf Klasing - (Université de Bordeaux)

Abstract:

Lundi 30 novembre : titre à définir Akka Zemmari - (Université de Bordeaux) /!\ Salle 75 /!\

Abstract:

Mardi 24 novembre (après-midi): Soutenance de thèse de David Bonnin

Abstract: 14h dans amphi du LaBRI.

Lundi 23 novembre et Mardi 24 novembre (matin): Journées du GT CoA

Abstract: Programme et inscription ici http://5.135.166.57/COA/index.php/welcome/pagePresentation

13 octobre 2015 à 18h54 par 180.9.247.71 -
13 octobre 2015 à 18h54 par 180.9.247.71 -
Lignes 38-42 ajoutées:

Lundi 16 novembre : Titre à définir David Ilcinkas - (LaBRI, Université de Bordeaux)
Abstract:

05 octobre 2015 à 13h33 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 42-44 modifiées:

Lundi 9 novembre : titre à définir ??? - ( xxx xxxx) /!\ SALLE 75

en:

Lundi 9 novembre : Classification automatique de graphes dynamique Yessin Neggaz - (LaBRI, Université de Bordeaux) /!\ SALLE 75 /!\

Lignes 45-46 modifiées:
en:

Étant donné un graphe dynamique, donné sous la forme d’une séquence de graphes statiques ou bien comme une succession d’évènements topologiques (apparitions/disparitions de liens de communication), on s’intéresse à tester automatiquement certaines propriétés temporelles sur le graphe. Les propriétés qui nous intéressent correspondent à des conditions nécessaires et/ou suffisantes pour la réalisation de tâches distribuées classiques (élection, diffusion, comptage, etc.) Nous avons répertorié à ce jour une vingtaine de propriétés. Par exemple, le réseau est-il temporellement connexe ? (existence d’un trajet, i.e. d’une succession d’arêtes dont les dates d’existence sont temporellement croissantes, depuis chaque sommet vers chaque autre sommet) ; certaines arêtes réapparaissent-elles dans un temps borné ou de manière périodique ? Leur ensemble vérifie-t-il certaines propriétés ? Être capable de vérifier ce type de propriété automatiquement nous permettrait de déterminer dans un contexte de mobilité donné (p. ex. drones, robots, voitures, dont on peut obtenir ou générer des traces de connexité), les tâches réalisables par l’ensemble des entités.

Lignes 92-94 modifiées:

Lundi 12 octobre : Classification automatique de graphes dynamique Yessin Neggaz - (LaBRI, Université de Bordeaux)

en:

Lundi 12 octobre : On Distinguishing Views in Symmetric Networks. Dominik Pająk - (University of Cambridge)

Lignes 95-112 modifiées:

Étant donné un graphe dynamique, donné sous la forme d’une séquence de graphes statiques ou bien comme une succession d’évènements topologiques (apparitions/disparitions de liens de communication), on s’intéresse à tester automatiquement certaines propriétés temporelles sur le graphe. Les propriétés qui nous intéressent correspondent à des conditions nécessaires et/ou suffisantes pour la réalisation de tâches distribuées classiques (élection, diffusion, comptage, etc.) Nous avons répertorié à ce jour une vingtaine de propriétés. Par exemple, le réseau est-il temporellement connexe ? (existence d’un trajet, i.e. d’une succession d’arêtes dont les dates d’existence sont temporellement croissantes, depuis chaque sommet vers chaque autre sommet) ; certaines arêtes réapparaissent-elles dans un temps borné ou de manière périodique ? Leur ensemble vérifie-t-il certaines propriétés ? Être capable de vérifier ce type de propriété automatiquement nous permettrait de déterminer dans un contexte de mobilité donné (p. ex. drones, robots, voitures, dont on peut obtenir ou générer des traces de connexité), les tâches réalisables par l’ensemble des entités.

en:

The view of a node in a port-labeled network is an infinite tree encoding all walks in the network originating from this node. It is an important concept in the context of symmetry breaking in distributed systems. For example a deterministic rendezvous is infeasible if the agents start from positions with the same views. We want to decide if two views are identical but we would like to compare the infinite trees truncated to certain depth d. We are looking for such d that if the views truncated to depth d are equal then the whole infinite trees are also equal and there are some nodes whose views differ only at depth d. It turns out that truncating to depth Theta(D*log(n/D)) (where D is the diameter and n is the number of nodes) is always sufficient and sometimes necessary to distinguish the views.

The talk will be based on two papers:

Views in a graph: to which depth must equality be checked? Julien M. Hendrickx

Distinguishing Views in Symmetric Networks: A Tight Lower Bound Dariusz Dereniowski, Adrian Kosowski, Dominik Pająk

02 octobre 2015 à 11h23 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 19-21 modifiées:

Lundi 23 novembre : titre à définir Akka Zemmari - (Université de Bordeaux) /!\ Salle 75 /!\

en:

Lundi 30 novembre : titre à définir Akka Zemmari - (Université de Bordeaux) /!\ Salle 75 /!\

Lignes 29-40 ajoutées:

Lundi 23 novembre : Pas d'exposé

Abstract: On pourra cependant assister à la soutenance de thèse de David Bonnin le 24 novembre à 14h dans l'amphi du LaBRI.

28 septembre 2015 à 16h02 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 19 modifiée:

Lundi 23 novembre : titre à définir Akka Zemmari - (Université de Bordeaux)\\

en:

Lundi 23 novembre : titre à définir Akka Zemmari - (Université de Bordeaux) /!\ Salle 75 /!\ \\

28 septembre 2015 à 15h59 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 30 modifiée:

Lundi 9 novembre : titre à définir ??? - ( xxx xxxx)\\

en:

Lundi 9 novembre : titre à définir ??? - ( xxx xxxx) /!\ SALLE 75 \\

22 septembre 2015 à 14h45 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 19 modifiée:

Lundi 16 novembre : titre à définir Akka Zemmari - (Université de Bordeaux)\\

en:

Lundi 23 novembre : titre à définir Akka Zemmari - (Université de Bordeaux)\\

21 septembre 2015 à 16h37 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 12-33 ajoutées:

Lundi 16 novembre : titre à définir Akka Zemmari - (Université de Bordeaux)

Abstract:

Lundi 9 novembre : titre à définir ??? - ( xxx xxxx)

Abstract:

21 septembre 2015 à 16h36 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 21-29 ajoutées:

Lundi 26 octobre : Pas d'exposé

Abstract: c'est les vacances

18 septembre 2015 à 18h20 par 81.220.47.212 -
Lignes 59-60 modifiées:

Analysis of two fundamental results of the self-stabilizing literature about silent BFS spanning tree constructions: the Dolev et al algorithm and the Huang and

  Chen's algorithm. More precisely, we propose in the composite  atomicity model three straightforward adaptations inspired from those algorithms. We then present a deep study of these three  algorithms.  Our results are related to both correctness (convergence and closure, assuming a distributed unfair daemon) and complexity (analysis of the stabilization time in terms of rounds and steps).

en:

Analysis of two fundamental results of the self-stabilizing literature about silent BFS spanning tree constructions: the Dolev et al algorithm and the Huang and Chen's algorithm. More precisely, we propose in the composite atomicity model three straightforward adaptations inspired from those algorithms. We then present a deep study of these three algorithms. Our results are related to both correctness (convergence and closure, assuming a distributed unfair daemon) and complexity (analysis of the stabilization time in terms of rounds and steps).

18 septembre 2015 à 18h19 par 81.220.47.212 -
Lignes 56-57 modifiées:

Lundi 5 octobre : titre à définir Colette Johnen - (LaBRI, Université de Bordeaux)

en:

Lundi 5 octobre : Silent Self-stabilizing BFS Tree Algorithms Revised Colette Johnen - (LaBRI, Université de Bordeaux)

Lignes 59-62 ajoutées:

Analysis of two fundamental results of the self-stabilizing literature about silent BFS spanning tree constructions: the Dolev et al algorithm and the Huang and

  Chen's algorithm. More precisely, we propose in the composite  atomicity model three straightforward adaptations inspired from those algorithms. We then present a deep study of these three  algorithms.  Our results are related to both correctness (convergence and closure, assuming a distributed unfair daemon) and complexity (analysis of the stabilization time in terms of rounds and steps).


(joint work with with Stéphane Devismes - VERIMAG)

15 septembre 2015 à 11h13 par 147.210.179.68 -
Lignes 17-19 modifiées:

Lundi 2 novembre : titre à définir Ralf Klasing/Yacine Neggaz- (LaBRI, Université de Bordeaux)

en:

Lundi 2 novembre : titre à définir Claire Capdevielle - (LaBRI, Université de Bordeaux)

Lignes 32-34 modifiées:

Lundi 12 octobre : titre à définir Claire Capdevielle - (LaBRI, Université de Bordeaux)

en:

Lundi 12 octobre : Classification automatique de graphes dynamique Yessin Neggaz - (LaBRI, Université de Bordeaux)

Lignes 36-53 modifiées:
en:

Étant donné un graphe dynamique, donné sous la forme d’une séquence de graphes statiques ou bien comme une succession d’évènements topologiques (apparitions/disparitions de liens de communication), on s’intéresse à tester automatiquement certaines propriétés temporelles sur le graphe. Les propriétés qui nous intéressent correspondent à des conditions nécessaires et/ou suffisantes pour la réalisation de tâches distribuées classiques (élection, diffusion, comptage, etc.) Nous avons répertorié à ce jour une vingtaine de propriétés. Par exemple, le réseau est-il temporellement connexe ? (existence d’un trajet, i.e. d’une succession d’arêtes dont les dates d’existence sont temporellement croissantes, depuis chaque sommet vers chaque autre sommet) ; certaines arêtes réapparaissent-elles dans un temps borné ou de manière périodique ? Leur ensemble vérifie-t-il certaines propriétés ? Être capable de vérifier ce type de propriété automatiquement nous permettrait de déterminer dans un contexte de mobilité donné (p. ex. drones, robots, voitures, dont on peut obtenir ou générer des traces de connexité), les tâches réalisables par l’ensemble des entités.

11 septembre 2015 à 14h05 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 16-18 modifiées:

Lundi : titre orateur - (affiliation)

en:

Lundi 2 novembre : titre à définir Ralf Klasing/Yacine Neggaz- (LaBRI, Université de Bordeaux)

Lignes 24-26 modifiées:

Lundi 2 novembre : titre Ralf Klasing/Yacine Neggaz- (LaBRI, Université de Bordeaux)

en:

Lundi 19 octobre : Algorithmes auto-stabilisants pour des paramètres de décomposition et de domination dans les graphes Mohammed Haddad - (Université de Lyon 1)

Lignes 28-29 modifiées:
en:

Un système distribué est dit auto-stabilisant s’il peut reprendre un comportement correct en un temps fini après l’occurrence de fautes et ce sans intervention extérieure. De ce fait, l’auto-stabilisation est une approche optimiste pour la tolérance aux fautes dans le sens où elle protège le système des fautes transitoires. Un algorithme auto-stabilisant peut être défini selon différents modèles de communication ainsi que différents modèles de calcul. En effet, prouver la convergence d'un algorithme auto-stabilisant se doit dêtre faite selon un démon/scheduler qui peut être centralisé ou distribué, équitable ou non. De de plus, la complexité de ces algorithmes peut se calculer selon différentes mesures : moves, steps ou rounds, chacune d'entre elles apportant une connaissance propre sur l'algorithme proposé. Cependant, réussir à borner l'ensemble de ces mesures n'est pas toujours trivial, en particulier pour les cas les plus généraux de démons. La littérature des algorithmes auto-stabilisants est très riches. Cependant, nous allons nous intéresser dans cet exposé aux algorithmes auto-stabilisants pour quelques paramètres de théorie des graphes. En particulier, nous nous focaliserons dans un premier temps sur des décompositions particulières des graphes : en triangles et en étoiles uniformes ainsi que des paramètres de domination. Nous nous attarderons par la suite sur les techniques de preuve de convergence utilisées pour ces algorithmes.

Lignes 32-34 modifiées:

Lundi 19 octobre : Algorithmes auto-stabilisants pour des paramètres de décomposition et de domination dans les graphes Mohammed Haddad - (Université de Lyon 1)

en:

Lundi 12 octobre : titre à définir Claire Capdevielle - (LaBRI, Université de Bordeaux)

Lignes 36-37 modifiées:

Un système distribué est dit auto-stabilisant s’il peut reprendre un comportement correct en un temps fini après l’occurrence de fautes et ce sans intervention extérieure. De ce fait, l’auto-stabilisation est une approche optimiste pour la tolérance aux fautes dans le sens où elle protège le système des fautes transitoires. Un algorithme auto-stabilisant peut être défini selon différents modèles de communication ainsi que différents modèles de calcul. En effet, prouver la convergence d'un algorithme auto-stabilisant se doit dêtre faite selon un démon/scheduler qui peut être centralisé ou distribué, équitable ou non. De de plus, la complexité de ces algorithmes peut se calculer selon différentes mesures : moves, steps ou rounds, chacune d'entre elles apportant une connaissance propre sur l'algorithme proposé. Cependant, réussir à borner l'ensemble de ces mesures n'est pas toujours trivial, en particulier pour les cas les plus généraux de démons. La littérature des algorithmes auto-stabilisants est très riches. Cependant, nous allons nous intéresser dans cet exposé aux algorithmes auto-stabilisants pour quelques paramètres de théorie des graphes. En particulier, nous nous focaliserons dans un premier temps sur des décompositions particulières des graphes : en triangles et en étoiles uniformes ainsi que des paramètres de domination. Nous nous attarderons par la suite sur les techniques de preuve de convergence utilisées pour ces algorithmes.

en:
Lignes 39-41 modifiées:

Lundi 12 octobre : titre Claire Capdevielle - (LaBRI, Université de Bordeaux)

en:

Lundi 5 octobre : titre à définir Colette Johnen - (LaBRI, Université de Bordeaux)

Lignes 45-46 modifiées:

Lundi 5 octobre : titre Colette Johnen - (LaBRI, Université de Bordeaux)

en:

Lundi 28 septembre : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

Lignes 49-52 modifiées:
en:

La suite de l'exposé du 18 mai. JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

Lignes 55-57 modifiées:

Lundi 28 septembre : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

en:

Lundi 21 septembre : Bridging the Gap between Performance and Bounds of Cholesky Factorization on Heterogeneous Platforms / Planar graphs and power domination + réunion de rentrée du thème Suraj Kumar/Claire Pennarun - (LaBRI, Université de Bordeaux)

Lignes 58-67 supprimées:

La suite de l'exposé du 18 mai. JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

Lundi 21 septembre : Bridging the Gap between Performance and Bounds of Cholesky Factorization on Heterogeneous Platforms / Planar graphs and power domination + réunion de rentrée du thème Suraj Kumar/Claire Pennarun - (LaBRI, Université de Bordeaux)

Abstract:

Lignes 71-78 ajoutées:

Lundi : '' titre à définir' orateur - (affiliation)

Abstract:

11 septembre 2015 à 14h03 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 12-13 ajoutées:
Lignes 16-18 modifiées:

Date à définir : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

en:

Lundi : titre orateur - (affiliation)

Lignes 20-23 modifiées:

La suite de l'exposé du 18 mai. JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

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Lignes 23-25 modifiées:

Lundi 29 juin : Spreading Influence in Social Networks with Time Constraints Joseph Peters - (Simon Fraser University)

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Lundi 2 novembre : titre Ralf Klasing/Yacine Neggaz- (LaBRI, Université de Bordeaux)

Lignes 27-29 modifiées:

In a social network, agents change their behaviours and opinions on the basis of information collected from their neighbours. Generally, recent information is more influential than older information, and information that is received in a short period of time is more influential than information received during a long period of time. An example of this phenomenon is consumer reviews on websites such as Amazon. Another example is viral marketing which attempts to influence consumer adoption of products. A third example is recent communication strategies of politicians.

In this talk, I will present a graph-based model of the spread of influence in networks that generalizes previous research by including temporal information. The goal is to identify a small set of nodes that eventually influences all nodes in the graph with the restriction that influence only lasts for a bounded time interval. The problem for general graphs is computationally difficult even for approximate solutions. The talk will focus on efficient algorithms for restricted families of graphs: paths, rings, trees, and complete graphs.

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Lignes 30-35 modifiées:

Lundi 22 juin : Upper and Lower Bounds for Online Routing on Delaunay Triangulations Nicolas Bonichon - (LaBRI, Université de Bordeaux)
Abstract: Consider a weighted graph G whose vertices are points in the plane and edges are line segments between pairs of points. The weight of each edge is the Euclidean distance between its two endpoints. A routing algorithm on G has a routing ratio of c if the length of the path produced by the algorithm from any vertex s to any vertex t is at most c|[st]|. The routing algorithm is online if it makes forwarding decisions based on 1) the k-neighborhood in G (for some integer constant k > 0) of the current position of the message and 2) limited information stored in the message header.

We present an online routing algorithm on the Delaunay triangulation with routing ratio less than 5.90. This improves upon the algorithm with best known routing ratio of 15.48. We also show that the routing ratios of any deterministic k-local algorithm is at least 1.70 for the Delaunay triangulation.

en:

Lundi 19 octobre : Algorithmes auto-stabilisants pour des paramètres de décomposition et de domination dans les graphes Mohammed Haddad - (Université de Lyon 1)

Abstract: Un système distribué est dit auto-stabilisant s’il peut reprendre un comportement correct en un temps fini après l’occurrence de fautes et ce sans intervention extérieure. De ce fait, l’auto-stabilisation est une approche optimiste pour la tolérance aux fautes dans le sens où elle protège le système des fautes transitoires. Un algorithme auto-stabilisant peut être défini selon différents modèles de communication ainsi que différents modèles de calcul. En effet, prouver la convergence d'un algorithme auto-stabilisant se doit dêtre faite selon un démon/scheduler qui peut être centralisé ou distribué, équitable ou non. De de plus, la complexité de ces algorithmes peut se calculer selon différentes mesures : moves, steps ou rounds, chacune d'entre elles apportant une connaissance propre sur l'algorithme proposé. Cependant, réussir à borner l'ensemble de ces mesures n'est pas toujours trivial, en particulier pour les cas les plus généraux de démons. La littérature des algorithmes auto-stabilisants est très riches. Cependant, nous allons nous intéresser dans cet exposé aux algorithmes auto-stabilisants pour quelques paramètres de théorie des graphes. En particulier, nous nous focaliserons dans un premier temps sur des décompositions particulières des graphes : en triangles et en étoiles uniformes ainsi que des paramètres de domination. Nous nous attarderons par la suite sur les techniques de preuve de convergence utilisées pour ces algorithmes.

Lignes 38-45 modifiées:

Lundi 15 juin : Station Assignment with Reallocation Miguel Mosteiro - (Kean University, NJ, USA)
Abstract: In this work, we studied a dynamic allocation problem that arises in various scenarios where mobile clients joining and leaving the system have to communicate with static stations via radio transmissions. Restrictions are a maximum delay, or laxity, between consecutive client transmissions and a maximum bandwidth that a station can share among its clients. We studied the problem of assigning clients to stations so that every client transmits to some station, satisfying those restrictions. We considered reallocation algorithms, where clients are revealed at its arrival time, the departure time is unknown until they leave, and clients may be reallocated to another station, but at a cost proportional to the reciprocal of the client’s laxity. I will present positive and negative results as well as the results of our simulations showing that our protocols behave even better than our theoretical guarantees.

This is joint work with Yulia Rossikova and Prudence W. H. Wong, and will be presented at SEA 2015.

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Lundi 12 octobre : titre Claire Capdevielle - (LaBRI, Université de Bordeaux)

Abstract:

Lignes 45-51 modifiées:

Lundi 8 juin : Proving correctness of distributed algorithms in a dynamic context. Faten Fakhfakh - (LaBRI, Université de Bordeaux)
Abstract: Proving the correctness of distributed algorithms is a hard task due to the lack of global state knowledge and the non-determinism in the processes execution. In dynamic networks, this task becomes more difficult because of dynamic behavior and time complexity. In this talk, we propose a reuse based approach for specifying and proving distributed algorithms in dynamic networks. It consists in developing a formal pattern using Event-B method, based on refinement technique. Our pattern allows to handle topological events in dynamic networks and to characterize the concept of time. The proposed solution relies on evolving graphs, as a powerful model to record the evolution of a network topology. To illustrate it, we investigate an example of a distributed algorithm encoded by local computations models.

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Lundi 5 octobre : titre Colette Johnen - (LaBRI, Université de Bordeaux)
Abstract:

Lignes 50-57 modifiées:

Lundi 1er juin : An overview of computational models for wireless sensor networks Nesrine Ouled Abdallah - (LaBRI, Université de Bordeaux)
Abstract: In this talk, we will give an overview of some computational models designed for networks of tiny artifacts with sensing capabilities and with limited resources. We will focus on the population protocols (PP) model of Angluin et al. which is based on pairwise interactions between anonymous passively mobile finite state agents. We will consider, among other examples, the PP that stably computes the OR predicate and that we applied to the broadcast problem. We will also consider works that extend the PP model such as the mediated population protocols. In all these models, the interacting pairs are supposed to be chosen by a fair scheduler. In this talk, we will present a new fair one based on the rendezvous algorithm.

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Lundi 28 septembre : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

Abstract: La suite de l'exposé du 18 mai. JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

Lignes 60-64 modifiées:

Lundi 25 mai : Pas d'exposé -
Abstract: Pentecôte

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Lundi 21 septembre : Bridging the Gap between Performance and Bounds of Cholesky Factorization on Heterogeneous Platforms / Planar graphs and power domination + réunion de rentrée du thème Suraj Kumar/Claire Pennarun - (LaBRI, Université de Bordeaux)

Abstract: Nous écouterons Claire et Suraj nous exposer brièvement leur sujet de thèse et leur premiers résultats. Les exposés seront suivi de la réunion de rentrée du thème.

Suraj Kumar: Bridging the Gap between Performance and Bounds of Cholesky Factorization on Heterogeneous Platforms

Abstract: We consider the scheduling problem of Cholesky factorization on heterogeneous system. In this context we investigate how to adding static information based on an offline analysis to the scheduler improve their performance. We are comparing simulated performance with different theoretical bounds which we introduce.

Claire Pennarun: Planar graphs and power domination

Lignes 76-728 supprimées:

Lundi 18 mai : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Arnaud Casteigts - (LaBRI, Université de Bordeaux)

Abstract: JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

Lundi 11 mai : Calculer les distances dans un graphe en temps constant avec des étiquettes de 0.793n bits. Cyril Gavoille - (LaBRI, Université de Bordeaux)
Abstract: Dans cet exposé je présenterai une structure de données compacte permettant de calculer en temps constant la distance entre n'importe quelle paire de sommets d'un graphe arbitraire à n sommets. Cette structure de données se présente sous forme d'étiquette associée à chacun des sommets, la distance entre les u et v étant décodée à partir d'un calcul impliquant seulement les étiquettes de u et de v. La solution triviale, à l'aide d'un vecteur de distances de taille n, produit des étiquettes de nlogn bits. En fait, aucune technique utilisant o(nlogn) bits et décodant en temps constant n'est connue. Cependant, si on relâche la contrainte du décodage en temps constant, des solutions avec O(n) bits existent. Une des meilleures d'entres elles utilisent 11n bits pour un décodage O(logn). Notre solution réduit la taille des étiquettes à 0.793n bits avec un décodage constant et s'étend naturellement aux graphes valués.

Lundi 4 mai : Pas d'exposé
On pourra par contre assister au séminaire de Tahiry Razafindralambo qui est candidat prof, même heure, amphi du LaBRI.
Titre : Controlled Mobility in Wireless Networks

Resumé : Mobility is the character or property of an object that has the capacity or the ability to move or be moved. It characterizes all things that can rapidly change shape, appearance or is unstable, variable or fluctuate in time and space. The introduction of mobility in networks is a milestone in the description and implementation of communication systems that must take into account the mobility of one or more entities that comprise this system.

In the early 2000, the research shows that mobility is not all a drawback by pointing out that mobility can increase the capacity, security and covered areas. These results raise two important points: (i) The contribution of mobility described in these articles are considered at application-level if we refer to the OSI model and (ii) mobility is undergone by the users or network entities.

The two points raised above will be addressed from different point of view. Regarding the first point the results I show here consider two aspects. The first issue focuses on the benefits of mobility at the application level and more specifically for coverage in wireless sensor networks. The second aspect considers the use of mobility as a network primitive and uses it to increase the performance of the protocol stack.

Lundi 27 avril : Pas d'exposé
Abstract: c'est les vacances

Lundi 20 avril : Extension du domaine algorithmique : les algorithmes de la nature - Ivan Lavallée
Abstract: Suite aux travaux de A.M.Turing, les algorithmes ont été vus comme l’abstraction à partir de laquelle on pouvait écrire des programmes pour des ordinateurs dont le principe était lui-même issu du concept théorique de machine de Turing.

Nous partons ici du constat que les les algorithmes de la nature, massivement parallèles, autoadaptatifs et auto reproductibles, dont on ne sait pas comment ils fonctionnent réellement, ni pourquoi, ne sont pas aisément spécifiés par le modèle théorique actuel de Machine de Turing Universelle, ou de Calculateur Universel ; en particulier les aspects de communications, de règles évolutives, d’événements aléatoires, à l’image du code génétique, ne sont pris en compte que par ajout d’artifices à la théorie. Nous nous proposons ici de montrer comment aborder ces problèmes en repensant le modèle théorique. Nous proposerons un modèle d’algorithme, appelé ici machine-α qui contient et généralise les modèles existants.

Lundi 13 avril : Verifying parametrized asynchronous systems Anca Muscholl
Abstract: The talk should be a (gentle) introduction to verification problems for concurrent, asynchronous systems. I will focuss on two models (among a large number!), one with shared memory and another one with asynchronous calls. The talk is based on the following papers:

Parameterized Verification of Asynchronous Shared-Memory Systems Javier Esparza, Pierre Ganty, and Rupak Majumdar CAV 2013

Safety of parametrized asynchronous shared-memory systems is almost always decidable S. La Torre, A. Muscholl, I. Walukiewicz 2015

Algorithmic Verification of Asynchronous Programs Pierre Ganty, and Rupak Majumdar ACM Transactions on Programming Languages and Systems 2012

Lundi 6 avril : Pas d'exposé
Abstract: c'est pââââââques

Lundi 30 mars : An introduction to Software Transactional Memory - Alessia Milani (Labri, Université de Bordeaux)
Abstract: Software Transactional memory (or STM for short) is a promising programming paradigm that aims at simplifying concurrent programming by using the notion of a transaction. A transaction executes a piece of code containing accesses to data items which are shared by several processes in a concurrent setting. By using transactions, the programmer needs only enhance its sequential code with invocations of special operations to read or write data items. It is guaranteed that if any operation of a transaction takes place, they all do, and that if they do, they appear to other threads to do so atomically, as one indivisible operation.

In this talk, I will present the STM paradigm and the main algorithmic techniques to implement it.

Lundi 23 mars : Algorithmes d'allocation pour le Cloud sous contrainte de fiabilité - Lionel Eyraud-Dubois (LaBRI, INRIA)
Abstract: Pour les services qui s'exécutent sur une plate-forme de Cloud Computing, la fiabilité et la disponibilité sont des problématiques clés : avec l'augmentation de la taille de ces plates-formes, les pannes de machines sont de plus en plus fréquentes et doivent être prises en compte en amont. À travers une analyse de traces d'un cluster de Google, cet exposé présente une formalisation du problème d'allocation des services sur une plate-forme de façon à pouvoir résister aux pannes, ainsi qu'un algorithme de résolution basée sur deux techniques : approximation binomiale et génération de colonnes. Travail en commun avec Olivier Beaumont, Paul Renaud-Goud, et Juan-Angel Lorenzo.

Lundi 16 mars : On Distributed Computing with Beeps, la suite Akka Zemmari (LaBRI, Université de Bordeaux)
Abstract: La suite de l'exposé du 2 mars !

Lundi 9 mars : On structural and Chromatic Properties of 1-planar Graphs. - Tomas Madaras (Pavol Jozef Šafárik University)
Abstract:The planar graphs have been, within decades of graph theory research, well explored yielding numerous results on their structural and chromatic properties. Along with this research, analogue problems were investigated for graphs which generalize - in various directions - the planar graphs. A particularly interesting generalization concerns the graph drawings in the plane which allow at most one crossing per edge, rising to the family of so called 1-planar graphs. These graphs, although introduced in late sixties of 20th century, were studied in a deeper detail only in the last decade. We survey known results on the global and local structure and chromaticity of 1-planar graphs with emphasis on similarities and fundamental differences when comparing with planar graphs, and several future research directions on an analogue of Steinberg conjecture for 1-planar graphs.

Remarque: Créneau emprunté par le GT Graphes et Applications

Lundi 2 mars : On Distributed Computing with Beeps Akka Zemmari (LaBRI, Université de Bordeaux)
Abstract: We consider networks of processes which interact with beeps. Various beeping models are used. The basic one, defined by Cornejo and Khun assumes that a process can choose either to beep or to listen. If it listens it can distinguish between silence or the presence of at least one beep. The aim of this paper is the study of the resolution of paradigms such as collision detection, computation of the degree of a vertex, of a MIS or a colouring in the framework of beeping models.

Join work with Yves Métivier and Mike Robson

Lundi 23 février: : Relâche
Abstract: c'est les

Lundi 16 février 2015: Self-Stabilizing Leader Election in Polynomial Steps Stéphane Devismes (Université Joseph Fourier, Grenoble I)
Abstract: We present a silent self-stabilizing leader election algorithm for bidirectional connected identified networks of arbitrary topology. This algorithm is written in the locally shared memory model. It assumes the distributed unfair daemon, the most general scheduling hypothesis of the model. Our algorithm requires no global knowledge on the network (such as an upper bound on the diameter or the number of processes, for example).

We show that its stabilization time is in Theta(n^3) steps in the worst case, where n is the number of processes. Its memory requirement is asymptotically optimal, i.e., Theta(log n) bits per processes. Its round complexity is of the same order of magnitude (i.e., Theta(n) rounds), as the best existing algorithm (proposed by Datta et al) designed with similar settings,i.e., it does not use global knowledge and is proven under the unfair daemon).

To the best of our knowledge, this is the first asynchronous self-stabilizing leader election algorithm for arbitrary identified networks that is proven to achieve a stabilization time polynomial in steps. By contrast, we show that the previous best existing algorithm designed with similar settings stabilizes in a non polynomial number of steps in the worst case.

P.S. : Il s'agit d'un exposé CPU.

Lundi 9 février 2015 : 'A Distributed Enumeration Algorithm and Applications to All Pairs Shortest Paths, Diameter...' Yves Métivier (LaBRI, Université de Bordeaux)
Abstract: We consider the standard message passing model; we assume the system is fully synchronous: all processes start at the same time and time proceeds in synchronised rounds. In each round each vertex can transmit a different message of size $O(1)$ to each of its neighbours. This paper proposes and analyses a distributed enumeration algorithm of vertices of a graph having a distinguished vertex which satisfies that two vertices with consecutive numbers are at distance at most $3$. We prove that its time complexity is $O(n)$ where $n$ is the number of vertices of the graph. Furthermore, the size of each message is $O(1)$ thus its bit complexity is also $O(n).$ We provide some links between this enumeration and Hamiltonian graphs from which we deduce that this enumeration is optimal in the sense that there does not exist an enumeration which satisfies that two vertices with consecutive numbers are at distance at most $2$.

We deduce from this enumeration algorithms which compute all pairs shortest paths and the diameter with a time complexity and a bit complexity equal to $O(n)$. This improves the best known distributed algorithms (under the same hypotheses) for computing all pairs shortest paths or the diameter presented in \cite{PRT12,HW12} having a time complexity equal to $O(n)$ and which use messages of size $O(\log n)$ bits.

Join work with Mike Robson and Akka Zemmari

Lundi 2 février 2015 : Pas d'exposé
Allez voir les exposés des 'Journées GDR IM' qui se tiennent au LaBRI les 2 et 3 février. Le programme est ici : http://gdrim2015.labri.fr

Lundi 26 janvier 2015 : Periodic Data Retrieval in asynchronous rings with a malicious host - Evangelos Bampas (LaBRI, Université de Bordeaux)
Abstract: The notion of "black hole" has been used extensively in the mobile agent literature to model a crashed node which kills incoming agents without leaving any trace of them. I will consider more powerful models of faulty (or malicious) hosts in the context of the Periodic Data Retrieval problem in asynchronous ring networks. The problem is to collect infinite streams of data generated at the nodes of the network and report them infinitely often to a prescribed safe node (the homebase). I will discuss lower and upper bounds on the optimal number of agents required to perform the task in the presence of a unique malicious host.

(joint work with Nikos Leonardos, Euripides Markou, Aris Pagourtzis, and Matoula Petrolia)

Lundi 19 janvier 2015 : " Équilibrage de charge dans des systèmes distribués" - Noel Gillet (LaBRI, Université de Bordeaux)
Abstract: L'expansion, au cours des deux dernières décennies des réseaux, et notamment d'Internet, a engendré une création importante de données, massives de par leur nombre et leur taille. De ce fait, des systèmes de stockages distribués (comme Cassandra par exemple) sont utilisés en pratique afin de stocker ces données.

Deux problématiques se posent alors : (1) comment répartir les données? (2) comment optimiser le traitement des requêtes sur ces données?

Nous nous intéressons ici à l'équilibrage des requêtes entre les différents noeuds d'un système distribué. Notre approche consiste à utiliser la réplication d'objet et nous proposons différents algorithmes d'affectation des requêtes en cherchant à optimiser le temps de complétion (temps de traitement) des requêtes.

(Travail en cours avec Nicolas Hanusse)

Lundi 12 janvier 2015 : "Distributedly Testing Cycle-Freeness" - David Ilcinkas (LaBRI, CNRS and Université de Bordeaux)
Abstract: We tackle local distributed testing of graph properties. This framework is well suited to contexts in which data dispersed among the nodes of a network can be collected by some central authority (like in, e.g., sensor networks). In local distributed testing, each node can provide the central authority with just a few information about what it perceives from its neighboring environment, and, based on the collected information, the central authority is aiming at deciding whether or not the network satisfies some property. We analyze in depth the prominent example of checking \emph{cycle-freeness}, and establish tight bounds on the amount of information to be transferred by each node to the central authority for deciding cycle-freeness. In particular, we show that distributedly testing cycle-freeness requires at least $\ceil{\log d}-1$ bits of information per node in graphs with maximum degree~$d$, even for connected graphs. Our proof is based on a novel version of the seminal result by Naor and Stockmeyer (1995) enabling to reduce the study of certain kinds of algorithms to order-invariant algorithms, and on an appropriate use of the known fact that every free group can be linearly ordered.

# Exposés passés

Lundi 15 décembre 2014 : "Splitting and renaming with a majority of faulty processes" - David Bonnin (LaBRI, Université de Bordeaux)
Abstract: The renaming problem has been introduced by Attiya et al. [1], and consists on the following : Each process start with a unique name in a large namespace (such as an IP address), and each process tries to acquire a new name such as, at the end of the algorithm, each process has a new unique name in a much smaller namespace. This problem was first solved in asynchronous message-passing systems with a strict minority of processes that might crash, and later largely studied in wait-free shared memory systems, which can themselves be simulated in the former model (as explained in [2]). Splitters are basic shared memory objects that were introduced in [3] in order to build a fast renaming algorithm, and extending the renaming to a long-lived'' version. A splitter is an object that can be accessed through one operation Split(), and returns a direction in {right, down, stop}, with the property that not all processes return right, not all return down, and at most 1 process may return stop.

In asynchronous message-passing systems with a majority of faulty processes, the renaming problem cannot be solved, and splitters cannot be implemented. But we extended these notions to k-renaming and k-splitters, both for one-shot and long-lived versions. Instead of having unique name for each process, each new name (in a small namespace) may be acquired by at most k processes, and at most k processes accessing a k-splitter may return stop. We developed an optimal algorithm for implementing k-splitters, i.e. the algorithm implements them with k = floor(n/(n-f)), where n in the number of processes and f the maximal number of faulty processes among them, and it is not possible to implement k'-splitters with k' < floor(n/(n-f)). Although the namespace is not optimal, especially in the long-lived version, k-renaming based on these k-splitters is optimal for the same reason that k=floor(n/(n-f)) is both a lower bound, and a reached upper bound.

[1] H. Attiya, A. Bar-Noy, D. Dolev, D. Peleg, and R. Reischuk. Renaming in an asynchronous environment. J. ACM, 37(3):524–548, July 1990. [2] H. Attiya, A. Bar-Noy, and D. Dolev. Sharing memory robustly in message-passing systems. J. ACM, 42(1):124–142, 1995. [3] M. Moir and J. H. Anderson. Wait-free algorithms for fast, long-lived renaming. Science of Computer Programming, 25(1):1 – 39, 1995.

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz et Matthieu Barjon, (LaBRI, Université de Bordeaux)

Lundi 01 décembre 2014 : "Towards a General Framework for Searching on a Line and Searching on m Rays" - Jean-Lou De Carufel (Carleton University)
Abstract: We revisit the problem of searching for a target at an unknown location on a line when given upper and lower bounds on the distance D that separates the initial position of the searcher from the target. We present tight bounds on the exact optimal competitive ratio achievable, parameterized in terms of the given range for D, along with an optimal search strategy that achieves this competitive ratio.

We present an optimal search strategy for the case where a fixed turn cost t is charged every time the searcher changes direction. Moreover, we generalize our results to the framework where the cost of moving distance x away from the origin is a x + b and the cost of moving distance y towards the origin is c y + d for constants a, b, c and d.

This is joint work with Prosenjit Bose (Carleton U.) and Stephane Durocher (U. of Manitoba).

Lundi 24 novembre 2014 : "ON THE POWER OF ONE BIT: HOW TO EXPLORE A GRAPH WHEN YOU CANNOT BACKTRACK?" - Dominik Pajak, (University of Cambridge)
Abstract: We study the problem of exploration of an anonymous undirected graph with n vertices, m edges and diameter D by a single mobile agent. The agent does not know the incoming port when entering to a vertex thus it cannot backtrack its moves. Each vertex of the graph is endowed with a whiteboard on which the agent can store information.

In this talk we will study tradeoffs between the exploration time and the existence of the internal memory available to the agent. We will first show an algorithm for an agent with 1 bit of memory completing exploration of any graph with stop in time O(m) using whiteboards of size O(log Delta) on each vertex with degree Delta.

An oblivious agent (with no internal memory) can explore any graph in time O(m D) using whiteboards of size O(log Delta) by applying the rotor-router mechanism. We will show that, even with unbounded whiteboards, there is no algorithm for oblivious agents that is better than the rotor-router in the worst case by showing a Omega(n3) lower bound for a specific class of graphs. We will also observe that any oblivious agent cannot stop after completing the task. This shows separation between oblivious and non-oblivious agents in terms of the exploration time and the stop property.

Lundi 17 novembre 2014 : "Group Search on the Line" - Leszek Gasieniec (University of Liverpool)

Lundi 10 novembre 2014 : "Patrolling by unreliable mobile robots" - Jurek Czyzowicz (Université du Québec en Outaouais)
Abstract: Mobile robots collaborate in order to solve efficiently the central problems in algorithmics of distributed computing like searching/exploration, rendez-vous or pattern formation. Patrolling is a perpetual traversal of an environment by a collection of mobile robots. The standard measure of efficiency of a patrolling algorithm is defined by its idleness – the minimal time interval during which every point of the environment is always visited by at least one robot. Boundary patrolling and fence patrolling were fundamental problems investigated by the robotics community in the last decade.

We sketch briefly previous results concerning the algorithms for the boundary and fence-patrolling problem. When some (unknown) robots of the collection cannot perform their duties, the fence patrolling algorithms become surprisingly unnatural. In more details we discuss a new algorithm for patrolling by unreliable robots. We show that the presented algorithm achieves the idleness, which is the best possible.

Lundi 03 novembre 2014 : "Coloration d'un cycle en temps log*(n): borne sup et borne inf" - Cyril Gavoille, (LaBRI, Université de Bordeaux)

Lundi 20 octobre 2014 : "Routage compact en pratique. Peut-on router avec des tables de routage de taille 6 ?" - Nicolas Hanusse , (LaBRI, Université de Bordeaux)
Abstract: Le projet européen EULER portant sur des propositions de nouveaux schéma de routage vient de se terminer. Je ferai une petite présentation de nos contributions sur des algorithmes de routage compact pour lesquels nous obtenons des garanties sur l'étirement, la taille des tables ou le cout de construction. Des simulations sur des cartes des systèmes autonomes d'Internet montrent que nous pouvons obtenir des tables de petite taille ...

Ce travail a été fait avec Cyril Gavoille, Christian Glacet et David Ilcinkas.

Lundi 03 octobre 2014 : "k-Partitionnement auto-stabilisant " - Yvan Rivierre, (LaBRI, Université de Bordeaux)
Abstract: Le k-partitionnement organise un réseau comme suit : ses nœuds sous répartis en sous-ensembles disjoints appelés grappes et pour chaque grappe, un nœud appelé tête est distingué, de sorte que chaque nœud d'une grappe est au plus à k sauts de la tête de grappe. Une application possible est de faire du routage hiérarchique en suivant des chemins entre les têtes de grappe pour l'acheminement de messages à travers le réseau. Ceci est particulièrement intéressant dans les réseaux à large échelle où la probabilité de panne est élevée. Les fautes transitoires sont des pannes non-définitives qui n'affectent que le contenu du réseau et non son code ou sa structure. Un algorithme est auto-stabilisant s'il garantit au système, une fois que les fautes transitoires cessent, de récupérer un fonctionnement normal, en temps fini et sans intervention extérieure.

Dans cet exposé, nous considérerons le problème du k-partitionnement auto-stabilisant. Il faut noter que construire un k-partitionnement de taille minimum est un problème NP-difficile. Nous proposerons un algorithme auto-stabilisant de k-partitionnement et étudierons ses propriétés dans l'arbre, dans un graphe connexe et dans un graphe de disques unitaires. Cette dernière topologie est généralement utilisée pour modéliser des réseaux de capteurs sans fil.

Lundi 22 septembre 2014 : Soutenance de thèse de Pierre Halftermeyer : "Connexité dans les Réseaux et Schémas d’Étiquetage Compact d’Urgence " - Amphi du LaBRI, 14h30
Abstract: On cherche à attribuer à tout sommet x d’un graphe G (à n sommets) une étiquette L(x), idéalement de taille O(log n), permettant de répondre à des requêtes de connexité avec panne Conn(u,v,X). C’est-à-dire qu’on veut, après un pré-traitement en temps O(|X|) des étiquettes des sommets de l’ensemble «en panne» X, répondre à partir des seules étiquettes L(u) et L(v), en un temps optimal O(log log n), à la question : u et v sont-ils connectés dans G\X ? On tâchera de traiter ce problème dans les graphes de genre borné ainsi que dans les graphes excluant un mineur fixé.

Lundi 07 juillet 2014 : "Solo-fast Universal Constructions for Deterministic Abortable Objects" - Claire Capdevielle, (LaBRI, Université de Bordeaux)
Abstract: In the context of shared memory model, we present our study on efficient implementations for deterministic abortable objects. Deterministic abortable objects behave like ordinary objects when accessed sequentially, but they may return a special response abort to indicate that the operation failed (and did not take effect) when there is contention.

It is impossible to implement deterministic abortable objects only with read/write registers. Thus, we study solo-fast implementations. These implementations use stronger synchronization primitives, e.g., CAS, only when there is contention. We consider interval contention.

We present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal constructionWe present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal construction is a method for obtaining a concurrent implementation of any object from its sequential code. The construction is non-trivial since in the resulting implementation a failed process can cause only a finite number of operations to abort. Our construction guarantees that operations that do not modify the object always return a legal response and do not use CAS. Moreover in case of contention, at least one writing operation succeeds. We prove that our construction has asymptotically optimal space complexity for objects whose size is constant.

Lundi 30 juin 2014 : "Rendez-vous d'agents mobiles tolérant aux pannes" - Arnaud Labourel, (LIF, Université Aix-Marseille)
'Abstract: Les systèmes d’agents mobiles sont des environnements distribués dans lequel les nœuds du réseau sont passifs et ce sont des agents mobiles qui s’occupent de l’exécution de l’algorithme. Le réseau est représenté par un graphe et les agents peuvent se déplacer d’un nœud à l’autre du graphe le long de ses arêtes. Dans cet exposé, on va chercher à trouver des algorithmes permettant à deux agents mobiles initialement dispersé dans le graphe de se rencontrer sur un nœud du graphe. Plus particulièrement, on s'intéressera à ce problème pour un modèle synchrone dans lequel une panne peut se produire lors de chaque tentative de déplacement des agents. On considérera trois types de pannes possibles : probabiliste (probabilité constante de panne), adversaire non borné ou borné (un adversaire peut empêcher un agent de bouger pendant un nombre de rondes fini ou bien borné par une constante). Je donnerai des bornes inférieures et supérieures sur le coût du rendez-vous (nombre de déplacements des agents avant le rendez-vous dans le pire des cas) ainsi que des résultats d'impossibilité pour ces trois types de pannes.

Lundi 23 juin 2014 : "Maintenance d'arbres et détection de déconnexion" - Christian Glacet, (LaBRI, Université de Bordeaux)
Abstract:Dans ce travail, nous proposons un algorithme auto-stabilisant de maintenance d'arbres de plus de courts chemins tout en gérant la déconnexion de graphes dynamiques ... ce qui résoud le problème du comptage à l'infini sans connaissance sur le graphe. Ce travail a été fait avec Colette Johnen, David Ilcinkas et Nicolas Hanusse.

Lundi 16 juin 2014 : Allyx Fontaine soutient sa thèse "Analyse et preuves formelles d’algorithmes distribués probabilistes" - Amphi du LaBRI
Abstract:

Lundi 05 mai 2014 : "Le codage de réseau aléatoire : une introduction " - Christine Bachoc, (IMB, Université de Bordeaux)
Abstract:

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

Lundi 31 mars 2014 : "Algebraic Removal Lemma" - Oriol Serra ( Barcelona, Spain)
Abstract: The removal lemma is a combinatorial result which, in its simpler form, says that a graph with n vertices and o(n^3) triangles can be made triangle free by deleting o(n^2) edges. It was used by Ruzsa and Szemerédi to provide a simple proof of Roth's theorem on 3-term arithmetic progressions in dense sets of integers. An analogous algebraic statement was formulated by Green in terms of solutions of linear equations in abelian groups. In the talk I will report on some contributions made jointly with Dan Král' and Lluís Vena to this algebraic version for linear systems in abelian groups and some consequences in arithmetic Ramsey theory. The latter include a version of Szemerédi theorem on arithmetic progressions in dense sets of finite abelian groups.

P.S. : Il s'agit d'un exposé CPU.

Lundi 24 mars 2014 : "Exploration and Diffusion in Graphs using Deterministic Walks " - Adrian Kosowski (LaBRI)
Abstract: In a continuous diffusive process, a certain amount of a resource, known as "load", is initially placed on the nodes of the graph, possibly in an unfair manner. In successive time steps, each node shares its load evenly among all its neighbors, until the load on the nodes of the graph eventually converges to its limit distribution (e.g., becomes uniform in the case of regular graphs). However, continuous diffusion cannot be applied to "granular load" which is not arbitrarily divisible, i.e., represented by unsplittable unit-load tokens (chips), which are placed on nodes and may be passed around the graph. In such a scenario, one natural way of simulating the continuous diffusion process is to require that each chip follows an independent random walk on the graph.

In this talk, we will instead focus on chip diffusion processes following rules which are both locally fair and deterministic. These rules include the so-called "rotor walk", in which chips are propagated by each node to its neighbors in round-robin fashion and, more broadly, rules in which each node attempts to send out roughly the same number of tokens through each of its outgoing arcs.

We will start by providing a description of the evolution and limit behavior of the rotor walk on the n-node ring with K << n chips. For general graphs, we will show bounds on the "cover time" of a rotor walk system with K chips, proving that in a graph with m edges and diameter D, all nodes will have been visited at least once by some chip during the first O(mD / log K) steps of the process. Finally, we will relate the "blanket time" (the time until all nodes of the graph have been visited by chips a similar number of times) and the "diffusion time" (the time until all nodes all host a similar number of chips, for K >> n) of fair deterministic walks to analogous parameters of the random walk. The latter results allow us to design surprisingly simple and efficient deterministic algorithms for load balancing in the diffusive model.

This talk includes an overview of results presented at PODC'13, STACS'14, and some current work in progress (joint work with: P. Berenbrink, D. Dereniowski, R. Klasing, F. Mallmann-Trent, D. Pajak, T. Sauerwald, P. Uznanski).

Lundi 03 mars 2014 : "Algorithmes de mise à jour locale pour des graphes aléatoires" - Romaric Duvignau (LaBRI)
Abstract: Afin de modéliser l'évolution de réseaux logiques dynamiques, nous proposons de maintenir exactement une distribution donnée de graphes aléatoires lors d'une séquence arbitraire d'insertions et de suppressions de sommets. Nous nous plaçons dans un modèle local où nous n'avons pas accès à l'ensemble des sommets, mais supposons à la place l'accès à une primitive globale renvoyant un sommet aléatoire uniforme du graphe. Dans cet exposé, nous nous intéressons à maintenir la distribution uniforme dans les graphes k-sortants (graphes dirigés où tous les sommets ont degré sortant k). Nous présenterons plusieurs algorithmes d'insertion et de suppression pour le problème de maintenance, dont les plus efficaces sont asymptotiquement optimaux.

Lundi 24 février 2014 : "Distributed anonymous discrete function computation" - Julien Hendrickx(Univ. Louvain)
Abstract: We propose a model for deterministic distributed function computation by a network of identical and anonymous nodes:. In this model, each node has bounded computation and storage capabilities that do not grow with the network size. Furthermore, each node only knows its neighbors, not the entire graph. Our goal is to characterize the class of functions that can be computed within this model. We provide a necessary condition for computability which we show to be nearly sufficient, in the sense that every function that violates this condition can at least be approximated. The problem of computing (suitably rounded) averages in a distributed manner plays a central role in our development; we provide an algorithm that solves it in time that grows quadratically with the size of the network.

Lundi 17 février 2014 : "The interplay between multidimensional skylines and functional dependencies " - Sofian Maabout (LaBRI)
Abstract: We show how functional dependencies, which are agnostoc to the orders defined over the dimensions domains, can help to optimize skyline queries which, by opposition are based on orders. We present some theoretical and experimental results.

Lundi 10 février 2014 : "Algorithmes auto-stabilisants barvards" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)
Abstract: Dans le contexte des réseaux à grande échelle, la prise en compte des pannes est une nécessité évidente. Ce séminaire traite de l’auto-stabilisation, une méthode qui vise à concevoir des algorithmes distribués se « réparant d’eux-même » en cas de pannes transitoires pouvant impliquer toute modification arbitraire de l’état des processus. Plusieurs paramètres peuvent être pris en compte pour mesurer l’efficacité d’un algorithme auto-stabilisant, dont en particulier le temps de convergence et la complexité mémoire. L’importance du temps de convergence vient de la nécessité évidente pour un système de retrouver le plus rapidement possible un état valide après une panne. La nécessité de minimiser la mémoire vient, d’une part, de l’importance grandissante de réseaux offrant des espaces mémoires restreints, comme par exemple certains réseaux de capteurs, et, d’autre part, de l’intérêt de minimiser à la fois l’échange et le stockage d’information afin de limiter les potentialités de corruption de cette information. Lors de ce séminaire, nous traiterons de la minimisation de la mémoire au travers d'un exemple, à savoir le problème de l’élection d’un leader. Une borne inférieure de Ω(log n) bits de mémoire par noeud a été établie par Dolev, Gouda et Schneider (1999) pour ce problème fondamental. Cette borne n'est toutefois valable que pour des algorithmes silencieux, c'est-à-dire des algorithmes dont les registres ne sont plus modifiés lorsque le système a rejoint un état légitime. Nous verrons que, si l'on autorise l’algorithme à rester bavard (non-silencieux) même après avoir rejoint un état légitime, alors l’espace mémoire peut être amélioré d’un facteur au moins exponentiel.

Lundi 6 Janvier 2014 : "Self-stabilizing k-independent dominating set construction" - Colette Johnen(LaBRI)
Abstract: A k-independent dominating set is a k-independent set and a k-dominating set. A set of nodes, I, is k-independent if the distance between any pair of nodes in I is at least k+1. A set of nodes, D, is a k-dominating if every node is within distance k of a node of D.

I propose two self-self-stabilizing algorithm building k-independent dominating sets. The both algorithm (SID and FID) are silent, and they converge under the unfair distributed scheduler (the weakest scheduling assumption).

The algorithm FID reaches a terminal (also legitimate) configuration in at most 4n+k rounds, where n is the network size. The algorithm FID requires (k+1)log(n+1) bits per node.

The protocol SID is memory efficient : it requires only 2log((k+1)n+1)+1 bits per node. The computation of the convergence time of the protocol SID is opened question.

Lundi 16 Décembre 2013 : "Large-scale Data Stream Analysis" - Yann Busnel (LINA - Université de Nantes)
Abstract: L'objectif de cet exposé est de dresser un court état de l'art autour de l'analyse des flux de données à grande échelle, lesquels sont souvent utilisés pour du monitoring et de la sécurité, à la fois dans les réseaux et les systèmes distribués jusqu'à l'internet des objets. La problématique de ce champs de recherche consiste à extraire de l'information pertinente d'un flux de données en une passe unique (en raison de la taille du flux et de sa rapidité), et ne nécessitant qu'une quantité mémoire très faible et une puissance de calcul très limitée. Je présenterai ensuite les dernières applications utilisant nos résultats récents, lesquels vont de la détection d'intrusion, la détection de DDoS, l'échantillonnage, etc.

Lundi 9 Décembre 2013 : "Simulating weak shared memory" - David Bonnin (LaBRI)
Abstract: It is well known that in an asynchronous message-passing system with crash faults, one can emulate an atomic register providing that more than half of the processes are non-faulty. By contrast, when a majority of the processes may fail, simulating atomic register is not possible. I will talk about weak variants of atomic registers that can be simulated tolerating a majority of processes failures. Specifically, I will introduce a new class of registers, called $\alpha$-registers. We found a lower bound of $\alpha = M+1$ with $M=2f-n+2$ for these registers, and an explicit algorithm can emulate them with $\alpha = 2M-1$. I will also probably talk about other approaches on weak shared memory : $M$-colored registers, and $k$-splitters. This is a joint work with C. Travers.

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nicolas Bonichon (LaBRI)
Abstract: This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

Lundi 25 Novembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)
Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a maximal matching for anonymous rings. Their bit complexity and time complexity are $O(\sqrt{\log n})$ with high probability. These algorithms are optimal modulo a multiplicative constant. Beyond the complexity results, the interest of this work stands in the description and the analysis of these algorithms which may be easily generalised. Furthermore, these results show a separation between the complexity of the MIS problem (and of the maximal matching problem) on the one hand and the colouring problem on the other. Colouring can be computed only in $\Omega(\log n)$ rounds on rings with high probability, while MIS is shown to have a faster algorithm. This is in contrast to other models, in which MIS is at least as hard as colouring. This is joint work with Y. Métivier, J.M. Robson and A. Zemmari

Lundi 4 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)
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Lundi 28 Octobre 2013 : "The Case for Reliable Software Transactional Networking" - Petr Kuznetsov (Paristech)
Abstract: Software-defined networking (SDN) is a novel paradigm that out-sources the control of packet-forwarding switches to a set of software controllers. The most fundamental task of these controllers is the correct implementation of the network policy, i.e., the intended network behavior. In essence, such a policy specifies the rules by which packets must be forwarded across the network. We initiate the study of the SDN control plane as a distributed system.

We introduce a formal model describing the interaction between the data plane and a distributed control plane (consisting of a collection of fault-prone controllers). Then we formulate the problem of consistentcomposition of concurrent network policy updates. The composition is enabled via a transactional interface with all-or-nothing semantics, which allows us to reason about possibilities and impossibilities in controller synchronization.

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

Lundi 23 Septembre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Miroslaw Korzeniowski
Abstract: Decentralized monitoring and alarming systems can be an attractive alternative to centralized architectures. Distributed sensor nodes (e.g., in the smart grid's distribution network) are closer to an observed event than a global and remote observer or controller. This improves the visibility and response time of the system. Moreover, in a distributed system, local problems may also be handled locally and without overloading the communication network.

This article initiates the study of alarming from a distributed computing perspective and under two fundamentally different scenarios: \emph{on-duty} and \emph{off-duty}. We model the alarming system as a sensor network consisting of a set of distributed nodes performing local measurements to sense events. In order to avoid false alarms, the sensor nodes cooperate and only escalate an event (i.e., raise an alarm) if the number of sensor nodes sensing an event exceeds a certain threshold. In the on-duty scenario, nodes not affected by the event can actively help in the communication process, while in the off-duty scenario non-event nodes are inactive.

This article presents and analyzes algorithms that minimize the reaction time of the monitoring system while avoiding unnecessary message transmissions. Moreover, lower bounds are derived that shed light on the limitations of distributed alarming systems.

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)
Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

Lundi 8 Juillet 2013 : "Dynamic Resource Allocation in Cloud Computing platforms" - Lionel Eyraud-Dubois (Labri)
Abstract: Je présente un problème d'allocation de ressources dans le contexte du Cloud Computing, où un ensemble de machines virtuelles (VM) doivent être allouées sur un ensemble de machines physiques (PMs). La particularité de ce problème vient du fait que la quantité de ressources dont chaque VM a besoin change au cours du temps, et qu'il est possible pour le fournisseur d'accès de changer l'allocation d'une VM par une opération de migration. Ce problème peut se modéliser sous la forme d'un problème de bin packing complètement dynamique, et je présente un algorithme d'approximation pour minimiser le nombre de PMs utilisées, tout en garantissant un petit nombre de migrations. Les propriétés de cet algorithme permettent également d'envisager une version distribuée.

Lundi 10 Juin 2013 : " The Heard-Of model: computing in distributed systems with benign failures" - Bernadette Charron-Bost (CNRS, Ecole polytechnique, Paris)
Abstract: Problems in fault-tolerant distributed computing have been studied in a va- riety of system models. These models are all based on the principle that it is usefull and even necessary to specify why and by whom errors occur. In this talk, we question this principle, and present a general computational model, called the Heard-Of model, suitable for describing any type of system, be it message passing, shared memory, synchronous, or asynchronous. In this model, computations evolve in rounds, and communication missed at a round is definitely lost. Only information transmission is represented: for each round r and each process p, our model specifies the set of processes that p “hears of” at round r (heard-of set) namely the processes from which p receives some message at round r. The features of a specific system are thus captured as a whole, just by a predicate over the collection of heard-of sets. Thus the Heard-Of model allows us to handle all types of benign failures, static or dynamic, permanent or transient, in a unified framework. Moreover, it unifies the most seemingly unrelated notions in distributing computing, namely synchrony and asynchrony. We further demonstrate how this unifying framework leads to new results and insights in fault-tolerant distributed computing. In particular, we show that some fundamental results for asynchronous systems can be advantageously transferred to synchronous systems. We also examine Consensus algorithms in the Heard-Of model: we show how our approach allows us to devise new solutions and to give simple correctness proofs of existing algorithms like Paxos.

Joint work with André Schiper, EPFL

Lundi 3 Juin 2013 : "Introduction to renaming" - Corentin Travers (Labri)
Abstract: Renaming is a fundamental coordination problem in distributed computing. It consists in assigning new names taken from a small name space to processes in such a way that no two processes obtain the same name. The talk will survey renaming algorithms suited for different models of distributed computing, including the wait-free shared memory and the synchronous crash-prone message-passing models.

Lundi 27 Mai 2013 : " Exploration des graphes dynamiques T-intervalle-connexes : le cas de l'anneau" - Wade Ahmed (Labri)
Abstract: Dans cet exposé, je vais parler de l'étude des graphes dynamiques T-intervalle-connexes du point de vue du temps nécessaire à leur exploration par une entité mobile (agent). Un graphe dynamique est T-intervalle-connexe (T \geq 1) si pour chaque fenêtre de T unités de temps, il existe un sous-graphe couvrant connexe stable. Cette propriété de stabilité de connexion au cours du temps a été introduite par Kuhn, Lynch et Oshman~\cite{KLO10} (STOC 2010). Nous nous concentrons sur le cas où le graphe sous-jacent est un anneau de taille n et nous montrons que la complexité en temps en pire cas est de 2n-T-\Theta(1) unités de temps si l'agent connaît la dynamique du graphe, et n+ \frac{n}{\max\{1,T-1\}} (\delta-1) \pm \Theta(\delta) unités de temps sinon, où \delta est le temps maximum entre deux apparitions successives d'une arête.

Keywords : Graphe dynamique, exploration, T-intervalle-connexité, agent mobile

Lundi 13 Mai 2013 : " Calcul Distribué et Fouille de Données" - Nicolas Hanusse (Labri)
Abstract: L'avènement de la production massive de données et la volonté de les exploiter sont limités par les systèmes de gestion de bases de données relationnelles classiques. Cet exposé consiste en une discussion sur les enjeux et problèmes algorithmiques engendrés par le calcul distribué et parallèle. Le calcul de corrélations servira d'illustration. C'est un travail en cours avec Sofian Maabout et Eve Garnaud.

Lundi 22 Avril 2013 : " A peer-to-peer-based virtual environment system" - Eliya Buyukkaya (ENSSAT-Université de Rennes I)
Abstract: Virtual environments (VEs) are 3-D virtual worlds in which a huge number of participants play roles and interact with their surroundings through virtual representations called avatars. VEs are traditionally supported by a client/server architecture. However, centralized architectures can lead to bottleneck on the server due to high communication and computation overhead during peak loads. Thus, P2P overlay networks are emerging as a promising architecture for VEs. However, exploiting P2P schemes in VEs is not straightforward, and several challenging issues related to data distribution and state consistency should be considered.

One of the key aspects of P2P-based VEs is the logical platform consisting of connectivity, communication and data architectures, on which the VE is based. The connectivity architecture is the overlay topology structure, which defines how peers are connected to each other. The communication architecture is the routing protocol defining how peers can exchange messages, while the data architecture defines how data are distributed over the logical overlay. The design of these architectures has significant influence on the performance and scalability of VEs.

First, we propose a scalable connectivity architecture based on a new triangulation algorithm reducing maintenance cost of the system. Second, we construct a communication architecture built on top of the connectivity architecture ensuring that each message reaches its intended destination. Finally, we propose a data architecture ensuring the management of data with different characteristics in terms of mobility in the VE, while providing a fair data distribution and low data transfer between peers in the VE.

Lundi 15 Avril 2013 : " Algorithms for the Vertex Cover Problem on Large Graphs with Low Memory Capacities" - Romain Campigotto (LIP6-Paris)
Abstract: Most of the known optimization algorithms need to explore, mark, modify, etc. the instance given as input before producing their results. To do that, the instance is entirely loaded into the memory of the computer and is manipulated by the algorithm. Often, "extra" data structures are also necessary to memorize parameters useful all along the computation or to update the current solution that will be returned as the final product of the program. However, this classical model is no more adapted for many new computing applications. Indeed, nowadays, many fields such as biology, meteorology, finance, etc. produce very large amount of data.

In our works, we have focused on the Vertex Cover problem on huge graphs: in the intrinsic NP-completeness is added the difficulty to manipulate graphs with severe constraints (mainly related to the low memory capacities). We defined a treatment model combining some properties of several existing models in the literature: streaming, online, I/O-efficient, etc. We initially considered three approximation algorithms, which are memory-efficient (they use a memory space in O(log n) bits). We analyzed their performance in terms of solution quality and complexity, in mean and worst cases. We then focused on algorithms that use memory space of n bits. We showed that it could be very worst with strictly less than n bits memory space. Subsequently, we conducted experiments on very large graphs (in the order of billions of vertices and edges). This study showed that in practice, memory-efficient algorithms are better suited to handle large graphs.

This is joint work with Eric Angel (IBISC, Univ. Évry) and Christian Laforest (LIMOS, ISIMA, Clermont-Ferrand).

Lundi 8 Avril 2013 : "Implémentation d'algorithmes distribués à l'aide de Visidia" - Mohamed Mosbah (Labri)
Abstract: Dans le cadre du projet visidia, une plate-forme logicielle est développée pour l'implantation et la visualisation d'algorithmes distribués. Après une introduction et quelques rappels, l'exposé consistera en une présentation de la plate-forme et de son utilisation pour programmer des exemples d'algorithmes. L'interface et l'API permettent de visualiser l'exécution d'algorithmes, d'implanter de nouveaux algorithmes, ou d'effectuer des statistiques. Les algorithmes peuvent être exprimés selon plusieurs modèles (calculs locaux, passage de messages, agents mobiles).

Lundi 25 Mars 2013 : "Simultaneous Consensus vs Set Agreement." - Zohir Bouzid (LIP6-Paris)
Abstract: In the traditional consensus task, processes are required to agree on a common value chosen among the initial values of the participants. It is well known that consensus cannot be solved in crashed-prone, asynchronous distributed systems. Two generalizations of the consensus problem have been introduced: k-set agreement and k-simultaneous consensus. The k-set agreement task has the same requirements as consensus except that processes are allowed to decide up to k distinct values. In the k-simultaneous consensus task, each process participates simultaneously in k instances of consensus and is required to decide in at least one of them; any two processes deciding in the same instance must decide the same value. In this talk, we compare the computability of these problems in two central models in distributed computing: shared memory and message passing. We show that even though the two problems are equivalent in shared memory, k-simultaneous consensus is strictly harder than k-set agreement in the message passing model. This result will serve as a basis for a discussion about different models of computation and their respective power.

Lundi 18 Mars 2013 : "Vers une classification des réseaux dynamiques en fonction des problèmes qu'on peut y résoudre." - Arnaud Casteigts (Labri)
Abstract: Derrière les notions de "graphe dynamique" ou de "réseau dynamique" se cache une très grande diversité de scénarios et d'hypothèses, allant de réseaux semi-statiques où la connexité est toujours assurée à des réseaux complètement mobiles, où la connexité ne s'établit qu'à travers le temps et l'espace (e.g. DTNs). Dans cet exposé, résolument transversal, je présenterai l'état d'avancement de nos recherches autour de la question suivante : quel lien existe-t-il entre la "faisabilité" de tâches distribuées et la dynamique du réseau. Les hypothèses résultantes sur la dynamique peuvent être vues comme autant de classes de graphes (ou alternativement, comme autant de puissances possibles pour un adversaire qui contrôlerait la topologie). Nous avons à ce jour caractérisé et/ou recensé une petite vingtaine de classes de ce type.

Certains de ces travaux ont été menés en collaboration avec Serge Chaumette et Afonso Ferreira. D'autres avec Paola Flocchini et Nicola Santoro.

Lundi 25 Février 2013 : "Sur les 1001 modèles en algorithmique distribuée." - Yves Metivier (Labri)
Abstract: Le but de cet "exposé-discussion" est de présenter quelques modèles en algorithmique distribuée et d'échanger sur leurs liens et leurs mérites.

Lundi 18 Février 2013 : "Distributed Calculation of Graph Diameter" - Mike Robson (Labri)
Abstract: We consider the problem of calculating the diameter of a graph given that there is a single vertex "Leader" and neighbouring vertices can exchange messages of a single bit at each round. We show that this can be achieved in the same O(n) time complexity as well known algorithms without this bound on message length. The techniques used can be applied to a number of other graph computations. We consider briefly how the algorithm behaves if applied in a situation where more than one vertex considers itself the Leader.

This is joint work with Yves Métivier and Akka Zemmari.

Lundi 11 Février 2013 : "Bounds for Communication in Wireless Grids" - Joseph Peters (Simon Fraser University)
Abstract: In a wireless network, a transmission can be received by a node if it is close enough to the sender. However, transmissions can interfere with each other and the interference distance is typically greater than the reception distance. Efficient communication protocols in these networks minimize the time to move information without interference. In this talk, I will describe optimal protocols for the problem of collecting information into a central node of a two-dimensional square or hexagonal grid graph. The optimality of the protocols is proved using a new lower bound technique that is an adaptation to a discrete environment of a method based on linear programming duality for continuous flows.

This is joint work with Jean-Claude Bermond, CNRS-INRIA-University of Nice.

Lundi 04 Février 2013 : "Distributed Detection of Clone Attacks in Wireless Sensor Networks" - Mauro Conti (University of Padua, Italy)
Abstract: Wireless Sensor Networks (WSNs) are often deployed in hostile environments where an adversary can physically capture some of the nodes, first can reprogram, and then, can replicate them in a large number of clones, easily taking control over the network. A few distributed solutions to address this fundamental problem have been recently proposed. However, these solutions are not satisfactory. First, they are energy and memory demanding: A serious drawback for any protocol to be used in the WSN-resource-constrained environment. Further, they are vulnerable to the specific adversary models that we introduced. The contributions of our work are threefold. First, we analyze the desirable properties of a distributed mechanism for the detection of node replication attacks. Second, we show that the known solutions for this problem do not completely meet our requirements. Third, we propose a new self-healing, Randomized, Efficient, and Distributed (RED) protocol for the detection of node replication attacks, and we show that it satisfies the introduced requirements. Finally, extensive simulations show that our protocol is highly efficient in communication, memory, and computation; is much more effective than competing solutions in the literature; and is resistant to the new kind of attacks introduced in our work, while other solutions are not.

Lundi 28 Janvier 2013 : "Distributed Exclusive Graph Searching in Trees" - Janna Burman (LRI-Université Paris-Sud)
Abstract: We consider a version of the well known graph searching problem, where a team of robots aims at clearing the contaminated edges of a graph. We study graph searching in the model of mobile computing where autonomous deterministic robots move between the graph nodes when operating in asynchronous cycles of Look-Compute-Move. Moreover, motivated by physical constraints, following some recent works, we consider the exclusivity property, stating that no two or more robots can occupy a same node at the same time. In addition, we assume that all the graph elements and the robots are anonymous. Robots are oblivious and have no sense of direction. Our objective is to characterize for a graph $G$, the set of integers $k$ such that graph searching can be achieved by a team of $k$ robots starting from any $k$ distinct nodes in $G$. Our main result consists in a full characterization for any asymmetric tree. Towards providing a characterization in the general case, including trees with non-trivial automorphisms, we provide a set of positive and negative results, including a full characterization for any line. All our positive results are based on the design of algorithms enabling perpetual graph searching to be achieved with the desired number of robots. We prove that, in addition to the distributed nature of our setting, the exclusivity property has a significant impact on the nature of the graph searching problem. Hence, the design of the algorithms requires to invent new methods.

Lundi 21 Janvier 2013 : "Présentation de Keep Alert, une solution pour la surveillance de marques sur Internet" - Anthony Don (Keep Alert)
Abstract: A destination des cabinets de propriété industrielle et des services juridiques, Keep Alert propose des surveillances de marque parmi les noms de domaine, les régies publicitaires et les réseaux sociaux. Anthony DON, directeur technique chez Keep Alert, présentera au groupe de travail, le fonctionnement global de la plateforme, puis abordera les problématiques actuelles et les perspectives de développement relatives à l'algorithmique distribuée.

Lundi 14 Janvier 2013 : "Two Monte-Carlo Election Algorithms for Anonymous Graphs without any Initial Knowledge" - Akka Zemmari (Labri)
Abstract: The paper proposes and analyses two Monte Carlo election algorithms for anonymous graphs without any initial knowledge. Both have a time complexity equal to $O(D)$, where $D$ is the diameter of the graph. The first is correct with probability $1-o(n^{-1})$ (where $n$ is the size of the graph). The size of messages is $O(\log n)$ with probability $1-o(n^{-1})$ and the expected value of the size of messages is also $O(\log n)$. The second is correct with probability $1-o(n^{-c})$ for any $c\geq 1$. The size of messages is $O\left((\log n)(\log^* n)^2 \right)$ with probability $1-o(n^{-c})$ for any $c\geq 1$; their expected size is $O\left((\log n)(\log^* n) \right)$.

This is a joint work with Y. Métivier and J. M. Robson

Lundi 10 Décembre 2012 : pas de seminaire. Soutenance de thèse-Florent Foucaud.

Lundi 3 Décembre 2012 : "Progress and Challenges for Labeling Schemes" - Cyril Gavoille (Labri)
Abstract: A fundamental question in Distributed Computing is to understand how localized and how much information are required to solve a task on a network. Typically, if the distance between any pair x,y of nodes in a network is asked, we would like to know which minimal information about x and y in the network are needed. The goal in labeling schemes is precisely to understand how much information must be attached to the nodes (formalized as labels) to solve a graph problem assuming the answer can be determined solely on the basis of the labels of the nodes invoked in the query. In this talk, I give a survey on labeling schemes, present some recent results with their techniques, and highlight new challenges.

Lundi 26 Novembre 2012: "Competitive Routing on a Variant of the Delaunay Triangulation" - Prosenjit Bose (Carleton University)
Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we showed how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.

Lundi 19 Novembre 2012: " Reliable Service Allocation in Clouds"- Lionel Eyraud-Dubois, Olivier Beaumont (Labri)
Abstract: We consider several reliability problems that arise when allocating applications to processing resources in a Cloud computing platform. More specifically, we assume on the one hand that each computing resource is associated to a capacity constraint and to a probability of failure. On the other hand, we assume that each service runs as a set of independent instances of identical Virtual Machines, and that the Service Level Agreement between the Cloud provider and the client states that a minimal number of instances of the service should run with a given probability. In this context, given the capacity and failure probabilities of the machines, and the capacity and reliability demands of the services, the question for the cloud provider is to find an allocation of the instances of the services (possibly using replication) onto machines satisfying all types of constraints. In this paper, our goal is to assess the impact of the reliability constraint on the complexity of resource allocation problems. We consider several variants this problem, depending on the number of services (one or many) and if their reliability demand is individual or global. We prove several fundamental complexity results ($\#$P and NP-completeness results) and we provide several optimal and approximation algorithms. In particular, we prove that a basic randomized allocation algorithm, that is easy to implement, provides optimal or quasi-optimal results in several contexts, and we show through simulations that it also achieves very good results in more general settings.

Lundi 12 Novembre 2012 : "MAXIMUM MATCHING IN MULTI-INTERFACE NETWORK"- Dominik Pająk (LaBRI)
Abstract: In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

Lundi 5 Novembre 2012 : pas de séminaire
Lundi 22 Octobre 2012 : Christian Glacet (LaBRI)
Lundi 15 Octobre: " NETWORK VERIFICATION VIA ROUTING TABLE QUERIES" - Ralf Klasing (LaBRI)
Abstract: We address the problem of verifying the accuracy of a map of a network by making as few measurements as possible on its nodes. This task can be formalized as an optimization problem that, given a graph G=(V,E), and a query model specifying the information returned by a query at a node, asks for finding a minimum-size subset of nodes of G to be queried so as to univocally identify G. This problem has been faced w.r.t. a couple of query models assuming that a node had some global knowledge about the network. Here, we propose a new query model based on the local knowledge a node instead usually has. Quite naturally, we assume that a query at a given node returns the associated routing table, i.e., a set of entries which provides, for each destination node, a corresponding (set of) first-hop node(s) along an underlying shortest path. First, we show that any network of n nodes needs Omega(log log n) queries to be verified. Then, we prove that there is no o(log n)-approximation algorithm for the problem, unless P=NP, even for networks of diameter 2. On the positive side, we provide an O(logn)-approximation algorithm to verify a network of diameter 2, and we give exact polynomial-time algorithms for paths, trees, and cycles of even length.

Lundi 8 Octobre 2012 : pas de séminaire
Lundi 1er Octobre 2012 : Réunion de rentrée du thème - Nicolas Hanusse (LaBRI)
Abstract: L'ordre du jour:

• projets: thèse, région, ingénieur, conférence
• organisation du groupe de travail: exposé à venir (projets à long terme, discussion sur les modèles, logiciels, ...), vitrine
• mise-à-jour site web
• enseignement: état des lieux des enseignements locaux
• stages X, ENS, ...

Lundi 21 Juin : "ABOUT RANDOMISED DISTRIBUTED GRAPH COLOURING AND GRAPH PARTITION ALGORITHMS" - Akka Zemmari (LaBRI)
Abstract: We present and analyse a very simple randomised distributed vertex colouring algorithm for arbitrary graphs of size $n$ that halts in time $O(log n)$ with probability $1-o(n^{-1}).$ Each message containing $1$ bit, its bit complexity per channel is $O(log n)$.
From this algorithm, we deduce and analyse a randomised distributed vertex colouring algorithm for arbitrary graphs of maximum degree $Delta$ and size $n$ that uses $Delta+1$ colours and halts in time $O(log n)$ with probability $1-o(n^{-1}).$
We also obtain a partition algorithm for arbitrary graphs of size $n$ that builds a spanning forest in time $O(log n)$ with probability $1-o(n^{-1})$. We study some parameters such as the number, the size or the radius of trees of the spanning forest.
We assume that graphs are anonymous; we only assume that each vertex distinguishes between its neighbours by locally known channel names. Furthermore we do not assume that the size (or an upper bound on the size) of graphs is known.
Joint work with Y. Métivier, N. Saheb and J.M. Robson

Lundi 14 Juin : Almost optimal asynchronous rendezvous in infinite multidimensional grids - Arnaud Labourel (LaBRI)
Abstract: Dans cet exposé, je montrerais comment deux agents mobiles peuvent se rencontrer dans une grille infinie de dimension supérieure à 2. On considère le modèle asynchrone. C'est-à-dire que la durée de traversée de chaque sommet par un agent est déterminée par un adversaire omniscient qui essaye d'empêcher le rendez-vous. On supposera que chaque agent connait sa position dans la grille mais pas celle de l'autre agent. Cette connaissance permet d'avoir un algorithme de rendez-vous ayant un coût, mesuré en terme de distance parcourue par les agents, quasiment optimal.

05 juillet 2015 à 23h04 par 109.214.245.140 -
Ligne 14 modifiée:

Lundi 6 juillet : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)\\

en:

Date à définir : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)\\

17 juin 2015 à 12h58 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 24-26 modifiées:

Lundi 29 juin : TBA Joseph Peters - (Simon Fraser UniversityVancouver)

en:

Lundi 29 juin : Spreading Influence in Social Networks with Time Constraints Joseph Peters - (Simon Fraser University)

Lignes 28-30 modifiées:
en:

In a social network, agents change their behaviours and opinions on the basis of information collected from their neighbours. Generally, recent information is more influential than older information, and information that is received in a short period of time is more influential than information received during a long period of time. An example of this phenomenon is consumer reviews on websites such as Amazon. Another example is viral marketing which attempts to influence consumer adoption of products. A third example is recent communication strategies of politicians.

In this talk, I will present a graph-based model of the spread of influence in networks that generalizes previous research by including temporal information. The goal is to identify a small set of nodes that eventually influences all nodes in the graph with the restriction that influence only lasts for a bounded time interval. The problem for general graphs is computationally difficult even for approximate solutions. The talk will focus on efficient algorithms for restricted families of graphs: paths, rings, trees, and complete graphs.

15 juin 2015 à 11h00 par 85.68.164.197 -
Lignes 14-16 modifiées:

Lundi 29 juin : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

en:

Lundi 6 juillet : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

Lignes 21-27 ajoutées:

Lundi 29 juin : TBA Joseph Peters - (Simon Fraser UniversityVancouver)

Abstract:

09 juin 2015 à 10h21 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 11 supprimée:
Lignes 13-16 modifiées:

Lundi 29 juin : TBA Nicolas Bonichon - (LaBRI, Université de Bordeaux)
Abstract:

en:

Lundi 29 juin : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

Abstract: La suite de l'exposé du 18 mai. JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

Lignes 24-25 modifiées:

Lundi 22 juin : Station Assignment with Reallocation Miguel Mosteiro - (Kean University, NJ, USA)

en:

Lundi 22 juin : Upper and Lower Bounds for Online Routing on Delaunay Triangulations Nicolas Bonichon - (LaBRI, Université de Bordeaux)
Abstract: Consider a weighted graph G whose vertices are points in the plane and edges are line segments between pairs of points. The weight of each edge is the Euclidean distance between its two endpoints. A routing algorithm on G has a routing ratio of c if the length of the path produced by the algorithm from any vertex s to any vertex t is at most c|[st]|. The routing algorithm is online if it makes forwarding decisions based on 1) the k-neighborhood in G (for some integer constant k > 0) of the current position of the message and 2) limited information stored in the message header.

We present an online routing algorithm on the Delaunay triangulation with routing ratio less than 5.90. This improves upon the algorithm with best known routing ratio of 15.48. We also show that the routing ratios of any deterministic k-local algorithm is at least 1.70 for the Delaunay triangulation.

Lundi 15 juin : Station Assignment with Reallocation Miguel Mosteiro - (Kean University, NJ, USA)

Lignes 41-49 supprimées:

Lundi 15 juin : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

Abstract: La suite de l'exposé du 18 mai. JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

07 juin 2015 à 08h00 par 85.171.72.69 -
Lignes 39-40 modifiées:

Lundi 8 juin : TBA Faten Fakhfakh - (LaBRI, Université de Bordeaux)

en:

Lundi 8 juin : Proving correctness of distributed algorithms in a dynamic context. Faten Fakhfakh - (LaBRI, Université de Bordeaux)

Lignes 42-43 ajoutées:

Proving the correctness of distributed algorithms is a hard task due to the lack of global state knowledge and the non-determinism in the processes execution. In dynamic networks, this task becomes more difficult because of dynamic behavior and time complexity. In this talk, we propose a reuse based approach for specifying and proving distributed algorithms in dynamic networks. It consists in developing a formal pattern using Event-B method, based on refinement technique. Our pattern allows to handle topological events in dynamic networks and to characterize the concept of time. The proposed solution relies on evolving graphs, as a powerful model to record the evolution of a network topology. To illustrate it, we investigate an example of a distributed algorithm encoded by local computations models.

01 juin 2015 à 13h28 par 95.245.7.126 -
Lignes 20-22 modifiées:

Lundi 22 juin : TBA Miguel Mosteiro - (Kean University, NJ, USA)
Abstract:

en:

Lundi 22 juin : Station Assignment with Reallocation Miguel Mosteiro - (Kean University, NJ, USA)
Abstract: In this work, we studied a dynamic allocation problem that arises in various scenarios where mobile clients joining and leaving the system have to communicate with static stations via radio transmissions. Restrictions are a maximum delay, or laxity, between consecutive client transmissions and a maximum bandwidth that a station can share among its clients. We studied the problem of assigning clients to stations so that every client transmits to some station, satisfying those restrictions. We considered reallocation algorithms, where clients are revealed at its arrival time, the departure time is unknown until they leave, and clients may be reallocated to another station, but at a cost proportional to the reciprocal of the client’s laxity. I will present positive and negative results as well as the results of our simulations showing that our protocols behave even better than our theoretical guarantees.

This is joint work with Yulia Rossikova and Prudence W. H. Wong, and will be presented at SEA 2015.

01 juin 2015 à 13h25 par 95.245.7.126 -
Ligne 12 ajoutée:
Lignes 14-16 modifiées:

Lundi 22 juin : TBA Miguel Mosteiro - (Kean University, NJ, USA)

en:

Lundi 29 juin : TBA Nicolas Bonichon - (LaBRI, Université de Bordeaux)

Lignes 20-25 ajoutées:

Lundi 22 juin : TBA Miguel Mosteiro - (Kean University, NJ, USA)
Abstract:

Ligne 35 modifiée:

Lundi 8 juin : TBA Nicolas Bonichon - (LaBRI, Université de Bordeaux) \\

en:

Lundi 8 juin : TBA Faten Fakhfakh - (LaBRI, Université de Bordeaux) \\

26 mai 2015 à 10h52 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 24-25 modifiées:

La suite de l'exposé du 18 mai,

 JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

en:

La suite de l'exposé du 18 mai. JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

26 mai 2015 à 10h50 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 24 supprimée:
26 mai 2015 à 10h48 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 17-26 ajoutées:

Lundi 15 juin : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Part 2 Arnaud Casteigts - (LaBRI, Université de Bordeaux)

Abstract: La suite de l'exposé du 18 mai,

 JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

06 mai 2015 à 16h00 par 85.171.72.69 -
Lignes 26-28 modifiées:

Lundi 1er juin : TBA Nesrine Ouled Abdallah - (LaBRI, Université de Bordeaux)
Abstract:

en:

Lundi 1er juin : An overview of computational models for wireless sensor networks Nesrine Ouled Abdallah - (LaBRI, Université de Bordeaux)
Abstract: In this talk, we will give an overview of some computational models designed for networks of tiny artifacts with sensing capabilities and with limited resources. We will focus on the population protocols (PP) model of Angluin et al. which is based on pairwise interactions between anonymous passively mobile finite state agents. We will consider, among other examples, the PP that stably computes the OR predicate and that we applied to the broadcast problem. We will also consider works that extend the PP model such as the mediated population protocols. In all these models, the interacting pairs are supposed to be chosen by a fair scheduler. In this talk, we will present a new fair one based on the rendezvous algorithm.

24 avril 2015 à 09h48 par 85.171.72.69 -
Ligne 18 ajoutée:
Lignes 20-25 modifiées:
en:

Lundi 8 juin : TBA Nicolas Bonichon - (LaBRI, Université de Bordeaux)
Abstract:

20 avril 2015 à 09h30 par 85.171.72.69 -
Ligne 53 modifiée:

Abstract: On pourra par contre assister au séminaire de Tahiry Razafindralambo qui est candidat prof, même heure, amphi du LaBRI.\\

en:

On pourra par contre assister au séminaire de Tahiry Razafindralambo qui est candidat prof, même heure, amphi du LaBRI.\\

20 avril 2015 à 09h21 par 85.171.72.69 -
20 avril 2015 à 09h13 par 85.171.72.69 -
Lignes 51-53 modifiées:

Lundi 4 mai : TBA - ??? ???
Abstract:

en:

Lundi 4 mai : Pas d'exposé
Abstract: On pourra par contre assister au séminaire de Tahiry Razafindralambo qui est candidat prof, même heure, amphi du LaBRI.
Titre : Controlled Mobility in Wireless Networks

Resumé : Mobility is the character or property of an object that has the capacity or the ability to move or be moved. It characterizes all things that can rapidly change shape, appearance or is unstable, variable or fluctuate in time and space. The introduction of mobility in networks is a milestone in the description and implementation of communication systems that must take into account the mobility of one or more entities that comprise this system.

In the early 2000, the research shows that mobility is not all a drawback by pointing out that mobility can increase the capacity, security and covered areas. These results raise two important points: (i) The contribution of mobility described in these articles are considered at application-level if we refer to the OSI model and (ii) mobility is undergone by the users or network entities.

The two points raised above will be addressed from different point of view. Regarding the first point the results I show here consider two aspects. The first issue focuses on the benefits of mobility at the application level and more specifically for coverage in wireless sensor networks. The second aspect considers the use of mobility as a network primitive and uses it to increase the performance of the protocol stack.

20 avril 2015 à 09h04 par 85.171.72.69 -
Lignes 43-45 modifiées:

Lundi 11 mai : TBA - ??? ???

\\Abstract:

en:

Lundi 11 mai : Calculer les distances dans un graphe en temps constant avec des étiquettes de 0.793n bits. Cyril Gavoille - (LaBRI, Université de Bordeaux)
Abstract: Dans cet exposé je présenterai une structure de données compacte permettant de calculer en temps constant la distance entre n'importe quelle paire de sommets d'un graphe arbitraire à n sommets. Cette structure de données se présente sous forme d'étiquette associée à chacun des sommets, la distance entre les u et v étant décodée à partir d'un calcul impliquant seulement les étiquettes de u et de v. La solution triviale, à l'aide d'un vecteur de distances de taille n, produit des étiquettes de nlogn bits. En fait, aucune technique utilisant o(nlogn) bits et décodant en temps constant n'est connue. Cependant, si on relâche la contrainte du décodage en temps constant, des solutions avec O(n) bits existent. Une des meilleures d'entres elles utilisent 11n bits pour un décodage O(logn). Notre solution réduit la taille des étiquettes à 0.793n bits avec un décodage constant et s'étend naturellement aux graphes valués.

Lignes 51-54 modifiées:

Lundi 4 mai : Calculer les distances dans un graphe en temps constant avec des étiquettes de 0.793n bits. Cyril Gavoille - (LaBRI, Université de Bordeaux)
Abstract: Dans cet exposé je présenterai une structure de données compacte permettant de calculer en temps constant la distance entre n'importe quelle paire de sommets d'un graphe arbitraire à n sommets. Cette structure de données se présente sous forme d'étiquette associée à chacun des sommets, la distance entre les u et v étant décodée à partir d'un calcul impliquant seulement les étiquettes de u et de v. La solution triviale, à l'aide d'un vecteur de distances de taille n, produit des étiquettes de nlogn bits. En fait, aucune technique utilisant o(nlogn) bits et décodant en temps constant n'est connue. Cependant, si on relâche la contrainte du décodage en temps constant, des solutions avec O(n) bits existent. Une des meilleures d'entres elles utilisent 11n bits pour un décodage O(logn). Notre solution réduit la taille des étiquettes à 0.793n bits avec un décodage constant et s'étend naturellement aux graphes valués.

en:

Lundi 4 mai : TBA - ??? ???
Abstract:

20 avril 2015 à 08h40 par 85.171.72.69 -
Lignes 34-38 modifiées:

Lundi 18 mai : TBA - ??? ???
Abstract:

en:

Lundi 18 mai : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Arnaud Casteigts - (LaBRI, Université de Bordeaux)

Abstract: JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

Lignes 43-46 modifiées:

Lundi 11 mai : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Arnaud Casteigts - (LaBRI, Université de Bordeaux)
Abstract: JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

en:

Lundi 11 mai : TBA - ??? ???

\\Abstract:

08 avril 2015 à 07h50 par 85.171.72.69 -
Lignes 64-67 modifiées:

Abstract:

en:

Abstract: Suite aux travaux de A.M.Turing, les algorithmes ont été vus comme l’abstraction à partir de laquelle on pouvait écrire des programmes pour des ordinateurs dont le principe était lui-même issu du concept théorique de machine de Turing.

Nous partons ici du constat que les les algorithmes de la nature, massivement parallèles, autoadaptatifs et auto reproductibles, dont on ne sait pas comment ils fonctionnent réellement, ni pourquoi, ne sont pas aisément spécifiés par le modèle théorique actuel de Machine de Turing Universelle, ou de Calculateur Universel ; en particulier les aspects de communications, de règles évolutives, d’événements aléatoires, à l’image du code génétique, ne sont pris en compte que par ajout d’artifices à la théorie. Nous nous proposons ici de montrer comment aborder ces problèmes en repensant le modèle théorique. Nous proposerons un modèle d’algorithme, appelé ici machine-α qui contient et généralise les modèles existants.

07 avril 2015 à 20h41 par 85.171.72.69 -
Lignes 69-70 modifiées:

Lundi 13 avril : TBA Anca Muscholl
Abstract:

en:

Lundi 13 avril : Verifying parametrized asynchronous systems Anca Muscholl
Abstract: The talk should be a (gentle) introduction to verification problems for concurrent, asynchronous systems. I will focuss on two models (among a large number!), one with shared memory and another one with asynchronous calls. The talk is based on the following papers:

Parameterized Verification of Asynchronous Shared-Memory Systems Javier Esparza, Pierre Ganty, and Rupak Majumdar CAV 2013

Safety of parametrized asynchronous shared-memory systems is almost always decidable S. La Torre, A. Muscholl, I. Walukiewicz 2015

Algorithmic Verification of Asynchronous Programs Pierre Ganty, and Rupak Majumdar ACM Transactions on Programming Languages and Systems 2012

29 mars 2015 à 19h48 par 85.171.72.69 -
Lignes 81-82 modifiées:

Abstract:

en:

Abstract: Software Transactional memory (or STM for short) is a promising programming paradigm that aims at simplifying concurrent programming by using the notion of a transaction. A transaction executes a piece of code containing accesses to data items which are shared by several processes in a concurrent setting. By using transactions, the programmer needs only enhance its sequential code with invocations of special operations to read or write data items. It is guaranteed that if any operation of a transaction takes place, they all do, and that if they do, they appear to other threads to do so atomically, as one indivisible operation.

In this talk, I will present the STM paradigm and the main algorithmic techniques to implement it.

23 mars 2015 à 09h41 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 79-80 modifiées:

Lundi 30 mars : ' An introduction to Software Transactional

                                 Memory' - Alessia Milani (Labri, Université de Bordeaux) \\

en:

Lundi 30 mars : An introduction to Software Transactional Memory - Alessia Milani (Labri, Université de Bordeaux) \\

23 mars 2015 à 09h39 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 79-80 modifiées:

Lundi 30 mars : TBA - ??? ???\\

en:

Lundi 30 mars : ' An introduction to Software Transactional

                                 Memory' - Alessia Milani (Labri, Université de Bordeaux) \\

20 mars 2015 à 18h21 par 147.210.204.186 -
Lignes 86-88 modifiées:

Lundi 23 mars : TBA - Lionel Eyraud-Dubois (LaBRI, INRIA)
Abstract:

en:

Lundi 23 mars : Algorithmes d'allocation pour le Cloud sous contrainte de fiabilité - Lionel Eyraud-Dubois (LaBRI, INRIA)
Abstract: Pour les services qui s'exécutent sur une plate-forme de Cloud Computing, la fiabilité et la disponibilité sont des problématiques clés : avec l'augmentation de la taille de ces plates-formes, les pannes de machines sont de plus en plus fréquentes et doivent être prises en compte en amont. À travers une analyse de traces d'un cluster de Google, cet exposé présente une formalisation du problème d'allocation des services sur une plate-forme de façon à pouvoir résister aux pannes, ainsi qu'un algorithme de résolution basée sur deux techniques : approximation binomiale et génération de colonnes. Travail en commun avec Olivier Beaumont, Paul Renaud-Goud, et Juan-Angel Lorenzo.

19 mars 2015 à 12h25 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 18-22 modifiées:
en:

Lundi 1er juin : TBA Nesrine Ouled Abdallah - (LaBRI, Université de Bordeaux)
Abstract:

18 mars 2015 à 10h56 par 147.210.204.186 -
Ligne 58 modifiée:

Lundi 20 avril : TBA - ??? ???\\

en:

Lundi 20 avril : Extension du domaine algorithmique : les algorithmes de la nature - Ivan Lavallée\\

15 mars 2015 à 23h05 par 81.67.198.101 -
Lignes 38-42 modifiées:

Lundi 11 mai : TBA - ??? ???
Abstract:

en:

Lundi 11 mai : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Arnaud Casteigts - (LaBRI, Université de Bordeaux)
Abstract: JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

Lignes 58-60 modifiées:

Lundi 20 avril : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Arnaud Casteigts - (LaBRI, Université de Bordeaux)
Abstract: JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

en:

Lundi 20 avril : TBA - ??? ???
Abstract:

10 mars 2015 à 09h42 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 17-42 ajoutées:

Lundi 25 mai : Pas d'exposé -
Abstract: Pentecôte

Lundi 18 mai : TBA - ??? ???
Abstract:

Lundi 11 mai : TBA - ??? ???
Abstract:

06 mars 2015 à 09h38 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 14 modifiée:

Lundi 15 juin : TBA Miguel Mosteiro - (Kean University, NJ, USA) \\

en:

Lundi 22 juin : TBA Miguel Mosteiro - (Kean University, NJ, USA) \\

05 mars 2015 à 18h25 par 81.67.198.101 -
05 mars 2015 à 18h25 par 81.67.198.101 -
05 mars 2015 à 18h22 par 81.67.198.101 -
Ligne 23 ajoutée:
Lignes 26-32 ajoutées:

Lundi 27 avril : Pas d'exposé
Abstract: c'est les vacances

Lignes 46-53 ajoutées:

Lundi 30 mars : TBA - ??? ???
Abstract:

04 mars 2015 à 16h01 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 31-35 ajoutées:

Lundi 13 avril : TBA Anca Muscholl
Abstract:

Ligne 68 modifiée:

Abstract: c'est les

en:

Abstract: c'est les

04 mars 2015 à 15h53 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 22 modifiée:

Abstract: Dans cet exposé je présenterai une structure de données compacte permettant de calculer en temps constant la distance entre n'importe quelle paire de sommets d'un graphe arbitraire à n sommets. Cette structure de données se présente sous forme d'étiquette associée à chacun des sommets, la distance entre les u et v étant décodée à partir d'un calcul impliquant seulement les étiquettes de u et de v. La solution triviale, à l'aide d'un vecteur de distances de taille n, produit des étiquettes de nlogn bits. En fait, aucune technique utilisant o(nlogn) bits et décodant en temps constant n'est connue. Cependant, si on relâche la contrainte du décodage en temps constant, des solutions avec O(n) bits existent. Une des meilleures d'entres elles utilisent 11n bits pour un décodage O(logn). Notre solution réduit la taille des étiquettes à 0.793n bits avec un décodage constant et s'étend naturellement aux graphes valués.

en:

Abstract: Dans cet exposé je présenterai une structure de données compacte permettant de calculer en temps constant la distance entre n'importe quelle paire de sommets d'un graphe arbitraire à n sommets. Cette structure de données se présente sous forme d'étiquette associée à chacun des sommets, la distance entre les u et v étant décodée à partir d'un calcul impliquant seulement les étiquettes de u et de v. La solution triviale, à l'aide d'un vecteur de distances de taille n, produit des étiquettes de nlogn bits. En fait, aucune technique utilisant o(nlogn) bits et décodant en temps constant n'est connue. Cependant, si on relâche la contrainte du décodage en temps constant, des solutions avec O(n) bits existent. Une des meilleures d'entres elles utilisent 11n bits pour un décodage O(logn). Notre solution réduit la taille des étiquettes à 0.793n bits avec un décodage constant et s'étend naturellement aux graphes valués.

Ligne 28 supprimée:
Lignes 31-34 ajoutées:

Lundi 6 avril : Pas d'exposé
Abstract: c'est pââââââques

Ligne 63 modifiée:

Abstract:

en:

Abstract: c'est les

04 mars 2015 à 15h35 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 20-22 modifiées:

Lundi 4 mai : TBA Cyril Gavoille - (LaBRI, Université de Bordeaux)
Abstract:

en:

Lundi 4 mai : Calculer les distances dans un graphe en temps constant avec des étiquettes de 0.793n bits. Cyril Gavoille - (LaBRI, Université de Bordeaux)
Abstract: Dans cet exposé je présenterai une structure de données compacte permettant de calculer en temps constant la distance entre n'importe quelle paire de sommets d'un graphe arbitraire à n sommets. Cette structure de données se présente sous forme d'étiquette associée à chacun des sommets, la distance entre les u et v étant décodée à partir d'un calcul impliquant seulement les étiquettes de u et de v. La solution triviale, à l'aide d'un vecteur de distances de taille n, produit des étiquettes de nlogn bits. En fait, aucune technique utilisant o(nlogn) bits et décodant en temps constant n'est connue. Cependant, si on relâche la contrainte du décodage en temps constant, des solutions avec O(n) bits existent. Une des meilleures d'entres elles utilisent 11n bits pour un décodage O(logn). Notre solution réduit la taille des étiquettes à 0.793n bits avec un décodage constant et s'étend naturellement aux graphes valués.

03 mars 2015 à 13h10 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 15-20 ajoutées:

Abstract:

Lundi 4 mai : TBA Cyril Gavoille - (LaBRI, Université de Bordeaux) \\

02 mars 2015 à 21h05 par 81.67.198.101 -
Lignes 12-13 modifiées:
en:

Lundi 15 juin : TBA Miguel Mosteiro - (Kean University, NJ, USA)
Abstract:

02 mars 2015 à 20h44 par 2a01:e35:8b51:3850:958:1d85:7408:cfd3 -
Ligne 16 modifiée:

Lundi 20 avril : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. - (LaBRI, Université de Bordeaux)\\

en:

Lundi 20 avril : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. Arnaud Casteigts - (LaBRI, Université de Bordeaux)\\

02 mars 2015 à 20h31 par 81.67.198.101 -
Ligne 13 ajoutée:
Lignes 15-18 modifiées:

Lundi 16 mars : TBA - Lionel Eyraud-Dubois (LaBRI, INRIA)
Abstract:

en:

Lundi 20 avril : JBotSim: a tool for fast prototyping distributed algorithms in dynamic networks. - (LaBRI, Université de Bordeaux)
Abstract: JBotSim is a java library that offers basic primitives for prototyping, running, and visualizing distributed algorithms in dynamic networks. With JBotSim, one can implement an idea in minutes and interact with it (e.g., add, move, or delete nodes) while it is running. JBotSim is well suited to prepare live demonstrations of your algorithms to colleagues or students; it can also be used to evaluate performance at the algorithmic level, i.e. in terms of the number of messages, number of rounds. Unlike most tools (OMnet, The One, Visidia), JBotSim is not an integrated environment. It is a lightweight *library* to be used in your program. In this talk, I will give an overview of its distinctive features and architecture, as well as many examples of algorithms and scenarios. This talk will also be the occasion to discuss recent hot topics in distributed computing, which are swarm algorithms and intelligence.

Lundi 23 mars : TBA - Lionel Eyraud-Dubois (LaBRI, INRIA)
Abstract:

Lundi 16 mars : On Distributed Computing with Beeps, la suite Akka Zemmari (LaBRI, Université de Bordeaux)
Abstract: La suite de l'exposé du 2 mars !

02 mars 2015 à 13h57 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 14-15 modifiées:

Lundi 9 mars : TBA - Lionel Eyraud-Dubois (LaBRI, INRIA)

en:

Lundi 16 mars : TBA - Lionel Eyraud-Dubois (LaBRI, INRIA)

Lignes 17-23 ajoutées:

Lundi 9 mars : On structural and Chromatic Properties of 1-planar Graphs. - Tomas Madaras (Pavol Jozef Šafárik University)
Abstract:The planar graphs have been, within decades of graph theory research, well explored yielding numerous results on their structural and chromatic properties. Along with this research, analogue problems were investigated for graphs which generalize - in various directions - the planar graphs. A particularly interesting generalization concerns the graph drawings in the plane which allow at most one crossing per edge, rising to the family of so called 1-planar graphs. These graphs, although introduced in late sixties of 20th century, were studied in a deeper detail only in the last decade. We survey known results on the global and local structure and chromaticity of 1-planar graphs with emphasis on similarities and fundamental differences when comparing with planar graphs, and several future research directions on an analogue of Steinberg conjecture for 1-planar graphs.

Remarque: Créneau emprunté par le GT Graphes et Applications

09 février 2015 à 10h16 par 147.210.204.186 -
Lignes 40-41 ajoutées:

P.S. : Il s'agit d'un exposé CPU.

06 février 2015 à 08h34 par 81.67.198.101 -
Lignes 33-34 modifiées:

Lundi 16 février 2015: Self-Stabilizing Leader Election in Polynomial Steps Stéphane Devisme (Université Joseph Fourier, Grenoble I)

en:

Lundi 16 février 2015: Self-Stabilizing Leader Election in Polynomial Steps Stéphane Devismes (Université Joseph Fourier, Grenoble I)

Lignes 69-70 ajoutées:

Join work with Mike Robson and Akka Zemmari

03 février 2015 à 12h27 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Lignes 19-20 modifiées:
 Lundi 2 mars :  On Distributed Computing with Beeps   Akka Zemmari (LaBRI, Université de Bordeaux)

en:

Lundi 2 mars : On Distributed Computing with Beeps Akka Zemmari (LaBRI, Université de Bordeaux)

Ligne 30 modifiée:

Abstract:

en:

Abstract:

03 février 2015 à 12h23 par 2001:660:6101:402:223:24ff:fe07:ab60 -
Ligne 12 ajoutée:
Lignes 14-15 modifiées:

Lundi 2 mars : TBA - Lionel Eyraud-Dubois (LaBRI, INRIA)

en:

Lundi 9 mars : TBA - Lionel Eyraud-Dubois (LaBRI, INRIA)

Lignes 19-27 modifiées:
en:
 Lundi 2 mars :  On Distributed Computing with Beeps   Akka Zemmari (LaBRI, Université de Bordeaux)


Abstract: We consider networks of processes which interact with beeps. Various beeping models are used. The basic one, defined by Cornejo and Khun assumes that a process can choose either to beep or to listen. If it listens it can distinguish between silence or the presence of at least one beep. The aim of this paper is the study of the resolution of paradigms such as collision detection, computation of the degree of a vertex, of a MIS or a colouring in the framework of beeping models.

Join work with Yves Métivier and Mike Robson

Lignes 30-31 modifiées:

Abstract:

en:

Abstract:

Lignes 33-39 modifiées:

Lundi 16 février 2015: On Distributed Computing with Beeps Akka Zemmari (LaBRI, Université de Bordeaux)
Abstract: We consider networks of processes which interact with beeps. Various beeping models are used. The basic one, defined by Cornejo and Khun assumes that a process can choose either to beep or to listen. If it listens it can distinguish between silence or the presence of at least one beep. The aim of this paper is the study of the resolution of paradigms such as collision detection, computation of the degree of a vertex, of a MIS or a colouring in the framework of beeping models.

Join work with Yves Métivier and Mike Robson

en:

Lundi 16 février 2015: Self-Stabilizing Leader Election in Polynomial Steps Stéphane Devisme (Université Joseph Fourier, Grenoble I)
Abstract: We present a silent self-stabilizing leader election algorithm for bidirectional connected identified networks of arbitrary topology. This algorithm is written in the locally shared memory model. It assumes the distributed unfair daemon, the most general scheduling hypothesis of the model. Our algorithm requires no global knowledge on the network (such as an upper bound on the diameter or the number of processes, for example).

We show that its stabilization time is in Theta(n^3) steps in the worst case, where n is the number of processes. Its memory requirement is asymptotically optimal, i.e., Theta(log n) bits per processes. Its round complexity is of the same order of magnitude (i.e., Theta(n) rounds), as the best existing algorithm (proposed by Datta et al) designed with similar settings,i.e., it does not use global knowledge and is proven under the unfair daemon).

To the best of our knowledge, this is the first asynchronous self-stabilizing leader election algorithm for arbitrary identified networks that is proven to achieve a stabilization time polynomial in steps. By contrast, we show that the previous best existing algorithm designed with similar settings stabilizes in a non polynomial number of steps in the worst case.

29 janvier 2015 à 13h35 par 147.210.179.69 -
Ligne 24 modifiée:

Lundi 16 février 2015: On Distributed Computing with Beeps Akka Zemarri (LaBRI, Université de Bordeaux) \\

en:

Lundi 16 février 2015: On Distributed Computing with Beeps Akka Zemmari (LaBRI, Université de Bordeaux) \\

27 janvier 2015 à 00h04 par 81.67.198.101 -
Ligne 32 modifiée:

Lundi 9 février 2015 : ' A Distributed Enumeration Algorithm and Applications to All Pairs

en:

Lundi 9 février 2015 : 'A Distributed Enumeration Algorithm and Applications to All Pairs

Lignes 36-37 modifiées:

synchronous: all processes start at the same time

 and time proceeds in synchronised rounds. In each round each vertex

en:

synchronous: all processes start at the same time and time proceeds in synchronised rounds. In each round each vertex

Lignes 47-48 modifiées:

from which we deduce

 that this enumeration is optimal in the sense that there

en:

from which we deduce that this enumeration is optimal in the sense that there

26 janvier 2015 à 23h55 par 81.67.198.101 -
26 janvier 2015 à 23h55 par 81.67.198.101 -
Lignes 32-35 modifiées:

Lundi 9 février 2015 : tba Yves Métivier
Abstract: TBA

en:

Lundi 9 février 2015 : ' A Distributed Enumeration Algorithm and Applications to All Pairs Shortest Paths, Diameter...' Yves Métivier (LaBRI, Université de Bordeaux)
Abstract: We consider the standard message passing model; we assume the system is fully synchronous: all processes start at the same time

 and time proceeds in synchronised rounds. In each round each vertex


can transmit a different message of size $O(1)$ to each of its neighbours. This paper proposes and analyses a distributed enumeration algorithm of vertices of a graph having a distinguished vertex which satisfies that two vertices with consecutive numbers are at distance at most $3$. We prove that its time complexity is $O(n)$ where $n$ is the number of vertices of the graph. Furthermore, the size of each message is $O(1)$ thus its bit complexity is also $O(n).$ We provide some links between this enumeration and Hamiltonian graphs from which we deduce

 that this enumeration is optimal in the sense that there


does not exist an enumeration which satisfies that two vertices with consecutive numbers are at distance at most $2$.

We deduce from this enumeration algorithms which compute all pairs shortest paths and the diameter with a time complexity and a bit complexity equal to $O(n)$. This improves the best known distributed algorithms (under the same hypotheses) for computing all pairs shortest paths or the diameter presented in \cite{PRT12,HW12} having a time complexity equal to $O(n)$ and which use messages of size $O(\log n)$ bits.

Lignes 216-532 modifiées:

We present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal construction

en:

We present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal constructionWe present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal construction is a method for obtaining a concurrent implementation of any object from its sequential code. The construction is non-trivial since in the resulting implementation a failed process can cause only a finite number of operations to abort. Our construction guarantees that operations that do not modify the object always return a legal response and do not use CAS. Moreover in case of contention, at least one writing operation succeeds. We prove that our construction has asymptotically optimal space complexity for objects whose size is constant.

Lundi 30 juin 2014 : "Rendez-vous d'agents mobiles tolérant aux pannes" - Arnaud Labourel, (LIF, Université Aix-Marseille)
'Abstract: Les systèmes d’agents mobiles sont des environnements distribués dans lequel les nœuds du réseau sont passifs et ce sont des agents mobiles qui s’occupent de l’exécution de l’algorithme. Le réseau est représenté par un graphe et les agents peuvent se déplacer d’un nœud à l’autre du graphe le long de ses arêtes. Dans cet exposé, on va chercher à trouver des algorithmes permettant à deux agents mobiles initialement dispersé dans le graphe de se rencontrer sur un nœud du graphe. Plus particulièrement, on s'intéressera à ce problème pour un modèle synchrone dans lequel une panne peut se produire lors de chaque tentative de déplacement des agents. On considérera trois types de pannes possibles : probabiliste (probabilité constante de panne), adversaire non borné ou borné (un adversaire peut empêcher un agent de bouger pendant un nombre de rondes fini ou bien borné par une constante). Je donnerai des bornes inférieures et supérieures sur le coût du rendez-vous (nombre de déplacements des agents avant le rendez-vous dans le pire des cas) ainsi que des résultats d'impossibilité pour ces trois types de pannes.

Lundi 23 juin 2014 : "Maintenance d'arbres et détection de déconnexion" - Christian Glacet, (LaBRI, Université de Bordeaux)
Abstract:Dans ce travail, nous proposons un algorithme auto-stabilisant de maintenance d'arbres de plus de courts chemins tout en gérant la déconnexion de graphes dynamiques ... ce qui résoud le problème du comptage à l'infini sans connaissance sur le graphe. Ce travail a été fait avec Colette Johnen, David Ilcinkas et Nicolas Hanusse.

Lundi 16 juin 2014 : Allyx Fontaine soutient sa thèse "Analyse et preuves formelles d’algorithmes distribués probabilistes" - Amphi du LaBRI
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Lundi 05 mai 2014 : "Le codage de réseau aléatoire : une introduction " - Christine Bachoc, (IMB, Université de Bordeaux)
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Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

Lundi 31 mars 2014 : "Algebraic Removal Lemma" - Oriol Serra ( Barcelona, Spain)
Abstract: The removal lemma is a combinatorial result which, in its simpler form, says that a graph with n vertices and o(n^3) triangles can be made triangle free by deleting o(n^2) edges. It was used by Ruzsa and Szemerédi to provide a simple proof of Roth's theorem on 3-term arithmetic progressions in dense sets of integers. An analogous algebraic statement was formulated by Green in terms of solutions of linear equations in abelian groups. In the talk I will report on some contributions made jointly with Dan Král' and Lluís Vena to this algebraic version for linear systems in abelian groups and some consequences in arithmetic Ramsey theory. The latter include a version of Szemerédi theorem on arithmetic progressions in dense sets of finite abelian groups.

P.S. : Il s'agit d'un exposé CPU.

Lundi 24 mars 2014 : "Exploration and Diffusion in Graphs using Deterministic Walks " - Adrian Kosowski (LaBRI)
Abstract: In a continuous diffusive process, a certain amount of a resource, known as "load", is initially placed on the nodes of the graph, possibly in an unfair manner. In successive time steps, each node shares its load evenly among all its neighbors, until the load on the nodes of the graph eventually converges to its limit distribution (e.g., becomes uniform in the case of regular graphs). However, continuous diffusion cannot be applied to "granular load" which is not arbitrarily divisible, i.e., represented by unsplittable unit-load tokens (chips), which are placed on nodes and may be passed around the graph. In such a scenario, one natural way of simulating the continuous diffusion process is to require that each chip follows an independent random walk on the graph.

In this talk, we will instead focus on chip diffusion processes following rules which are both locally fair and deterministic. These rules include the so-called "rotor walk", in which chips are propagated by each node to its neighbors in round-robin fashion and, more broadly, rules in which each node attempts to send out roughly the same number of tokens through each of its outgoing arcs.

We will start by providing a description of the evolution and limit behavior of the rotor walk on the n-node ring with K << n chips. For general graphs, we will show bounds on the "cover time" of a rotor walk system with K chips, proving that in a graph with m edges and diameter D, all nodes will have been visited at least once by some chip during the first O(mD / log K) steps of the process. Finally, we will relate the "blanket time" (the time until all nodes of the graph have been visited by chips a similar number of times) and the "diffusion time" (the time until all nodes all host a similar number of chips, for K >> n) of fair deterministic walks to analogous parameters of the random walk. The latter results allow us to design surprisingly simple and efficient deterministic algorithms for load balancing in the diffusive model.

This talk includes an overview of results presented at PODC'13, STACS'14, and some current work in progress (joint work with: P. Berenbrink, D. Dereniowski, R. Klasing, F. Mallmann-Trent, D. Pajak, T. Sauerwald, P. Uznanski).

Lundi 03 mars 2014 : "Algorithmes de mise à jour locale pour des graphes aléatoires" - Romaric Duvignau (LaBRI)
Abstract: Afin de modéliser l'évolution de réseaux logiques dynamiques, nous proposons de maintenir exactement une distribution donnée de graphes aléatoires lors d'une séquence arbitraire d'insertions et de suppressions de sommets. Nous nous plaçons dans un modèle local où nous n'avons pas accès à l'ensemble des sommets, mais supposons à la place l'accès à une primitive globale renvoyant un sommet aléatoire uniforme du graphe. Dans cet exposé, nous nous intéressons à maintenir la distribution uniforme dans les graphes k-sortants (graphes dirigés où tous les sommets ont degré sortant k). Nous présenterons plusieurs algorithmes d'insertion et de suppression pour le problème de maintenance, dont les plus efficaces sont asymptotiquement optimaux.

Lundi 24 février 2014 : "Distributed anonymous discrete function computation" - Julien Hendrickx(Univ. Louvain)
Abstract: We propose a model for deterministic distributed function computation by a network of identical and anonymous nodes:. In this model, each node has bounded computation and storage capabilities that do not grow with the network size. Furthermore, each node only knows its neighbors, not the entire graph. Our goal is to characterize the class of functions that can be computed within this model. We provide a necessary condition for computability which we show to be nearly sufficient, in the sense that every function that violates this condition can at least be approximated. The problem of computing (suitably rounded) averages in a distributed manner plays a central role in our development; we provide an algorithm that solves it in time that grows quadratically with the size of the network.

Lundi 17 février 2014 : "The interplay between multidimensional skylines and functional dependencies " - Sofian Maabout (LaBRI)
Abstract: We show how functional dependencies, which are agnostoc to the orders defined over the dimensions domains, can help to optimize skyline queries which, by opposition are based on orders. We present some theoretical and experimental results.

Lundi 10 février 2014 : "Algorithmes auto-stabilisants barvards" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)
Abstract: Dans le contexte des réseaux à grande échelle, la prise en compte des pannes est une nécessité évidente. Ce séminaire traite de l’auto-stabilisation, une méthode qui vise à concevoir des algorithmes distribués se « réparant d’eux-même » en cas de pannes transitoires pouvant impliquer toute modification arbitraire de l’état des processus. Plusieurs paramètres peuvent être pris en compte pour mesurer l’efficacité d’un algorithme auto-stabilisant, dont en particulier le temps de convergence et la complexité mémoire. L’importance du temps de convergence vient de la nécessité évidente pour un système de retrouver le plus rapidement possible un état valide après une panne. La nécessité de minimiser la mémoire vient, d’une part, de l’importance grandissante de réseaux offrant des espaces mémoires restreints, comme par exemple certains réseaux de capteurs, et, d’autre part, de l’intérêt de minimiser à la fois l’échange et le stockage d’information afin de limiter les potentialités de corruption de cette information. Lors de ce séminaire, nous traiterons de la minimisation de la mémoire au travers d'un exemple, à savoir le problème de l’élection d’un leader. Une borne inférieure de Ω(log n) bits de mémoire par noeud a été établie par Dolev, Gouda et Schneider (1999) pour ce problème fondamental. Cette borne n'est toutefois valable que pour des algorithmes silencieux, c'est-à-dire des algorithmes dont les registres ne sont plus modifiés lorsque le système a rejoint un état légitime. Nous verrons que, si l'on autorise l’algorithme à rester bavard (non-silencieux) même après avoir rejoint un état légitime, alors l’espace mémoire peut être amélioré d’un facteur au moins exponentiel.

Lundi 6 Janvier 2014 : "Self-stabilizing k-independent dominating set construction" - Colette Johnen(LaBRI)
Abstract: A k-independent dominating set is a k-independent set and a k-dominating set. A set of nodes, I, is k-independent if the distance between any pair of nodes in I is at least k+1. A set of nodes, D, is a k-dominating if every node is within distance k of a node of D.

I propose two self-self-stabilizing algorithm building k-independent dominating sets. The both algorithm (SID and FID) are silent, and they converge under the unfair distributed scheduler (the weakest scheduling assumption).

The algorithm FID reaches a terminal (also legitimate) configuration in at most 4n+k rounds, where n is the network size. The algorithm FID requires (k+1)log(n+1) bits per node.

The protocol SID is memory efficient : it requires only 2log((k+1)n+1)+1 bits per node. The computation of the convergence time of the protocol SID is opened question.

Lundi 16 Décembre 2013 : "Large-scale Data Stream Analysis" - Yann Busnel (LINA - Université de Nantes)
Abstract: L'objectif de cet exposé est de dresser un court état de l'art autour de l'analyse des flux de données à grande échelle, lesquels sont souvent utilisés pour du monitoring et de la sécurité, à la fois dans les réseaux et les systèmes distribués jusqu'à l'internet des objets. La problématique de ce champs de recherche consiste à extraire de l'information pertinente d'un flux de données en une passe unique (en raison de la taille du flux et de sa rapidité), et ne nécessitant qu'une quantité mémoire très faible et une puissance de calcul très limitée. Je présenterai ensuite les dernières applications utilisant nos résultats récents, lesquels vont de la détection d'intrusion, la détection de DDoS, l'échantillonnage, etc.

Lundi 9 Décembre 2013 : "Simulating weak shared memory" - David Bonnin (LaBRI)
Abstract: It is well known that in an asynchronous message-passing system with crash faults, one can emulate an atomic register providing that more than half of the processes are non-faulty. By contrast, when a majority of the processes may fail, simulating atomic register is not possible. I will talk about weak variants of atomic registers that can be simulated tolerating a majority of processes failures. Specifically, I will introduce a new class of registers, called $\alpha$-registers. We found a lower bound of $\alpha = M+1$ with $M=2f-n+2$ for these registers, and an explicit algorithm can emulate them with $\alpha = 2M-1$. I will also probably talk about other approaches on weak shared memory : $M$-colored registers, and $k$-splitters. This is a joint work with C. Travers.

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nicolas Bonichon (LaBRI)
Abstract: This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

Lundi 25 Novembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)
Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a maximal matching for anonymous rings. Their bit complexity and time complexity are $O(\sqrt{\log n})$ with high probability. These algorithms are optimal modulo a multiplicative constant. Beyond the complexity results, the interest of this work stands in the description and the analysis of these algorithms which may be easily generalised. Furthermore, these results show a separation between the complexity of the MIS problem (and of the maximal matching problem) on the one hand and the colouring problem on the other. Colouring can be computed only in $\Omega(\log n)$ rounds on rings with high probability, while MIS is shown to have a faster algorithm. This is in contrast to other models, in which MIS is at least as hard as colouring. This is joint work with Y. Métivier, J.M. Robson and A. Zemmari

Lundi 4 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)
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Lundi 28 Octobre 2013 : "The Case for Reliable Software Transactional Networking" - Petr Kuznetsov (Paristech)
Abstract: Software-defined networking (SDN) is a novel paradigm that out-sources the control of packet-forwarding switches to a set of software controllers. The most fundamental task of these controllers is the correct implementation of the network policy, i.e., the intended network behavior. In essence, such a policy specifies the rules by which packets must be forwarded across the network. We initiate the study of the SDN control plane as a distributed system.

We introduce a formal model describing the interaction between the data plane and a distributed control plane (consisting of a collection of fault-prone controllers). Then we formulate the problem of consistentcomposition of concurrent network policy updates. The composition is enabled via a transactional interface with all-or-nothing semantics, which allows us to reason about possibilities and impossibilities in controller synchronization.

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

Lundi 23 Septembre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Miroslaw Korzeniowski
Abstract: Decentralized monitoring and alarming systems can be an attractive alternative to centralized architectures. Distributed sensor nodes (e.g., in the smart grid's distribution network) are closer to an observed event than a global and remote observer or controller. This improves the visibility and response time of the system. Moreover, in a distributed system, local problems may also be handled locally and without overloading the communication network.

This article initiates the study of alarming from a distributed computing perspective and under two fundamentally different scenarios: \emph{on-duty} and \emph{off-duty}. We model the alarming system as a sensor network consisting of a set of distributed nodes performing local measurements to sense events. In order to avoid false alarms, the sensor nodes cooperate and only escalate an event (i.e., raise an alarm) if the number of sensor nodes sensing an event exceeds a certain threshold. In the on-duty scenario, nodes not affected by the event can actively help in the communication process, while in the off-duty scenario non-event nodes are inactive.

This article presents and analyzes algorithms that minimize the reaction time of the monitoring system while avoiding unnecessary message transmissions. Moreover, lower bounds are derived that shed light on the limitations of distributed alarming systems.

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)
Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

Lundi 8 Juillet 2013 : "Dynamic Resource Allocation in Cloud Computing platforms" - Lionel Eyraud-Dubois (Labri)
Abstract: Je présente un problème d'allocation de ressources dans le contexte du Cloud Computing, où un ensemble de machines virtuelles (VM) doivent être allouées sur un ensemble de machines physiques (PMs). La particularité de ce problème vient du fait que la quantité de ressources dont chaque VM a besoin change au cours du temps, et qu'il est possible pour le fournisseur d'accès de changer l'allocation d'une VM par une opération de migration. Ce problème peut se modéliser sous la forme d'un problème de bin packing complètement dynamique, et je présente un algorithme d'approximation pour minimiser le nombre de PMs utilisées, tout en garantissant un petit nombre de migrations. Les propriétés de cet algorithme permettent également d'envisager une version distribuée.

Lundi 10 Juin 2013 : " The Heard-Of model: computing in distributed systems with benign failures" - Bernadette Charron-Bost (CNRS, Ecole polytechnique, Paris)
Abstract: Problems in fault-tolerant distributed computing have been studied in a va- riety of system models. These models are all based on the principle that it is usefull and even necessary to specify why and by whom errors occur. In this talk, we question this principle, and present a general computational model, called the Heard-Of model, suitable for describing any type of system, be it message passing, shared memory, synchronous, or asynchronous. In this model, computations evolve in rounds, and communication missed at a round is definitely lost. Only information transmission is represented: for each round r and each process p, our model specifies the set of processes that p “hears of” at round r (heard-of set) namely the processes from which p receives some message at round r. The features of a specific system are thus captured as a whole, just by a predicate over the collection of heard-of sets. Thus the Heard-Of model allows us to handle all types of benign failures, static or dynamic, permanent or transient, in a unified framework. Moreover, it unifies the most seemingly unrelated notions in distributing computing, namely synchrony and asynchrony. We further demonstrate how this unifying framework leads to new results and insights in fault-tolerant distributed computing. In particular, we show that some fundamental results for asynchronous systems can be advantageously transferred to synchronous systems. We also examine Consensus algorithms in the Heard-Of model: we show how our approach allows us to devise new solutions and to give simple correctness proofs of existing algorithms like Paxos.

Joint work with André Schiper, EPFL

Lundi 3 Juin 2013 : "Introduction to renaming" - Corentin Travers (Labri)
Abstract: Renaming is a fundamental coordination problem in distributed computing. It consists in assigning new names taken from a small name space to processes in such a way that no two processes obtain the same name. The talk will survey renaming algorithms suited for different models of distributed computing, including the wait-free shared memory and the synchronous crash-prone message-passing models.

Lundi 27 Mai 2013 : " Exploration des graphes dynamiques T-intervalle-connexes : le cas de l'anneau" - Wade Ahmed (Labri)
Abstract: Dans cet exposé, je vais parler de l'étude des graphes dynamiques T-intervalle-connexes du point de vue du temps nécessaire à leur exploration par une entité mobile (agent). Un graphe dynamique est T-intervalle-connexe (T \geq 1) si pour chaque fenêtre de T unités de temps, il existe un sous-graphe couvrant connexe stable. Cette propriété de stabilité de connexion au cours du temps a été introduite par Kuhn, Lynch et Oshman~\cite{KLO10} (STOC 2010). Nous nous concentrons sur le cas où le graphe sous-jacent est un anneau de taille n et nous montrons que la complexité en temps en pire cas est de 2n-T-\Theta(1) unités de temps si l'agent connaît la dynamique du graphe, et n+ \frac{n}{\max\{1,T-1\}} (\delta-1) \pm \Theta(\delta) unités de temps sinon, où \delta est le temps maximum entre deux apparitions successives d'une arête.

Keywords : Graphe dynamique, exploration, T-intervalle-connexité, agent mobile

Lundi 13 Mai 2013 : " Calcul Distribué et Fouille de Données" - Nicolas Hanusse (Labri)
Abstract: L'avènement de la production massive de données et la volonté de les exploiter sont limités par les systèmes de gestion de bases de données relationnelles classiques. Cet exposé consiste en une discussion sur les enjeux et problèmes algorithmiques engendrés par le calcul distribué et parallèle. Le calcul de corrélations servira d'illustration. C'est un travail en cours avec Sofian Maabout et Eve Garnaud.

Lundi 22 Avril 2013 : " A peer-to-peer-based virtual environment system" - Eliya Buyukkaya (ENSSAT-Université de Rennes I)
Abstract: Virtual environments (VEs) are 3-D virtual worlds in which a huge number of participants play roles and interact with their surroundings through virtual representations called avatars. VEs are traditionally supported by a client/server architecture. However, centralized architectures can lead to bottleneck on the server due to high communication and computation overhead during peak loads. Thus, P2P overlay networks are emerging as a promising architecture for VEs. However, exploiting P2P schemes in VEs is not straightforward, and several challenging issues related to data distribution and state consistency should be considered.

One of the key aspects of P2P-based VEs is the logical platform consisting of connectivity, communication and data architectures, on which the VE is based. The connectivity architecture is the overlay topology structure, which defines how peers are connected to each other. The communication architecture is the routing protocol defining how peers can exchange messages, while the data architecture defines how data are distributed over the logical overlay. The design of these architectures has significant influence on the performance and scalability of VEs.

First, we propose a scalable connectivity architecture based on a new triangulation algorithm reducing maintenance cost of the system. Second, we construct a communication architecture built on top of the connectivity architecture ensuring that each message reaches its intended destination. Finally, we propose a data architecture ensuring the management of data with different characteristics in terms of mobility in the VE, while providing a fair data distribution and low data transfer between peers in the VE.

Lundi 15 Avril 2013 : " Algorithms for the Vertex Cover Problem on Large Graphs with Low Memory Capacities" - Romain Campigotto (LIP6-Paris)
Abstract: Most of the known optimization algorithms need to explore, mark, modify, etc. the instance given as input before producing their results. To do that, the instance is entirely loaded into the memory of the computer and is manipulated by the algorithm. Often, "extra" data structures are also necessary to memorize parameters useful all along the computation or to update the current solution that will be returned as the final product of the program. However, this classical model is no more adapted for many new computing applications. Indeed, nowadays, many fields such as biology, meteorology, finance, etc. produce very large amount of data.

In our works, we have focused on the Vertex Cover problem on huge graphs: in the intrinsic NP-completeness is added the difficulty to manipulate graphs with severe constraints (mainly related to the low memory capacities). We defined a treatment model combining some properties of several existing models in the literature: streaming, online, I/O-efficient, etc. We initially considered three approximation algorithms, which are memory-efficient (they use a memory space in O(log n) bits). We analyzed their performance in terms of solution quality and complexity, in mean and worst cases. We then focused on algorithms that use memory space of n bits. We showed that it could be very worst with strictly less than n bits memory space. Subsequently, we conducted experiments on very large graphs (in the order of billions of vertices and edges). This study showed that in practice, memory-efficient algorithms are better suited to handle large graphs.

This is joint work with Eric Angel (IBISC, Univ. Évry) and Christian Laforest (LIMOS, ISIMA, Clermont-Ferrand).

Lundi 8 Avril 2013 : "Implémentation d'algorithmes distribués à l'aide de Visidia" - Mohamed Mosbah (Labri)
Abstract: Dans le cadre du projet visidia, une plate-forme logicielle est développée pour l'implantation et la visualisation d'algorithmes distribués. Après une introduction et quelques rappels, l'exposé consistera en une présentation de la plate-forme et de son utilisation pour programmer des exemples d'algorithmes. L'interface et l'API permettent de visualiser l'exécution d'algorithmes, d'implanter de nouveaux algorithmes, ou d'effectuer des statistiques. Les algorithmes peuvent être exprimés selon plusieurs modèles (calculs locaux, passage de messages, agents mobiles).

Lundi 25 Mars 2013 : "Simultaneous Consensus vs Set Agreement." - Zohir Bouzid (LIP6-Paris)
Abstract: In the traditional consensus task, processes are required to agree on a common value chosen among the initial values of the participants. It is well known that consensus cannot be solved in crashed-prone, asynchronous distributed systems. Two generalizations of the consensus problem have been introduced: k-set agreement and k-simultaneous consensus. The k-set agreement task has the same requirements as consensus except that processes are allowed to decide up to k distinct values. In the k-simultaneous consensus task, each process participates simultaneously in k instances of consensus and is required to decide in at least one of them; any two processes deciding in the same instance must decide the same value. In this talk, we compare the computability of these problems in two central models in distributed computing: shared memory and message passing. We show that even though the two problems are equivalent in shared memory, k-simultaneous consensus is strictly harder than k-set agreement in the message passing model. This result will serve as a basis for a discussion about different models of computation and their respective power.

Lundi 18 Mars 2013 : "Vers une classification des réseaux dynamiques en fonction des problèmes qu'on peut y résoudre." - Arnaud Casteigts (Labri)
Abstract: Derrière les notions de "graphe dynamique" ou de "réseau dynamique" se cache une très grande diversité de scénarios et d'hypothèses, allant de réseaux semi-statiques où la connexité est toujours assurée à des réseaux complètement mobiles, où la connexité ne s'établit qu'à travers le temps et l'espace (e.g. DTNs). Dans cet exposé, résolument transversal, je présenterai l'état d'avancement de nos recherches autour de la question suivante : quel lien existe-t-il entre la "faisabilité" de tâches distribuées et la dynamique du réseau. Les hypothèses résultantes sur la dynamique peuvent être vues comme autant de classes de graphes (ou alternativement, comme autant de puissances possibles pour un adversaire qui contrôlerait la topologie). Nous avons à ce jour caractérisé et/ou recensé une petite vingtaine de classes de ce type.

Certains de ces travaux ont été menés en collaboration avec Serge Chaumette et Afonso Ferreira. D'autres avec Paola Flocchini et Nicola Santoro.

Lundi 25 Février 2013 : "Sur les 1001 modèles en algorithmique distribuée." - Yves Metivier (Labri)
Abstract: Le but de cet "exposé-discussion" est de présenter quelques modèles en algorithmique distribuée et d'échanger sur leurs liens et leurs mérites.

Lundi 18 Février 2013 : "Distributed Calculation of Graph Diameter" - Mike Robson (Labri)
Abstract: We consider the problem of calculating the diameter of a graph given that there is a single vertex "Leader" and neighbouring vertices can exchange messages of a single bit at each round. We show that this can be achieved in the same O(n) time complexity as well known algorithms without this bound on message length. The techniques used can be applied to a number of other graph computations. We consider briefly how the algorithm behaves if applied in a situation where more than one vertex considers itself the Leader.

This is joint work with Yves Métivier and Akka Zemmari.

Lundi 11 Février 2013 : "Bounds for Communication in Wireless Grids" - Joseph Peters (Simon Fraser University)
Abstract: In a wireless network, a transmission can be received by a node if it is close enough to the sender. However, transmissions can interfere with each other and the interference distance is typically greater than the reception distance. Efficient communication protocols in these networks minimize the time to move information without interference. In this talk, I will describe optimal protocols for the problem of collecting information into a central node of a two-dimensional square or hexagonal grid graph. The optimality of the protocols is proved using a new lower bound technique that is an adaptation to a discrete environment of a method based on linear programming duality for continuous flows.

This is joint work with Jean-Claude Bermond, CNRS-INRIA-University of Nice.

Lundi 04 Février 2013 : "Distributed Detection of Clone Attacks in Wireless Sensor Networks" - Mauro Conti (University of Padua, Italy)
Abstract: Wireless Sensor Networks (WSNs) are often deployed in hostile environments where an adversary can physically capture some of the nodes, first can reprogram, and then, can replicate them in a large number of clones, easily taking control over the network. A few distributed solutions to address this fundamental problem have been recently proposed. However, these solutions are not satisfactory. First, they are energy and memory demanding: A serious drawback for any protocol to be used in the WSN-resource-constrained environment. Further, they are vulnerable to the specific adversary models that we introduced. The contributions of our work are threefold. First, we analyze the desirable properties of a distributed mechanism for the detection of node replication attacks. Second, we show that the known solutions for this problem do not completely meet our requirements. Third, we propose a new self-healing, Randomized, Efficient, and Distributed (RED) protocol for the detection of node replication attacks, and we show that it satisfies the introduced requirements. Finally, extensive simulations show that our protocol is highly efficient in communication, memory, and computation; is much more effective than competing solutions in the literature; and is resistant to the new kind of attacks introduced in our work, while other solutions are not.

Lundi 28 Janvier 2013 : "Distributed Exclusive Graph Searching in Trees" - Janna Burman (LRI-Université Paris-Sud)
Abstract: We consider a version of the well known graph searching problem, where a team of robots aims at clearing the contaminated edges of a graph. We study graph searching in the model of mobile computing where autonomous deterministic robots move between the graph nodes when operating in asynchronous cycles of Look-Compute-Move. Moreover, motivated by physical constraints, following some recent works, we consider the exclusivity property, stating that no two or more robots can occupy a same node at the same time. In addition, we assume that all the graph elements and the robots are anonymous. Robots are oblivious and have no sense of direction. Our objective is to characterize for a graph $G$, the set of integers $k$ such that graph searching can be achieved by a team of $k$ robots starting from any $k$ distinct nodes in $G$. Our main result consists in a full characterization for any asymmetric tree. Towards providing a characterization in the general case, including trees with non-trivial automorphisms, we provide a set of positive and negative results, including a full characterization for any line. All our positive results are based on the design of algorithms enabling perpetual graph searching to be achieved with the desired number of robots. We prove that, in addition to the distributed nature of our setting, the exclusivity property has a significant impact on the nature of the graph searching problem. Hence, the design of the algorithms requires to invent new methods.

Lundi 21 Janvier 2013 : "Présentation de Keep Alert, une solution pour la surveillance de marques sur Internet" - Anthony Don (Keep Alert)
Abstract: A destination des cabinets de propriété industrielle et des services juridiques, Keep Alert propose des surveillances de marque parmi les noms de domaine, les régies publicitaires et les réseaux sociaux. Anthony DON, directeur technique chez Keep Alert, présentera au groupe de travail, le fonctionnement global de la plateforme, puis abordera les problématiques actuelles et les perspectives de développement relatives à l'algorithmique distribuée.

Lundi 14 Janvier 2013 : "Two Monte-Carlo Election Algorithms for Anonymous Graphs without any Initial Knowledge" - Akka Zemmari (Labri)
Abstract: The paper proposes and analyses two Monte Carlo election algorithms for anonymous graphs without any initial knowledge. Both have a time complexity equal to $O(D)$, where $D$ is the diameter of the graph. The first is correct with probability $1-o(n^{-1})$ (where $n$ is the size of the graph). The size of messages is $O(\log n)$ with probability $1-o(n^{-1})$ and the expected value of the size of messages is also $O(\log n)$. The second is correct with probability $1-o(n^{-c})$ for any $c\geq 1$. The size of messages is $O\left((\log n)(\log^* n)^2 \right)$ with probability $1-o(n^{-c})$ for any $c\geq 1$; their expected size is $O\left((\log n)(\log^* n) \right)$.

This is a joint work with Y. Métivier and J. M. Robson

Lundi 10 Décembre 2012 : pas de seminaire. Soutenance de thèse-Florent Foucaud.

Lundi 3 Décembre 2012 : "Progress and Challenges for Labeling Schemes" - Cyril Gavoille (Labri)
Abstract: A fundamental question in Distributed Computing is to understand how localized and how much information are required to solve a task on a network. Typically, if the distance between any pair x,y of nodes in a network is asked, we would like to know which minimal information about x and y in the network are needed. The goal in labeling schemes is precisely to understand how much information must be attached to the nodes (formalized as labels) to solve a graph problem assuming the answer can be determined solely on the basis of the labels of the nodes invoked in the query. In this talk, I give a survey on labeling schemes, present some recent results with their techniques, and highlight new challenges.

Lundi 26 Novembre 2012: "Competitive Routing on a Variant of the Delaunay Triangulation" - Prosenjit Bose (Carleton University)
Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we showed how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.

Lundi 19 Novembre 2012: " Reliable Service Allocation in Clouds"- Lionel Eyraud-Dubois, Olivier Beaumont (Labri)
Abstract: We consider several reliability problems that arise when allocating applications to processing resources in a Cloud computing platform. More specifically, we assume on the one hand that each computing resource is associated to a capacity constraint and to a probability of failure. On the other hand, we assume that each service runs as a set of independent instances of identical Virtual Machines, and that the Service Level Agreement between the Cloud provider and the client states that a minimal number of instances of the service should run with a given probability. In this context, given the capacity and failure probabilities of the machines, and the capacity and reliability demands of the services, the question for the cloud provider is to find an allocation of the instances of the services (possibly using replication) onto machines satisfying all types of constraints. In this paper, our goal is to assess the impact of the reliability constraint on the complexity of resource allocation problems. We consider several variants this problem, depending on the number of services (one or many) and if their reliability demand is individual or global. We prove several fundamental complexity results ($\#$P and NP-completeness results) and we provide several optimal and approximation algorithms. In particular, we prove that a basic randomized allocation algorithm, that is easy to implement, provides optimal or quasi-optimal results in several contexts, and we show through simulations that it also achieves very good results in more general settings.

Lundi 12 Novembre 2012 : "MAXIMUM MATCHING IN MULTI-INTERFACE NETWORK"- Dominik Pająk (LaBRI)
Abstract: In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

Lundi 5 Novembre 2012 : pas de séminaire
Lundi 22 Octobre 2012 : Christian Glacet (LaBRI)
Lundi 15 Octobre: " NETWORK VERIFICATION VIA ROUTING TABLE QUERIES" - Ralf Klasing (LaBRI)
Abstract: We address the problem of verifying the accuracy of a map of a network by making as few measurements as possible on its nodes. This task can be formalized as an optimization problem that, given a graph G=(V,E), and a query model specifying the information returned by a query at a node, asks for finding a minimum-size subset of nodes of G to be queried so as to univocally identify G. This problem has been faced w.r.t. a couple of query models assuming that a node had some global knowledge about the network. Here, we propose a new query model based on the local knowledge a node instead usually has. Quite naturally, we assume that a query at a given node returns the associated routing table, i.e., a set of entries which provides, for each destination node, a corresponding (set of) first-hop node(s) along an underlying shortest path. First, we show that any network of n nodes needs Omega(log log n) queries to be verified. Then, we prove that there is no o(log n)-approximation algorithm for the problem, unless P=NP, even for networks of diameter 2. On the positive side, we provide an O(logn)-approximation algorithm to verify a network of diameter 2, and we give exact polynomial-time algorithms for paths, trees, and cycles of even length.

Lundi 8 Octobre 2012 : pas de séminaire
Lundi 1er Octobre 2012 : Réunion de rentrée du thème - Nicolas Hanusse (LaBRI)
Abstract: L'ordre du jour:

• projets: thèse, région, ingénieur, conférence
• organisation du groupe de travail: exposé à venir (projets à long terme, discussion sur les modèles, logiciels, ...), vitrine
• mise-à-jour site web
• enseignement: état des lieux des enseignements locaux
• stages X, ENS, ...

Lundi 21 Juin : "ABOUT RANDOMISED DISTRIBUTED GRAPH COLOURING AND GRAPH PARTITION ALGORITHMS" - Akka Zemmari (LaBRI)
Abstract: We present and analyse a very simple randomised distributed vertex colouring algorithm for arbitrary graphs of size $n$ that halts in time $O(log n)$ with probability $1-o(n^{-1}).$ Each message containing $1$ bit, its bit complexity per channel is $O(log n)$.
From this algorithm, we deduce and analyse a randomised distributed vertex colouring algorithm for arbitrary graphs of maximum degree $Delta$ and size $n$ that uses $Delta+1$ colours and halts in time $O(log n)$ with probability $1-o(n^{-1}).$
We also obtain a partition algorithm for arbitrary graphs of size $n$ that builds a spanning forest in time $O(log n)$ with probability $1-o(n^{-1})$. We study some parameters such as the number, the size or the radius of trees of the spanning forest.
We assume that graphs are anonymous; we only assume that each vertex distinguishes between its neighbours by locally known channel names. Furthermore we do not assume that the size (or an upper bound on the size) of graphs is known.
Joint work with Y. Métivier, N. Saheb and J.M. Robson

Lundi 14 Juin : Almost optimal asynchronous rendezvous in infinite multidimensional grids - Arnaud Labourel (LaBRI)
Abstract: Dans cet exposé, je montrerais comment deux agents mobiles peuvent se rencontrer dans une grille infinie de dimension supérieure à 2. On considère le modèle asynchrone. C'est-à-dire que la durée de traversée de chaque sommet par un agent est déterminée par un adversaire omniscient qui essaye d'empêcher le rendez-vous. On supposera que chaque agent connait sa position dans la grille mais pas celle de l'autre agent. Cette connaissance permet d'avoir un algorithme de rendez-vous ayant un coût, mesuré en terme de distance parcourue par les agents, quasiment optimal.

19 janvier 2015 à 21h23 par 81.67.198.101 -
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We present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal construction is a method for obtaining a concurrent implementation of any object from its sequential code. The construction is non-trivial since in the resulting implementation a failed process can cause only a finite number of operations to abort. Our construction guarantees that operations that do not modify the object always return a legal response and do not use CAS. Moreover in case of contention, at least one writing operation succeeds. We prove that our construction has asymptotically optimal space complexity for objects whose size is constant.

Lundi 30 juin 2014 : "Rendez-vous d'agents mobiles tolérant aux pannes" - Arnaud Labourel, (LIF, Université Aix-Marseille)
'Abstract: Les systèmes d’agents mobiles sont des environnements distribués dans lequel les nœuds du réseau sont passifs et ce sont des agents mobiles qui s’occupent de l’exécution de l’algorithme. Le réseau est représenté par un graphe et les agents peuvent se déplacer d’un nœud à l’autre du graphe le long de ses arêtes. Dans cet exposé, on va chercher à trouver des algorithmes permettant à deux agents mobiles initialement dispersé dans le graphe de se rencontrer sur un nœud du graphe. Plus particulièrement, on s'intéressera à ce problème pour un modèle synchrone dans lequel une panne peut se produire lors de chaque tentative de déplacement des agents. On considérera trois types de pannes possibles : probabiliste (probabilité constante de panne), adversaire non borné ou borné (un adversaire peut empêcher un agent de bouger pendant un nombre de rondes fini ou bien borné par une constante). Je donnerai des bornes inférieures et supérieures sur le coût du rendez-vous (nombre de déplacements des agents avant le rendez-vous dans le pire des cas) ainsi que des résultats d'impossibilité pour ces trois types de pannes.

Lundi 23 juin 2014 : "Maintenance d'arbres et détection de déconnexion" - Christian Glacet, (LaBRI, Université de Bordeaux)
Abstract:Dans ce travail, nous proposons un algorithme auto-stabilisant de maintenance d'arbres de plus de courts chemins tout en gérant la déconnexion de graphes dynamiques ... ce qui résoud le problème du comptage à l'infini sans connaissance sur le graphe. Ce travail a été fait avec Colette Johnen, David Ilcinkas et Nicolas Hanusse.

Lundi 16 juin 2014 : Allyx Fontaine soutient sa thèse "Analyse et preuves formelles d’algorithmes distribués probabilistes" - Amphi du LaBRI
Abstract:

Lundi 05 mai 2014 : "Le codage de réseau aléatoire : une introduction " - Christine Bachoc, (IMB, Université de Bordeaux)
Abstract:

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

Lundi 31 mars 2014 : "Algebraic Removal Lemma" - Oriol Serra ( Barcelona, Spain)
Abstract: The removal lemma is a combinatorial result which, in its simpler form, says that a graph with n vertices and o(n^3) triangles can be made triangle free by deleting o(n^2) edges. It was used by Ruzsa and Szemerédi to provide a simple proof of Roth's theorem on 3-term arithmetic progressions in dense sets of integers. An analogous algebraic statement was formulated by Green in terms of solutions of linear equations in abelian groups. In the talk I will report on some contributions made jointly with Dan Král' and Lluís Vena to this algebraic version for linear systems in abelian groups and some consequences in arithmetic Ramsey theory. The latter include a version of Szemerédi theorem on arithmetic progressions in dense sets of finite abelian groups.

P.S. : Il s'agit d'un exposé CPU.

Lundi 24 mars 2014 : "Exploration and Diffusion in Graphs using Deterministic Walks " - Adrian Kosowski (LaBRI)
Abstract: In a continuous diffusive process, a certain amount of a resource, known as "load", is initially placed on the nodes of the graph, possibly in an unfair manner. In successive time steps, each node shares its load evenly among all its neighbors, until the load on the nodes of the graph eventually converges to its limit distribution (e.g., becomes uniform in the case of regular graphs). However, continuous diffusion cannot be applied to "granular load" which is not arbitrarily divisible, i.e., represented by unsplittable unit-load tokens (chips), which are placed on nodes and may be passed around the graph. In such a scenario, one natural way of simulating the continuous diffusion process is to require that each chip follows an independent random walk on the graph.

In this talk, we will instead focus on chip diffusion processes following rules which are both locally fair and deterministic. These rules include the so-called "rotor walk", in which chips are propagated by each node to its neighbors in round-robin fashion and, more broadly, rules in which each node attempts to send out roughly the same number of tokens through each of its outgoing arcs.

We will start by providing a description of the evolution and limit behavior of the rotor walk on the n-node ring with K << n chips. For general graphs, we will show bounds on the "cover time" of a rotor walk system with K chips, proving that in a graph with m edges and diameter D, all nodes will have been visited at least once by some chip during the first O(mD / log K) steps of the process. Finally, we will relate the "blanket time" (the time until all nodes of the graph have been visited by chips a similar number of times) and the "diffusion time" (the time until all nodes all host a similar number of chips, for K >> n) of fair deterministic walks to analogous parameters of the random walk. The latter results allow us to design surprisingly simple and efficient deterministic algorithms for load balancing in the diffusive model.

This talk includes an overview of results presented at PODC'13, STACS'14, and some current work in progress (joint work with: P. Berenbrink, D. Dereniowski, R. Klasing, F. Mallmann-Trent, D. Pajak, T. Sauerwald, P. Uznanski).

Lundi 03 mars 2014 : "Algorithmes de mise à jour locale pour des graphes aléatoires" - Romaric Duvignau (LaBRI)
Abstract: Afin de modéliser l'évolution de réseaux logiques dynamiques, nous proposons de maintenir exactement une distribution donnée de graphes aléatoires lors d'une séquence arbitraire d'insertions et de suppressions de sommets. Nous nous plaçons dans un modèle local où nous n'avons pas accès à l'ensemble des sommets, mais supposons à la place l'accès à une primitive globale renvoyant un sommet aléatoire uniforme du graphe. Dans cet exposé, nous nous intéressons à maintenir la distribution uniforme dans les graphes k-sortants (graphes dirigés où tous les sommets ont degré sortant k). Nous présenterons plusieurs algorithmes d'insertion et de suppression pour le problème de maintenance, dont les plus efficaces sont asymptotiquement optimaux.

Lundi 24 février 2014 : "Distributed anonymous discrete function computation" - Julien Hendrickx(Univ. Louvain)
Abstract: We propose a model for deterministic distributed function computation by a network of identical and anonymous nodes:. In this model, each node has bounded computation and storage capabilities that do not grow with the network size. Furthermore, each node only knows its neighbors, not the entire graph. Our goal is to characterize the class of functions that can be computed within this model. We provide a necessary condition for computability which we show to be nearly sufficient, in the sense that every function that violates this condition can at least be approximated. The problem of computing (suitably rounded) averages in a distributed manner plays a central role in our development; we provide an algorithm that solves it in time that grows quadratically with the size of the network.

Lundi 17 février 2014 : "The interplay between multidimensional skylines and functional dependencies " - Sofian Maabout (LaBRI)
Abstract: We show how functional dependencies, which are agnostoc to the orders defined over the dimensions domains, can help to optimize skyline queries which, by opposition are based on orders. We present some theoretical and experimental results.

Lundi 10 février 2014 : "Algorithmes auto-stabilisants barvards" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)
Abstract: Dans le contexte des réseaux à grande échelle, la prise en compte des pannes est une nécessité évidente. Ce séminaire traite de l’auto-stabilisation, une méthode qui vise à concevoir des algorithmes distribués se « réparant d’eux-même » en cas de pannes transitoires pouvant impliquer toute modification arbitraire de l’état des processus. Plusieurs paramètres peuvent être pris en compte pour mesurer l’efficacité d’un algorithme auto-stabilisant, dont en particulier le temps de convergence et la complexité mémoire. L’importance du temps de convergence vient de la nécessité évidente pour un système de retrouver le plus rapidement possible un état valide après une panne. La nécessité de minimiser la mémoire vient, d’une part, de l’importance grandissante de réseaux offrant des espaces mémoires restreints, comme par exemple certains réseaux de capteurs, et, d’autre part, de l’intérêt de minimiser à la fois l’échange et le stockage d’information afin de limiter les potentialités de corruption de cette information. Lors de ce séminaire, nous traiterons de la minimisation de la mémoire au travers d'un exemple, à savoir le problème de l’élection d’un leader. Une borne inférieure de Ω(log n) bits de mémoire par noeud a été établie par Dolev, Gouda et Schneider (1999) pour ce problème fondamental. Cette borne n'est toutefois valable que pour des algorithmes silencieux, c'est-à-dire des algorithmes dont les registres ne sont plus modifiés lorsque le système a rejoint un état légitime. Nous verrons que, si l'on autorise l’algorithme à rester bavard (non-silencieux) même après avoir rejoint un état légitime, alors l’espace mémoire peut être amélioré d’un facteur au moins exponentiel.

Lundi 6 Janvier 2014 : "Self-stabilizing k-independent dominating set construction" - Colette Johnen(LaBRI)
Abstract: A k-independent dominating set is a k-independent set and a k-dominating set. A set of nodes, I, is k-independent if the distance between any pair of nodes in I is at least k+1. A set of nodes, D, is a k-dominating if every node is within distance k of a node of D.

I propose two self-self-stabilizing algorithm building k-independent dominating sets. The both algorithm (SID and FID) are silent, and they converge under the unfair distributed scheduler (the weakest scheduling assumption).

The algorithm FID reaches a terminal (also legitimate) configuration in at most 4n+k rounds, where n is the network size. The algorithm FID requires (k+1)log(n+1) bits per node.

The protocol SID is memory efficient : it requires only 2log((k+1)n+1)+1 bits per node. The computation of the convergence time of the protocol SID is opened question.

Lundi 16 Décembre 2013 : "Large-scale Data Stream Analysis" - Yann Busnel (LINA - Université de Nantes)
Abstract: L'objectif de cet exposé est de dresser un court état de l'art autour de l'analyse des flux de données à grande échelle, lesquels sont souvent utilisés pour du monitoring et de la sécurité, à la fois dans les réseaux et les systèmes distribués jusqu'à l'internet des objets. La problématique de ce champs de recherche consiste à extraire de l'information pertinente d'un flux de données en une passe unique (en raison de la taille du flux et de sa rapidité), et ne nécessitant qu'une quantité mémoire très faible et une puissance de calcul très limitée. Je présenterai ensuite les dernières applications utilisant nos résultats récents, lesquels vont de la détection d'intrusion, la détection de DDoS, l'échantillonnage, etc.

Lundi 9 Décembre 2013 : "Simulating weak shared memory" - David Bonnin (LaBRI)
Abstract: It is well known that in an asynchronous message-passing system with crash faults, one can emulate an atomic register providing that more than half of the processes are non-faulty. By contrast, when a majority of the processes may fail, simulating atomic register is not possible. I will talk about weak variants of atomic registers that can be simulated tolerating a majority of processes failures. Specifically, I will introduce a new class of registers, called $\alpha$-registers. We found a lower bound of $\alpha = M+1$ with $M=2f-n+2$ for these registers, and an explicit algorithm can emulate them with $\alpha = 2M-1$. I will also probably talk about other approaches on weak shared memory : $M$-colored registers, and $k$-splitters. This is a joint work with C. Travers.

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nicolas Bonichon (LaBRI)
Abstract: This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

Lundi 25 Novembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)
Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a maximal matching for anonymous rings. Their bit complexity and time complexity are $O(\sqrt{\log n})$ with high probability. These algorithms are optimal modulo a multiplicative constant. Beyond the complexity results, the interest of this work stands in the description and the analysis of these algorithms which may be easily generalised. Furthermore, these results show a separation between the complexity of the MIS problem (and of the maximal matching problem) on the one hand and the colouring problem on the other. Colouring can be computed only in $\Omega(\log n)$ rounds on rings with high probability, while MIS is shown to have a faster algorithm. This is in contrast to other models, in which MIS is at least as hard as colouring. This is joint work with Y. Métivier, J.M. Robson and A. Zemmari

Lundi 4 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)
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Lundi 28 Octobre 2013 : "The Case for Reliable Software Transactional Networking" - Petr Kuznetsov (Paristech)
Abstract: Software-defined networking (SDN) is a novel paradigm that out-sources the control of packet-forwarding switches to a set of software controllers. The most fundamental task of these controllers is the correct implementation of the network policy, i.e., the intended network behavior. In essence, such a policy specifies the rules by which packets must be forwarded across the network. We initiate the study of the SDN control plane as a distributed system.

We introduce a formal model describing the interaction between the data plane and a distributed control plane (consisting of a collection of fault-prone controllers). Then we formulate the problem of consistentcomposition of concurrent network policy updates. The composition is enabled via a transactional interface with all-or-nothing semantics, which allows us to reason about possibilities and impossibilities in controller synchronization.

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

Lundi 23 Septembre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Miroslaw Korzeniowski
Abstract: Decentralized monitoring and alarming systems can be an attractive alternative to centralized architectures. Distributed sensor nodes (e.g., in the smart grid's distribution network) are closer to an observed event than a global and remote observer or controller. This improves the visibility and response time of the system. Moreover, in a distributed system, local problems may also be handled locally and without overloading the communication network.

This article initiates the study of alarming from a distributed computing perspective and under two fundamentally different scenarios: \emph{on-duty} and \emph{off-duty}. We model the alarming system as a sensor network consisting of a set of distributed nodes performing local measurements to sense events. In order to avoid false alarms, the sensor nodes cooperate and only escalate an event (i.e., raise an alarm) if the number of sensor nodes sensing an event exceeds a certain threshold. In the on-duty scenario, nodes not affected by the event can actively help in the communication process, while in the off-duty scenario non-event nodes are inactive.

This article presents and analyzes algorithms that minimize the reaction time of the monitoring system while avoiding unnecessary message transmissions. Moreover, lower bounds are derived that shed light on the limitations of distributed alarming systems.

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)
Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

Lundi 8 Juillet 2013 : "Dynamic Resource Allocation in Cloud Computing platforms" - Lionel Eyraud-Dubois (Labri)
Abstract: Je présente un problème d'allocation de ressources dans le contexte du Cloud Computing, où un ensemble de machines virtuelles (VM) doivent être allouées sur un ensemble de machines physiques (PMs). La particularité de ce problème vient du fait que la quantité de ressources dont chaque VM a besoin change au cours du temps, et qu'il est possible pour le fournisseur d'accès de changer l'allocation d'une VM par une opération de migration. Ce problème peut se modéliser sous la forme d'un problème de bin packing complètement dynamique, et je présente un algorithme d'approximation pour minimiser le nombre de PMs utilisées, tout en garantissant un petit nombre de migrations. Les propriétés de cet algorithme permettent également d'envisager une version distribuée.

Lundi 10 Juin 2013 : " The Heard-Of model: computing in distributed systems with benign failures" - Bernadette Charron-Bost (CNRS, Ecole polytechnique, Paris)
Abstract: Problems in fault-tolerant distributed computing have been studied in a va- riety of system models. These models are all based on the principle that it is usefull and even necessary to specify why and by whom errors occur. In this talk, we question this principle, and present a general computational model, called the Heard-Of model, suitable for describing any type of system, be it message passing, shared memory, synchronous, or asynchronous. In this model, computations evolve in rounds, and communication missed at a round is definitely lost. Only information transmission is represented: for each round r and each process p, our model specifies the set of processes that p “hears of” at round r (heard-of set) namely the processes from which p receives some message at round r. The features of a specific system are thus captured as a whole, just by a predicate over the collection of heard-of sets. Thus the Heard-Of model allows us to handle all types of benign failures, static or dynamic, permanent or transient, in a unified framework. Moreover, it unifies the most seemingly unrelated notions in distributing computing, namely synchrony and asynchrony. We further demonstrate how this unifying framework leads to new results and insights in fault-tolerant distributed computing. In particular, we show that some fundamental results for asynchronous systems can be advantageously transferred to synchronous systems. We also examine Consensus algorithms in the Heard-Of model: we show how our approach allows us to devise new solutions and to give simple correctness proofs of existing algorithms like Paxos.

Joint work with André Schiper, EPFL

Lundi 3 Juin 2013 : "Introduction to renaming" - Corentin Travers (Labri)
Abstract: Renaming is a fundamental coordination problem in distributed computing. It consists in assigning new names taken from a small name space to processes in such a way that no two processes obtain the same name. The talk will survey renaming algorithms suited for different models of distributed computing, including the wait-free shared memory and the synchronous crash-prone message-passing models.

Lundi 27 Mai 2013 : " Exploration des graphes dynamiques T-intervalle-connexes : le cas de l'anneau" - Wade Ahmed (Labri)
Abstract: Dans cet exposé, je vais parler de l'étude des graphes dynamiques T-intervalle-connexes du point de vue du temps nécessaire à leur exploration par une entité mobile (agent). Un graphe dynamique est T-intervalle-connexe (T \geq 1) si pour chaque fenêtre de T unités de temps, il existe un sous-graphe couvrant connexe stable. Cette propriété de stabilité de connexion au cours du temps a été introduite par Kuhn, Lynch et Oshman~\cite{KLO10} (STOC 2010). Nous nous concentrons sur le cas où le graphe sous-jacent est un anneau de taille n et nous montrons que la complexité en temps en pire cas est de 2n-T-\Theta(1) unités de temps si l'agent connaît la dynamique du graphe, et n+ \frac{n}{\max\{1,T-1\}} (\delta-1) \pm \Theta(\delta) unités de temps sinon, où \delta est le temps maximum entre deux apparitions successives d'une arête.

Keywords : Graphe dynamique, exploration, T-intervalle-connexité, agent mobile

Lundi 13 Mai 2013 : " Calcul Distribué et Fouille de Données" - Nicolas Hanusse (Labri)
Abstract: L'avènement de la production massive de données et la volonté de les exploiter sont limités par les systèmes de gestion de bases de données relationnelles classiques. Cet exposé consiste en une discussion sur les enjeux et problèmes algorithmiques engendrés par le calcul distribué et parallèle. Le calcul de corrélations servira d'illustration. C'est un travail en cours avec Sofian Maabout et Eve Garnaud.

Lundi 22 Avril 2013 : " A peer-to-peer-based virtual environment system" - Eliya Buyukkaya (ENSSAT-Université de Rennes I)
Abstract: Virtual environments (VEs) are 3-D virtual worlds in which a huge number of participants play roles and interact with their surroundings through virtual representations called avatars. VEs are traditionally supported by a client/server architecture. However, centralized architectures can lead to bottleneck on the server due to high communication and computation overhead during peak loads. Thus, P2P overlay networks are emerging as a promising architecture for VEs. However, exploiting P2P schemes in VEs is not straightforward, and several challenging issues related to data distribution and state consistency should be considered.

One of the key aspects of P2P-based VEs is the logical platform consisting of connectivity, communication and data architectures, on which the VE is based. The connectivity architecture is the overlay topology structure, which defines how peers are connected to each other. The communication architecture is the routing protocol defining how peers can exchange messages, while the data architecture defines how data are distributed over the logical overlay. The design of these architectures has significant influence on the performance and scalability of VEs.

First, we propose a scalable connectivity architecture based on a new triangulation algorithm reducing maintenance cost of the system. Second, we construct a communication architecture built on top of the connectivity architecture ensuring that each message reaches its intended destination. Finally, we propose a data architecture ensuring the management of data with different characteristics in terms of mobility in the VE, while providing a fair data distribution and low data transfer between peers in the VE.

Lundi 15 Avril 2013 : " Algorithms for the Vertex Cover Problem on Large Graphs with Low Memory Capacities" - Romain Campigotto (LIP6-Paris)
Abstract: Most of the known optimization algorithms need to explore, mark, modify, etc. the instance given as input before producing their results. To do that, the instance is entirely loaded into the memory of the computer and is manipulated by the algorithm. Often, "extra" data structures are also necessary to memorize parameters useful all along the computation or to update the current solution that will be returned as the final product of the program. However, this classical model is no more adapted for many new computing applications. Indeed, nowadays, many fields such as biology, meteorology, finance, etc. produce very large amount of data.

In our works, we have focused on the Vertex Cover problem on huge graphs: in the intrinsic NP-completeness is added the difficulty to manipulate graphs with severe constraints (mainly related to the low memory capacities). We defined a treatment model combining some properties of several existing models in the literature: streaming, online, I/O-efficient, etc. We initially considered three approximation algorithms, which are memory-efficient (they use a memory space in O(log n) bits). We analyzed their performance in terms of solution quality and complexity, in mean and worst cases. We then focused on algorithms that use memory space of n bits. We showed that it could be very worst with strictly less than n bits memory space. Subsequently, we conducted experiments on very large graphs (in the order of billions of vertices and edges). This study showed that in practice, memory-efficient algorithms are better suited to handle large graphs.

This is joint work with Eric Angel (IBISC, Univ. Évry) and Christian Laforest (LIMOS, ISIMA, Clermont-Ferrand).

Lundi 8 Avril 2013 : "Implémentation d'algorithmes distribués à l'aide de Visidia" - Mohamed Mosbah (Labri)
Abstract: Dans le cadre du projet visidia, une plate-forme logicielle est développée pour l'implantation et la visualisation d'algorithmes distribués. Après une introduction et quelques rappels, l'exposé consistera en une présentation de la plate-forme et de son utilisation pour programmer des exemples d'algorithmes. L'interface et l'API permettent de visualiser l'exécution d'algorithmes, d'implanter de nouveaux algorithmes, ou d'effectuer des statistiques. Les algorithmes peuvent être exprimés selon plusieurs modèles (calculs locaux, passage de messages, agents mobiles).

Lundi 25 Mars 2013 : "Simultaneous Consensus vs Set Agreement." - Zohir Bouzid (LIP6-Paris)
Abstract: In the traditional consensus task, processes are required to agree on a common value chosen among the initial values of the participants. It is well known that consensus cannot be solved in crashed-prone, asynchronous distributed systems. Two generalizations of the consensus problem have been introduced: k-set agreement and k-simultaneous consensus. The k-set agreement task has the same requirements as consensus except that processes are allowed to decide up to k distinct values. In the k-simultaneous consensus task, each process participates simultaneously in k instances of consensus and is required to decide in at least one of them; any two processes deciding in the same instance must decide the same value. In this talk, we compare the computability of these problems in two central models in distributed computing: shared memory and message passing. We show that even though the two problems are equivalent in shared memory, k-simultaneous consensus is strictly harder than k-set agreement in the message passing model. This result will serve as a basis for a discussion about different models of computation and their respective power.

Lundi 18 Mars 2013 : "Vers une classification des réseaux dynamiques en fonction des problèmes qu'on peut y résoudre." - Arnaud Casteigts (Labri)
Abstract: Derrière les notions de "graphe dynamique" ou de "réseau dynamique" se cache une très grande diversité de scénarios et d'hypothèses, allant de réseaux semi-statiques où la connexité est toujours assurée à des réseaux complètement mobiles, où la connexité ne s'établit qu'à travers le temps et l'espace (e.g. DTNs). Dans cet exposé, résolument transversal, je présenterai l'état d'avancement de nos recherches autour de la question suivante : quel lien existe-t-il entre la "faisabilité" de tâches distribuées et la dynamique du réseau. Les hypothèses résultantes sur la dynamique peuvent être vues comme autant de classes de graphes (ou alternativement, comme autant de puissances possibles pour un adversaire qui contrôlerait la topologie). Nous avons à ce jour caractérisé et/ou recensé une petite vingtaine de classes de ce type.

Certains de ces travaux ont été menés en collaboration avec Serge Chaumette et Afonso Ferreira. D'autres avec Paola Flocchini et Nicola Santoro.

Lundi 25 Février 2013 : "Sur les 1001 modèles en algorithmique distribuée." - Yves Metivier (Labri)
Abstract: Le but de cet "exposé-discussion" est de présenter quelques modèles en algorithmique distribuée et d'échanger sur leurs liens et leurs mérites.

Lundi 18 Février 2013 : "Distributed Calculation of Graph Diameter" - Mike Robson (Labri)
Abstract: We consider the problem of calculating the diameter of a graph given that there is a single vertex "Leader" and neighbouring vertices can exchange messages of a single bit at each round. We show that this can be achieved in the same O(n) time complexity as well known algorithms without this bound on message length. The techniques used can be applied to a number of other graph computations. We consider briefly how the algorithm behaves if applied in a situation where more than one vertex considers itself the Leader.

This is joint work with Yves Métivier and Akka Zemmari.

Lundi 11 Février 2013 : "Bounds for Communication in Wireless Grids" - Joseph Peters (Simon Fraser University)
Abstract: In a wireless network, a transmission can be received by a node if it is close enough to the sender. However, transmissions can interfere with each other and the interference distance is typically greater than the reception distance. Efficient communication protocols in these networks minimize the time to move information without interference. In this talk, I will describe optimal protocols for the problem of collecting information into a central node of a two-dimensional square or hexagonal grid graph. The optimality of the protocols is proved using a new lower bound technique that is an adaptation to a discrete environment of a method based on linear programming duality for continuous flows.

This is joint work with Jean-Claude Bermond, CNRS-INRIA-University of Nice.

Lundi 04 Février 2013 : "Distributed Detection of Clone Attacks in Wireless Sensor Networks" - Mauro Conti (University of Padua, Italy)
Abstract: Wireless Sensor Networks (WSNs) are often deployed in hostile environments where an adversary can physically capture some of the nodes, first can reprogram, and then, can replicate them in a large number of clones, easily taking control over the network. A few distributed solutions to address this fundamental problem have been recently proposed. However, these solutions are not satisfactory. First, they are energy and memory demanding: A serious drawback for any protocol to be used in the WSN-resource-constrained environment. Further, they are vulnerable to the specific adversary models that we introduced. The contributions of our work are threefold. First, we analyze the desirable properties of a distributed mechanism for the detection of node replication attacks. Second, we show that the known solutions for this problem do not completely meet our requirements. Third, we propose a new self-healing, Randomized, Efficient, and Distributed (RED) protocol for the detection of node replication attacks, and we show that it satisfies the introduced requirements. Finally, extensive simulations show that our protocol is highly efficient in communication, memory, and computation; is much more effective than competing solutions in the literature; and is resistant to the new kind of attacks introduced in our work, while other solutions are not.

Lundi 28 Janvier 2013 : "Distributed Exclusive Graph Searching in Trees" - Janna Burman (LRI-Université Paris-Sud)
Abstract: We consider a version of the well known graph searching problem, where a team of robots aims at clearing the contaminated edges of a graph. We study graph searching in the model of mobile computing where autonomous deterministic robots move between the graph nodes when operating in asynchronous cycles of Look-Compute-Move. Moreover, motivated by physical constraints, following some recent works, we consider the exclusivity property, stating that no two or more robots can occupy a same node at the same time. In addition, we assume that all the graph elements and the robots are anonymous. Robots are oblivious and have no sense of direction. Our objective is to characterize for a graph $G$, the set of integers $k$ such that graph searching can be achieved by a team of $k$ robots starting from any $k$ distinct nodes in $G$. Our main result consists in a full characterization for any asymmetric tree. Towards providing a characterization in the general case, including trees with non-trivial automorphisms, we provide a set of positive and negative results, including a full characterization for any line. All our positive results are based on the design of algorithms enabling perpetual graph searching to be achieved with the desired number of robots. We prove that, in addition to the distributed nature of our setting, the exclusivity property has a significant impact on the nature of the graph searching problem. Hence, the design of the algorithms requires to invent new methods.

Lundi 21 Janvier 2013 : "Présentation de Keep Alert, une solution pour la surveillance de marques sur Internet" - Anthony Don (Keep Alert)
Abstract: A destination des cabinets de propriété industrielle et des services juridiques, Keep Alert propose des surveillances de marque parmi les noms de domaine, les régies publicitaires et les réseaux sociaux. Anthony DON, directeur technique chez Keep Alert, présentera au groupe de travail, le fonctionnement global de la plateforme, puis abordera les problématiques actuelles et les perspectives de développement relatives à l'algorithmique distribuée.

Lundi 14 Janvier 2013 : "Two Monte-Carlo Election Algorithms for Anonymous Graphs without any Initial Knowledge" - Akka Zemmari (Labri)
Abstract: The paper proposes and analyses two Monte Carlo election algorithms for anonymous graphs without any initial knowledge. Both have a time complexity equal to $O(D)$, where $D$ is the diameter of the graph. The first is correct with probability $1-o(n^{-1})$ (where $n$ is the size of the graph). The size of messages is $O(\log n)$ with probability $1-o(n^{-1})$ and the expected value of the size of messages is also $O(\log n)$. The second is correct with probability $1-o(n^{-c})$ for any $c\geq 1$. The size of messages is $O\left((\log n)(\log^* n)^2 \right)$ with probability $1-o(n^{-c})$ for any $c\geq 1$; their expected size is $O\left((\log n)(\log^* n) \right)$.

This is a joint work with Y. Métivier and J. M. Robson

Lundi 10 Décembre 2012 : pas de seminaire. Soutenance de thèse-Florent Foucaud.

Lundi 3 Décembre 2012 : "Progress and Challenges for Labeling Schemes" - Cyril Gavoille (Labri)
Abstract: A fundamental question in Distributed Computing is to understand how localized and how much information are required to solve a task on a network. Typically, if the distance between any pair x,y of nodes in a network is asked, we would like to know which minimal information about x and y in the network are needed. The goal in labeling schemes is precisely to understand how much information must be attached to the nodes (formalized as labels) to solve a graph problem assuming the answer can be determined solely on the basis of the labels of the nodes invoked in the query. In this talk, I give a survey on labeling schemes, present some recent results with their techniques, and highlight new challenges.

Lundi 26 Novembre 2012: "Competitive Routing on a Variant of the Delaunay Triangulation" - Prosenjit Bose (Carleton University)
Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we showed how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.

Lundi 19 Novembre 2012: " Reliable Service Allocation in Clouds"- Lionel Eyraud-Dubois, Olivier Beaumont (Labri)
Abstract: We consider several reliability problems that arise when allocating applications to processing resources in a Cloud computing platform. More specifically, we assume on the one hand that each computing resource is associated to a capacity constraint and to a probability of failure. On the other hand, we assume that each service runs as a set of independent instances of identical Virtual Machines, and that the Service Level Agreement between the Cloud provider and the client states that a minimal number of instances of the service should run with a given probability. In this context, given the capacity and failure probabilities of the machines, and the capacity and reliability demands of the services, the question for the cloud provider is to find an allocation of the instances of the services (possibly using replication) onto machines satisfying all types of constraints. In this paper, our goal is to assess the impact of the reliability constraint on the complexity of resource allocation problems. We consider several variants this problem, depending on the number of services (one or many) and if their reliability demand is individual or global. We prove several fundamental complexity results ($\#$P and NP-completeness results) and we provide several optimal and approximation algorithms. In particular, we prove that a basic randomized allocation algorithm, that is easy to implement, provides optimal or quasi-optimal results in several contexts, and we show through simulations that it also achieves very good results in more general settings.

Lundi 12 Novembre 2012 : "MAXIMUM MATCHING IN MULTI-INTERFACE NETWORK"- Dominik Pająk (LaBRI)
Abstract: In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

Lundi 5 Novembre 2012 : pas de séminaire
Lundi 22 Octobre 2012 : Christian Glacet (LaBRI)
Lundi 15 Octobre: " NETWORK VERIFICATION VIA ROUTING TABLE QUERIES" - Ralf Klasing (LaBRI)
Abstract: We address the problem of verifying the accuracy of a map of a network by making as few measurements as possible on its nodes. This task can be formalized as an optimization problem that, given a graph G=(V,E), and a query model specifying the information returned by a query at a node, asks for finding a minimum-size subset of nodes of G to be queried so as to univocally identify G. This problem has been faced w.r.t. a couple of query models assuming that a node had some global knowledge about the network. Here, we propose a new query model based on the local knowledge a node instead usually has. Quite naturally, we assume that a query at a given node returns the associated routing table, i.e., a set of entries which provides, for each destination node, a corresponding (set of) first-hop node(s) along an underlying shortest path. First, we show that any network of n nodes needs Omega(log log n) queries to be verified. Then, we prove that there is no o(log n)-approximation algorithm for the problem, unless P=NP, even for networks of diameter 2. On the positive side, we provide an O(logn)-approximation algorithm to verify a network of diameter 2, and we give exact polynomial-time algorithms for paths, trees, and cycles of even length.

Lundi 8 Octobre 2012 : pas de séminaire
Lundi 1er Octobre 2012 : Réunion de rentrée du thème - Nicolas Hanusse (LaBRI)
Abstract: L'ordre du jour:

• projets: thèse, région, ingénieur, conférence
• organisation du groupe de travail: exposé à venir (projets à long terme, discussion sur les modèles, logiciels, ...), vitrine
• mise-à-jour site web
• enseignement: état des lieux des enseignements locaux
• stages X, ENS, ...

Lundi 21 Juin : "ABOUT RANDOMISED DISTRIBUTED GRAPH COLOURING AND GRAPH PARTITION ALGORITHMS" - Akka Zemmari (LaBRI)
Abstract: We present and analyse a very simple randomised distributed vertex colouring algorithm for arbitrary graphs of size $n$ that halts in time $O(log n)$ with probability $1-o(n^{-1}).$ Each message containing $1$ bit, its bit complexity per channel is $O(log n)$.
From this algorithm, we deduce and analyse a randomised distributed vertex colouring algorithm for arbitrary graphs of maximum degree $Delta$ and size $n$ that uses $Delta+1$ colours and halts in time $O(log n)$ with probability $1-o(n^{-1}).$
We also obtain a partition algorithm for arbitrary graphs of size $n$ that builds a spanning forest in time $O(log n)$ with probability $1-o(n^{-1})$. We study some parameters such as the number, the size or the radius of trees of the spanning forest.
We assume that graphs are anonymous; we only assume that each vertex distinguishes between its neighbours by locally known channel names. Furthermore we do not assume that the size (or an upper bound on the size) of graphs is known.
Joint work with Y. Métivier, N. Saheb and J.M. Robson

Lundi 14 Juin : Almost optimal asynchronous rendezvous in infinite multidimensional grids - Arnaud Labourel (LaBRI)
Abstract: Dans cet exposé, je montrerais comment deux agents mobiles peuvent se rencontrer dans une grille infinie de dimension supérieure à 2. On considère le modèle asynchrone. C'est-à-dire que la durée de traversée de chaque sommet par un agent est déterminée par un adversaire omniscient qui essaye d'empêcher le rendez-vous. On supposera que chaque agent connait sa position dans la grille mais pas celle de l'autre agent. Cette connaissance permet d'avoir un algorithme de rendez-vous ayant un coût, mesuré en terme de distance parcourue par les agents, quasiment optimal.

en:

We present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal construction

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Lundi 2 mars : TBA - Lionel Eyraud-Dubois (LaBRI, INRIA)
'Abstract:'

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Lundi 23 février: : Relâche

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Join work with Yves Métivier and Mike Robson

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The aim of this paper is the study of the resolution of paradigms such as collision detection, computation of the degree of a vertex, of a MIS or a colouring in the framework of beeping models.

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Lundi 16 février 2015: On Distributed Computing with Beeps Akka Zemarri
Abstract: We consider networks of processes which interact with beeps. Various beeping models are used. The basic one, defined by Cornejo and Khun.

en:

Lundi 16 février 2015: On Distributed Computing with Beeps Akka Zemarri (LaBRI, Université de Bordeaux)
Abstract: We consider networks of processes which interact with beeps. Various beeping models are used. The basic one, defined by Cornejo and Khun assumes that a process can choose either to beep or to listen. If it listens it can distinguish between silence or the presence of at least one beep.

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Abstract:

en:

Abstract: We consider networks of processes which interact with beeps. Various beeping models are used. The basic one, defined by Cornejo and Khun.

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Lundi 16 février 2015: On Distributed Computing with Beeps Akka Zemarri
Abstract:

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Lundi 9 février 2015 : tba Yves Métivier
Abstract: TBA

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Lundi 2 février 2015 : Pas d'exposé
Allez voir les exposés des 'Journées GDR IM' qui se tiennent au LaBRI les 2 et 3 février. Le programme est ici : http://gdrim2015.labri.fr

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(joint work with Nikos Leonardos, Euripides Markou, Aris Pagourtzis, and Matoula Petrolia)""

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(joint work with Nikos Leonardos, Euripides Markou, Aris Pagourtzis, and Matoula Petrolia)

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Lundi 26 janvier 2015 : Periodic Data Retrieval in asynchronous rings with a malicious host - Evangelos Bampas (LaBRI, Université de Bordeaux)\\

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Lundi 26 janvier 2015 : Periodic Data Retrieval in asynchronous rings with a malicious host - Evangelos Bampas (LaBRI, Université de Bordeaux)\\

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 Lundi 26 janvier 2015 :  Periodic Data Retrieval in asynchronous rings with a malicious host -  Evangelos Bampas (LaBRI, Université de Bordeaux)\\

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Lundi 26 janvier 2015 : Periodic Data Retrieval in asynchronous rings with a malicious host - Evangelos Bampas (LaBRI, Université de Bordeaux)\\

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Lundi 26 janvier 2015 : Periodic Data Retrieval in asynchronous rings with a malicious host - Evangelos Bampas (LaBRI, Université de Bordeaux)

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 Lundi 26 janvier 2015 :  Periodic Data Retrieval in asynchronous rings with a malicious host -  Evangelos Bampas (LaBRI, Université de Bordeaux)

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L'exp

en:

L'expansion, au cours des deux dernières décennies des réseaux, et notamment d'Internet, a engendré une création importante de données, massives de par leur nombre et leur taille. De ce fait, des systèmes de stockages distribués (comme Cassandra par exemple) sont utilisés en pratique afin de stocker ces données.

Deux problématiques se posent alors : (1) comment répartir les données? (2) comment optimiser le traitement des requêtes sur ces données?

Nous nous intéressons ici à l'équilibrage des requêtes entre les différents noeuds d'un système distribué. Notre approche consiste à utiliser la réplication d'objet et nous proposons différents algorithmes d'affectation des requêtes en cherchant à optimiser le temps de complétion (temps de traitement) des requêtes.

(Travail en cours avec Nicolas Hanusse)

Lundi 12 janvier 2015 : "Distributedly Testing Cycle-Freeness" - David Ilcinkas (LaBRI, CNRS and Université de Bordeaux)
Abstract: We tackle local distributed testing of graph properties. This framework is well suited to contexts in which data dispersed among the nodes of a network can be collected by some central authority (like in, e.g., sensor networks). In local distributed testing, each node can provide the central authority with just a few information about what it perceives from its neighboring environment, and, based on the collected information, the central authority is aiming at deciding whether or not the network satisfies some property. We analyze in depth the prominent example of checking \emph{cycle-freeness}, and establish tight bounds on the amount of information to be transferred by each node to the central authority for deciding cycle-freeness. In particular, we show that distributedly testing cycle-freeness requires at least $\ceil{\log d}-1$ bits of information per node in graphs with maximum degree~$d$, even for connected graphs. Our proof is based on a novel version of the seminal result by Naor and Stockmeyer (1995) enabling to reduce the study of certain kinds of algorithms to order-invariant algorithms, and on an appropriate use of the known fact that every free group can be linearly ordered.

# Exposés passés

Lundi 15 décembre 2014 : "Splitting and renaming with a majority of faulty processes" - David Bonnin (LaBRI, Université de Bordeaux)
Abstract: The renaming problem has been introduced by Attiya et al. [1], and consists on the following : Each process start with a unique name in a large namespace (such as an IP address), and each process tries to acquire a new name such as, at the end of the algorithm, each process has a new unique name in a much smaller namespace. This problem was first solved in asynchronous message-passing systems with a strict minority of processes that might crash, and later largely studied in wait-free shared memory systems, which can themselves be simulated in the former model (as explained in [2]). Splitters are basic shared memory objects that were introduced in [3] in order to build a fast renaming algorithm, and extending the renaming to a long-lived'' version. A splitter is an object that can be accessed through one operation Split(), and returns a direction in {right, down, stop}, with the property that not all processes return right, not all return down, and at most 1 process may return stop.

In asynchronous message-passing systems with a majority of faulty processes, the renaming problem cannot be solved, and splitters cannot be implemented. But we extended these notions to k-renaming and k-splitters, both for one-shot and long-lived versions. Instead of having unique name for each process, each new name (in a small namespace) may be acquired by at most k processes, and at most k processes accessing a k-splitter may return stop. We developed an optimal algorithm for implementing k-splitters, i.e. the algorithm implements them with k = floor(n/(n-f)), where n in the number of processes and f the maximal number of faulty processes among them, and it is not possible to implement k'-splitters with k' < floor(n/(n-f)). Although the namespace is not optimal, especially in the long-lived version, k-renaming based on these k-splitters is optimal for the same reason that k=floor(n/(n-f)) is both a lower bound, and a reached upper bound.

[1] H. Attiya, A. Bar-Noy, D. Dolev, D. Peleg, and R. Reischuk. Renaming in an asynchronous environment. J. ACM, 37(3):524–548, July 1990. [2] H. Attiya, A. Bar-Noy, and D. Dolev. Sharing memory robustly in message-passing systems. J. ACM, 42(1):124–142, 1995. [3] M. Moir and J. H. Anderson. Wait-free algorithms for fast, long-lived renaming. Science of Computer Programming, 25(1):1 – 39, 1995.

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz et Matthieu Barjon, (LaBRI, Université de Bordeaux)

Lundi 01 décembre 2014 : "Towards a General Framework for Searching on a Line and Searching on m Rays" - Jean-Lou De Carufel (Carleton University)
Abstract: We revisit the problem of searching for a target at an unknown location on a line when given upper and lower bounds on the distance D that separates the initial position of the searcher from the target. We present tight bounds on the exact optimal competitive ratio achievable, parameterized in terms of the given range for D, along with an optimal search strategy that achieves this competitive ratio.

We present an optimal search strategy for the case where a fixed turn cost t is charged every time the searcher changes direction. Moreover, we generalize our results to the framework where the cost of moving distance x away from the origin is a x + b and the cost of moving distance y towards the origin is c y + d for constants a, b, c and d.

This is joint work with Prosenjit Bose (Carleton U.) and Stephane Durocher (U. of Manitoba).

Lundi 24 novembre 2014 : "ON THE POWER OF ONE BIT: HOW TO EXPLORE A GRAPH WHEN YOU CANNOT BACKTRACK?" - Dominik Pajak, (University of Cambridge)
Abstract: We study the problem of exploration of an anonymous undirected graph with n vertices, m edges and diameter D by a single mobile agent. The agent does not know the incoming port when entering to a vertex thus it cannot backtrack its moves. Each vertex of the graph is endowed with a whiteboard on which the agent can store information.

In this talk we will study tradeoffs between the exploration time and the existence of the internal memory available to the agent. We will first show an algorithm for an agent with 1 bit of memory completing exploration of any graph with stop in time O(m) using whiteboards of size O(log Delta) on each vertex with degree Delta.

An oblivious agent (with no internal memory) can explore any graph in time O(m D) using whiteboards of size O(log Delta) by applying the rotor-router mechanism. We will show that, even with unbounded whiteboards, there is no algorithm for oblivious agents that is better than the rotor-router in the worst case by showing a Omega(n3) lower bound for a specific class of graphs. We will also observe that any oblivious agent cannot stop after completing the task. This shows separation between oblivious and non-oblivious agents in terms of the exploration time and the stop property.

Lundi 17 novembre 2014 : "Group Search on the Line" - Leszek Gasieniec (University of Liverpool)

Lundi 10 novembre 2014 : "Patrolling by unreliable mobile robots" - Jurek Czyzowicz (Université du Québec en Outaouais)
Abstract: Mobile robots collaborate in order to solve efficiently the central problems in algorithmics of distributed computing like searching/exploration, rendez-vous or pattern formation. Patrolling is a perpetual traversal of an environment by a collection of mobile robots. The standard measure of efficiency of a patrolling algorithm is defined by its idleness – the minimal time interval during which every point of the environment is always visited by at least one robot. Boundary patrolling and fence patrolling were fundamental problems investigated by the robotics community in the last decade.

We sketch briefly previous results concerning the algorithms for the boundary and fence-patrolling problem. When some (unknown) robots of the collection cannot perform their duties, the fence patrolling algorithms become surprisingly unnatural. In more details we discuss a new algorithm for patrolling by unreliable robots. We show that the presented algorithm achieves the idleness, which is the best possible.

Lundi 03 novembre 2014 : "Coloration d'un cycle en temps log*(n): borne sup et borne inf" - Cyril Gavoille, (LaBRI, Université de Bordeaux)

Lundi 20 octobre 2014 : "Routage compact en pratique. Peut-on router avec des tables de routage de taille 6 ?" - Nicolas Hanusse , (LaBRI, Université de Bordeaux)
Abstract: Le projet européen EULER portant sur des propositions de nouveaux schéma de routage vient de se terminer. Je ferai une petite présentation de nos contributions sur des algorithmes de routage compact pour lesquels nous obtenons des garanties sur l'étirement, la taille des tables ou le cout de construction. Des simulations sur des cartes des systèmes autonomes d'Internet montrent que nous pouvons obtenir des tables de petite taille ...

Ce travail a été fait avec Cyril Gavoille, Christian Glacet et David Ilcinkas.

Lundi 03 octobre 2014 : "k-Partitionnement auto-stabilisant " - Yvan Rivierre, (LaBRI, Université de Bordeaux)
Abstract: Le k-partitionnement organise un réseau comme suit : ses nœuds sous répartis en sous-ensembles disjoints appelés grappes et pour chaque grappe, un nœud appelé tête est distingué, de sorte que chaque nœud d'une grappe est au plus à k sauts de la tête de grappe. Une application possible est de faire du routage hiérarchique en suivant des chemins entre les têtes de grappe pour l'acheminement de messages à travers le réseau. Ceci est particulièrement intéressant dans les réseaux à large échelle où la probabilité de panne est élevée. Les fautes transitoires sont des pannes non-définitives qui n'affectent que le contenu du réseau et non son code ou sa structure. Un algorithme est auto-stabilisant s'il garantit au système, une fois que les fautes transitoires cessent, de récupérer un fonctionnement normal, en temps fini et sans intervention extérieure.

Dans cet exposé, nous considérerons le problème du k-partitionnement auto-stabilisant. Il faut noter que construire un k-partitionnement de taille minimum est un problème NP-difficile. Nous proposerons un algorithme auto-stabilisant de k-partitionnement et étudierons ses propriétés dans l'arbre, dans un graphe connexe et dans un graphe de disques unitaires. Cette dernière topologie est généralement utilisée pour modéliser des réseaux de capteurs sans fil.

Lundi 22 septembre 2014 : Soutenance de thèse de Pierre Halftermeyer : "Connexité dans les Réseaux et Schémas d’Étiquetage Compact d’Urgence " - Amphi du LaBRI, 14h30
Abstract: On cherche à attribuer à tout sommet x d’un graphe G (à n sommets) une étiquette L(x), idéalement de taille O(log n), permettant de répondre à des requêtes de connexité avec panne Conn(u,v,X). C’est-à-dire qu’on veut, après un pré-traitement en temps O(|X|) des étiquettes des sommets de l’ensemble «en panne» X, répondre à partir des seules étiquettes L(u) et L(v), en un temps optimal O(log log n), à la question : u et v sont-ils connectés dans G\X ? On tâchera de traiter ce problème dans les graphes de genre borné ainsi que dans les graphes excluant un mineur fixé.

Lundi 07 juillet 2014 : "Solo-fast Universal Constructions for Deterministic Abortable Objects" - Claire Capdevielle, (LaBRI, Université de Bordeaux)
Abstract: In the context of shared memory model, we present our study on efficient implementations for deterministic abortable objects. Deterministic abortable objects behave like ordinary objects when accessed sequentially, but they may return a special response abort to indicate that the operation failed (and did not take effect) when there is contention.

It is impossible to implement deterministic abortable objects only with read/write registers. Thus, we study solo-fast implementations. These implementations use stronger synchronization primitives, e.g., CAS, only when there is contention. We consider interval contention.

We present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal construction is a method for obtaining a concurrent implementation of any object from its sequential code. The construction is non-trivial since in the resulting implementation a failed process can cause only a finite number of operations to abort. Our construction guarantees that operations that do not modify the object always return a legal response and do not use CAS. Moreover in case of contention, at least one writing operation succeeds. We prove that our construction has asymptotically optimal space complexity for objects whose size is constant.

Lundi 30 juin 2014 : "Rendez-vous d'agents mobiles tolérant aux pannes" - Arnaud Labourel, (LIF, Université Aix-Marseille)
'Abstract: Les systèmes d’agents mobiles sont des environnements distribués dans lequel les nœuds du réseau sont passifs et ce sont des agents mobiles qui s’occupent de l’exécution de l’algorithme. Le réseau est représenté par un graphe et les agents peuvent se déplacer d’un nœud à l’autre du graphe le long de ses arêtes. Dans cet exposé, on va chercher à trouver des algorithmes permettant à deux agents mobiles initialement dispersé dans le graphe de se rencontrer sur un nœud du graphe. Plus particulièrement, on s'intéressera à ce problème pour un modèle synchrone dans lequel une panne peut se produire lors de chaque tentative de déplacement des agents. On considérera trois types de pannes possibles : probabiliste (probabilité constante de panne), adversaire non borné ou borné (un adversaire peut empêcher un agent de bouger pendant un nombre de rondes fini ou bien borné par une constante). Je donnerai des bornes inférieures et supérieures sur le coût du rendez-vous (nombre de déplacements des agents avant le rendez-vous dans le pire des cas) ainsi que des résultats d'impossibilité pour ces trois types de pannes.

Lundi 23 juin 2014 : "Maintenance d'arbres et détection de déconnexion" - Christian Glacet, (LaBRI, Université de Bordeaux)
Abstract:Dans ce travail, nous proposons un algorithme auto-stabilisant de maintenance d'arbres de plus de courts chemins tout en gérant la déconnexion de graphes dynamiques ... ce qui résoud le problème du comptage à l'infini sans connaissance sur le graphe. Ce travail a été fait avec Colette Johnen, David Ilcinkas et Nicolas Hanusse.

Lundi 16 juin 2014 : Allyx Fontaine soutient sa thèse "Analyse et preuves formelles d’algorithmes distribués probabilistes" - Amphi du LaBRI
Abstract:

Lundi 05 mai 2014 : "Le codage de réseau aléatoire : une introduction " - Christine Bachoc, (IMB, Université de Bordeaux)
Abstract:

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

Lundi 31 mars 2014 : "Algebraic Removal Lemma" - Oriol Serra ( Barcelona, Spain)
Abstract: The removal lemma is a combinatorial result which, in its simpler form, says that a graph with n vertices and o(n^3) triangles can be made triangle free by deleting o(n^2) edges. It was used by Ruzsa and Szemerédi to provide a simple proof of Roth's theorem on 3-term arithmetic progressions in dense sets of integers. An analogous algebraic statement was formulated by Green in terms of solutions of linear equations in abelian groups. In the talk I will report on some contributions made jointly with Dan Král' and Lluís Vena to this algebraic version for linear systems in abelian groups and some consequences in arithmetic Ramsey theory. The latter include a version of Szemerédi theorem on arithmetic progressions in dense sets of finite abelian groups.

P.S. : Il s'agit d'un exposé CPU.

Lundi 24 mars 2014 : "Exploration and Diffusion in Graphs using Deterministic Walks " - Adrian Kosowski (LaBRI)
Abstract: In a continuous diffusive process, a certain amount of a resource, known as "load", is initially placed on the nodes of the graph, possibly in an unfair manner. In successive time steps, each node shares its load evenly among all its neighbors, until the load on the nodes of the graph eventually converges to its limit distribution (e.g., becomes uniform in the case of regular graphs). However, continuous diffusion cannot be applied to "granular load" which is not arbitrarily divisible, i.e., represented by unsplittable unit-load tokens (chips), which are placed on nodes and may be passed around the graph. In such a scenario, one natural way of simulating the continuous diffusion process is to require that each chip follows an independent random walk on the graph.

In this talk, we will instead focus on chip diffusion processes following rules which are both locally fair and deterministic. These rules include the so-called "rotor walk", in which chips are propagated by each node to its neighbors in round-robin fashion and, more broadly, rules in which each node attempts to send out roughly the same number of tokens through each of its outgoing arcs.

We will start by providing a description of the evolution and limit behavior of the rotor walk on the n-node ring with K << n chips. For general graphs, we will show bounds on the "cover time" of a rotor walk system with K chips, proving that in a graph with m edges and diameter D, all nodes will have been visited at least once by some chip during the first O(mD / log K) steps of the process. Finally, we will relate the "blanket time" (the time until all nodes of the graph have been visited by chips a similar number of times) and the "diffusion time" (the time until all nodes all host a similar number of chips, for K >> n) of fair deterministic walks to analogous parameters of the random walk. The latter results allow us to design surprisingly simple and efficient deterministic algorithms for load balancing in the diffusive model.

This talk includes an overview of results presented at PODC'13, STACS'14, and some current work in progress (joint work with: P. Berenbrink, D. Dereniowski, R. Klasing, F. Mallmann-Trent, D. Pajak, T. Sauerwald, P. Uznanski).

Lundi 03 mars 2014 : "Algorithmes de mise à jour locale pour des graphes aléatoires" - Romaric Duvignau (LaBRI)
Abstract: Afin de modéliser l'évolution de réseaux logiques dynamiques, nous proposons de maintenir exactement une distribution donnée de graphes aléatoires lors d'une séquence arbitraire d'insertions et de suppressions de sommets. Nous nous plaçons dans un modèle local où nous n'avons pas accès à l'ensemble des sommets, mais supposons à la place l'accès à une primitive globale renvoyant un sommet aléatoire uniforme du graphe. Dans cet exposé, nous nous intéressons à maintenir la distribution uniforme dans les graphes k-sortants (graphes dirigés où tous les sommets ont degré sortant k). Nous présenterons plusieurs algorithmes d'insertion et de suppression pour le problème de maintenance, dont les plus efficaces sont asymptotiquement optimaux.

Lundi 24 février 2014 : "Distributed anonymous discrete function computation" - Julien Hendrickx(Univ. Louvain)
Abstract: We propose a model for deterministic distributed function computation by a network of identical and anonymous nodes:. In this model, each node has bounded computation and storage capabilities that do not grow with the network size. Furthermore, each node only knows its neighbors, not the entire graph. Our goal is to characterize the class of functions that can be computed within this model. We provide a necessary condition for computability which we show to be nearly sufficient, in the sense that every function that violates this condition can at least be approximated. The problem of computing (suitably rounded) averages in a distributed manner plays a central role in our development; we provide an algorithm that solves it in time that grows quadratically with the size of the network.

Lundi 17 février 2014 : "The interplay between multidimensional skylines and functional dependencies " - Sofian Maabout (LaBRI)
Abstract: We show how functional dependencies, which are agnostoc to the orders defined over the dimensions domains, can help to optimize skyline queries which, by opposition are based on orders. We present some theoretical and experimental results.

Lundi 10 février 2014 : "Algorithmes auto-stabilisants barvards" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)
Abstract: Dans le contexte des réseaux à grande échelle, la prise en compte des pannes est une nécessité évidente. Ce séminaire traite de l’auto-stabilisation, une méthode qui vise à concevoir des algorithmes distribués se « réparant d’eux-même » en cas de pannes transitoires pouvant impliquer toute modification arbitraire de l’état des processus. Plusieurs paramètres peuvent être pris en compte pour mesurer l’efficacité d’un algorithme auto-stabilisant, dont en particulier le temps de convergence et la complexité mémoire. L’importance du temps de convergence vient de la nécessité évidente pour un système de retrouver le plus rapidement possible un état valide après une panne. La nécessité de minimiser la mémoire vient, d’une part, de l’importance grandissante de réseaux offrant des espaces mémoires restreints, comme par exemple certains réseaux de capteurs, et, d’autre part, de l’intérêt de minimiser à la fois l’échange et le stockage d’information afin de limiter les potentialités de corruption de cette information. Lors de ce séminaire, nous traiterons de la minimisation de la mémoire au travers d'un exemple, à savoir le problème de l’élection d’un leader. Une borne inférieure de Ω(log n) bits de mémoire par noeud a été établie par Dolev, Gouda et Schneider (1999) pour ce problème fondamental. Cette borne n'est toutefois valable que pour des algorithmes silencieux, c'est-à-dire des algorithmes dont les registres ne sont plus modifiés lorsque le système a rejoint un état légitime. Nous verrons que, si l'on autorise l’algorithme à rester bavard (non-silencieux) même après avoir rejoint un état légitime, alors l’espace mémoire peut être amélioré d’un facteur au moins exponentiel.

Lundi 6 Janvier 2014 : "Self-stabilizing k-independent dominating set construction" - Colette Johnen(LaBRI)
Abstract: A k-independent dominating set is a k-independent set and a k-dominating set. A set of nodes, I, is k-independent if the distance between any pair of nodes in I is at least k+1. A set of nodes, D, is a k-dominating if every node is within distance k of a node of D.

I propose two self-self-stabilizing algorithm building k-independent dominating sets. The both algorithm (SID and FID) are silent, and they converge under the unfair distributed scheduler (the weakest scheduling assumption).

The algorithm FID reaches a terminal (also legitimate) configuration in at most 4n+k rounds, where n is the network size. The algorithm FID requires (k+1)log(n+1) bits per node.

The protocol SID is memory efficient : it requires only 2log((k+1)n+1)+1 bits per node. The computation of the convergence time of the protocol SID is opened question.

Lundi 16 Décembre 2013 : "Large-scale Data Stream Analysis" - Yann Busnel (LINA - Université de Nantes)
Abstract: L'objectif de cet exposé est de dresser un court état de l'art autour de l'analyse des flux de données à grande échelle, lesquels sont souvent utilisés pour du monitoring et de la sécurité, à la fois dans les réseaux et les systèmes distribués jusqu'à l'internet des objets. La problématique de ce champs de recherche consiste à extraire de l'information pertinente d'un flux de données en une passe unique (en raison de la taille du flux et de sa rapidité), et ne nécessitant qu'une quantité mémoire très faible et une puissance de calcul très limitée. Je présenterai ensuite les dernières applications utilisant nos résultats récents, lesquels vont de la détection d'intrusion, la détection de DDoS, l'échantillonnage, etc.

Lundi 9 Décembre 2013 : "Simulating weak shared memory" - David Bonnin (LaBRI)
Abstract: It is well known that in an asynchronous message-passing system with crash faults, one can emulate an atomic register providing that more than half of the processes are non-faulty. By contrast, when a majority of the processes may fail, simulating atomic register is not possible. I will talk about weak variants of atomic registers that can be simulated tolerating a majority of processes failures. Specifically, I will introduce a new class of registers, called $\alpha$-registers. We found a lower bound of $\alpha = M+1$ with $M=2f-n+2$ for these registers, and an explicit algorithm can emulate them with $\alpha = 2M-1$. I will also probably talk about other approaches on weak shared memory : $M$-colored registers, and $k$-splitters. This is a joint work with C. Travers.

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nicolas Bonichon (LaBRI)
Abstract: This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

Lundi 25 Novembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)
Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a maximal matching for anonymous rings. Their bit complexity and time complexity are $O(\sqrt{\log n})$ with high probability. These algorithms are optimal modulo a multiplicative constant. Beyond the complexity results, the interest of this work stands in the description and the analysis of these algorithms which may be easily generalised. Furthermore, these results show a separation between the complexity of the MIS problem (and of the maximal matching problem) on the one hand and the colouring problem on the other. Colouring can be computed only in $\Omega(\log n)$ rounds on rings with high probability, while MIS is shown to have a faster algorithm. This is in contrast to other models, in which MIS is at least as hard as colouring. This is joint work with Y. Métivier, J.M. Robson and A. Zemmari

Lundi 4 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)
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Lundi 28 Octobre 2013 : "The Case for Reliable Software Transactional Networking" - Petr Kuznetsov (Paristech)
Abstract: Software-defined networking (SDN) is a novel paradigm that out-sources the control of packet-forwarding switches to a set of software controllers. The most fundamental task of these controllers is the correct implementation of the network policy, i.e., the intended network behavior. In essence, such a policy specifies the rules by which packets must be forwarded across the network. We initiate the study of the SDN control plane as a distributed system.

We introduce a formal model describing the interaction between the data plane and a distributed control plane (consisting of a collection of fault-prone controllers). Then we formulate the problem of consistentcomposition of concurrent network policy updates. The composition is enabled via a transactional interface with all-or-nothing semantics, which allows us to reason about possibilities and impossibilities in controller synchronization.

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

Lundi 23 Septembre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Miroslaw Korzeniowski
Abstract: Decentralized monitoring and alarming systems can be an attractive alternative to centralized architectures. Distributed sensor nodes (e.g., in the smart grid's distribution network) are closer to an observed event than a global and remote observer or controller. This improves the visibility and response time of the system. Moreover, in a distributed system, local problems may also be handled locally and without overloading the communication network.

This article initiates the study of alarming from a distributed computing perspective and under two fundamentally different scenarios: \emph{on-duty} and \emph{off-duty}. We model the alarming system as a sensor network consisting of a set of distributed nodes performing local measurements to sense events. In order to avoid false alarms, the sensor nodes cooperate and only escalate an event (i.e., raise an alarm) if the number of sensor nodes sensing an event exceeds a certain threshold. In the on-duty scenario, nodes not affected by the event can actively help in the communication process, while in the off-duty scenario non-event nodes are inactive.

This article presents and analyzes algorithms that minimize the reaction time of the monitoring system while avoiding unnecessary message transmissions. Moreover, lower bounds are derived that shed light on the limitations of distributed alarming systems.

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)
Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

Lundi 8 Juillet 2013 : "Dynamic Resource Allocation in Cloud Computing platforms" - Lionel Eyraud-Dubois (Labri)
Abstract: Je présente un problème d'allocation de ressources dans le contexte du Cloud Computing, où un ensemble de machines virtuelles (VM) doivent être allouées sur un ensemble de machines physiques (PMs). La particularité de ce problème vient du fait que la quantité de ressources dont chaque VM a besoin change au cours du temps, et qu'il est possible pour le fournisseur d'accès de changer l'allocation d'une VM par une opération de migration. Ce problème peut se modéliser sous la forme d'un problème de bin packing complètement dynamique, et je présente un algorithme d'approximation pour minimiser le nombre de PMs utilisées, tout en garantissant un petit nombre de migrations. Les propriétés de cet algorithme permettent également d'envisager une version distribuée.

Lundi 10 Juin 2013 : " The Heard-Of model: computing in distributed systems with benign failures" - Bernadette Charron-Bost (CNRS, Ecole polytechnique, Paris)
Abstract: Problems in fault-tolerant distributed computing have been studied in a va- riety of system models. These models are all based on the principle that it is usefull and even necessary to specify why and by whom errors occur. In this talk, we question this principle, and present a general computational model, called the Heard-Of model, suitable for describing any type of system, be it message passing, shared memory, synchronous, or asynchronous. In this model, computations evolve in rounds, and communication missed at a round is definitely lost. Only information transmission is represented: for each round r and each process p, our model specifies the set of processes that p “hears of” at round r (heard-of set) namely the processes from which p receives some message at round r. The features of a specific system are thus captured as a whole, just by a predicate over the collection of heard-of sets. Thus the Heard-Of model allows us to handle all types of benign failures, static or dynamic, permanent or transient, in a unified framework. Moreover, it unifies the most seemingly unrelated notions in distributing computing, namely synchrony and asynchrony. We further demonstrate how this unifying framework leads to new results and insights in fault-tolerant distributed computing. In particular, we show that some fundamental results for asynchronous systems can be advantageously transferred to synchronous systems. We also examine Consensus algorithms in the Heard-Of model: we show how our approach allows us to devise new solutions and to give simple correctness proofs of existing algorithms like Paxos.

Joint work with André Schiper, EPFL

Lundi 3 Juin 2013 : "Introduction to renaming" - Corentin Travers (Labri)
Abstract: Renaming is a fundamental coordination problem in distributed computing. It consists in assigning new names taken from a small name space to processes in such a way that no two processes obtain the same name. The talk will survey renaming algorithms suited for different models of distributed computing, including the wait-free shared memory and the synchronous crash-prone message-passing models.

Lundi 27 Mai 2013 : " Exploration des graphes dynamiques T-intervalle-connexes : le cas de l'anneau" - Wade Ahmed (Labri)
Abstract: Dans cet exposé, je vais parler de l'étude des graphes dynamiques T-intervalle-connexes du point de vue du temps nécessaire à leur exploration par une entité mobile (agent). Un graphe dynamique est T-intervalle-connexe (T \geq 1) si pour chaque fenêtre de T unités de temps, il existe un sous-graphe couvrant connexe stable. Cette propriété de stabilité de connexion au cours du temps a été introduite par Kuhn, Lynch et Oshman~\cite{KLO10} (STOC 2010). Nous nous concentrons sur le cas où le graphe sous-jacent est un anneau de taille n et nous montrons que la complexité en temps en pire cas est de 2n-T-\Theta(1) unités de temps si l'agent connaît la dynamique du graphe, et n+ \frac{n}{\max\{1,T-1\}} (\delta-1) \pm \Theta(\delta) unités de temps sinon, où \delta est le temps maximum entre deux apparitions successives d'une arête.

Keywords : Graphe dynamique, exploration, T-intervalle-connexité, agent mobile

Lundi 13 Mai 2013 : " Calcul Distribué et Fouille de Données" - Nicolas Hanusse (Labri)
Abstract: L'avènement de la production massive de données et la volonté de les exploiter sont limités par les systèmes de gestion de bases de données relationnelles classiques. Cet exposé consiste en une discussion sur les enjeux et problèmes algorithmiques engendrés par le calcul distribué et parallèle. Le calcul de corrélations servira d'illustration. C'est un travail en cours avec Sofian Maabout et Eve Garnaud.

Lundi 22 Avril 2013 : " A peer-to-peer-based virtual environment system" - Eliya Buyukkaya (ENSSAT-Université de Rennes I)
Abstract: Virtual environments (VEs) are 3-D virtual worlds in which a huge number of participants play roles and interact with their surroundings through virtual representations called avatars. VEs are traditionally supported by a client/server architecture. However, centralized architectures can lead to bottleneck on the server due to high communication and computation overhead during peak loads. Thus, P2P overlay networks are emerging as a promising architecture for VEs. However, exploiting P2P schemes in VEs is not straightforward, and several challenging issues related to data distribution and state consistency should be considered.

One of the key aspects of P2P-based VEs is the logical platform consisting of connectivity, communication and data architectures, on which the VE is based. The connectivity architecture is the overlay topology structure, which defines how peers are connected to each other. The communication architecture is the routing protocol defining how peers can exchange messages, while the data architecture defines how data are distributed over the logical overlay. The design of these architectures has significant influence on the performance and scalability of VEs.

First, we propose a scalable connectivity architecture based on a new triangulation algorithm reducing maintenance cost of the system. Second, we construct a communication architecture built on top of the connectivity architecture ensuring that each message reaches its intended destination. Finally, we propose a data architecture ensuring the management of data with different characteristics in terms of mobility in the VE, while providing a fair data distribution and low data transfer between peers in the VE.

Lundi 15 Avril 2013 : " Algorithms for the Vertex Cover Problem on Large Graphs with Low Memory Capacities" - Romain Campigotto (LIP6-Paris)
Abstract: Most of the known optimization algorithms need to explore, mark, modify, etc. the instance given as input before producing their results. To do that, the instance is entirely loaded into the memory of the computer and is manipulated by the algorithm. Often, "extra" data structures are also necessary to memorize parameters useful all along the computation or to update the current solution that will be returned as the final product of the program. However, this classical model is no more adapted for many new computing applications. Indeed, nowadays, many fields such as biology, meteorology, finance, etc. produce very large amount of data.

In our works, we have focused on the Vertex Cover problem on huge graphs: in the intrinsic NP-completeness is added the difficulty to manipulate graphs with severe constraints (mainly related to the low memory capacities). We defined a treatment model combining some properties of several existing models in the literature: streaming, online, I/O-efficient, etc. We initially considered three approximation algorithms, which are memory-efficient (they use a memory space in O(log n) bits). We analyzed their performance in terms of solution quality and complexity, in mean and worst cases. We then focused on algorithms that use memory space of n bits. We showed that it could be very worst with strictly less than n bits memory space. Subsequently, we conducted experiments on very large graphs (in the order of billions of vertices and edges). This study showed that in practice, memory-efficient algorithms are better suited to handle large graphs.

This is joint work with Eric Angel (IBISC, Univ. Évry) and Christian Laforest (LIMOS, ISIMA, Clermont-Ferrand).

Lundi 8 Avril 2013 : "Implémentation d'algorithmes distribués à l'aide de Visidia" - Mohamed Mosbah (Labri)
Abstract: Dans le cadre du projet visidia, une plate-forme logicielle est développée pour l'implantation et la visualisation d'algorithmes distribués. Après une introduction et quelques rappels, l'exposé consistera en une présentation de la plate-forme et de son utilisation pour programmer des exemples d'algorithmes. L'interface et l'API permettent de visualiser l'exécution d'algorithmes, d'implanter de nouveaux algorithmes, ou d'effectuer des statistiques. Les algorithmes peuvent être exprimés selon plusieurs modèles (calculs locaux, passage de messages, agents mobiles).

Lundi 25 Mars 2013 : "Simultaneous Consensus vs Set Agreement." - Zohir Bouzid (LIP6-Paris)
Abstract: In the traditional consensus task, processes are required to agree on a common value chosen among the initial values of the participants. It is well known that consensus cannot be solved in crashed-prone, asynchronous distributed systems. Two generalizations of the consensus problem have been introduced: k-set agreement and k-simultaneous consensus. The k-set agreement task has the same requirements as consensus except that processes are allowed to decide up to k distinct values. In the k-simultaneous consensus task, each process participates simultaneously in k instances of consensus and is required to decide in at least one of them; any two processes deciding in the same instance must decide the same value. In this talk, we compare the computability of these problems in two central models in distributed computing: shared memory and message passing. We show that even though the two problems are equivalent in shared memory, k-simultaneous consensus is strictly harder than k-set agreement in the message passing model. This result will serve as a basis for a discussion about different models of computation and their respective power.

Lundi 18 Mars 2013 : "Vers une classification des réseaux dynamiques en fonction des problèmes qu'on peut y résoudre." - Arnaud Casteigts (Labri)
Abstract: Derrière les notions de "graphe dynamique" ou de "réseau dynamique" se cache une très grande diversité de scénarios et d'hypothèses, allant de réseaux semi-statiques où la connexité est toujours assurée à des réseaux complètement mobiles, où la connexité ne s'établit qu'à travers le temps et l'espace (e.g. DTNs). Dans cet exposé, résolument transversal, je présenterai l'état d'avancement de nos recherches autour de la question suivante : quel lien existe-t-il entre la "faisabilité" de tâches distribuées et la dynamique du réseau. Les hypothèses résultantes sur la dynamique peuvent être vues comme autant de classes de graphes (ou alternativement, comme autant de puissances possibles pour un adversaire qui contrôlerait la topologie). Nous avons à ce jour caractérisé et/ou recensé une petite vingtaine de classes de ce type.

Certains de ces travaux ont été menés en collaboration avec Serge Chaumette et Afonso Ferreira. D'autres avec Paola Flocchini et Nicola Santoro.

Lundi 25 Février 2013 : "Sur les 1001 modèles en algorithmique distribuée." - Yves Metivier (Labri)
Abstract: Le but de cet "exposé-discussion" est de présenter quelques modèles en algorithmique distribuée et d'échanger sur leurs liens et leurs mérites.

Lundi 18 Février 2013 : "Distributed Calculation of Graph Diameter" - Mike Robson (Labri)
Abstract: We consider the problem of calculating the diameter of a graph given that there is a single vertex "Leader" and neighbouring vertices can exchange messages of a single bit at each round. We show that this can be achieved in the same O(n) time complexity as well known algorithms without this bound on message length. The techniques used can be applied to a number of other graph computations. We consider briefly how the algorithm behaves if applied in a situation where more than one vertex considers itself the Leader.

This is joint work with Yves Métivier and Akka Zemmari.

Lundi 11 Février 2013 : "Bounds for Communication in Wireless Grids" - Joseph Peters (Simon Fraser University)
Abstract: In a wireless network, a transmission can be received by a node if it is close enough to the sender. However, transmissions can interfere with each other and the interference distance is typically greater than the reception distance. Efficient communication protocols in these networks minimize the time to move information without interference. In this talk, I will describe optimal protocols for the problem of collecting information into a central node of a two-dimensional square or hexagonal grid graph. The optimality of the protocols is proved using a new lower bound technique that is an adaptation to a discrete environment of a method based on linear programming duality for continuous flows.

This is joint work with Jean-Claude Bermond, CNRS-INRIA-University of Nice.

Lundi 04 Février 2013 : "Distributed Detection of Clone Attacks in Wireless Sensor Networks" - Mauro Conti (University of Padua, Italy)
Abstract: Wireless Sensor Networks (WSNs) are often deployed in hostile environments where an adversary can physically capture some of the nodes, first can reprogram, and then, can replicate them in a large number of clones, easily taking control over the network. A few distributed solutions to address this fundamental problem have been recently proposed. However, these solutions are not satisfactory. First, they are energy and memory demanding: A serious drawback for any protocol to be used in the WSN-resource-constrained environment. Further, they are vulnerable to the specific adversary models that we introduced. The contributions of our work are threefold. First, we analyze the desirable properties of a distributed mechanism for the detection of node replication attacks. Second, we show that the known solutions for this problem do not completely meet our requirements. Third, we propose a new self-healing, Randomized, Efficient, and Distributed (RED) protocol for the detection of node replication attacks, and we show that it satisfies the introduced requirements. Finally, extensive simulations show that our protocol is highly efficient in communication, memory, and computation; is much more effective than competing solutions in the literature; and is resistant to the new kind of attacks introduced in our work, while other solutions are not.

Lundi 28 Janvier 2013 : "Distributed Exclusive Graph Searching in Trees" - Janna Burman (LRI-Université Paris-Sud)
Abstract: We consider a version of the well known graph searching problem, where a team of robots aims at clearing the contaminated edges of a graph. We study graph searching in the model of mobile computing where autonomous deterministic robots move between the graph nodes when operating in asynchronous cycles of Look-Compute-Move. Moreover, motivated by physical constraints, following some recent works, we consider the exclusivity property, stating that no two or more robots can occupy a same node at the same time. In addition, we assume that all the graph elements and the robots are anonymous. Robots are oblivious and have no sense of direction. Our objective is to characterize for a graph $G$, the set of integers $k$ such that graph searching can be achieved by a team of $k$ robots starting from any $k$ distinct nodes in $G$. Our main result consists in a full characterization for any asymmetric tree. Towards providing a characterization in the general case, including trees with non-trivial automorphisms, we provide a set of positive and negative results, including a full characterization for any line. All our positive results are based on the design of algorithms enabling perpetual graph searching to be achieved with the desired number of robots. We prove that, in addition to the distributed nature of our setting, the exclusivity property has a significant impact on the nature of the graph searching problem. Hence, the design of the algorithms requires to invent new methods.

Lundi 21 Janvier 2013 : "Présentation de Keep Alert, une solution pour la surveillance de marques sur Internet" - Anthony Don (Keep Alert)
Abstract: A destination des cabinets de propriété industrielle et des services juridiques, Keep Alert propose des surveillances de marque parmi les noms de domaine, les régies publicitaires et les réseaux sociaux. Anthony DON, directeur technique chez Keep Alert, présentera au groupe de travail, le fonctionnement global de la plateforme, puis abordera les problématiques actuelles et les perspectives de développement relatives à l'algorithmique distribuée.

Lundi 14 Janvier 2013 : "Two Monte-Carlo Election Algorithms for Anonymous Graphs without any Initial Knowledge" - Akka Zemmari (Labri)
Abstract: The paper proposes and analyses two Monte Carlo election algorithms for anonymous graphs without any initial knowledge. Both have a time complexity equal to $O(D)$, where $D$ is the diameter of the graph. The first is correct with probability $1-o(n^{-1})$ (where $n$ is the size of the graph). The size of messages is $O(\log n)$ with probability $1-o(n^{-1})$ and the expected value of the size of messages is also $O(\log n)$. The second is correct with probability $1-o(n^{-c})$ for any $c\geq 1$. The size of messages is $O\left((\log n)(\log^* n)^2 \right)$ with probability $1-o(n^{-c})$ for any $c\geq 1$; their expected size is $O\left((\log n)(\log^* n) \right)$.

This is a joint work with Y. Métivier and J. M. Robson

Lundi 10 Décembre 2012 : pas de seminaire. Soutenance de thèse-Florent Foucaud.

Lundi 3 Décembre 2012 : "Progress and Challenges for Labeling Schemes" - Cyril Gavoille (Labri)
Abstract: A fundamental question in Distributed Computing is to understand how localized and how much information are required to solve a task on a network. Typically, if the distance between any pair x,y of nodes in a network is asked, we would like to know which minimal information about x and y in the network are needed. The goal in labeling schemes is precisely to understand how much information must be attached to the nodes (formalized as labels) to solve a graph problem assuming the answer can be determined solely on the basis of the labels of the nodes invoked in the query. In this talk, I give a survey on labeling schemes, present some recent results with their techniques, and highlight new challenges.

Lundi 26 Novembre 2012: "Competitive Routing on a Variant of the Delaunay Triangulation" - Prosenjit Bose (Carleton University)
Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we showed how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.

Lundi 19 Novembre 2012: " Reliable Service Allocation in Clouds"- Lionel Eyraud-Dubois, Olivier Beaumont (Labri)
Abstract: We consider several reliability problems that arise when allocating applications to processing resources in a Cloud computing platform. More specifically, we assume on the one hand that each computing resource is associated to a capacity constraint and to a probability of failure. On the other hand, we assume that each service runs as a set of independent instances of identical Virtual Machines, and that the Service Level Agreement between the Cloud provider and the client states that a minimal number of instances of the service should run with a given probability. In this context, given the capacity and failure probabilities of the machines, and the capacity and reliability demands of the services, the question for the cloud provider is to find an allocation of the instances of the services (possibly using replication) onto machines satisfying all types of constraints. In this paper, our goal is to assess the impact of the reliability constraint on the complexity of resource allocation problems. We consider several variants this problem, depending on the number of services (one or many) and if their reliability demand is individual or global. We prove several fundamental complexity results ($\#$P and NP-completeness results) and we provide several optimal and approximation algorithms. In particular, we prove that a basic randomized allocation algorithm, that is easy to implement, provides optimal or quasi-optimal results in several contexts, and we show through simulations that it also achieves very good results in more general settings.

Lundi 12 Novembre 2012 : "MAXIMUM MATCHING IN MULTI-INTERFACE NETWORK"- Dominik Pająk (LaBRI)
Abstract: In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

Lundi 5 Novembre 2012 : pas de séminaire
Lundi 22 Octobre 2012 : Christian Glacet (LaBRI)
Lundi 15 Octobre: " NETWORK VERIFICATION VIA ROUTING TABLE QUERIES" - Ralf Klasing (LaBRI)
Abstract: We address the problem of verifying the accuracy of a map of a network by making as few measurements as possible on its nodes. This task can be formalized as an optimization problem that, given a graph G=(V,E), and a query model specifying the information returned by a query at a node, asks for finding a minimum-size subset of nodes of G to be queried so as to univocally identify G. This problem has been faced w.r.t. a couple of query models assuming that a node had some global knowledge about the network. Here, we propose a new query model based on the local knowledge a node instead usually has. Quite naturally, we assume that a query at a given node returns the associated routing table, i.e., a set of entries which provides, for each destination node, a corresponding (set of) first-hop node(s) along an underlying shortest path. First, we show that any network of n nodes needs Omega(log log n) queries to be verified. Then, we prove that there is no o(log n)-approximation algorithm for the problem, unless P=NP, even for networks of diameter 2. On the positive side, we provide an O(logn)-approximation algorithm to verify a network of diameter 2, and we give exact polynomial-time algorithms for paths, trees, and cycles of even length.

Lundi 8 Octobre 2012 : pas de séminaire
Lundi 1er Octobre 2012 : Réunion de rentrée du thème - Nicolas Hanusse (LaBRI)
Abstract: L'ordre du jour:

• projets: thèse, région, ingénieur, conférence
• organisation du groupe de travail: exposé à venir (projets à long terme, discussion sur les modèles, logiciels, ...), vitrine
• mise-à-jour site web
• enseignement: état des lieux des enseignements locaux
• stages X, ENS, ...

Lundi 21 Juin : "ABOUT RANDOMISED DISTRIBUTED GRAPH COLOURING AND GRAPH PARTITION ALGORITHMS" - Akka Zemmari (LaBRI)
Abstract: We present and analyse a very simple randomised distributed vertex colouring algorithm for arbitrary graphs of size $n$ that halts in time $O(log n)$ with probability $1-o(n^{-1}).$ Each message containing $1$ bit, its bit complexity per channel is $O(log n)$.
From this algorithm, we deduce and analyse a randomised distributed vertex colouring algorithm for arbitrary graphs of maximum degree $Delta$ and size $n$ that uses $Delta+1$ colours and halts in time $O(log n)$ with probability $1-o(n^{-1}).$
We also obtain a partition algorithm for arbitrary graphs of size $n$ that builds a spanning forest in time $O(log n)$ with probability $1-o(n^{-1})$. We study some parameters such as the number, the size or the radius of trees of the spanning forest.
We assume that graphs are anonymous; we only assume that each vertex distinguishes between its neighbours by locally known channel names. Furthermore we do not assume that the size (or an upper bound on the size) of graphs is known.
Joint work with Y. Métivier, N. Saheb and J.M. Robson

Lundi 14 Juin : Almost optimal asynchronous rendezvous in infinite multidimensional grids - Arnaud Labourel (LaBRI)
Abstract: Dans cet exposé, je montrerais comment deux agents mobiles peuvent se rencontrer dans une grille infinie de dimension supérieure à 2. On considère le modèle asynchrone. C'est-à-dire que la durée de traversée de chaque sommet par un agent est déterminée par un adversaire omniscient qui essaye d'empêcher le rendez-vous. On supposera que chaque agent connait sa position dans la grille mais pas celle de l'autre agent. Cette connaissance permet d'avoir un algorithme de rendez-vous ayant un coût, mesuré en terme de distance parcourue par les agents, quasiment optimal.

19 janvier 2015 à 20h33 par 81.67.198.101 -
Lignes 12-13 modifiées:

Lundi 26 janvier 2015 : 'Periodic Data Retrieval in asynchronous rings with a malicious host' - Evangelos Bampas (LaBRI, Université de Bordeaux)

en:

Lundi 26 janvier 2015 : Periodic Data Retrieval in asynchronous rings with a malicious host - Evangelos Bampas (LaBRI, Université de Bordeaux)

Lignes 23-474 modifiées:

L'expansion, au cours des deux dernières décennies des réseaux, et notamment d'Internet, a engendré une création importante de données, massives de par leur nombre et leur taille. De ce fait, des systèmes de stockages distribués (comme Cassandra par exemple) sont utilisés en pratique afin de stocker ces données.

Deux problématiques se posent alors : (1) comment répartir les données? (2) comment optimiser le traitement des requêtes sur ces données?

Nous nous intéressons ici à l'équilibrage des requêtes entre les différents noeuds d'un système distribué. Notre approche consiste à utiliser la réplication d'objet et nous proposons différents algorithmes d'affectation des requêtes en cherchant à optimiser le temps de complétion (temps de traitement) des requêtes.

(Travail en cours avec Nicolas Hanusse)

Lundi 12 janvier 2015 : "Distributedly Testing Cycle-Freeness" - David Ilcinkas (LaBRI, CNRS and Université de Bordeaux)
Abstract: We tackle local distributed testing of graph properties. This framework is well suited to contexts in which data dispersed among the nodes of a network can be collected by some central authority (like in, e.g., sensor networks). In local distributed testing, each node can provide the central authority with just a few information about what it perceives from its neighboring environment, and, based on the collected information, the central authority is aiming at deciding whether or not the network satisfies some property. We analyze in depth the prominent example of checking \emph{cycle-freeness}, and establish tight bounds on the amount of information to be transferred by each node to the central authority for deciding cycle-freeness. In particular, we show that distributedly testing cycle-freeness requires at least $\ceil{\log d}-1$ bits of information per node in graphs with maximum degree~$d$, even for connected graphs. Our proof is based on a novel version of the seminal result by Naor and Stockmeyer (1995) enabling to reduce the study of certain kinds of algorithms to order-invariant algorithms, and on an appropriate use of the known fact that every free group can be linearly ordered.

# Exposés passés

Lundi 15 décembre 2014 : "Splitting and renaming with a majority of faulty processes" - David Bonnin (LaBRI, Université de Bordeaux)
Abstract: The renaming problem has been introduced by Attiya et al. [1], and consists on the following : Each process start with a unique name in a large namespace (such as an IP address), and each process tries to acquire a new name such as, at the end of the algorithm, each process has a new unique name in a much smaller namespace. This problem was first solved in asynchronous message-passing systems with a strict minority of processes that might crash, and later largely studied in wait-free shared memory systems, which can themselves be simulated in the former model (as explained in [2]). Splitters are basic shared memory objects that were introduced in [3] in order to build a fast renaming algorithm, and extending the renaming to a long-lived'' version. A splitter is an object that can be accessed through one operation Split(), and returns a direction in {right, down, stop}, with the property that not all processes return right, not all return down, and at most 1 process may return stop.

In asynchronous message-passing systems with a majority of faulty processes, the renaming problem cannot be solved, and splitters cannot be implemented. But we extended these notions to k-renaming and k-splitters, both for one-shot and long-lived versions. Instead of having unique name for each process, each new name (in a small namespace) may be acquired by at most k processes, and at most k processes accessing a k-splitter may return stop. We developed an optimal algorithm for implementing k-splitters, i.e. the algorithm implements them with k = floor(n/(n-f)), where n in the number of processes and f the maximal number of faulty processes among them, and it is not possible to implement k'-splitters with k' < floor(n/(n-f)). Although the namespace is not optimal, especially in the long-lived version, k-renaming based on these k-splitters is optimal for the same reason that k=floor(n/(n-f)) is both a lower bound, and a reached upper bound.

[1] H. Attiya, A. Bar-Noy, D. Dolev, D. Peleg, and R. Reischuk. Renaming in an asynchronous environment. J. ACM, 37(3):524–548, July 1990. [2] H. Attiya, A. Bar-Noy, and D. Dolev. Sharing memory robustly in message-passing systems. J. ACM, 42(1):124–142, 1995. [3] M. Moir and J. H. Anderson. Wait-free algorithms for fast, long-lived renaming. Science of Computer Programming, 25(1):1 – 39, 1995.

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz et Matthieu Barjon, (LaBRI, Université de Bordeaux)

Lundi 01 décembre 2014 : "Towards a General Framework for Searching on a Line and Searching on m Rays" - Jean-Lou De Carufel (Carleton University)
Abstract: We revisit the problem of searching for a target at an unknown location on a line when given upper and lower bounds on the distance D that separates the initial position of the searcher from the target. We present tight bounds on the exact optimal competitive ratio achievable, parameterized in terms of the given range for D, along with an optimal search strategy that achieves this competitive ratio.

We present an optimal search strategy for the case where a fixed turn cost t is charged every time the searcher changes direction. Moreover, we generalize our results to the framework where the cost of moving distance x away from the origin is a x + b and the cost of moving distance y towards the origin is c y + d for constants a, b, c and d.

This is joint work with Prosenjit Bose (Carleton U.) and Stephane Durocher (U. of Manitoba).

Lundi 24 novembre 2014 : "ON THE POWER OF ONE BIT: HOW TO EXPLORE A GRAPH WHEN YOU CANNOT BACKTRACK?" - Dominik Pajak, (University of Cambridge)
Abstract: We study the problem of exploration of an anonymous undirected graph with n vertices, m edges and diameter D by a single mobile agent. The agent does not know the incoming port when entering to a vertex thus it cannot backtrack its moves. Each vertex of the graph is endowed with a whiteboard on which the agent can store information.

In this talk we will study tradeoffs between the exploration time and the existence of the internal memory available to the agent. We will first show an algorithm for an agent with 1 bit of memory completing exploration of any graph with stop in time O(m) using whiteboards of size O(log Delta) on each vertex with degree Delta.

An oblivious agent (with no internal memory) can explore any graph in time O(m D) using whiteboards of size O(log Delta) by applying the rotor-router mechanism. We will show that, even with unbounded whiteboards, there is no algorithm for oblivious agents that is better than the rotor-router in the worst case by showing a Omega(n3) lower bound for a specific class of graphs. We will also observe that any oblivious agent cannot stop after completing the task. This shows separation between oblivious and non-oblivious agents in terms of the exploration time and the stop property.

Lundi 17 novembre 2014 : "Group Search on the Line" - Leszek Gasieniec (University of Liverpool)

Lundi 10 novembre 2014 : "Patrolling by unreliable mobile robots" - Jurek Czyzowicz (Université du Québec en Outaouais)
Abstract: Mobile robots collaborate in order to solve efficiently the central problems in algorithmics of distributed computing like searching/exploration, rendez-vous or pattern formation. Patrolling is a perpetual traversal of an environment by a collection of mobile robots. The standard measure of efficiency of a patrolling algorithm is defined by its idleness – the minimal time interval during which every point of the environment is always visited by at least one robot. Boundary patrolling and fence patrolling were fundamental problems investigated by the robotics community in the last decade.

We sketch briefly previous results concerning the algorithms for the boundary and fence-patrolling problem. When some (unknown) robots of the collection cannot perform their duties, the fence patrolling algorithms become surprisingly unnatural. In more details we discuss a new algorithm for patrolling by unreliable robots. We show that the presented algorithm achieves the idleness, which is the best possible.

Lundi 03 novembre 2014 : "Coloration d'un cycle en temps log*(n): borne sup et borne inf" - Cyril Gavoille, (LaBRI, Université de Bordeaux)

Lundi 20 octobre 2014 : "Routage compact en pratique. Peut-on router avec des tables de routage de taille 6 ?" - Nicolas Hanusse , (LaBRI, Université de Bordeaux)
Abstract: Le projet européen EULER portant sur des propositions de nouveaux schéma de routage vient de se terminer. Je ferai une petite présentation de nos contributions sur des algorithmes de routage compact pour lesquels nous obtenons des garanties sur l'étirement, la taille des tables ou le cout de construction. Des simulations sur des cartes des systèmes autonomes d'Internet montrent que nous pouvons obtenir des tables de petite taille ...

Ce travail a été fait avec Cyril Gavoille, Christian Glacet et David Ilcinkas.

Lundi 03 octobre 2014 : "k-Partitionnement auto-stabilisant " - Yvan Rivierre, (LaBRI, Université de Bordeaux)
Abstract: Le k-partitionnement organise un réseau comme suit : ses nœuds sous répartis en sous-ensembles disjoints appelés grappes et pour chaque grappe, un nœud appelé tête est distingué, de sorte que chaque nœud d'une grappe est au plus à k sauts de la tête de grappe. Une application possible est de faire du routage hiérarchique en suivant des chemins entre les têtes de grappe pour l'acheminement de messages à travers le réseau. Ceci est particulièrement intéressant dans les réseaux à large échelle où la probabilité de panne est élevée. Les fautes transitoires sont des pannes non-définitives qui n'affectent que le contenu du réseau et non son code ou sa structure. Un algorithme est auto-stabilisant s'il garantit au système, une fois que les fautes transitoires cessent, de récupérer un fonctionnement normal, en temps fini et sans intervention extérieure.

Dans cet exposé, nous considérerons le problème du k-partitionnement auto-stabilisant. Il faut noter que construire un k-partitionnement de taille minimum est un problème NP-difficile. Nous proposerons un algorithme auto-stabilisant de k-partitionnement et étudierons ses propriétés dans l'arbre, dans un graphe connexe et dans un graphe de disques unitaires. Cette dernière topologie est généralement utilisée pour modéliser des réseaux de capteurs sans fil.

Lundi 22 septembre 2014 : Soutenance de thèse de Pierre Halftermeyer : "Connexité dans les Réseaux et Schémas d’Étiquetage Compact d’Urgence " - Amphi du LaBRI, 14h30
Abstract: On cherche à attribuer à tout sommet x d’un graphe G (à n sommets) une étiquette L(x), idéalement de taille O(log n), permettant de répondre à des requêtes de connexité avec panne Conn(u,v,X). C’est-à-dire qu’on veut, après un pré-traitement en temps O(|X|) des étiquettes des sommets de l’ensemble «en panne» X, répondre à partir des seules étiquettes L(u) et L(v), en un temps optimal O(log log n), à la question : u et v sont-ils connectés dans G\X ? On tâchera de traiter ce problème dans les graphes de genre borné ainsi que dans les graphes excluant un mineur fixé.

Lundi 07 juillet 2014 : "Solo-fast Universal Constructions for Deterministic Abortable Objects" - Claire Capdevielle, (LaBRI, Université de Bordeaux)
Abstract: In the context of shared memory model, we present our study on efficient implementations for deterministic abortable objects. Deterministic abortable objects behave like ordinary objects when accessed sequentially, but they may return a special response abort to indicate that the operation failed (and did not take effect) when there is contention.

It is impossible to implement deterministic abortable objects only with read/write registers. Thus, we study solo-fast implementations. These implementations use stronger synchronization primitives, e.g., CAS, only when there is contention. We consider interval contention.

We present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal construction is a method for obtaining a concurrent implementation of any object from its sequential code. The construction is non-trivial since in the resulting implementation a failed process can cause only a finite number of operations to abort. Our construction guarantees that operations that do not modify the object always return a legal response and do not use CAS. Moreover in case of contention, at least one writing operation succeeds. We prove that our construction has asymptotically optimal space complexity for objects whose size is constant.

Lundi 30 juin 2014 : "Rendez-vous d'agents mobiles tolérant aux pannes" - Arnaud Labourel, (LIF, Université Aix-Marseille)
'Abstract: Les systèmes d’agents mobiles sont des environnements distribués dans lequel les nœuds du réseau sont passifs et ce sont des agents mobiles qui s’occupent de l’exécution de l’algorithme. Le réseau est représenté par un graphe et les agents peuvent se déplacer d’un nœud à l’autre du graphe le long de ses arêtes. Dans cet exposé, on va chercher à trouver des algorithmes permettant à deux agents mobiles initialement dispersé dans le graphe de se rencontrer sur un nœud du graphe. Plus particulièrement, on s'intéressera à ce problème pour un modèle synchrone dans lequel une panne peut se produire lors de chaque tentative de déplacement des agents. On considérera trois types de pannes possibles : probabiliste (probabilité constante de panne), adversaire non borné ou borné (un adversaire peut empêcher un agent de bouger pendant un nombre de rondes fini ou bien borné par une constante). Je donnerai des bornes inférieures et supérieures sur le coût du rendez-vous (nombre de déplacements des agents avant le rendez-vous dans le pire des cas) ainsi que des résultats d'impossibilité pour ces trois types de pannes.

Lundi 23 juin 2014 : "Maintenance d'arbres et détection de déconnexion" - Christian Glacet, (LaBRI, Université de Bordeaux)
Abstract:Dans ce travail, nous proposons un algorithme auto-stabilisant de maintenance d'arbres de plus de courts chemins tout en gérant la déconnexion de graphes dynamiques ... ce qui résoud le problème du comptage à l'infini sans connaissance sur le graphe. Ce travail a été fait avec Colette Johnen, David Ilcinkas et Nicolas Hanusse.

Lundi 16 juin 2014 : Allyx Fontaine soutient sa thèse "Analyse et preuves formelles d’algorithmes distribués probabilistes" - Amphi du LaBRI
Abstract:

Lundi 05 mai 2014 : "Le codage de réseau aléatoire : une introduction " - Christine Bachoc, (IMB, Université de Bordeaux)
Abstract:

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

Lundi 31 mars 2014 : "Algebraic Removal Lemma" - Oriol Serra ( Barcelona, Spain)
Abstract: The removal lemma is a combinatorial result which, in its simpler form, says that a graph with n vertices and o(n^3) triangles can be made triangle free by deleting o(n^2) edges. It was used by Ruzsa and Szemerédi to provide a simple proof of Roth's theorem on 3-term arithmetic progressions in dense sets of integers. An analogous algebraic statement was formulated by Green in terms of solutions of linear equations in abelian groups. In the talk I will report on some contributions made jointly with Dan Král' and Lluís Vena to this algebraic version for linear systems in abelian groups and some consequences in arithmetic Ramsey theory. The latter include a version of Szemerédi theorem on arithmetic progressions in dense sets of finite abelian groups.

P.S. : Il s'agit d'un exposé CPU.

Lundi 24 mars 2014 : "Exploration and Diffusion in Graphs using Deterministic Walks " - Adrian Kosowski (LaBRI)
Abstract: In a continuous diffusive process, a certain amount of a resource, known as "load", is initially placed on the nodes of the graph, possibly in an unfair manner. In successive time steps, each node shares its load evenly among all its neighbors, until the load on the nodes of the graph eventually converges to its limit distribution (e.g., becomes uniform in the case of regular graphs). However, continuous diffusion cannot be applied to "granular load" which is not arbitrarily divisible, i.e., represented by unsplittable unit-load tokens (chips), which are placed on nodes and may be passed around the graph. In such a scenario, one natural way of simulating the continuous diffusion process is to require that each chip follows an independent random walk on the graph.

In this talk, we will instead focus on chip diffusion processes following rules which are both locally fair and deterministic. These rules include the so-called "rotor walk", in which chips are propagated by each node to its neighbors in round-robin fashion and, more broadly, rules in which each node attempts to send out roughly the same number of tokens through each of its outgoing arcs.

We will start by providing a description of the evolution and limit behavior of the rotor walk on the n-node ring with K << n chips. For general graphs, we will show bounds on the "cover time" of a rotor walk system with K chips, proving that in a graph with m edges and diameter D, all nodes will have been visited at least once by some chip during the first O(mD / log K) steps of the process. Finally, we will relate the "blanket time" (the time until all nodes of the graph have been visited by chips a similar number of times) and the "diffusion time" (the time until all nodes all host a similar number of chips, for K >> n) of fair deterministic walks to analogous parameters of the random walk. The latter results allow us to design surprisingly simple and efficient deterministic algorithms for load balancing in the diffusive model.

This talk includes an overview of results presented at PODC'13, STACS'14, and some current work in progress (joint work with: P. Berenbrink, D. Dereniowski, R. Klasing, F. Mallmann-Trent, D. Pajak, T. Sauerwald, P. Uznanski).

Lundi 03 mars 2014 : "Algorithmes de mise à jour locale pour des graphes aléatoires" - Romaric Duvignau (LaBRI)
Abstract: Afin de modéliser l'évolution de réseaux logiques dynamiques, nous proposons de maintenir exactement une distribution donnée de graphes aléatoires lors d'une séquence arbitraire d'insertions et de suppressions de sommets. Nous nous plaçons dans un modèle local où nous n'avons pas accès à l'ensemble des sommets, mais supposons à la place l'accès à une primitive globale renvoyant un sommet aléatoire uniforme du graphe. Dans cet exposé, nous nous intéressons à maintenir la distribution uniforme dans les graphes k-sortants (graphes dirigés où tous les sommets ont degré sortant k). Nous présenterons plusieurs algorithmes d'insertion et de suppression pour le problème de maintenance, dont les plus efficaces sont asymptotiquement optimaux.

Lundi 24 février 2014 : "Distributed anonymous discrete function computation" - Julien Hendrickx(Univ. Louvain)
Abstract: We propose a model for deterministic distributed function computation by a network of identical and anonymous nodes:. In this model, each node has bounded computation and storage capabilities that do not grow with the network size. Furthermore, each node only knows its neighbors, not the entire graph. Our goal is to characterize the class of functions that can be computed within this model. We provide a necessary condition for computability which we show to be nearly sufficient, in the sense that every function that violates this condition can at least be approximated. The problem of computing (suitably rounded) averages in a distributed manner plays a central role in our development; we provide an algorithm that solves it in time that grows quadratically with the size of the network.

Lundi 17 février 2014 : "The interplay between multidimensional skylines and functional dependencies " - Sofian Maabout (LaBRI)
Abstract: We show how functional dependencies, which are agnostoc to the orders defined over the dimensions domains, can help to optimize skyline queries which, by opposition are based on orders. We present some theoretical and experimental results.

Lundi 10 février 2014 : "Algorithmes auto-stabilisants barvards" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)
Abstract: Dans le contexte des réseaux à grande échelle, la prise en compte des pannes est une nécessité évidente. Ce séminaire traite de l’auto-stabilisation, une méthode qui vise à concevoir des algorithmes distribués se « réparant d’eux-même » en cas de pannes transitoires pouvant impliquer toute modification arbitraire de l’état des processus. Plusieurs paramètres peuvent être pris en compte pour mesurer l’efficacité d’un algorithme auto-stabilisant, dont en particulier le temps de convergence et la complexité mémoire. L’importance du temps de convergence vient de la nécessité évidente pour un système de retrouver le plus rapidement possible un état valide après une panne. La nécessité de minimiser la mémoire vient, d’une part, de l’importance grandissante de réseaux offrant des espaces mémoires restreints, comme par exemple certains réseaux de capteurs, et, d’autre part, de l’intérêt de minimiser à la fois l’échange et le stockage d’information afin de limiter les potentialités de corruption de cette information. Lors de ce séminaire, nous traiterons de la minimisation de la mémoire au travers d'un exemple, à savoir le problème de l’élection d’un leader. Une borne inférieure de Ω(log n) bits de mémoire par noeud a été établie par Dolev, Gouda et Schneider (1999) pour ce problème fondamental. Cette borne n'est toutefois valable que pour des algorithmes silencieux, c'est-à-dire des algorithmes dont les registres ne sont plus modifiés lorsque le système a rejoint un état légitime. Nous verrons que, si l'on autorise l’algorithme à rester bavard (non-silencieux) même après avoir rejoint un état légitime, alors l’espace mémoire peut être amélioré d’un facteur au moins exponentiel.

Lundi 6 Janvier 2014 : "Self-stabilizing k-independent dominating set construction" - Colette Johnen(LaBRI)
Abstract: A k-independent dominating set is a k-independent set and a k-dominating set. A set of nodes, I, is k-independent if the distance between any pair of nodes in I is at least k+1. A set of nodes, D, is a k-dominating if every node is within distance k of a node of D.

I propose two self-self-stabilizing algorithm building k-independent dominating sets. The both algorithm (SID and FID) are silent, and they converge under the unfair distributed scheduler (the weakest scheduling assumption).

The algorithm FID reaches a terminal (also legitimate) configuration in at most 4n+k rounds, where n is the network size. The algorithm FID requires (k+1)log(n+1) bits per node.

The protocol SID is memory efficient : it requires only 2log((k+1)n+1)+1 bits per node. The computation of the convergence time of the protocol SID is opened question.

Lundi 16 Décembre 2013 : "Large-scale Data Stream Analysis" - Yann Busnel (LINA - Université de Nantes)
Abstract: L'objectif de cet exposé est de dresser un court état de l'art autour de l'analyse des flux de données à grande échelle, lesquels sont souvent utilisés pour du monitoring et de la sécurité, à la fois dans les réseaux et les systèmes distribués jusqu'à l'internet des objets. La problématique de ce champs de recherche consiste à extraire de l'information pertinente d'un flux de données en une passe unique (en raison de la taille du flux et de sa rapidité), et ne nécessitant qu'une quantité mémoire très faible et une puissance de calcul très limitée. Je présenterai ensuite les dernières applications utilisant nos résultats récents, lesquels vont de la détection d'intrusion, la détection de DDoS, l'échantillonnage, etc.

Lundi 9 Décembre 2013 : "Simulating weak shared memory" - David Bonnin (LaBRI)
Abstract: It is well known that in an asynchronous message-passing system with crash faults, one can emulate an atomic register providing that more than half of the processes are non-faulty. By contrast, when a majority of the processes may fail, simulating atomic register is not possible. I will talk about weak variants of atomic registers that can be simulated tolerating a majority of processes failures. Specifically, I will introduce a new class of registers, called $\alpha$-registers. We found a lower bound of $\alpha = M+1$ with $M=2f-n+2$ for these registers, and an explicit algorithm can emulate them with $\alpha = 2M-1$. I will also probably talk about other approaches on weak shared memory : $M$-colored registers, and $k$-splitters. This is a joint work with C. Travers.

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nicolas Bonichon (LaBRI)
Abstract: This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

Lundi 25 Novembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)
Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a maximal matching for anonymous rings. Their bit complexity and time complexity are $O(\sqrt{\log n})$ with high probability. These algorithms are optimal modulo a multiplicative constant. Beyond the complexity results, the interest of this work stands in the description and the analysis of these algorithms which may be easily generalised. Furthermore, these results show a separation between the complexity of the MIS problem (and of the maximal matching problem) on the one hand and the colouring problem on the other. Colouring can be computed only in $\Omega(\log n)$ rounds on rings with high probability, while MIS is shown to have a faster algorithm. This is in contrast to other models, in which MIS is at least as hard as colouring. This is joint work with Y. Métivier, J.M. Robson and A. Zemmari

Lundi 4 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)
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Lundi 28 Octobre 2013 : "The Case for Reliable Software Transactional Networking" - Petr Kuznetsov (Paristech)
Abstract: Software-defined networking (SDN) is a novel paradigm that out-sources the control of packet-forwarding switches to a set of software controllers. The most fundamental task of these controllers is the correct implementation of the network policy, i.e., the intended network behavior. In essence, such a policy specifies the rules by which packets must be forwarded across the network. We initiate the study of the SDN control plane as a distributed system.

We introduce a formal model describing the interaction between the data plane and a distributed control plane (consisting of a collection of fault-prone controllers). Then we formulate the problem of consistentcomposition of concurrent network policy updates. The composition is enabled via a transactional interface with all-or-nothing semantics, which allows us to reason about possibilities and impossibilities in controller synchronization.

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

Lundi 23 Septembre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Miroslaw Korzeniowski
Abstract: Decentralized monitoring and alarming systems can be an attractive alternative to centralized architectures. Distributed sensor nodes (e.g., in the smart grid's distribution network) are closer to an observed event than a global and remote observer or controller. This improves the visibility and response time of the system. Moreover, in a distributed system, local problems may also be handled locally and without overloading the communication network.

This article initiates the study of alarming from a distributed computing perspective and under two fundamentally different scenarios: \emph{on-duty} and \emph{off-duty}. We model the alarming system as a sensor network consisting of a set of distributed nodes performing local measurements to sense events. In order to avoid false alarms, the sensor nodes cooperate and only escalate an event (i.e., raise an alarm) if the number of sensor nodes sensing an event exceeds a certain threshold. In the on-duty scenario, nodes not affected by the event can actively help in the communication process, while in the off-duty scenario non-event nodes are inactive.

This article presents and analyzes algorithms that minimize the reaction time of the monitoring system while avoiding unnecessary message transmissions. Moreover, lower bounds are derived that shed light on the limitations of distributed alarming systems.

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)
Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

Lundi 8 Juillet 2013 : "Dynamic Resource Allocation in Cloud Computing platforms" - Lionel Eyraud-Dubois (Labri)
Abstract: Je présente un problème d'allocation de ressources dans le contexte du Cloud Computing, où un ensemble de machines virtuelles (VM) doivent être allouées sur un ensemble de machines physiques (PMs). La particularité de ce problème vient du fait que la quantité de ressources dont chaque VM a besoin change au cours du temps, et qu'il est possible pour le fournisseur d'accès de changer l'allocation d'une VM par une opération de migration. Ce problème peut se modéliser sous la forme d'un problème de bin packing complètement dynamique, et je présente un algorithme d'approximation pour minimiser le nombre de PMs utilisées, tout en garantissant un petit nombre de migrations. Les propriétés de cet algorithme permettent également d'envisager une version distribuée.

Lundi 10 Juin 2013 : " The Heard-Of model: computing in distributed systems with benign failures" - Bernadette Charron-Bost (CNRS, Ecole polytechnique, Paris)
Abstract: Problems in fault-tolerant distributed computing have been studied in a va- riety of system models. These models are all based on the principle that it is usefull and even necessary to specify why and by whom errors occur. In this talk, we question this principle, and present a general computational model, called the Heard-Of model, suitable for describing any type of system, be it message passing, shared memory, synchronous, or asynchronous. In this model, computations evolve in rounds, and communication missed at a round is definitely lost. Only information transmission is represented: for each round r and each process p, our model specifies the set of processes that p “hears of” at round r (heard-of set) namely the processes from which p receives some message at round r. The features of a specific system are thus captured as a whole, just by a predicate over the collection of heard-of sets. Thus the Heard-Of model allows us to handle all types of benign failures, static or dynamic, permanent or transient, in a unified framework. Moreover, it unifies the most seemingly unrelated notions in distributing computing, namely synchrony and asynchrony. We further demonstrate how this unifying framework leads to new results and insights in fault-tolerant distributed computing. In particular, we show that some fundamental results for asynchronous systems can be advantageously transferred to synchronous systems. We also examine Consensus algorithms in the Heard-Of model: we show how our approach allows us to devise new solutions and to give simple correctness proofs of existing algorithms like Paxos.

Joint work with André Schiper, EPFL

Lundi 3 Juin 2013 : "Introduction to renaming" - Corentin Travers (Labri)
Abstract: Renaming is a fundamental coordination problem in distributed computing. It consists in assigning new names taken from a small name space to processes in such a way that no two processes obtain the same name. The talk will survey renaming algorithms suited for different models of distributed computing, including the wait-free shared memory and the synchronous crash-prone message-passing models.

Lundi 27 Mai 2013 : " Exploration des graphes dynamiques T-intervalle-connexes : le cas de l'anneau" - Wade Ahmed (Labri)
Abstract: Dans cet exposé, je vais parler de l'étude des graphes dynamiques T-intervalle-connexes du point de vue du temps nécessaire à leur exploration par une entité mobile (agent). Un graphe dynamique est T-intervalle-connexe (T \geq 1) si pour chaque fenêtre de T unités de temps, il existe un sous-graphe couvrant connexe stable. Cette propriété de stabilité de connexion au cours du temps a été introduite par Kuhn, Lynch et Oshman~\cite{KLO10} (STOC 2010). Nous nous concentrons sur le cas où le graphe sous-jacent est un anneau de taille n et nous montrons que la complexité en temps en pire cas est de 2n-T-\Theta(1) unités de temps si l'agent connaît la dynamique du graphe, et n+ \frac{n}{\max\{1,T-1\}} (\delta-1) \pm \Theta(\delta) unités de temps sinon, où \delta est le temps maximum entre deux apparitions successives d'une arête.

Keywords : Graphe dynamique, exploration, T-intervalle-connexité, agent mobile

Lundi 13 Mai 2013 : " Calcul Distribué et Fouille de Données" - Nicolas Hanusse (Labri)
Abstract: L'avènement de la production massive de données et la volonté de les exploiter sont limités par les systèmes de gestion de bases de données relationnelles classiques. Cet exposé consiste en une discussion sur les enjeux et problèmes algorithmiques engendrés par le calcul distribué et parallèle. Le calcul de corrélations servira d'illustration. C'est un travail en cours avec Sofian Maabout et Eve Garnaud.

Lundi 22 Avril 2013 : " A peer-to-peer-based virtual environment system" - Eliya Buyukkaya (ENSSAT-Université de Rennes I)
Abstract: Virtual environments (VEs) are 3-D virtual worlds in which a huge number of participants play roles and interact with their surroundings through virtual representations called avatars. VEs are traditionally supported by a client/server architecture. However, centralized architectures can lead to bottleneck on the server due to high communication and computation overhead during peak loads. Thus, P2P overlay networks are emerging as a promising architecture for VEs. However, exploiting P2P schemes in VEs is not straightforward, and several challenging issues related to data distribution and state consistency should be considered.

One of the key aspects of P2P-based VEs is the logical platform consisting of connectivity, communication and data architectures, on which the VE is based. The connectivity architecture is the overlay topology structure, which defines how peers are connected to each other. The communication architecture is the routing protocol defining how peers can exchange messages, while the data architecture defines how data are distributed over the logical overlay. The design of these architectures has significant influence on the performance and scalability of VEs.

First, we propose a scalable connectivity architecture based on a new triangulation algorithm reducing maintenance cost of the system. Second, we construct a communication architecture built on top of the connectivity architecture ensuring that each message reaches its intended destination. Finally, we propose a data architecture ensuring the management of data with different characteristics in terms of mobility in the VE, while providing a fair data distribution and low data transfer between peers in the VE.

Lundi 15 Avril 2013 : " Algorithms for the Vertex Cover Problem on Large Graphs with Low Memory Capacities" - Romain Campigotto (LIP6-Paris)
Abstract: Most of the known optimization algorithms need to explore, mark, modify, etc. the instance given as input before producing their results. To do that, the instance is entirely loaded into the memory of the computer and is manipulated by the algorithm. Often, "extra" data structures are also necessary to memorize parameters useful all along the computation or to update the current solution that will be returned as the final product of the program. However, this classical model is no more adapted for many new computing applications. Indeed, nowadays, many fields such as biology, meteorology, finance, etc. produce very large amount of data.

In our works, we have focused on the Vertex Cover problem on huge graphs: in the intrinsic NP-completeness is added the difficulty to manipulate graphs with severe constraints (mainly related to the low memory capacities). We defined a treatment model combining some properties of several existing models in the literature: streaming, online, I/O-efficient, etc. We initially considered three approximation algorithms, which are memory-efficient (they use a memory space in O(log n) bits). We analyzed their performance in terms of solution quality and complexity, in mean and worst cases. We then focused on algorithms that use memory space of n bits. We showed that it could be very worst with strictly less than n bits memory space. Subsequently, we conducted experiments on very large graphs (in the order of billions of vertices and edges). This study showed that in practice, memory-efficient algorithms are better suited to handle large graphs.

This is joint work with Eric Angel (IBISC, Univ. Évry) and Christian Laforest (LIMOS, ISIMA, Clermont-Ferrand).

Lundi 8 Avril 2013 : "Implémentation d'algorithmes distribués à l'aide de Visidia" - Mohamed Mosbah (Labri)
Abstract: Dans le cadre du projet visidia, une plate-forme logicielle est développée pour l'implantation et la visualisation d'algorithmes distribués. Après une introduction et quelques rappels, l'exposé consistera en une présentation de la plate-forme et de son utilisation pour programmer des exemples d'algorithmes. L'interface et l'API permettent de visualiser l'exécution d'algorithmes, d'implanter de nouveaux algorithmes, ou d'effectuer des statistiques. Les algorithmes peuvent être exprimés selon plusieurs modèles (calculs locaux, passage de messages, agents mobiles).

Lundi 25 Mars 2013 : "Simultaneous Consensus vs Set Agreement." - Zohir Bouzid (LIP6-Paris)
Abstract: In the traditional consensus task, processes are required to agree on a common value chosen among the initial values of the participants. It is well known that consensus cannot be solved in crashed-prone, asynchronous distributed systems. Two generalizations of the consensus problem have been introduced: k-set agreement and k-simultaneous consensus. The k-set agreement task has the same requirements as consensus except that processes are allowed to decide up to k distinct values. In the k-simultaneous consensus task, each process participates simultaneously in k instances of consensus and is required to decide in at least one of them; any two processes deciding in the same instance must decide the same value. In this talk, we compare the computability of these problems in two central models in distributed computing: shared memory and message passing. We show that even though the two problems are equivalent in shared memory, k-simultaneous consensus is strictly harder than k-set agreement in the message passing model. This result will serve as a basis for a discussion about different models of computation and their respective power.

Lundi 18 Mars 2013 : "Vers une classification des réseaux dynamiques en fonction des problèmes qu'on peut y résoudre." - Arnaud Casteigts (Labri)
Abstract: Derrière les notions de "graphe dynamique" ou de "réseau dynamique" se cache une très grande diversité de scénarios et d'hypothèses, allant de réseaux semi-statiques où la connexité est toujours assurée à des réseaux complètement mobiles, où la connexité ne s'établit qu'à travers le temps et l'espace (e.g. DTNs). Dans cet exposé, résolument transversal, je présenterai l'état d'avancement de nos recherches autour de la question suivante : quel lien existe-t-il entre la "faisabilité" de tâches distribuées et la dynamique du réseau. Les hypothèses résultantes sur la dynamique peuvent être vues comme autant de classes de graphes (ou alternativement, comme autant de puissances possibles pour un adversaire qui contrôlerait la topologie). Nous avons à ce jour caractérisé et/ou recensé une petite vingtaine de classes de ce type.

Certains de ces travaux ont été menés en collaboration avec Serge Chaumette et Afonso Ferreira. D'autres avec Paola Flocchini et Nicola Santoro.

Lundi 25 Février 2013 : "Sur les 1001 modèles en algorithmique distribuée." - Yves Metivier (Labri)
Abstract: Le but de cet "exposé-discussion" est de présenter quelques modèles en algorithmique distribuée et d'échanger sur leurs liens et leurs mérites.

Lundi 18 Février 2013 : "Distributed Calculation of Graph Diameter" - Mike Robson (Labri)
Abstract: We consider the problem of calculating the diameter of a graph given that there is a single vertex "Leader" and neighbouring vertices can exchange messages of a single bit at each round. We show that this can be achieved in the same O(n) time complexity as well known algorithms without this bound on message length. The techniques used can be applied to a number of other graph computations. We consider briefly how the algorithm behaves if applied in a situation where more than one vertex considers itself the Leader.

This is joint work with Yves Métivier and Akka Zemmari.

Lundi 11 Février 2013 : "Bounds for Communication in Wireless Grids" - Joseph Peters (Simon Fraser University)
Abstract: In a wireless network, a transmission can be received by a node if it is close enough to the sender. However, transmissions can interfere with each other and the interference distance is typically greater than the reception distance. Efficient communication protocols in these networks minimize the time to move information without interference. In this talk, I will describe optimal protocols for the problem of collecting information into a central node of a two-dimensional square or hexagonal grid graph. The optimality of the protocols is proved using a new lower bound technique that is an adaptation to a discrete environment of a method based on linear programming duality for continuous flows.

This is joint work with Jean-Claude Bermond, CNRS-INRIA-University of Nice.

Lundi 04 Février 2013 : "Distributed Detection of Clone Attacks in Wireless Sensor Networks" - Mauro Conti (University of Padua, Italy)
Abstract: Wireless Sensor Networks (WSNs) are often deployed in hostile environments where an adversary can physically capture some of the nodes, first can reprogram, and then, can replicate them in a large number of clones, easily taking control over the network. A few distributed solutions to address this fundamental problem have been recently proposed. However, these solutions are not satisfactory. First, they are energy and memory demanding: A serious drawback for any protocol to be used in the WSN-resource-constrained environment. Further, they are vulnerable to the specific adversary models that we introduced. The contributions of our work are threefold. First, we analyze the desirable properties of a distributed mechanism for the detection of node replication attacks. Second, we show that the known solutions for this problem do not completely meet our requirements. Third, we propose a new self-healing, Randomized, Efficient, and Distributed (RED) protocol for the detection of node replication attacks, and we show that it satisfies the introduced requirements. Finally, extensive simulations show that our protocol is highly efficient in communication, memory, and computation; is much more effective than competing solutions in the literature; and is resistant to the new kind of attacks introduced in our work, while other solutions are not.

Lundi 28 Janvier 2013 : "Distributed Exclusive Graph Searching in Trees" - Janna Burman (LRI-Université Paris-Sud)
Abstract: We consider a version of the well known graph searching problem, where a team of robots aims at clearing the contaminated edges of a graph. We study graph searching in the model of mobile computing where autonomous deterministic robots move between the graph nodes when operating in asynchronous cycles of Look-Compute-Move. Moreover, motivated by physical constraints, following some recent works, we consider the exclusivity property, stating that no two or more robots can occupy a same node at the same time. In addition, we assume that all the graph elements and the robots are anonymous. Robots are oblivious and have no sense of direction. Our objective is to characterize for a graph $G$, the set of integers $k$ such that graph searching can be achieved by a team of $k$ robots starting from any $k$ distinct nodes in $G$. Our main result consists in a full characterization for any asymmetric tree. Towards providing a characterization in the general case, including trees with non-trivial automorphisms, we provide a set of positive and negative results, including a full characterization for any line. All our positive results are based on the design of algorithms enabling perpetual graph searching to be achieved with the desired number of robots. We prove that, in addition to the distributed nature of our setting, the exclusivity property has a significant impact on the nature of the graph searching problem. Hence, the design of the algorithms requires to invent new methods.

Lundi 21 Janvier 2013 : "Présentation de Keep Alert, une solution pour la surveillance de marques sur Internet" - Anthony Don (Keep Alert)
Abstract: A destination des cabinets de propriété industrielle et des services juridiques, Keep Alert propose des surveillances de marque parmi les noms de domaine, les régies publicitaires et les réseaux sociaux. Anthony DON, directeur technique chez Keep Alert, présentera au groupe de travail, le fonctionnement global de la plateforme, puis abordera les problématiques actuelles et les perspectives de développement relatives à l'algorithmique distribuée.

Lundi 14 Janvier 2013 : "Two Monte-Carlo Election Algorithms for Anonymous Graphs without any Initial Knowledge" - Akka Zemmari (Labri)
Abstract: The paper proposes and analyses two Monte Carlo election algorithms for anonymous graphs without any initial knowledge. Both have a time complexity equal to $O(D)$, where $D$ is the diameter of the graph. The first is correct with probability $1-o(n^{-1})$ (where $n$ is the size of the graph). The size of messages is $O(\log n)$ with probability $1-o(n^{-1})$ and the expected value of the size of messages is also $O(\log n)$. The second is correct with probability $1-o(n^{-c})$ for any $c\geq 1$. The size of messages is $O\left((\log n)(\log^* n)^2 \right)$ with probability $1-o(n^{-c})$ for any $c\geq 1$; their expected size is $O\left((\log n)(\log^* n) \right)$.

This is a joint work with Y. Métivier and J. M. Robson

Lundi 10 Décembre 2012 : pas de seminaire. Soutenance de thèse-Florent Foucaud.

Lundi 3 Décembre 2012 : "Progress and Challenges for Labeling Schemes" - Cyril Gavoille (Labri)
Abstract: A fundamental question in Distributed Computing is to understand how localized and how much information are required to solve a task on a network. Typically, if the distance between any pair x,y of nodes in a network is asked, we would like to know which minimal information about x and y in the network are needed. The goal in labeling schemes is precisely to understand how much information must be attached to the nodes (formalized as labels) to solve a graph problem assuming the answer can be determined solely on the basis of the labels of the nodes invoked in the query. In this talk, I give a survey on labeling schemes, present some recent results with their techniques, and highlight new challenges.

Lundi 26 Novembre 2012: "Competitive Routing on a Variant of the Delaunay Triangulation" - Prosenjit Bose (Carleton University)
Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we showed how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.

Lundi 19 Novembre 2012: " Reliable Service Allocation in Clouds"- Lionel Eyraud-Dubois, Olivier Beaumont (Labri)
Abstract: We consider several reliability problems that arise when allocating applications to processing resources in a Cloud computing platform. More specifically, we assume on the one hand that each computing resource is associated to a capacity constraint and to a probability of failure. On the other hand, we assume that each service runs as a set of independent instances of identical Virtual Machines, and that the Service Level Agreement between the Cloud provider and the client states that a minimal number of instances of the service should run with a given probability. In this context, given the capacity and failure probabilities of the machines, and the capacity and reliability demands of the services, the question for the cloud provider is to find an allocation of the instances of the services (possibly using replication) onto machines satisfying all types of constraints. In this paper, our goal is to assess the impact of the reliability constraint on the complexity of resource allocation problems. We consider several variants this problem, depending on the number of services (one or many) and if their reliability demand is individual or global. We prove several fundamental complexity results ($\#$P and NP-completeness results) and we provide several optimal and approximation algorithms. In particular, we prove that a basic randomized allocation algorithm, that is easy to implement, provides optimal or quasi-optimal results in several contexts, and we show through simulations that it also achieves very good results in more general settings.

Lundi 12 Novembre 2012 : "MAXIMUM MATCHING IN MULTI-INTERFACE NETWORK"- Dominik Pająk (LaBRI)
Abstract: In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

Lundi 5 Novembre 2012 : pas de séminaire
Lundi 22 Octobre 2012 : Christian Glacet (LaBRI)
Lundi 15 Octobre: " NETWORK VERIFICATION VIA ROUTING TABLE QUERIES" - Ralf Klasing (LaBRI)
Abstract: We address the problem of verifying the accuracy of a map of a network by making as few measurements as possible on its nodes. This task can be formalized as an optimization problem that, given a graph G=(V,E), and a query model specifying the information returned by a query at a node, asks for finding a minimum-size subset of nodes of G to be queried so as to univocally identify G. This problem has been faced w.r.t. a couple of query models assuming that a node had some global knowledge about the network. Here, we propose a new query model based on the local knowledge a node instead usually has. Quite naturally, we assume that a query at a given node returns the associated routing table, i.e., a set of entries which provides, for each destination node, a corresponding (set of) first-hop node(s) along an underlying shortest path. First, we show that any network of n nodes needs Omega(log log n) queries to be verified. Then, we prove that there is no o(log n)-approximation algorithm for the problem, unless P=NP, even for networks of diameter 2. On the positive side, we provide an O(logn)-approximation algorithm to verify a network of diameter 2, and we give exact polynomial-time algorithms for paths, trees, and cycles of even length.

Lundi 8 Octobre 2012 : pas de séminaire
Lundi 1er Octobre 2012 : Réunion de rentrée du thème - Nicolas Hanusse (LaBRI)
Abstract: L'ordre du jour:

• projets: thèse, région, ingénieur, conférence
• organisation du groupe de travail: exposé à venir (projets à long terme, discussion sur les modèles, logiciels, ...), vitrine
• mise-à-jour site web
• enseignement: état des lieux des enseignements locaux
• stages X, ENS, ...

Lundi 21 Juin : "ABOUT RANDOMISED DISTRIBUTED GRAPH COLOURING AND GRAPH PARTITION ALGORITHMS" - Akka Zemmari (LaBRI)
Abstract: We present and analyse a very simple randomised distributed vertex colouring algorithm for arbitrary graphs of size $n$ that halts in time $O(log n)$ with probability $1-o(n^{-1}).$ Each message containing $1$ bit, its bit complexity per channel is $O(log n)$.
From this algorithm, we deduce and analyse a randomised distributed vertex colouring algorithm for arbitrary graphs of maximum degree $Delta$ and size $n$ that uses $Delta+1$ colours and halts in time $O(log n)$ with probability $1-o(n^{-1}).$
We also obtain a partition algorithm for arbitrary graphs of size $n$ that builds a spanning forest in time $O(log n)$ with probability $1-o(n^{-1})$. We study some parameters such as the number, the size or the radius of trees of the spanning forest.
We assume that graphs are anonymous; we only assume that each vertex distinguishes between its neighbours by locally known channel names. Furthermore we do not assume that the size (or an upper bound on the size) of graphs is known.
Joint work with Y. Métivier, N. Saheb and J.M. Robson

Lundi 14 Juin : Almost optimal asynchronous rendezvous in infinite multidimensional grids - Arnaud Labourel (LaBRI)
Abstract: Dans cet exposé, je montrerais comment deux agents mobiles peuvent se rencontrer dans une grille infinie de dimension supérieure à 2. On considère le modèle asynchrone. C'est-à-dire que la durée de traversée de chaque sommet par un agent est déterminée par un adversaire omniscient qui essaye d'empêcher le rendez-vous. On supposera que chaque agent connait sa position dans la grille mais pas celle de l'autre agent. Cette connaissance permet d'avoir un algorithme de rendez-vous ayant un coût, mesuré en terme de distance parcourue par les agents, quasiment optimal.

en:

L'exp

19 janvier 2015 à 20h32 par 81.67.198.101 -
Lignes 12-14 modifiées:

Lundi 26 janvier 2015 : ""Periodic Data Retrieval in asynchronous rings with a malicious host"" - Evangelos Bampas (LaBRI, Université de Bordeaux)
'Abstract:'

en:

Lundi 26 janvier 2015 : 'Periodic Data Retrieval in asynchronous rings with a malicious host' - Evangelos Bampas (LaBRI, Université de Bordeaux)
Abstract:

19 janvier 2015 à 20h28 par 81.67.198.101 -
Lignes 12-17 modifiées:

Lundi 26 janvier 2015 : TBA - Evangelos Bampas (LaBRI, Université de Bordeaux)\\

en:

Lundi 26 janvier 2015 : ""Periodic Data Retrieval in asynchronous rings with a malicious host"" - Evangelos Bampas (LaBRI, Université de Bordeaux)
'Abstract:' The notion of "black hole" has been used extensively in the mobile agent literature to model a crashed node which kills incoming agents without leaving any trace of them. I will consider more powerful models of faulty (or malicious) hosts in the context of the Periodic Data Retrieval problem in asynchronous ring networks. The problem is to collect infinite streams of data generated at the nodes of the network and report them infinitely often to a prescribed safe node (the homebase). I will discuss lower and upper bounds on the optimal number of agents required to perform the task in the presence of a unique malicious host.

(joint work with Nikos Leonardos, Euripides Markou, Aris Pagourtzis, and Matoula Petrolia)""

08 janvier 2015 à 22h16 par 81.67.198.101 -
Lignes 12-13 modifiées:

Lundi 26 janvier 2015 : " " - Evangelos Bampas (LaBRI, Université de Bordeaux)
TBA

en:

Lundi 26 janvier 2015 : TBA - Evangelos Bampas (LaBRI, Université de Bordeaux)

Ligne 17 modifiée:

""Abstract:""

en:

Abstract:

Lignes 28-30 modifiées:

Abstract:

 We tackle \emph{local distributed testing} of graph properties. This framework is well suited to contexts in which data dispersed among the nodes of a network can be collected by some central authority (like in, e.g., sensor networks). In local distributed testing, each node can provide the central authority with just a few information about what it perceives from its neighboring environment, and, based on the collected information, the central authority is aiming at deciding whether  or not the network satisfies some property.

en:

Abstract: We tackle local distributed testing of graph properties. This framework is well suited to contexts in which data dispersed among the nodes of a network can be collected by some central authority (like in, e.g., sensor networks). In local distributed testing, each node can provide the central authority with just a few information about what it perceives from its neighboring environment, and, based on the collected information, the central authority is aiming at deciding whether or not the network satisfies some property.

08 janvier 2015 à 22h11 par 81.67.198.101 -
Lignes 10-11 supprimées:
Lignes 12-28 modifiées:

Lundi 15 décembre 2014 : "Splitting and renaming with a majority of faulty processes" - David Bonnin (LaBRI, Université de Bordeaux)
Abstract: The renaming problem has been introduced by Attiya et al. [1], and consists on the following : Each process start with a unique name in a large namespace (such as an IP address), and each process tries to acquire a new name such as, at the end of the algorithm, each process has a new unique name in a much smaller namespace. This problem was first solved in asynchronous message-passing systems with a strict minority of processes that might crash, and later largely studied in wait-free shared memory systems, which can themselves be simulated in the former model (as explained in [2]). Splitters are basic shared memory objects that were introduced in [3] in order to build a fast renaming algorithm, and extending the renaming to a long-lived'' version. A splitter is an object that can be accessed through one operation Split(), and returns a direction in {right, down, stop}, with the property that not all processes return right, not all return down, and at most 1 process may return stop.

In asynchronous message-passing systems with a majority of faulty processes, the renaming problem cannot be solved, and splitters cannot be implemented. But we extended these notions to k-renaming and k-splitters, both for one-shot and long-lived versions. Instead of having unique name for each process, each new name (in a small namespace) may be acquired by at most k processes, and at most k processes accessing a k-splitter may return stop. We developed an optimal algorithm for implementing k-splitters, i.e. the algorithm implements them with k = floor(n/(n-f)), where n in the number of processes and f the maximal number of faulty processes among them, and it is not possible to implement k'-splitters with k' < floor(n/(n-f)). Although the namespace is not optimal, especially in the long-lived version, k-renaming based on these k-splitters is optimal for the same reason that k=floor(n/(n-f)) is both a lower bound, and a reached upper bound.

[1] H. Attiya, A. Bar-Noy, D. Dolev, D. Peleg, and R. Reischuk. Renaming in an asynchronous environment. J. ACM, 37(3):524–548, July 1990. [2] H. Attiya, A. Bar-Noy, and D. Dolev. Sharing memory robustly in message-passing systems. J. ACM, 42(1):124–142, 1995. [3] M. Moir and J. H. Anderson. Wait-free algorithms for fast, long-lived renaming. Science of Computer Programming, 25(1):1 – 39, 1995.

en:

Lundi 26 janvier 2015 : " " - Evangelos Bampas (LaBRI, Université de Bordeaux)
TBA

Lignes 16-17 modifiées:

# Exposés passés

en:

Lundi 19 janvier 2015 : " Équilibrage de charge dans des systèmes distribués" - Noel Gillet (LaBRI, Université de Bordeaux)
""Abstract:"" L'expansion, au cours des deux dernières décennies des réseaux, et notamment d'Internet, a engendré une création importante de données, massives de par leur nombre et leur taille. De ce fait, des systèmes de stockages distribués (comme Cassandra par exemple) sont utilisés en pratique afin de stocker ces données.

Deux problématiques se posent alors : (1) comment répartir les données? (2) comment optimiser le traitement des requêtes sur ces données?

Nous nous intéressons ici à l'équilibrage des requêtes entre les différents noeuds d'un système distribué. Notre approche consiste à utiliser la réplication d'objet et nous proposons différents algorithmes d'affectation des requêtes en cherchant à optimiser le temps de complétion (temps de traitement) des requêtes.

(Travail en cours avec Nicolas Hanusse)

Lignes 27-30 modifiées:

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz et Matthieu Barjon, (LaBRI, Université de Bordeaux)

en:

Lundi 12 janvier 2015 : "Distributedly Testing Cycle-Freeness" - David Ilcinkas (LaBRI, CNRS and Université de Bordeaux)
Abstract:

 We tackle \emph{local distributed testing} of graph properties. This framework is well suited to contexts in which data dispersed among the nodes of a network can be collected by some central authority (like in, e.g., sensor networks). In local distributed testing, each node can provide the central authority with just a few information about what it perceives from its neighboring environment, and, based on the collected information, the central authority is aiming at deciding whether  or not the network satisfies some property.


We analyze in depth the prominent example of checking \emph{cycle-freeness}, and establish tight bounds on the amount of information to be transferred by each node to the central authority for deciding cycle-freeness. In particular, we show that distributedly testing cycle-freeness requires at least $\ceil{\log d}-1$ bits of information per node in graphs with maximum degree~$d$, even for connected graphs. Our proof is based on a novel version of the seminal result by Naor and Stockmeyer (1995) enabling to reduce the study of certain kinds of algorithms to order-invariant algorithms, and on an appropriate use of the known fact that every free group can be linearly ordered.

# Exposés passés

Lundi 15 décembre 2014 : "Splitting and renaming with a majority of faulty processes" - David Bonnin (LaBRI, Université de Bordeaux)
Abstract: The renaming problem has been introduced by Attiya et al. [1], and consists on the following : Each process start with a unique name in a large namespace (such as an IP address), and each process tries to acquire a new name such as, at the end of the algorithm, each process has a new unique name in a much smaller namespace. This problem was first solved in asynchronous message-passing systems with a strict minority of processes that might crash, and later largely studied in wait-free shared memory systems, which can themselves be simulated in the former model (as explained in [2]). Splitters are basic shared memory objects that were introduced in [3] in order to build a fast renaming algorithm, and extending the renaming to a long-lived'' version. A splitter is an object that can be accessed through one operation Split(), and returns a direction in {right, down, stop}, with the property that not all processes return right, not all return down, and at most 1 process may return stop.

In asynchronous message-passing systems with a majority of faulty processes, the renaming problem cannot be solved, and splitters cannot be implemented. But we extended these notions to k-renaming and k-splitters, both for one-shot and long-lived versions. Instead of having unique name for each process, each new name (in a small namespace) may be acquired by at most k processes, and at most k processes accessing a k-splitter may return stop. We developed an optimal algorithm for implementing k-splitters, i.e. the algorithm implements them with k = floor(n/(n-f)), where n in the number of processes and f the maximal number of faulty processes among them, and it is not possible to implement k'-splitters with k' < floor(n/(n-f)). Although the namespace is not optimal, especially in the long-lived version, k-renaming based on these k-splitters is optimal for the same reason that k=floor(n/(n-f)) is both a lower bound, and a reached upper bound.

[1] H. Attiya, A. Bar-Noy, D. Dolev, D. Peleg, and R. Reischuk. Renaming in an asynchronous environment. J. ACM, 37(3):524–548, July 1990. [2] H. Attiya, A. Bar-Noy, and D. Dolev. Sharing memory robustly in message-passing systems. J. ACM, 42(1):124–142, 1995. [3] M. Moir and J. H. Anderson. Wait-free algorithms for fast, long-lived renaming. Science of Computer Programming, 25(1):1 – 39, 1995.

12 décembre 2014 à 17h16 par 193.51.236.181 -
Lignes 15-20 modifiées:

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz et Matthieu Barjon, (LaBRI, Université de Bordeaux)

Lundi 15 décembre 2014 (13h30): "Splitting and renaming with a majority of faulty processes" - David Bonnin (LaBRI, Université de Bordeaux)\\

en:

Lundi 15 décembre 2014 : "Splitting and renaming with a majority of faulty processes" - David Bonnin (LaBRI, Université de Bordeaux)\\

Lignes 35-39 ajoutées:

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz et Matthieu Barjon, (LaBRI, Université de Bordeaux)

08 décembre 2014 à 09h59 par 2001:660:6101:403::1:b4 -
Lignes 15-38 supprimées:

Lundi 01 décembre 2014 : "Towards a General Framework for Searching on a Line and Searching on m Rays" - Jean-Lou De Carufel (Carleton University)
Abstract: We revisit the problem of searching for a target at an unknown location on a line when given upper and lower bounds on the distance D that separates the initial position of the searcher from the target. We present tight bounds on the exact optimal competitive ratio achievable, parameterized in terms of the given range for D, along with an optimal search strategy that achieves this competitive ratio.

We present an optimal search strategy for the case where a fixed turn cost t is charged every time the searcher changes direction. Moreover, we generalize our results to the framework where the cost of moving distance x away from the origin is a x + b and the cost of moving distance y towards the origin is c y + d for constants a, b, c and d.

This is joint work with Prosenjit Bose (Carleton U.) and Stephane Durocher (U. of Manitoba).

Lignes 42-61 ajoutées:

Lundi 01 décembre 2014 : "Towards a General Framework for Searching on a Line and Searching on m Rays" - Jean-Lou De Carufel (Carleton University)
Abstract: We revisit the problem of searching for a target at an unknown location on a line when given upper and lower bounds on the distance D that separates the initial position of the searcher from the target. We present tight bounds on the exact optimal competitive ratio achievable, parameterized in terms of the given range for D, along with an optimal search strategy that achieves this competitive ratio.

We present an optimal search strategy for the case where a fixed turn cost t is charged every time the searcher changes direction. Moreover, we generalize our results to the framework where the cost of moving distance x away from the origin is a x + b and the cost of moving distance y towards the origin is c y + d for constants a, b, c and d.

This is joint work with Prosenjit Bose (Carleton U.) and Stephane Durocher (U. of Manitoba).

25 novembre 2014 à 09h41 par 147.210.128.139 -
Ligne 20 modifiée:

on $m$ Rays" - Jean-Lou De Carufel (Carleton University)\\

en:

on m Rays" - Jean-Lou De Carufel (Carleton University)\\

Ligne 22 modifiée:

location on a line when given upper and lower bounds on the distance $D$

en:

location on a line when given upper and lower bounds on the distance D

Ligne 25 modifiée:

parameterized in terms of the given range for $D$, along with an optimal

en:

parameterized in terms of the given range for D, along with an optimal

Ligne 29 modifiée:

cost $t$ is charged every time the searcher changes direction. Moreover,

en:

cost t is charged every time the searcher changes direction. Moreover,

Lignes 31-34 modifiées:

distance $x$ away from the origin is $a x + b$ and the cost of moving distance $y$ towards the origin is $c y + d$ for constants $a$, $b$, $c$ and $d$.

en:

distance x away from the origin is a x + b and the cost of moving distance y towards the origin is c y + d for constants a, b, c and d.

Lignes 44-58 modifiées:

Lundi 15 décembre 2014 (13h30): "Titre à préciser" - David Bonnin (LaBRI, Université de Bordeaux)\\

en:

Lundi 15 décembre 2014 (13h30): "Splitting and renaming with a majority of faulty processes" - David Bonnin (LaBRI, Université de Bordeaux)
Abstract: The renaming problem has been introduced by Attiya et al. [1], and consists on the following : Each process start with a unique name in a large namespace (such as an IP address), and each process tries to acquire a new name such as, at the end of the algorithm, each process has a new unique name in a much smaller namespace. This problem was first solved in asynchronous message-passing systems with a strict minority of processes that might crash, and later largely studied in wait-free shared memory systems, which can themselves be simulated in the former model (as explained in [2]). Splitters are basic shared memory objects that were introduced in [3] in order to build a fast renaming algorithm, and extending the renaming to a long-lived'' version. A splitter is an object that can be accessed through one operation Split(), and returns a direction in {right, down, stop}, with the property that not all processes return right, not all return down, and at most 1 process may return stop.

In asynchronous message-passing systems with a majority of faulty processes, the renaming problem cannot be solved, and splitters cannot be implemented. But we extended these notions to k-renaming and k-splitters, both for one-shot and long-lived versions. Instead of having unique name for each process, each new name (in a small namespace) may be acquired by at most k processes, and at most k processes accessing a k-splitter may return stop. We developed an optimal algorithm for implementing k-splitters, i.e. the algorithm implements them with k = floor(n/(n-f)), where n in the number of processes and f the maximal number of faulty processes among them, and it is not possible to implement k'-splitters with k' < floor(n/(n-f)). Although the namespace is not optimal, especially in the long-lived version, k-renaming based on these k-splitters is optimal for the same reason that k=floor(n/(n-f)) is both a lower bound, and a reached upper bound.

[1] H. Attiya, A. Bar-Noy, D. Dolev, D. Peleg, and R. Reischuk. Renaming in an asynchronous environment. J. ACM, 37(3):524–548, July 1990. [2] H. Attiya, A. Bar-Noy, and D. Dolev. Sharing memory robustly in message-passing systems. J. ACM, 42(1):124–142, 1995. [3] M. Moir and J. H. Anderson. Wait-free algorithms for fast, long-lived renaming. Science of Computer Programming, 25(1):1 – 39, 1995.

25 novembre 2014 à 09h37 par 147.210.128.139 -
Lignes 18-23 modifiées:

Lundi 24 novembre 2014 : "ON THE POWER OF ONE BIT: HOW TO EXPLORE A GRAPH WHEN YOU CANNOT BACKTRACK?" - Dominik Pajak, (University of Cambridge)
Abstract: We study the problem of exploration of an anonymous undirected graph with n vertices, m edges and diameter D by a single mobile agent. The agent does not know the incoming port when entering to a vertex thus it cannot backtrack its moves. Each vertex of the graph is endowed with a whiteboard on which the agent can store information.

In this talk we will study tradeoffs between the exploration time and the existence of the internal memory available to the agent. We will first show an algorithm for an agent with 1 bit of memory completing exploration of any graph with stop in time O(m) using whiteboards of size O(log Delta) on each vertex with degree Delta.

An oblivious agent (with no internal memory) can explore any graph in time O(m D) using whiteboards of size O(log Delta) by applying the rotor-router mechanism. We will show that, even with unbounded whiteboards, there is no algorithm for oblivious agents that is better than the rotor-router in the worst case by showing a Omega(n3) lower bound for a specific class of graphs. We will also observe that any oblivious agent cannot stop after completing the task. This shows separation between oblivious and non-oblivious agents in terms of the exploration time and the stop property.

en:

Lundi 01 décembre 2014 : "Towards a General Framework for Searching on a Line and Searching on $m$ Rays" - Jean-Lou De Carufel (Carleton University)
Abstract: We revisit the problem of searching for a target at an unknown location on a line when given upper and lower bounds on the distance $D$ that separates the initial position of the searcher from the target. We present tight bounds on the exact optimal competitive ratio achievable, parameterized in terms of the given range for $D$, along with an optimal search strategy that achieves this competitive ratio.

We present an optimal search strategy for the case where a fixed turn cost $t$ is charged every time the searcher changes direction. Moreover, we generalize our results to the framework where the cost of moving distance $x$ away from the origin is $a x + b$ and the cost of moving distance $y$ towards the origin is $c y + d$ for constants $a$, $b$, $c$ and $d$.

This is joint work with Prosenjit Bose (Carleton U.) and Stephane Durocher (U. of Manitoba).

Lignes 39-42 supprimées:

Lundi 01 décembre 2014 : "Titre à préciser" - David Bonnin (LaBRI, Université de Bordeaux)

Lignes 44-57 modifiées:

# Exposés passés

en:

Lundi 15 décembre 2014 (13h30): "Titre à préciser" - David Bonnin (LaBRI, Université de Bordeaux)

# Exposés passés

Lundi 24 novembre 2014 : "ON THE POWER OF ONE BIT: HOW TO EXPLORE A GRAPH WHEN YOU CANNOT BACKTRACK?" - Dominik Pajak, (University of Cambridge)
Abstract: We study the problem of exploration of an anonymous undirected graph with n vertices, m edges and diameter D by a single mobile agent. The agent does not know the incoming port when entering to a vertex thus it cannot backtrack its moves. Each vertex of the graph is endowed with a whiteboard on which the agent can store information.

In this talk we will study tradeoffs between the exploration time and the existence of the internal memory available to the agent. We will first show an algorithm for an agent with 1 bit of memory completing exploration of any graph with stop in time O(m) using whiteboards of size O(log Delta) on each vertex with degree Delta.

An oblivious agent (with no internal memory) can explore any graph in time O(m D) using whiteboards of size O(log Delta) by applying the rotor-router mechanism. We will show that, even with unbounded whiteboards, there is no algorithm for oblivious agents that is better than the rotor-router in the worst case by showing a Omega(n3) lower bound for a specific class of graphs. We will also observe that any oblivious agent cannot stop after completing the task. This shows separation between oblivious and non-oblivious agents in terms of the exploration time and the stop property.

21 novembre 2014 à 15h26 par 147.210.179.69 -
Ligne 26 modifiée:

Lundi 01 décembre 2014 : "Titre à préciser" - Noël Gillet, (LaBRI, Université de Bordeaux)\\

en:

Lundi 01 décembre 2014 : "Titre à préciser" - David Bonnin (LaBRI, Université de Bordeaux)\\

21 novembre 2014 à 15h19 par 147.210.179.69 -
Lignes 18-19 modifiées:

Lundi 24 novembre 2014 : "Titre à préciser" - Evangelos Bampas, (LaBRI, Université de Bordeaux)

en:

Lundi 24 novembre 2014 : "ON THE POWER OF ONE BIT: HOW TO EXPLORE A GRAPH WHEN YOU CANNOT BACKTRACK?" - Dominik Pajak, (University of Cambridge)
Abstract: We study the problem of exploration of an anonymous undirected graph with n vertices, m edges and diameter D by a single mobile agent. The agent does not know the incoming port when entering to a vertex thus it cannot backtrack its moves. Each vertex of the graph is endowed with a whiteboard on which the agent can store information.

In this talk we will study tradeoffs between the exploration time and the existence of the internal memory available to the agent. We will first show an algorithm for an agent with 1 bit of memory completing exploration of any graph with stop in time O(m) using whiteboards of size O(log Delta) on each vertex with degree Delta.

An oblivious agent (with no internal memory) can explore any graph in time O(m D) using whiteboards of size O(log Delta) by applying the rotor-router mechanism. We will show that, even with unbounded whiteboards, there is no algorithm for oblivious agents that is better than the rotor-router in the worst case by showing a Omega(n3) lower bound for a specific class of graphs. We will also observe that any oblivious agent cannot stop after completing the task. This shows separation between oblivious and non-oblivious agents in terms of the exploration time and the stop property.

21 novembre 2014 à 15h05 par 147.210.179.69 -
Lignes 17-20 modifiées:

Lundi 17 novembre 2014 : "Group Search on the Line" - Leszek Gasieniec (University of Liverpool)

en:
Lignes 31-34 ajoutées:

Lundi 17 novembre 2014 : "Group Search on the Line" - Leszek Gasieniec (University of Liverpool)

13 novembre 2014 à 16h10 par 2001:660:6101:402:20f:feff:fef6:6e1e -
Ligne 17 modifiée:

Lundi 17 novembre 2014 : "Titre à préciser" - Leszek Gasieniec (University of Liverpool) \\

en:

Lundi 17 novembre 2014 : "Group Search on the Line" - Leszek Gasieniec (University of Liverpool) \\

13 novembre 2014 à 16h06 par 2001:660:6101:402:20f:feff:fef6:6e1e -
Ligne 17 modifiée:

Lundi 17 novembre 2014 : "Titre à préciser" - David Ilcinkas, (LaBRI, Université de Bordeaux)\\

en:

Lundi 17 novembre 2014 : "Titre à préciser" - Leszek Gasieniec (University of Liverpool) \\

13 novembre 2014 à 16h02 par 2001:660:6101:402:20f:feff:fef6:6e1e -
Lignes 15-34 ajoutées:

Lundi 17 novembre 2014 : "Titre à préciser" - David Ilcinkas, (LaBRI, Université de Bordeaux)

Lundi 24 novembre 2014 : "Titre à préciser" - Evangelos Bampas, (LaBRI, Université de Bordeaux)

Lundi 01 décembre 2014 : "Titre à préciser" - Noël Gillet, (LaBRI, Université de Bordeaux)

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz et Matthieu Barjon, (LaBRI, Université de Bordeaux)

# Exposés passés

Lignes 50-68 supprimées:

Lundi 17 novembre 2014 : "Titre à préciser" - David Ilcinkas, (LaBRI, Université de Bordeaux)

Lundi 24 novembre 2014 : "Titre à préciser" - Evangelos Bampas, (LaBRI, Université de Bordeaux)

Lundi 01 décembre 2014 : "Titre à préciser" - Noël Gillet, (LaBRI, Université de Bordeaux)

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz et Matthieu Barjon, (LaBRI, Université de Bordeaux)

# Exposés passés

13 novembre 2014 à 15h57 par 147.210.129.217 -
05 novembre 2014 à 08h21 par 147.210.179.69 -
Ligne 53 ajoutée:
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05 novembre 2014 à 08h19 par 147.210.179.69 -
Ligne 12 ajoutée:
Lignes 14-23 modifiées:

Lundi 20 octobre 2014 : "Routage compact en pratique. Peut-on router avec des tables de routage de taille 6 ?" - Nicolas Hanusse , (LaBRI, Université de Bordeaux)
Abstract: Le projet européen EULER portant sur des propositions de nouveaux schéma de routage vient de se terminer. Je ferai une petite présentation de nos contributions sur des algorithmes de routage compact pour lesquels nous obtenons des garanties sur l'étirement, la taille des tables ou le cout de construction. Des simulations sur des cartes des systèmes autonomes d'Internet montrent que nous pouvons obtenir des tables de petite taille ...

Ce travail a été fait avec Cyril Gavoille, Christian Glacet et David Ilcinkas.

Lundi 03 novembre 2014 : "Coloration d'un cycle en temps log*(n): borne sup et borne inf" - Cyril Gavoille, (LaBRI, Université de Bordeaux)

en:
Ligne 16 modifiée:

Abstract:Mobile robots collaborate in order to solve efficiently the central problems

en:

Abstract: Mobile robots collaborate in order to solve efficiently the central problems

Lignes 50-59 ajoutées:

Lundi 03 novembre 2014 : "Coloration d'un cycle en temps log*(n): borne sup et borne inf" - Cyril Gavoille, (LaBRI, Université de Bordeaux)
---- Lundi 20 octobre 2014 : "Routage compact en pratique. Peut-on router avec des tables de routage de taille 6 ?" - Nicolas Hanusse , (LaBRI, Université de Bordeaux)
Abstract: Le projet européen EULER portant sur des propositions de nouveaux schéma de routage vient de se terminer. Je ferai une petite présentation de nos contributions sur des algorithmes de routage compact pour lesquels nous obtenons des garanties sur l'étirement, la taille des tables ou le cout de construction. Des simulations sur des cartes des systèmes autonomes d'Internet montrent que nous pouvons obtenir des tables de petite taille ...

Ce travail a été fait avec Cyril Gavoille, Christian Glacet et David Ilcinkas.

05 novembre 2014 à 08h18 par 147.210.179.69 -
Lignes 23-24 modifiées:

Lundi 10 novembre 2014 : "Titre à préciser" - Evangelos Bampas , (LaBRI, Université de Bordeaux)

en:

Lundi 10 novembre 2014 : "Patrolling by unreliable mobile robots" - Jurek Czyzowicz (Université du Québec en Outaouais)
Abstract:Mobile robots collaborate in order to solve efficiently the central problems in algorithmics of distributed computing like searching/exploration, rendez-vous or pattern formation. Patrolling is a perpetual traversal of an environment by a collection of mobile robots. The standard measure of efficiency of a patrolling algorithm is defined by its idleness – the minimal time interval during which every point of the environment is always visited by at least one robot. Boundary patrolling and fence patrolling were fundamental problems investigated by the robotics community in the last decade.

We sketch briefly previous results concerning the algorithms for the boundary and fence-patrolling problem. When some (unknown) robots of the collection cannot perform their duties, the fence patrolling algorithms become surprisingly unnatural. In more details we discuss a new algorithm for patrolling by unreliable robots. We show that the presented algorithm achieves the idleness, which is the best possible.

Ligne 45 modifiée:

Lundi 24 novembre 2014 : "Distributed Computing with Beeps" - Akka Zemmari, (LaBRI, Université de Bordeaux)\\

en:

Lundi 24 novembre 2014 : "Titre à préciser" - Evangelos Bampas, (LaBRI, Université de Bordeaux)\\

17 octobre 2014 à 17h13 par 147.210.129.217 -
Lignes 13-14 modifiées:

Lundi 20 octobre 2014 : "Titre à préciser" - Nicolas Hanusse , (LaBRI, Université de Bordeaux)

en:

Lundi 20 octobre 2014 : "Routage compact en pratique. Peut-on router avec des tables de routage de taille 6 ?" - Nicolas Hanusse , (LaBRI, Université de Bordeaux)
Abstract: Le projet européen EULER portant sur des propositions de nouveaux schéma de routage vient de se terminer. Je ferai une petite présentation de nos contributions sur des algorithmes de routage compact pour lesquels nous obtenons des garanties sur l'étirement, la taille des tables ou le cout de construction. Des simulations sur des cartes des systèmes autonomes d'Internet montrent que nous pouvons obtenir des tables de petite taille ...

Ce travail a été fait avec Cyril Gavoille, Christian Glacet et David Ilcinkas.

15 octobre 2014 à 14h11 par 2001:660:6101:402:dad3:85ff:fe91:721e -
Ligne 37 modifiée:

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz, (LaBRI, Université de Bordeaux)\\

en:

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz et Matthieu Barjon, (LaBRI, Université de Bordeaux)\\

15 octobre 2014 à 14h09 par 2001:660:6101:402:dad3:85ff:fe91:721e -
Ligne 37 modifiée:

Lundi 08 décembre 2014 : "Titre à préciser" - Yves Métivier, (LaBRI, Université de Bordeaux)\\

en:

Lundi 08 décembre 2014 : "Maintaining a Spanning Forest in Highly Dynamic Networks: The Synchronous Case" - Yessin Neggaz, (LaBRI, Université de Bordeaux)\\

13 octobre 2014 à 14h43 par 147.210.129.217 -
Ligne 18 ajoutée:
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13 octobre 2014 à 14h42 par 147.210.129.217 -
Ligne 14 ajoutée:
13 octobre 2014 à 14h40 par 2001:660:6101:403::1:b4 -
Ligne 15 ajoutée:
Ligne 18 ajoutée:
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13 octobre 2014 à 14h39 par 2001:660:6101:403::1:b4 -
Ligne 11 supprimée:
Lignes 13-29 ajoutées:

Lundi 20 octobre 2014 : "Titre à préciser" - Nicolas Hanusse , (LaBRI, Université de Bordeaux)
---- Lundi 03 novembre 2014 : "Coloration d'un cycle en temps log*(n): borne sup et borne inf" - Cyril Gavoille, (LaBRI, Université de Bordeaux)
---- Lundi 10 novembre 2014 : "Titre à préciser" - Evangelos Bampas , (LaBRI, Université de Bordeaux)
---- Lundi 17 novembre 2014 : "Titre à préciser" - David Ilcinkas, (LaBRI, Université de Bordeaux)
---- Lundi 24 novembre 2014 : "Distributed Computing with Beeps" - Akka Zemmari, (LaBRI, Université de Bordeaux)
---- Lundi 01 décembre 2014 : "Titre à préciser" - Noël Gillet, (LaBRI, Université de Bordeaux)
---- Lundi 08 décembre 2014 : "Titre à préciser" - Yves Métivier, (LaBRI, Université de Bordeaux)
----

# Exposés passés

Lignes 51-53 supprimées:

# Exposés passés

03 octobre 2014 à 08h40 par 147.210.179.67 -
Ligne 14 modifiée:

Lundi 29 septembre 2014 : "k-Partitionnement auto-stabilisant " - Yvan Rivierre, (LaBRI, Université de Bordeaux)\\

en:

Lundi 03 octobre 2014 : "k-Partitionnement auto-stabilisant " - Yvan Rivierre, (LaBRI, Université de Bordeaux)\\

24 septembre 2014 à 08h15 par 147.210.179.69 -
Lignes 11-12 ajoutées:
Lignes 13-19 supprimées:

Lundi 22 septembre 2014 : Soutenance de thèse de Pierre Halftermeyer : "Connexité dans les Réseaux et Schémas d’Étiquetage Compact d’Urgence " - Amphi du LaBRI, 14h30
Abstract: On cherche à attribuer à tout sommet x d’un graphe G (à n sommets) une étiquette L(x), idéalement de taille O(log n), permettant de répondre à des requêtes de connexité avec panne Conn(u,v,X). C’est-à-dire qu’on veut, après un pré-traitement en temps O(|X|) des étiquettes des sommets de l’ensemble «en panne» X, répondre à partir des seules étiquettes L(u) et L(v), en un temps optimal O(log log n), à la question : u et v sont-ils connectés dans G\X ? On tâchera de traiter ce problème dans les graphes de genre borné ainsi que dans les graphes excluant un mineur fixé.

Lignes 15-35 modifiées:
en:

Abstract: Le k-partitionnement organise un réseau comme suit : ses nœuds sous répartis en sous-ensembles disjoints appelés grappes et pour chaque grappe, un nœud appelé tête est distingué, de sorte que chaque nœud d'une grappe est au plus à k sauts de la tête de grappe. Une application possible est de faire du routage hiérarchique en suivant des chemins entre les têtes de grappe pour l'acheminement de messages à travers le réseau. Ceci est particulièrement intéressant dans les réseaux à large échelle où la probabilité de panne est élevée. Les fautes transitoires sont des pannes non-définitives qui n'affectent que le contenu du réseau et non son code ou sa structure. Un algorithme est auto-stabilisant s'il garantit au système, une fois que les fautes transitoires cessent, de récupérer un fonctionnement normal, en temps fini et sans intervention extérieure.

Dans cet exposé, nous considérerons le problème du k-partitionnement auto-stabilisant. Il faut noter que construire un k-partitionnement de taille minimum est un problème NP-difficile. Nous proposerons un algorithme auto-stabilisant de k-partitionnement et étudierons ses propriétés dans l'arbre, dans un graphe connexe et dans un graphe de disques unitaires. Cette dernière topologie est généralement utilisée pour modéliser des réseaux de capteurs sans fil.

Lignes 39-44 ajoutées:

Lundi 22 septembre 2014 : Soutenance de thèse de Pierre Halftermeyer : "Connexité dans les Réseaux et Schémas d’Étiquetage Compact d’Urgence " - Amphi du LaBRI, 14h30
Abstract: On cherche à attribuer à tout sommet x d’un graphe G (à n sommets) une étiquette L(x), idéalement de taille O(log n), permettant de répondre à des requêtes de connexité avec panne Conn(u,v,X). C’est-à-dire qu’on veut, après un pré-traitement en temps O(|X|) des étiquettes des sommets de l’ensemble «en panne» X, répondre à partir des seules étiquettes L(u) et L(v), en un temps optimal O(log log n), à la question : u et v sont-ils connectés dans G\X ? On tâchera de traiter ce problème dans les graphes de genre borné ainsi que dans les graphes excluant un mineur fixé.

14 septembre 2014 à 21h22 par 82.239.41.63 -
Lignes 20-21 modifiées:

Abstract:

en:
Lignes 22-24 ajoutées:

# Exposés passés

Lignes 34-36 supprimées:

# Exposés passés

14 septembre 2014 à 21h19 par 82.239.41.63 -
Lignes 11-14 modifiées:
en:

Lundi 22 septembre 2014 : Soutenance de thèse de Pierre Halftermeyer : "Connexité dans les Réseaux et Schémas d’Étiquetage Compact d’Urgence " - Amphi du LaBRI, 14h30
Abstract: On cherche à attribuer à tout sommet x d’un graphe G (à n sommets) une étiquette L(x), idéalement de taille O(log n), permettant de répondre à des requêtes de connexité avec panne Conn(u,v,X). C’est-à-dire qu’on veut, après un pré-traitement en temps O(|X|) des étiquettes des sommets de l’ensemble «en panne» X, répondre à partir des seules étiquettes L(u) et L(v), en un temps optimal O(log log n), à la question : u et v sont-ils connectés dans G\X ? On tâchera de traiter ce problème dans les graphes de genre borné ainsi que dans les graphes excluant un mineur fixé.

Lundi 29 septembre 2014 : "k-Partitionnement auto-stabilisant " - Yvan Rivierre, (LaBRI, Université de Bordeaux)
Abstract:

06 juillet 2014 à 11h49 par 82.239.41.63 -
Ligne 14 ajoutée:
Lignes 15-17 supprimées:

Lundi 30 juin 2014 : "Rendez-vous d'agents mobiles tolérant aux pannes" - Arnaud Labourel, (LIF, Université Aix-Marseille)
'Abstract: Les systèmes d’agents mobiles sont des environnements distribués dans lequel les nœuds du réseau sont passifs et ce sont des agents mobiles qui s’occupent de l’exécution de l’algorithme. Le réseau est représenté par un graphe et les agents peuvent se déplacer d’un nœud à l’autre du graphe le long de ses arêtes. Dans cet exposé, on va chercher à trouver des algorithmes permettant à deux agents mobiles initialement dispersé dans le graphe de se rencontrer sur un nœud du graphe. Plus particulièrement, on s'intéressera à ce problème pour un modèle synchrone dans lequel une panne peut se produire lors de chaque tentative de déplacement des agents. On considérera trois types de pannes possibles : probabiliste (probabilité constante de panne), adversaire non borné ou borné (un adversaire peut empêcher un agent de bouger pendant un nombre de rondes fini ou bien borné par une constante). Je donnerai des bornes inférieures et supérieures sur le coût du rendez-vous (nombre de déplacements des agents avant le rendez-vous dans le pire des cas) ainsi que des résultats d'impossibilité pour ces trois types de pannes.

Lignes 22-25 ajoutées:

Lundi 30 juin 2014 : "Rendez-vous d'agents mobiles tolérant aux pannes" - Arnaud Labourel, (LIF, Université Aix-Marseille)
'Abstract: Les systèmes d’agents mobiles sont des environnements distribués dans lequel les nœuds du réseau sont passifs et ce sont des agents mobiles qui s’occupent de l’exécution de l’algorithme. Le réseau est représenté par un graphe et les agents peuvent se déplacer d’un nœud à l’autre du graphe le long de ses arêtes. Dans cet exposé, on va chercher à trouver des algorithmes permettant à deux agents mobiles initialement dispersé dans le graphe de se rencontrer sur un nœud du graphe. Plus particulièrement, on s'intéressera à ce problème pour un modèle synchrone dans lequel une panne peut se produire lors de chaque tentative de déplacement des agents. On considérera trois types de pannes possibles : probabiliste (probabilité constante de panne), adversaire non borné ou borné (un adversaire peut empêcher un agent de bouger pendant un nombre de rondes fini ou bien borné par une constante). Je donnerai des bornes inférieures et supérieures sur le coût du rendez-vous (nombre de déplacements des agents avant le rendez-vous dans le pire des cas) ainsi que des résultats d'impossibilité pour ces trois types de pannes.

26 juin 2014 à 10h08 par 147.210.179.67 -
Ligne 13 ajoutée:
Lignes 14-16 supprimées:

Lundi 23 juin 2014 : "Maintenance d'arbres et détection de déconnexion" - Christian Glacet, (LaBRI, Université de Bordeaux)
Abstract:Dans ce travail, nous proposons un algorithme auto-stabilisant de maintenance d'arbres de plus de courts chemins tout en gérant la déconnexion de graphes dynamiques ... ce qui résoud le problème du comptage à l'infini sans connaissance sur le graphe. Ce travail a été fait avec Colette Johnen, David Ilcinkas et Nicolas Hanusse.

Lignes 27-29 ajoutées:

Lundi 23 juin 2014 : "Maintenance d'arbres et détection de déconnexion" - Christian Glacet, (LaBRI, Université de Bordeaux)
Abstract:Dans ce travail, nous proposons un algorithme auto-stabilisant de maintenance d'arbres de plus de courts chemins tout en gérant la déconnexion de graphes dynamiques ... ce qui résoud le problème du comptage à l'infini sans connaissance sur le graphe. Ce travail a été fait avec Colette Johnen, David Ilcinkas et Nicolas Hanusse.

20 juin 2014 à 09h22 par 147.210.128.51 -
Ligne 12 ajoutée:
Lignes 13-15 supprimées:

Lundi 16 juin 2014 : Allyx Fontaine soutient sa thèse "Analyse et preuves formelles d’algorithmes distribués probabilistes" - Amphi du LaBRI
Abstract:

Lignes 17-19 ajoutées:

Lundi 30 juin 2014 : "Rendez-vous d'agents mobiles tolérant aux pannes" - Arnaud Labourel, (LIF, Université Aix-Marseille)
'Abstract: Les systèmes d’agents mobiles sont des environnements distribués dans lequel les nœuds du réseau sont passifs et ce sont des agents mobiles qui s’occupent de l’exécution de l’algorithme. Le réseau est représenté par un graphe et les agents peuvent se déplacer d’un nœud à l’autre du graphe le long de ses arêtes. Dans cet exposé, on va chercher à trouver des algorithmes permettant à deux agents mobiles initialement dispersé dans le graphe de se rencontrer sur un nœud du graphe. Plus particulièrement, on s'intéressera à ce problème pour un modèle synchrone dans lequel une panne peut se produire lors de chaque tentative de déplacement des agents. On considérera trois types de pannes possibles : probabiliste (probabilité constante de panne), adversaire non borné ou borné (un adversaire peut empêcher un agent de bouger pendant un nombre de rondes fini ou bien borné par une constante). Je donnerai des bornes inférieures et supérieures sur le coût du rendez-vous (nombre de déplacements des agents avant le rendez-vous dans le pire des cas) ainsi que des résultats d'impossibilité pour ces trois types de pannes.

Lignes 29-31 ajoutées:

Lundi 16 juin 2014 : Allyx Fontaine soutient sa thèse "Analyse et preuves formelles d’algorithmes distribués probabilistes" - Amphi du LaBRI
Abstract:

10 juin 2014 à 23h54 par 82.239.41.63 -
Ligne 13 modifiée:

Lundi 05 mai 2014 : "Le codage de réseau aléatoire : une introduction " - Christine Bachoc, (IMB, Université de Bordeaux)\\

en:

Lundi 16 juin 2014 : Allyx Fontaine soutient sa thèse "Analyse et preuves formelles d’algorithmes distribués probabilistes" - Amphi du LaBRI\\

Lignes 16-17 modifiées:

# Exposés passés

en:

Lundi 23 juin 2014 : "Maintenance d'arbres et détection de déconnexion" - Christian Glacet, (LaBRI, Université de Bordeaux)
Abstract:Dans ce travail, nous proposons un algorithme auto-stabilisant de maintenance d'arbres de plus de courts chemins tout en gérant la déconnexion de graphes dynamiques ... ce qui résoud le problème du comptage à l'infini sans connaissance sur le graphe. Ce travail a été fait avec Colette Johnen, David Ilcinkas et Nicolas Hanusse.

Lundi 07 juillet 2014 : "Solo-fast Universal Constructions for Deterministic Abortable Objects" - Claire Capdevielle, (LaBRI, Université de Bordeaux)
Abstract: In the context of shared memory model, we present our study on efficient implementations for deterministic abortable objects. Deterministic abortable objects behave like ordinary objects when accessed sequentially, but they may return a special response abort to indicate that the operation failed (and did not take effect) when there is contention.

It is impossible to implement deterministic abortable objects only with read/write registers. Thus, we study solo-fast implementations. These implementations use stronger synchronization primitives, e.g., CAS, only when there is contention. We consider interval contention.

We present a non-trivial solo-fast universal construction for deterministic abortable objects. A universal construction is a method for obtaining a concurrent implementation of any object from its sequential code. The construction is non-trivial since in the resulting implementation a failed process can cause only a finite number of operations to abort. Our construction guarantees that operations that do not modify the object always return a legal response and do not use CAS. Moreover in case of contention, at least one writing operation succeeds. We prove that our construction has asymptotically optimal space complexity for objects whose size is constant.

# Exposés passés

Lundi 05 mai 2014 : "Le codage de réseau aléatoire : une introduction " - Christine Bachoc, (IMB, Université de Bordeaux)
Abstract:

21 mai 2014 à 09h57 par 147.210.9.157 -
Ligne 11 supprimée:
Lignes 13-14 modifiées:

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

en:

Lundi 05 mai 2014 : "Le codage de réseau aléatoire : une introduction " - Christine Bachoc, (IMB, Université de Bordeaux)
Abstract:

Lignes 18-20 ajoutées:

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

29 avril 2014 à 10h18 par 147.210.9.157 -
Ligne 12 ajoutée:
Lignes 13-16 supprimées:

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

Lignes 19-22 ajoutées:

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

09 avril 2014 à 09h18 par 147.210.128.51 -
Ligne 11 ajoutée:
Lignes 13-22 ajoutées:

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

# Exposés passés

Lignes 37-47 modifiées:

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

# Exposés passés

en:
28 mars 2014 à 09h57 par 147.210.9.157 -
Lignes 12-13 modifiées:

Lundi 31 mars 2014 : "Titre à préciser" - Oriol Serra ( Barcelona, Spain)
Abstract:

en:

Lundi 31 mars 2014 : "Algebraic Removal Lemma" - Oriol Serra ( Barcelona, Spain)
Abstract: The removal lemma is a combinatorial result which, in its simpler form, says that a graph with n vertices and o(n^3) triangles can be made triangle free by deleting o(n^2) edges. It was used by Ruzsa and Szemerédi to provide a simple proof of Roth's theorem on 3-term arithmetic progressions in dense sets of integers. An analogous algebraic statement was formulated by Green in terms of solutions of linear equations in abelian groups. In the talk I will report on some contributions made jointly with Dan Král' and Lluís Vena to this algebraic version for linear systems in abelian groups and some consequences in arithmetic Ramsey theory. The latter include a version of Szemerédi theorem on arithmetic progressions in dense sets of finite abelian groups.

P.S. : Il s'agit d'un exposé CPU.

24 mars 2014 à 15h45 par 147.210.128.51 -
Ligne 14 ajoutée:
Lignes 15-17 supprimées:

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

Lignes 19-21 modifiées:
en:

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

24 mars 2014 à 15h44 par 147.210.128.51 -
Lignes 12-19 modifiées:

Lundi 24 mars 2014 : "Exploration and Diffusion in Graphs using Deterministic Walks " - Adrian Kosowski (LaBRI)
Abstract: In a continuous diffusive process, a certain amount of a resource, known as "load", is initially placed on the nodes of the graph, possibly in an unfair manner. In successive time steps, each node shares its load evenly among all its neighbors, until the load on the nodes of the graph eventually converges to its limit distribution (e.g., becomes uniform in the case of regular graphs). However, continuous diffusion cannot be applied to "granular load" which is not arbitrarily divisible, i.e., represented by unsplittable unit-load tokens (chips), which are placed on nodes and may be passed around the graph. In such a scenario, one natural way of simulating the continuous diffusion process is to require that each chip follows an independent random walk on the graph.

In this talk, we will instead focus on chip diffusion processes following rules which are both locally fair and deterministic. These rules include the so-called "rotor walk", in which chips are propagated by each node to its neighbors in round-robin fashion and, more broadly, rules in which each node attempts to send out roughly the same number of tokens through each of its outgoing arcs.

We will start by providing a description of the evolution and limit behavior of the rotor walk on the n-node ring with K << n chips. For general graphs, we will show bounds on the "cover time" of a rotor walk system with K chips, proving that in a graph with m edges and diameter D, all nodes will have been visited at least once by some chip during the first O(mD / log K) steps of the process. Finally, we will relate the "blanket time" (the time until all nodes of the graph have been visited by chips a similar number of times) and the "diffusion time" (the time until all nodes all host a similar number of chips, for K >> n) of fair deterministic walks to analogous parameters of the random walk. The latter results allow us to design surprisingly simple and efficient deterministic algorithms for load balancing in the diffusive model.

This talk includes an overview of results presented at PODC'13, STACS'14, and some current work in progress (joint work with: P. Berenbrink, D. Dereniowski, R. Klasing, F. Mallmann-Trent, D. Pajak, T. Sauerwald, P. Uznanski).

en:

Lundi 31 mars 2014 : "Titre à préciser" - Oriol Serra ( Barcelona, Spain)
Abstract:

Ligne 15 modifiée:

Lundi 31 mars 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)\\

en:

Lundi 05 mai 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)\\

Lignes 25-34 ajoutées:

Lundi 24 mars 2014 : "Exploration and Diffusion in Graphs using Deterministic Walks " - Adrian Kosowski (LaBRI)
Abstract: In a continuous diffusive process, a certain amount of a resource, known as "load", is initially placed on the nodes of the graph, possibly in an unfair manner. In successive time steps, each node shares its load evenly among all its neighbors, until the load on the nodes of the graph eventually converges to its limit distribution (e.g., becomes uniform in the case of regular graphs). However, continuous diffusion cannot be applied to "granular load" which is not arbitrarily divisible, i.e., represented by unsplittable unit-load tokens (chips), which are placed on nodes and may be passed around the graph. In such a scenario, one natural way of simulating the continuous diffusion process is to require that each chip follows an independent random walk on the graph.

In this talk, we will instead focus on chip diffusion processes following rules which are both locally fair and deterministic. These rules include the so-called "rotor walk", in which chips are propagated by each node to its neighbors in round-robin fashion and, more broadly, rules in which each node attempts to send out roughly the same number of tokens through each of its outgoing arcs.

We will start by providing a description of the evolution and limit behavior of the rotor walk on the n-node ring with K << n chips. For general graphs, we will show bounds on the "cover time" of a rotor walk system with K chips, proving that in a graph with m edges and diameter D, all nodes will have been visited at least once by some chip during the first O(mD / log K) steps of the process. Finally, we will relate the "blanket time" (the time until all nodes of the graph have been visited by chips a similar number of times) and the "diffusion time" (the time until all nodes all host a similar number of chips, for K >> n) of fair deterministic walks to analogous parameters of the random walk. The latter results allow us to design surprisingly simple and efficient deterministic algorithms for load balancing in the diffusive model.

This talk includes an overview of results presented at PODC'13, STACS'14, and some current work in progress (joint work with: P. Berenbrink, D. Dereniowski, R. Klasing, F. Mallmann-Trent, D. Pajak, T. Sauerwald, P. Uznanski).

20 mars 2014 à 16h19 par 147.210.128.51 -
Ligne 24 modifiée:

Lundi 14 avril 2014 : "" - Stephen Alstrup (University of Copenhagen, DK)\\

en:

Lundi 14 avril 2014 : "Some recent results for labeling schemes" - Stephen Alstrup (University of Copenhagen, DK)\\

20 mars 2014 à 16h12 par 147.210.128.51 -
Lignes 24-25 modifiées:

Lundi 14 avril 2014 : "Titre à préciser" - Stephen Alstrup (University of Copenhagen, DK)
Abstract:

en:

Lundi 14 avril 2014 : "" - Stephen Alstrup (University of Copenhagen, DK)
Abstract: We describe methods to assign to each node in a graph a label, such that given the labels of two nodes it is possible to decide (alone from the labels) if they are adjacent in the graph. This is a labeling scheme. The objective is to minimize the maximum number of bits needed to represent a label associated to a node. We will also relate this to induced universal and universal graphs. We will look at various graphs, and in addition to adjacency, we will also look at distance functions and nearest common ancestor computation in trees. The presentation will cover some recent progress including results from SODA’14.

20 mars 2014 à 13h49 par 147.210.128.51 -
Lignes 21-22 modifiées:

Lundi 7 avril 2014 : "Titre à préciser" - Cyril Gavoille (LaBRI)
Abstract:

en:

Lundi 31 mars 2014 : "Data Structures for Emergency Planning" - Cyril Gavoille (LaBRI)
Abstract: We present in this talk different techniques for quickly answer graph problems where some of the nodes may be turn off. Typical graph problems are such as connectivity or distances between pair of nodes but not only. Emergency planning for such problems is achieved by pre-processing the graphs and by virtually preventing all possible subsequent node removals. To obtain efficient data structures, the idea is to attach very little and localized information to nodes of the input graph so that queries can be solved using solely on these information. Contexts and solutions for several problems will be surveyed.

Ligne 24 modifiée:

Lundi 14 avril 2014 : "Titre à préciser" - Stephen Alstrup (University of Copenhagen)\\

en:

Lundi 14 avril 2014 : "Titre à préciser" - Stephen Alstrup (University of Copenhagen, DK)\\

20 mars 2014 à 10h29 par 147.210.9.157 -
Lignes 10-12 supprimées:
Lignes 12-13 modifiées:

Lundi 03 mars 2014 : "Algorithmes de mise à jour locale pour des graphes aléatoires" - Romaric Duvignau (LaBRI)
Abstract: Afin de modéliser l'évolution de réseaux logiques dynamiques, nous proposons de maintenir exactement une distribution donnée de graphes aléatoires lors d'une séquence arbitraire d'insertions et de suppressions de sommets. Nous nous plaçons dans un modèle local où nous n'avons pas accès à l'ensemble des sommets, mais supposons à la place l'accès à une primitive globale renvoyant un sommet aléatoire uniforme du graphe. Dans cet exposé, nous nous intéressons à maintenir la distribution uniforme dans les graphes k-sortants (graphes dirigés où tous les sommets ont degré sortant k). Nous présenterons plusieurs algorithmes d'insertion et de suppression pour le problème de maintenance, dont les plus efficaces sont asymptotiquement optimaux.

en:

Lundi 24 mars 2014 : "Exploration and Diffusion in Graphs using Deterministic Walks " - Adrian Kosowski (LaBRI)
Abstract: In a continuous diffusive process, a certain amount of a resource, known as "load", is initially placed on the nodes of the graph, possibly in an unfair manner. In successive time steps, each node shares its load evenly among all its neighbors, until the load on the nodes of the graph eventually converges to its limit distribution (e.g., becomes uniform in the case of regular graphs). However, continuous diffusion cannot be applied to "granular load" which is not arbitrarily divisible, i.e., represented by unsplittable unit-load tokens (chips), which are placed on nodes and may be passed around the graph. In such a scenario, one natural way of simulating the continuous diffusion process is to require that each chip follows an independent random walk on the graph.

In this talk, we will instead focus on chip diffusion processes following rules which are both locally fair and deterministic. These rules include the so-called "rotor walk", in which chips are propagated by each node to its neighbors in round-robin fashion and, more broadly, rules in which each node attempts to send out roughly the same number of tokens through each of its outgoing arcs.

We will start by providing a description of the evolution and limit behavior of the rotor walk on the n-node ring with K << n chips. For general graphs, we will show bounds on the "cover time" of a rotor walk system with K chips, proving that in a graph with m edges and diameter D, all nodes will have been visited at least once by some chip during the first O(mD / log K) steps of the process. Finally, we will relate the "blanket time" (the time until all nodes of the graph have been visited by chips a similar number of times) and the "diffusion time" (the time until all nodes all host a similar number of chips, for K >> n) of fair deterministic walks to analogous parameters of the random walk. The latter results allow us to design surprisingly simple and efficient deterministic algorithms for load balancing in the diffusive model.

This talk includes an overview of results presented at PODC'13, STACS'14, and some current work in progress (joint work with: P. Berenbrink, D. Dereniowski, R. Klasing, F. Mallmann-Trent, D. Pajak, T. Sauerwald, P. Uznanski).

Lignes 21-22 modifiées:

# Exposés passés

en:

Lundi 7 avril 2014 : "Titre à préciser" - Cyril Gavoille (LaBRI)
Abstract:

Lundi 14 avril 2014 : "Titre à préciser" - Stephen Alstrup (University of Copenhagen)
Abstract:

# Exposés passés

Lundi 03 mars 2014 : "Algorithmes de mise à jour locale pour des graphes aléatoires" - Romaric Duvignau (LaBRI)
Abstract: Afin de modéliser l'évolution de réseaux logiques dynamiques, nous proposons de maintenir exactement une distribution donnée de graphes aléatoires lors d'une séquence arbitraire d'insertions et de suppressions de sommets. Nous nous plaçons dans un modèle local où nous n'avons pas accès à l'ensemble des sommets, mais supposons à la place l'accès à une primitive globale renvoyant un sommet aléatoire uniforme du graphe. Dans cet exposé, nous nous intéressons à maintenir la distribution uniforme dans les graphes k-sortants (graphes dirigés où tous les sommets ont degré sortant k). Nous présenterons plusieurs algorithmes d'insertion et de suppression pour le problème de maintenance, dont les plus efficaces sont asymptotiquement optimaux.

03 mars 2014 à 11h43 par 147.210.128.51 -
Lignes 12-13 ajoutées:
Lignes 14-18 supprimées:

Lundi 24 février 2014 : "Distributed anonymous discrete function computation" - Julien Hendrickx(Univ. Louvain)
Abstract: We propose a model for deterministic distributed function computation by a network of identical and anonymous nodes:. In this model, each node has bounded computation and storage capabilities that do not grow with the network size. Furthermore, each node only knows its neighbors, not the entire graph. Our goal is to characterize the class of functions that can be computed within this model. We provide a necessary condition for computability which we show to be nearly sufficient, in the sense that every function that violates this condition can at least be approximated. The problem of computing (suitably rounded) averages in a distributed manner plays a central role in our development; we provide an algorithm that solves it in time that grows quadratically with the size of the network.

Lignes 20-23 ajoutées:

Lundi 24 février 2014 : "Distributed anonymous discrete function computation" - Julien Hendrickx(Univ. Louvain)
Abstract: We propose a model for deterministic distributed function computation by a network of identical and anonymous nodes:. In this model, each node has bounded computation and storage capabilities that do not grow with the network size. Furthermore, each node only knows its neighbors, not the entire graph. Our goal is to characterize the class of functions that can be computed within this model. We provide a necessary condition for computability which we show to be nearly sufficient, in the sense that every function that violates this condition can at least be approximated. The problem of computing (suitably rounded) averages in a distributed manner plays a central role in our development; we provide an algorithm that solves it in time that grows quadratically with the size of the network.

20 février 2014 à 16h45 par 147.210.128.51 -
Lignes 12-14 supprimées:

Lundi 17 février 2014 : "The interplay between multidimensional skylines and functional dependencies " - Sofian Maabout (LaBRI)
Abstract: We show how functional dependencies, which are agnostoc to the orders defined over the dimensions domains, can help to optimize skyline queries which, by opposition are based on orders. We present some theoretical and experimental results.

Lignes 18-19 modifiées:

# Exposés passés

en:

Lundi 03 mars 2014 : "Algorithmes de mise à jour locale pour des graphes aléatoires" - Romaric Duvignau (LaBRI)
Abstract: Afin de modéliser l'évolution de réseaux logiques dynamiques, nous proposons de maintenir exactement une distribution donnée de graphes aléatoires lors d'une séquence arbitraire d'insertions et de suppressions de sommets. Nous nous plaçons dans un modèle local où nous n'avons pas accès à l'ensemble des sommets, mais supposons à la place l'accès à une primitive globale renvoyant un sommet aléatoire uniforme du graphe. Dans cet exposé, nous nous intéressons à maintenir la distribution uniforme dans les graphes k-sortants (graphes dirigés où tous les sommets ont degré sortant k). Nous présenterons plusieurs algorithmes d'insertion et de suppression pour le problème de maintenance, dont les plus efficaces sont asymptotiquement optimaux.

# Exposés passés

Lundi 17 février 2014 : "The interplay between multidimensional skylines and functional dependencies " - Sofian Maabout (LaBRI)
Abstract: We show how functional dependencies, which are agnostoc to the orders defined over the dimensions domains, can help to optimize skyline queries which, by opposition are based on orders. We present some theoretical and experimental results.

14 février 2014 à 15h20 par 147.210.179.68 -
Lignes 15-18 ajoutées:

Lundi 24 février 2014 : "Distributed anonymous discrete function computation" - Julien Hendrickx(Univ. Louvain)
Abstract: We propose a model for deterministic distributed function computation by a network of identical and anonymous nodes:. In this model, each node has bounded computation and storage capabilities that do not grow with the network size. Furthermore, each node only knows its neighbors, not the entire graph. Our goal is to characterize the class of functions that can be computed within this model. We provide a necessary condition for computability which we show to be nearly sufficient, in the sense that every function that violates this condition can at least be approximated. The problem of computing (suitably rounded) averages in a distributed manner plays a central role in our development; we provide an algorithm that solves it in time that grows quadratically with the size of the network.

13 février 2014 à 09h26 par 147.210.9.157 -
Lignes 13-14 modifiées:

Lundi 10 février 2014 : "Algorithmes auto-stabilisants barvards" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)
Abstract: Dans le contexte des réseaux à grande échelle, la prise en compte des pannes est une nécessité évidente. Ce séminaire traite de l’auto-stabilisation, une méthode qui vise à concevoir des algorithmes distribués se « réparant d’eux-même » en cas de pannes transitoires pouvant impliquer toute modification arbitraire de l’état des processus. Plusieurs paramètres peuvent être pris en compte pour mesurer l’efficacité d’un algorithme auto-stabilisant, dont en particulier le temps de convergence et la complexité mémoire. L’importance du temps de convergence vient de la nécessité évidente pour un système de retrouver le plus rapidement possible un état valide après une panne. La nécessité de minimiser la mémoire vient, d’une part, de l’importance grandissante de réseaux offrant des espaces mémoires restreints, comme par exemple certains réseaux de capteurs, et, d’autre part, de l’intérêt de minimiser à la fois l’échange et le stockage d’information afin de limiter les potentialités de corruption de cette information. Lors de ce séminaire, nous traiterons de la minimisation de la mémoire au travers d'un exemple, à savoir le problème de l’élection d’un leader. Une borne inférieure de Ω(log n) bits de mémoire par noeud a été établie par Dolev, Gouda et Schneider (1999) pour ce problème fondamental. Cette borne n'est toutefois valable que pour des algorithmes silencieux, c'est-à-dire des algorithmes dont les registres ne sont plus modifiés lorsque le système a rejoint un état légitime. Nous verrons que, si l'on autorise l’algorithme à rester bavard (non-silencieux) même après avoir rejoint un état légitime, alors l’espace mémoire peut être amélioré d’un facteur au moins exponentiel.

en:

Lundi 17 février 2014 : "The interplay between multidimensional skylines and functional dependencies " - Sofian Maabout (LaBRI)
Abstract: We show how functional dependencies, which are agnostoc to the orders defined over the dimensions domains, can help to optimize skyline queries which, by opposition are based on orders. We present some theoretical and experimental results.

Ligne 17 ajoutée:
Lignes 19-21 ajoutées:

Lundi 10 février 2014 : "Algorithmes auto-stabilisants barvards" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)
Abstract: Dans le contexte des réseaux à grande échelle, la prise en compte des pannes est une nécessité évidente. Ce séminaire traite de l’auto-stabilisation, une méthode qui vise à concevoir des algorithmes distribués se « réparant d’eux-même » en cas de pannes transitoires pouvant impliquer toute modification arbitraire de l’état des processus. Plusieurs paramètres peuvent être pris en compte pour mesurer l’efficacité d’un algorithme auto-stabilisant, dont en particulier le temps de convergence et la complexité mémoire. L’importance du temps de convergence vient de la nécessité évidente pour un système de retrouver le plus rapidement possible un état valide après une panne. La nécessité de minimiser la mémoire vient, d’une part, de l’importance grandissante de réseaux offrant des espaces mémoires restreints, comme par exemple certains réseaux de capteurs, et, d’autre part, de l’intérêt de minimiser à la fois l’échange et le stockage d’information afin de limiter les potentialités de corruption de cette information. Lors de ce séminaire, nous traiterons de la minimisation de la mémoire au travers d'un exemple, à savoir le problème de l’élection d’un leader. Une borne inférieure de Ω(log n) bits de mémoire par noeud a été établie par Dolev, Gouda et Schneider (1999) pour ce problème fondamental. Cette borne n'est toutefois valable que pour des algorithmes silencieux, c'est-à-dire des algorithmes dont les registres ne sont plus modifiés lorsque le système a rejoint un état légitime. Nous verrons que, si l'on autorise l’algorithme à rester bavard (non-silencieux) même après avoir rejoint un état légitime, alors l’espace mémoire peut être amélioré d’un facteur au moins exponentiel.

05 février 2014 à 09h20 par 147.210.179.66 -
Lignes 10-11 supprimées:

Lundi 20 janvier 2014 : "Réunion administrative" - Nicolas Hanusse\\

20 janvier 2014 à 14h12 par 147.210.128.246 -
Lignes 15-16 modifiées:

Lundi 10 février 2014 : "Titre à préciser" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)

en:

Lundi 10 février 2014 : "Algorithmes auto-stabilisants barvards" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)
Abstract: Dans le contexte des réseaux à grande échelle, la prise en compte des pannes est une nécessité évidente. Ce séminaire traite de l’auto-stabilisation, une méthode qui vise à concevoir des algorithmes distribués se « réparant d’eux-même » en cas de pannes transitoires pouvant impliquer toute modification arbitraire de l’état des processus. Plusieurs paramètres peuvent être pris en compte pour mesurer l’efficacité d’un algorithme auto-stabilisant, dont en particulier le temps de convergence et la complexité mémoire. L’importance du temps de convergence vient de la nécessité évidente pour un système de retrouver le plus rapidement possible un état valide après une panne. La nécessité de minimiser la mémoire vient, d’une part, de l’importance grandissante de réseaux offrant des espaces mémoires restreints, comme par exemple certains réseaux de capteurs, et, d’autre part, de l’intérêt de minimiser à la fois l’échange et le stockage d’information afin de limiter les potentialités de corruption de cette information. Lors de ce séminaire, nous traiterons de la minimisation de la mémoire au travers d'un exemple, à savoir le problème de l’élection d’un leader. Une borne inférieure de Ω(log n) bits de mémoire par noeud a été établie par Dolev, Gouda et Schneider (1999) pour ce problème fondamental. Cette borne n'est toutefois valable que pour des algorithmes silencieux, c'est-à-dire des algorithmes dont les registres ne sont plus modifiés lorsque le système a rejoint un état légitime. Nous verrons que, si l'on autorise l’algorithme à rester bavard (non-silencieux) même après avoir rejoint un état légitime, alors l’espace mémoire peut être amélioré d’un facteur au moins exponentiel.

07 janvier 2014 à 14h56 par 147.210.129.41 -
Ligne 13 ajoutée:
Ligne 16 ajoutée:
07 janvier 2014 à 14h55 par 147.210.129.41 -
Ligne 14 supprimée:
07 janvier 2014 à 14h53 par 147.210.129.41 -
Ligne 10 supprimée:
Lignes 12-18 ajoutées:

Lundi 20 janvier 2014 : "Réunion administrative" - Nicolas Hanusse
---- Lundi 10 février 2014 : "Titre à préciser" - Lélia Blin (LIP6 - Université Pierre et Marie Curie)

# Exposés passés

Lignes 27-29 supprimées:

# Exposés passés

06 janvier 2014 à 09h04 par 147.210.179.69 -
Lignes 12-14 supprimées:

Lundi 16 Décembre 2013 : "Large-scale Data Stream Analysis" - Yann Busnel (LINA - Université de Nantes)
Abstract: L'objectif de cet exposé est de dresser un court état de l'art autour de l'analyse des flux de données à grande échelle, lesquels sont souvent utilisés pour du monitoring et de la sécurité, à la fois dans les réseaux et les systèmes distribués jusqu'à l'internet des objets. La problématique de ce champs de recherche consiste à extraire de l'information pertinente d'un flux de données en une passe unique (en raison de la taille du flux et de sa rapidité), et ne nécessitant qu'une quantité mémoire très faible et une puissance de calcul très limitée. Je présenterai ensuite les dernières applications utilisant nos résultats récents, lesquels vont de la détection d'intrusion, la détection de DDoS, l'échantillonnage, etc.

Lignes 25-27 ajoutées:

Lundi 16 Décembre 2013 : "Large-scale Data Stream Analysis" - Yann Busnel (LINA - Université de Nantes)
Abstract: L'objectif de cet exposé est de dresser un court état de l'art autour de l'analyse des flux de données à grande échelle, lesquels sont souvent utilisés pour du monitoring et de la sécurité, à la fois dans les réseaux et les systèmes distribués jusqu'à l'internet des objets. La problématique de ce champs de recherche consiste à extraire de l'information pertinente d'un flux de données en une passe unique (en raison de la taille du flux et de sa rapidité), et ne nécessitant qu'une quantité mémoire très faible et une puissance de calcul très limitée. Je présenterai ensuite les dernières applications utilisant nos résultats récents, lesquels vont de la détection d'intrusion, la détection de DDoS, l'échantillonnage, etc.

14 décembre 2013 à 10h44 par 82.239.41.63 -
Lignes 13-18 modifiées:

Lundi 9 Décembre 2013 : "Simulating weak shared memory" - David Bonnin (LaBRI)
Abstract: It is well known that in an asynchronous message-passing system with crash faults, one can emulate an atomic register providing that more than half of the processes are non-faulty. By contrast, when a majority of the processes may fail, simulating atomic register is not possible. I will talk about weak variants of atomic registers that can be simulated tolerating a majority of processes failures. Specifically, I will introduce a new class of registers, called $\alpha$-registers. We found a lower bound of $\alpha = M+1$ with $M=2f-n+2$ for these registers, and an explicit algorithm can emulate them with $\alpha = 2M-1$. I will also probably talk about other approaches on weak shared memory : $M$-colored registers, and $k$-splitters. This is a joint work with C. Travers.

en:

Lundi 16 Décembre 2013 : "Large-scale Data Stream Analysis" - Yann Busnel (LINA - Université de Nantes)
Abstract: L'objectif de cet exposé est de dresser un court état de l'art autour de l'analyse des flux de données à grande échelle, lesquels sont souvent utilisés pour du monitoring et de la sécurité, à la fois dans les réseaux et les systèmes distribués jusqu'à l'internet des objets. La problématique de ce champs de recherche consiste à extraire de l'information pertinente d'un flux de données en une passe unique (en raison de la taille du flux et de sa rapidité), et ne nécessitant qu'une quantité mémoire très faible et une puissance de calcul très limitée. Je présenterai ensuite les dernières applications utilisant nos résultats récents, lesquels vont de la détection d'intrusion, la détection de DDoS, l'échantillonnage, etc.

Lignes 15-17 supprimées:

Lundi 16 Décembre 2013 : "Titre à préciser" - Yann Busnel (LINA - Université de Nantes)
Abstract:

Lignes 28-34 ajoutées:

Lundi 9 Décembre 2013 : "Simulating weak shared memory" - David Bonnin (LaBRI)
Abstract: It is well known that in an asynchronous message-passing system with crash faults, one can emulate an atomic register providing that more than half of the processes are non-faulty. By contrast, when a majority of the processes may fail, simulating atomic register is not possible. I will talk about weak variants of atomic registers that can be simulated tolerating a majority of processes failures. Specifically, I will introduce a new class of registers, called $\alpha$-registers. We found a lower bound of $\alpha = M+1$ with $M=2f-n+2$ for these registers, and an explicit algorithm can emulate them with $\alpha = 2M-1$. I will also probably talk about other approaches on weak shared memory : $M$-colored registers, and $k$-splitters. This is a joint work with C. Travers.

09 décembre 2013 à 14h40 par 147.210.128.246 -
Ligne 21 ajoutée:

Abstract:

06 décembre 2013 à 09h30 par 147.210.179.67 -
Ligne 11 ajoutée:
Lignes 12-14 supprimées:

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nicolas Bonichon (LaBRI)
Abstract: This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

Ligne 18 supprimée:
Lignes 20-21 ajoutées:

Lundi 16 Décembre 2013 : "Titre à préciser" - Yann Busnel (LINA - Université de Nantes)
----

Lignes 34-36 ajoutées:

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nicolas Bonichon (LaBRI)
Abstract: This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

02 décembre 2013 à 10h43 par 147.210.128.51 -
Ligne 12 modifiée:

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nocolas Bonichon (LaBRI)\\

en:

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nicolas Bonichon (LaBRI)\\

Lignes 15-16 modifiées:

Lundi 9 Décembre 2013 : "Titre à préciser" - David Bonnin (LaBRI)
Abstract:

en:

Lundi 9 Décembre 2013 : "Simulating weak shared memory" - David Bonnin (LaBRI)
Abstract: It is well known that in an asynchronous message-passing system with crash faults, one can emulate an atomic register providing that more than half of the processes are non-faulty. By contrast, when a majority of the processes may fail, simulating atomic register is not possible. I will talk about weak variants of atomic registers that can be simulated tolerating a majority of processes failures. Specifically, I will introduce a new class of registers, called $\alpha$-registers. We found a lower bound of $\alpha = M+1$ with $M=2f-n+2$ for these registers, and an explicit algorithm can emulate them with $\alpha = 2M-1$. I will also probably talk about other approaches on weak shared memory : $M$-colored registers, and $k$-splitters. This is a joint work with C. Travers.

26 novembre 2013 à 21h17 par 82.239.41.63 -
Ligne 13 modifiée:

Abstract: Spanners planaires de degré borné This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

en:

Abstract: This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

26 novembre 2013 à 21h16 par 82.239.41.63 -
Lignes 11-13 ajoutées:

Lundi 2 Décembre 2013 : "Spanners planaires de degré borné" - Nocolas Bonichon (LaBRI)
Abstract: Spanners planaires de degré borné This talk considers the question: « What is the smallest maximum degree that can be achieved for a plane spanner of a complete Euclidean graph? » Without the planarity constraint, it is known that the answer is 3 which is also the best known lower bound on the degree of any plane spanner. With the planarity requirement, the best known upper bound on the maximum degree is 6, the last in a long sequence of results improving the upper bound. In this talk we show that the complete Euclidean graph always contains a plane spanner of maximum degree 4.

26 novembre 2013 à 14h15 par 147.210.128.51 -
Lignes 10-11 supprimées:
Lignes 12-15 ajoutées:

Lundi 9 Décembre 2013 : "Titre à préciser" - David Bonnin (LaBRI)
Abstract:

Lignes 25-27 supprimées:

Lundi 9 Décembre 2013 : "Titre à préciser" - David Bonnin (LaBRI)
Abstract:

26 novembre 2013 à 10h02 par 147.210.179.66 -
Lignes 12-14 supprimées:
Lignes 14-16 modifiées:

Lundi 25 Novembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)
Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a maximal matching for anonymous rings. Their bit complexity and time complexity are $O(\sqrt{\log n})$ with high probability. These algorithms are optimal modulo a multiplicative constant. Beyond the complexity results, the interest of this work stands in the description and the analysis of these algorithms which may be easily generalised. Furthermore, these results show a separation between the complexity of the MIS problem (and of the maximal matching problem) on the one hand and the colouring problem on the other. Colouring can be computed only in $\Omega(\log n)$ rounds on rings with high probability, while MIS is shown to have a faster algorithm. This is in contrast to other models, in which MIS is at least as hard as colouring. This is joint work with Y. Métivier, J.M. Robson and A. Zemmari

en:

Lundi 6 Janvier 2014 : "Self-stabilizing k-independent dominating set construction" - Colette Johnen(LaBRI)
Abstract: A k-independent dominating set is a k-independent set and a k-dominating set. A set of nodes, I, is k-independent if the distance between any pair of nodes in I is at least k+1. A set of nodes, D, is a k-dominating if every node is within distance k of a node of D.

I propose two self-self-stabilizing algorithm building k-independent dominating sets. The both algorithm (SID and FID) are silent, and they converge under the unfair distributed scheduler (the weakest scheduling assumption).

The algorithm FID reaches a terminal (also legitimate) configuration in at most 4n+k rounds, where n is the network size. The algorithm FID requires (k+1)log(n+1) bits per node.

The protocol SID is memory efficient : it requires only 2log((k+1)n+1)+1 bits per node. The computation of the convergence time of the protocol SID is opened question.

Lignes 29-32 ajoutées:

Lundi 25 Novembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)
Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a maximal matching for anonymous rings. Their bit complexity and time complexity are $O(\sqrt{\log n})$ with high probability. These algorithms are optimal modulo a multiplicative constant. Beyond the complexity results, the interest of this work stands in the description and the analysis of these algorithms which may be easily generalised. Furthermore, these results show a separation between the complexity of the MIS problem (and of the maximal matching problem) on the one hand and the colouring problem on the other. Colouring can be computed only in $\Omega(\log n)$ rounds on rings with high probability, while MIS is shown to have a faster algorithm. This is in contrast to other models, in which MIS is at least as hard as colouring. This is joint work with Y. Métivier, J.M. Robson and A. Zemmari

21 novembre 2013 à 23h49 par 82.239.41.63 -
Ligne 28 ajoutée:
21 novembre 2013 à 23h48 par 82.239.41.63 -
Lignes 17-20 modifiées:

Lundi 25 Novembre 2013 : "Titre à préciser" - Kévin Huguenin, (EPFL)
Abstract:

Lundi 2 Décembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)\\

en:

Lundi 25 Novembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)\\

10 novembre 2013 à 19h15 par 82.239.41.63 -
Ligne 22 modifiée:
en:

This is joint work with Y. Métivier, J.M. Robson and A. Zemmari

10 novembre 2013 à 19h14 par 82.239.41.63 -
Ligne 15 ajoutée:
Ligne 17 modifiée:

Lundi 4 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)\\

en:

Lundi 25 Novembre 2013 : "Titre à préciser" - Kévin Huguenin, (EPFL)\\

Lignes 20-21 modifiées:

Lundi 25 Novembre 2013 : "Titre à préciser" - Kévin Huguenin, (EPFL)
Abstract:

en:

Lundi 2 Décembre 2013 : "Optimal Bit Complexity Randomised Distributed MIS and Maximal Matching Algorithms for Anonymous Rings" - Allyx Fontaine (LaBRI)
Abstract: We present and analyse Las Vegas distributed algorithms which compute a MIS or a maximal matching for anonymous rings. Their bit complexity and time complexity are $O(\sqrt{\log n})$ with high probability. These algorithms are optimal modulo a multiplicative constant. Beyond the complexity results, the interest of this work stands in the description and the analysis of these algorithms which may be easily generalised. Furthermore, these results show a separation between the complexity of the MIS problem (and of the maximal matching problem) on the one hand and the colouring problem on the other. Colouring can be computed only in $\Omega(\log n)$ rounds on rings with high probability, while MIS is shown to have a faster algorithm. This is in contrast to other models, in which MIS is at least as hard as colouring.

Ligne 24 modifiée:

Lundi 2 Décembre 2013 : "Titre à préciser" - Allyx Fontaine (LaBRI)\\

en:

Lundi 9 Décembre 2013 : "Titre à préciser" - David Bonnin (LaBRI)\\

Lignes 26-28 supprimées:

Lundi 9 Décembre 2013 : "Titre à préciser" - David Bonnin (LaBRI)
Abstract:

Lignes 28-29 ajoutées:

Lundi 4 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)\\

04 novembre 2013 à 11h54 par 147.210.128.51 -
Lignes 15-16 supprimées:
Lignes 19-20 modifiées:

# Exposés passés

en:

Lundi 25 Novembre 2013 : "Titre à préciser" - Kévin Huguenin, (EPFL)
Abstract:

Lundi 2 Décembre 2013 : "Titre à préciser" - Allyx Fontaine (LaBRI)
Abstract:

Lundi 9 Décembre 2013 : "Titre à préciser" - David Bonnin (LaBRI)
Abstract:

31 octobre 2013 à 14h58 par 147.210.128.51 -
Lignes 17-23 supprimées:

Lundi 28 Octobre 2013 : "The Case for Reliable Software Transactional Networking" - Petr Kuznetsov (Paristech)
Abstract: Software-defined networking (SDN) is a novel paradigm that out-sources the control of packet-forwarding switches to a set of software controllers. The most fundamental task of these controllers is the correct implementation of the network policy, i.e., the intended network behavior. In essence, such a policy specifies the rules by which packets must be forwarded across the network. We initiate the study of the SDN control plane as a distributed system.

We introduce a formal model describing the interaction between the data plane and a distributed control plane (consisting of a collection of fault-prone controllers). Then we formulate the problem of consistentcomposition of concurrent network policy updates. The composition is enabled via a transactional interface with all-or-nothing semantics, which allows us to reason about possibilities and impossibilities in controller synchronization.

Lignes 23-27 ajoutées:

Lundi 28 Octobre 2013 : "The Case for Reliable Software Transactional Networking" - Petr Kuznetsov (Paristech)
Abstract: Software-defined networking (SDN) is a novel paradigm that out-sources the control of packet-forwarding switches to a set of software controllers. The most fundamental task of these controllers is the correct implementation of the network policy, i.e., the intended network behavior. In essence, such a policy specifies the rules by which packets must be forwarded across the network. We initiate the study of the SDN control plane as a distributed system.

We introduce a formal model describing the interaction between the data plane and a distributed control plane (consisting of a collection of fault-prone controllers). Then we formulate the problem of consistentcomposition of concurrent network policy updates. The composition is enabled via a transactional interface with all-or-nothing semantics, which allows us to reason about possibilities and impossibilities in controller synchronization.

15 octobre 2013 à 13h46 par 147.210.128.51 -
15 octobre 2013 à 13h45 par 147.210.128.51 -
Lignes 19-20 modifiées:

Lundi 28 Octobre 2013 : "Titre à préciser" - Petr Kuznetsov (Paristech)

en:

Lundi 28 Octobre 2013 : "The Case for Reliable Software Transactional Networking" - Petr Kuznetsov (Paristech)
Abstract: Software-defined networking (SDN) is a novel paradigm that out-sources the control of packet-forwarding switches to a set of software controllers. The most fundamental task of these controllers is the correct implementation of the network policy, i.e., the intended network behavior. In essence, such a policy specifies the rules by which packets must be forwarded across the network. We initiate the study of the SDN control plane as a distributed system.

We introduce a formal model describing the interaction between the data plane and a distributed control plane (consisting of a collection of fault-prone controllers). Then we formulate the problem of consistentcomposition of concurrent network policy updates. The composition is enabled via a transactional interface with all-or-nothing semantics, which allows us to reason about possibilities and impossibilities in controller synchronization.

15 octobre 2013 à 13h43 par 147.210.128.51 -
Lignes 17-23 modifiées:

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

en:
Lignes 29-34 modifiées:
en:

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

08 octobre 2013 à 15h52 par 147.210.9.157 -
Ligne 28 modifiée:

Lundi 3 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)\\

en:

Lundi 4 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)\\

30 septembre 2013 à 10h19 par 147.210.9.157 -
30 septembre 2013 à 10h18 par 147.210.9.157 -
Lignes 29-32 modifiées:

Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

en:

Abstract:

30 septembre 2013 à 10h18 par 147.210.9.157 -
30 septembre 2013 à 10h17 par 147.210.9.157 -
Lignes 28-33 modifiées:
en:

Lundi 3 Novembre 2013 : "Palindrome Recognition In The Streaming Model" - Frederik Mallmann-Trenn, (Simon Fraser University)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

30 septembre 2013 à 10h15 par 147.210.9.157 -
30 septembre 2013 à 10h13 par 147.210.9.157 -
Lignes 13-14 ajoutées:
Lignes 17-32 ajoutées:

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

Lundi 28 Octobre 2013 : "Titre à préciser" - Petr Kuznetsov (Paristech)

# Exposés passés

Lignes 58-72 supprimées:

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

Lundi 28 Octobre 2013 : "Titre à préciser" - Petr Kuznetsov (Paristech)

# Exposés passés

19 septembre 2013 à 15h24 par 147.210.9.157 -
Lignes 48-51 ajoutées:

Lundi 28 Octobre 2013 : "Titre à préciser" - Petr Kuznetsov (Paristech)\\

19 septembre 2013 à 15h22 par 147.210.9.157 -
Ligne 15 modifiée:

Lundi 23 Septembre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Petr Kuznetsov (Paristech)\\

en:

Lundi 23 Septembre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Miroslaw Korzeniowski \\

Ligne 41 ajoutée:
Lignes 43-50 modifiées:

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)
Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

en:
Lignes 52-58 ajoutées:

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)
Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

19 septembre 2013 à 15h18 par 147.210.9.157 -
Lignes 12-16 modifiées:

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)
Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

en:
Lignes 40-46 ajoutées:

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)
Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

11 septembre 2013 à 21h41 par 82.239.41.63 -
Lignes 19-20 modifiées:

Lundi 28 Octobre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Petr Kuznetsov (Paristech)\\

en:

Lundi 23 Septembre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Petr Kuznetsov (Paristech)\\

11 septembre 2013 à 21h40 par 82.239.41.63 -
Lignes 19-47 ajoutées:

Lundi 28 Octobre 2013 : "Computing Connected Components, Distributed DisasterDisclosure, and Event Extent Estimation" - Petr Kuznetsov (Paristech)
Abstract: Decentralized monitoring and alarming systems can be an attractive alternative to centralized architectures. Distributed sensor nodes (e.g., in the smart grid's distribution network) are closer to an observed event than a global and remote observer or controller. This improves the visibility and response time of the system. Moreover, in a distributed system, local problems may also be handled locally and without overloading the communication network.

This article initiates the study of alarming from a distributed computing perspective and under two fundamentally different scenarios: \emph{on-duty} and \emph{off-duty}. We model the alarming system as a sensor network consisting of a set of distributed nodes performing local measurements to sense events. In order to avoid false alarms, the sensor nodes cooperate and only escalate an event (i.e., raise an alarm) if the number of sensor nodes sensing an event exceeds a certain threshold. In the on-duty scenario, nodes not affected by the event can actively help in the communication process, while in the off-duty scenario non-event nodes are inactive.

This article presents and analyzes algorithms that minimize the reaction time of the monitoring system while avoiding unnecessary message transmissions. Moreover, lower bounds are derived that shed light on the limitations of distributed alarming systems.

Lignes 52-54 modifiées:

Lundi 28 Octobre 2013 : "Titre à préciser" - Petr Kuznetsov (Paristech)\\

en:
10 septembre 2013 à 10h51 par 147.210.128.51 -
Ligne 26 ajoutée:

05 septembre 2013 à 11h27 par 147.210.179.67 -
Ligne 19 modifiée:

Lundi 16 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)\\

en:

Lundi 14 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)\\

Lignes 23-25 ajoutées:

Lundi 28 Octobre 2013 : "Titre à préciser" - Petr Kuznetsov (Paristech)\\

05 septembre 2013 à 11h23 par 147.210.179.67 -
Ligne 12 modifiée:

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Elle, (University of Toronto)\\

en:

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Ellen, (University of Toronto)\\

Lignes 17-23 ajoutées:

Lundi 16 Octobre 2013 : "The philosopher diner revisited : a new algebraic approach for an old modeling problem ?" - David Janin, (LaBRI)
Abstract: In the field of distributed algorithm, the philosopher diner is a typical algorithmical and modeling problem. How to model distributed states ? Local transitions ? Their combinations ? Resulting global transitions ? Correctness criterion ? There are many already many modeling proposal. In this talk, we will provide yet another one. We will show how inverse semigroup theory -- a mathematical theory developed since the 50's yet quite unknown in computer science -- and the associated language theory provide robust concepts and tools for that modeling. This is a joint (exploratory) work with Anne Dicky to be presented at MSR 2013.

05 septembre 2013 à 10h59 par 147.210.179.67 -
Ligne 13 modifiée:

""Abstract:"" We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed

en:

Abstract: We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed

05 septembre 2013 à 10h58 par 147.210.179.67 -
Lignes 11-16 ajoutées:

Lundi 16 Septembre 2013 : "A General Technique for Non-blocking Trees" - Faith Elle, (University of Toronto)
""Abstract:"" We describe a general method for obtaining non-blocking implementations of a large class of tree structures where pointers are directed from parents to children. Our construction uses LLX and SCX operations, which are multi-word generalizations of the standard LL (load-link) and SC (store-conditional) operations. These operations are, in turn, implemented from single-word CAS instructions. A non-blocking implementation of a chromatic tree will be described as an example. Its height is guaranteed to be O(log n + c), where n is the number of keys stored in the tree and c is the number of incomplete update operations.

This is joint work with Trevor Brown and Eric Ruppert.

Ligne 199 modifiée:

en:

05 septembre 2013 à 10h55 par 147.210.179.67 -
Lignes 11-12 ajoutées:

# Exposés passés

Lignes 17-18 modifiées:

# Exposés passés

en:
Ligne 193 supprimée:
03 juillet 2013 à 13h20 par 147.210.8.81 -
Lignes 11-12 modifiées:

Lundi 3 Juin 2013 : "Introduction to renaming" - Corentin Travers (Labri)
Abstract: Renaming is a fundamental coordination problem in distributed computing. It consists in assigning new names taken from a small name space to processes in such a way that no two processes obtain the same name. The talk will survey renaming algorithms suited for different models of distributed computing, including the wait-free shared memory and the synchronous crash-prone message-passing models.

en:

Lundi 8 Juillet 2013 : "Dynamic Resource Allocation in Cloud Computing platforms" - Lionel Eyraud-Dubois (Labri)
Abstract: Je présente un problème d'allocation de ressources dans le contexte du Cloud Computing, où un ensemble de machines virtuelles (VM) doivent être allouées sur un ensemble de machines physiques (PMs). La particularité de ce problème vient du fait que la quantité de ressources dont chaque VM a besoin change au cours du temps, et qu'il est possible pour le fournisseur d'accès de changer l'allocation d'une VM par une opération de migration. Ce problème peut se modéliser sous la forme d'un problème de bin packing complètement dynamique, et je présente un algorithme d'approximation pour minimiser le nombre de PMs utilisées, tout en garantissant un petit nombre de migrations. Les propriétés de cet algorithme permettent également d'envisager une version distribuée.

Lignes 15-16 ajoutées:

# Exposés passés

Lignes 24-25 modifiées:

# Exposés passés

en:

Lundi 3 Juin 2013 : "Introduction to renaming" - Corentin Travers (Labri)
Abstract: Renaming is a fundamental coordination problem in distributed computing. It consists in assigning new names taken from a small name space to processes in such a way that no two processes obtain the same name. The talk will survey renaming algorithms suited for different models of distributed computing, including the wait-free shared memory and the synchronous crash-prone message-passing models.

30 mai 2013 à 13h58 par 85.68.151.221 -
Lignes 11-15 modifiées:

Lundi 27 Mai 2013 : " Exploration des graphes dynamiques T-intervalle-connexes : le cas de l'anneau" - Wade Ahmed (Labri)
Abstract: Dans cet exposé, je vais parler de l'étude des graphes dynamiques T-intervalle-connexes du point de vue du temps nécessaire à leur exploration par une entité mobile (agent). Un graphe dynamique est T-intervalle-connexe (T \geq 1) si pour chaque fenêtre de T unités de temps, il existe un sous-graphe couvrant connexe stable. Cette propriété de stabilité de connexion au cours du temps a été introduite par Kuhn, Lynch et Oshman~\cite{KLO10} (STOC 2010). Nous nous concentrons sur le cas où le graphe sous-jacent est un anneau de taille n et nous montrons que la complexité en temps en pire cas est de 2n-T-\Theta(1) unités de temps si l'agent connaît la dynamique du graphe, et n+ \frac{n}{\max\{1,T-1\}} (\delta-1) \pm \Theta(\delta) unités de temps sinon, où \delta est le temps maximum entre deux apparitions successives d'une arête.

Keywords : Graphe dynamique, exploration, T-intervalle-connexité, agent mobile

en:

Lundi 3 Juin 2013 : "Introduction to renaming" - Corentin Travers (Labri)
Abstract: Renaming is a fundamental coordination problem in distributed computing. It consists in assigning new names taken from a small name space to processes in such a way that no two processes obtain the same name. The talk will survey renaming algorithms suited for different models of distributed computing, including the wait-free shared memory and the synchronous crash-prone message-passing models.

Lignes 14-17 supprimées:

Lundi 3 Juin 2013 : - Corentin Travers (Labri)
Abstract: TBA

Lignes 24-28 ajoutées:

Lundi 27 Mai 2013 : " Exploration des graphes dynamiques T-intervalle-connexes : le cas de l'anneau" - Wade Ahmed (Labri)
Abstract: Dans cet exposé, je vais parler de l'étude des graphes dynamiques T-intervalle-connexes du point de vue du temps nécessaire à leur exploration par une entité mobile (agent). Un graphe dynamique est T-intervalle-connexe (T \geq 1) si pour chaque fenêtre de T unités de temps, il existe un sous-graphe couvrant connexe stable. Cette propriété de stabilité de connexion au cours du temps a été introduite par Kuhn, Lynch et Oshman~\cite{KLO10} (STOC 2010). Nous nous concentrons sur le cas où le graphe sous-jacent est un anneau de taille n et nous montrons que la complexité en temps en pire cas est de 2n-T-\Theta(1) unités de temps si l'agent connaît la dynamique du graphe, et n+ \frac{n}{\max\{1,T-1\}} (\delta-1) \pm \Theta(\delta) unités de temps sinon, où \delta est le temps maximum entre deux apparitions successives d'une arête.

Keywords : Graphe dynamique, exploration, T-intervalle-connexité, agent mobile

21 mai 2013 à 14h52 par 147.210.8.81 -
Lignes 18-28 modifiées:
en:

Lundi 3 Juin 2013 : - Corentin Travers (Labri)
Abstract: TBA

Lundi 10 Juin 2013 : " The Heard-Of model: computing in distributed systems with benign failures" - Bernadette Charron-Bost (CNRS, Ecole polytechnique, Paris)
Abstract: Problems in fault-tolerant distributed computing have been studied in a va- riety of system models. These models are all based on the principle that it is usefull and even necessary to specify why and by whom errors occur. In this talk, we question this principle, and present a general computational model, called the Heard-Of model, suitable for describing any type of system, be it message passing, shared memory, synchronous, or asynchronous. In this model, computations evolve in rounds, and communication missed at a round is definitely lost. Only information transmission is represented: for each round r and each process p, our model specifies the set of processes that p “hears of” at round r (heard-of set) namely the processes from which p receives some message at round r. The features of a specific system are thus captured as a whole, just by a predicate over the collection of heard-of sets. Thus the Heard-Of model allows us to handle all types of benign failures, static or dynamic, permanent or transient, in a unified framework. Moreover, it unifies the most seemingly unrelated notions in distributing computing, namely synchrony and asynchrony. We further demonstrate how this unifying framework leads to new results and insights in fault-tolerant distributed computing. In particular, we show that some fundamental results for asynchronous systems can be advantageously transferred to synchronous systems. We also examine Consensus algorithms in the Heard-Of model: we show how our approach allows us to devise new solutions and to give simple correctness proofs of existing algorithms like Paxos.

Joint work with André Schiper, EPFL

20 mai 2013 à 10h29 par 85.68.151.221 -
Lignes 12-13 modifiées:

Lundi 13 Mai 2013 : " Calcul Distribué et Fouille de Données" - Nicolas Hanusse (Labri)
Abstract: L'avènement de la production massive de données et la volonté de les exploiter sont limités par les systèmes de gestion de bases de données relationnelles classiques. Cet exposé consiste en une discussion sur les enjeux et problèmes algorithmiques engendrés par le calcul distribué et parallèle. Le calcul de corrélations servira d'illustration. C'est un travail en cours avec Sofian Maabout et Eve Garnaud.

en:

Lundi 27 Mai 2013 : " Exploration des graphes dynamiques T-intervalle-connexes : le cas de l'anneau" - Wade Ahmed (Labri)
Abstract: Dans cet exposé, je vais parler de l'étude des graphes dynamiques T-intervalle-connexes du point de vue du temps nécessaire à leur exploration par une entité mobile (agent). Un graphe dynamique est T-intervalle-connexe (T \geq 1) si pour chaque fenêtre de T unités de temps, il existe un sous-graphe couvrant connexe stable. Cette propriété de stabilité de connexion au cours du temps a été introduite par Kuhn, Lynch et Oshman~\cite{KLO10} (STOC 2010). Nous nous concentrons sur le cas où le graphe sous-jacent est un anneau de taille n et nous montrons que la complexité en temps en pire cas est de 2n-T-\Theta(1) unités de temps si l'agent connaît la dynamique du graphe, et n+ \frac{n}{\max\{1,T-1\}} (\delta-1) \pm \Theta(\delta) unités de temps sinon, où \delta est le temps maximum entre deux apparitions successives d'une arête.

Keywords : Graphe dynamique, exploration, T-intervalle-connexité, agent mobile

Lignes 21-24 ajoutées:

Lundi 13 Mai 2013 : " Calcul Distribué et Fouille de Données" - Nicolas Hanusse (Labri)
Abstract: L'avènement de la production massive de données et la volonté de les exploiter sont limités par les systèmes de gestion de bases de données relationnelles classiques. Cet exposé consiste en une discussion sur les enjeux et problèmes algorithmiques engendrés par le calcul distribué et parallèle. Le calcul de corrélations servira d'illustration. C'est un travail en cours avec Sofian Maabout et Eve Garnaud.

08 mai 2013 à 20h07 par 85.68.151.221 -
Lignes 15-19 ajoutées:

# Exposés passés

Lignes 59-61 supprimées:

# Exposés passés

08 mai 2013 à 20h02 par 85.68.151.221 -
Ligne 9 supprimée:
Lignes 11-14 ajoutées:

Lundi 13 Mai 2013 : " Calcul Distribué et Fouille de Données" - Nicolas Hanusse (Labri)
Abstract: L'avènement de la production massive de données et la volonté de les exploiter sont limités par les systèmes de gestion de bases de données relationnelles classiques. Cet exposé consiste en une discussion sur les enjeux et problèmes algorithmiques engendrés par le calcul distribué et parallèle. Le calcul de corrélations servira d'illustration. C'est un travail en cours avec Sofian Maabout et Eve Garnaud.

18 avril 2013 à 20h00 par 85.68.151.221 -
Lignes 12-20 ajoutées:

Lundi 22 Avril 2013 : " A peer-to-peer-based virtual environment system" - Eliya Buyukkaya (ENSSAT-Université de Rennes I)
Abstract: Virtual environments (VEs) are 3-D virtual worlds in which a huge number of participants play roles and interact with their surroundings through virtual representations called avatars. VEs are traditionally supported by a client/server architecture. However, centralized architectures can lead to bottleneck on the server due to high communication and computation overhead during peak loads. Thus, P2P overlay networks are emerging as a promising architecture for VEs. However, exploiting P2P schemes in VEs is not straightforward, and several challenging issues related to data distribution and state consistency should be considered.

One of the key aspects of P2P-based VEs is the logical platform consisting of connectivity, communication and data architectures, on which the VE is based. The connectivity architecture is the overlay topology structure, which defines how peers are connected to each other. The communication architecture is the routing protocol defining how peers can exchange messages, while the data architecture defines how data are distributed over the logical overlay. The design of these architectures has significant influence on the performance and scalability of VEs.

First, we propose a scalable connectivity architecture based on a new triangulation algorithm reducing maintenance cost of the system. Second, we construct a communication architecture built on top of the connectivity architecture ensuring that each message reaches its intended destination. Finally, we propose a data architecture ensuring the management of data with different characteristics in terms of mobility in the VE, while providing a fair data distribution and low data transfer between peers in the VE.

09 avril 2013 à 20h06 par 85.68.151.221 -
Ligne 12 modifiée:

Lundi 15 Avril 2013 : " Algorithms for the Vertex Cover Problem on Large Graphs with Low Memory Capacities" - Romain Campigotto (LIP6)\\

en:

Lundi 15 Avril 2013 : " Algorithms for the Vertex Cover Problem on Large Graphs with Low Memory Capacities" - Romain Campigotto (LIP6-Paris)\\

09 avril 2013 à 19h58 par 85.68.151.221 -
Lignes 12-21 ajoutées:

Lundi 15 Avril 2013 : " Algorithms for the Vertex Cover Problem on Large Graphs with Low Memory Capacities" - Romain Campigotto (LIP6)
Abstract: Most of the known optimization algorithms need to explore, mark, modify, etc. the instance given as input before producing their results. To do that, the instance is entirely loaded into the memory of the computer and is manipulated by the algorithm. Often, "extra" data structures are also necessary to memorize parameters useful all along the computation or to update the current solution that will be returned as the final product of the program. However, this classical model is no more adapted for many new computing applications. Indeed, nowadays, many fields such as biology, meteorology, finance, etc. produce very large amount of data.

In our works, we have focused on the Vertex Cover problem on huge graphs: in the intrinsic NP-completeness is added the difficulty to manipulate graphs with severe constraints (mainly related to the low memory capacities). We defined a treatment model combining some properties of several existing models in the literature: streaming, online, I/O-efficient, etc. We initially considered three approximation algorithms, which are memory-efficient (they use a memory space in O(log n) bits). We analyzed their performance in terms of solution quality and complexity, in mean and worst cases. We then focused on algorithms that use memory space of n bits. We showed that it could be very worst with strictly less than n bits memory space. Subsequently, we conducted experiments on very large graphs (in the order of billions of vertices and edges). This study showed that in practice, memory-efficient algorithms are better suited to handle large graphs.

This is joint work with Eric Angel (IBISC, Univ. Évry) and Christian Laforest (LIMOS, ISIMA, Clermont-Ferrand).

03 avril 2013 à 00h33 par 85.68.151.221 -
Lignes 12-16 ajoutées:

Lundi 8 Avril 2013 : "Implémentation d'algorithmes distribués à l'aide de Visidia" - Mohamed Mosbah (Labri)
Abstract: Dans le cadre du projet visidia, une plate-forme logicielle est développée pour l'implantation et la visualisation d'algorithmes distribués. Après une introduction et quelques rappels, l'exposé consistera en une présentation de la plate-forme et de son utilisation pour programmer des exemples d'algorithmes. L'interface et l'API permettent de visualiser l'exécution d'algorithmes, d'implanter de nouveaux algorithmes, ou d'effectuer des statistiques. Les algorithmes peuvent être exprimés selon plusieurs modèles (calculs locaux, passage de messages, agents mobiles).

08 mars 2013 à 09h36 par 85.68.151.221 -
Lignes 13-14 modifiées:

Lundi 25 Mars 2013 : "Simultaneous Consensus vs Set Agreement." - Zohir Bouzid (LIP6-Paris)

en:

Lundi 25 Mars 2013 : "Simultaneous Consensus vs Set Agreement." - Zohir Bouzid (LIP6-Paris)

Lignes 28-30 ajoutées:

# Exposés passés

08 mars 2013 à 09h32 par 85.68.151.221 -
Lignes 12-19 ajoutées:

Lundi 25 Mars 2013 : "Simultaneous Consensus vs Set Agreement." - Zohir Bouzid (LIP6-Paris)
Abstract: In the traditional consensus task, processes are required to agree on a common value chosen among the initial values of the participants. It is well known that consensus cannot be solved in crashed-prone, asynchronous distributed systems. Two generalizations of the consensus problem have been introduced: k-set agreement and k-simultaneous consensus. The k-set agreement task has the same requirements as consensus except that processes are allowed to decide up to k distinct values. In the k-simultaneous consensus task, each process participates simultaneously in k instances of consensus and is required to decide in at least one of them; any two processes deciding in the same instance must decide the same value. In this talk, we compare the computability of these problems in two central models in distributed computing: shared memory and message passing. We show that even though the two problems are equivalent in shared memory, k-simultaneous consensus is strictly harder than k-set agreement in the message passing model. This result will serve as a basis for a discussion about different models of computation and their respective power.

Ligne 22 modifiée:

'Abstract: Derrière les notions de "graphe dynamique" ou de "réseau dynamique" se cache une très grande diversité de scénarios et d'hypothèses, allant de réseaux semi-statiques où la connexité est toujours assurée à des réseaux complètement mobiles, où la connexité ne s'établit qu'à travers le temps et l'espace (e.g. DTNs).

en:

Abstract: Derrière les notions de "graphe dynamique" ou de "réseau dynamique" se cache une très grande diversité de scénarios et d'hypothèses, allant de réseaux semi-statiques où la connexité est toujours assurée à des réseaux complètement mobiles, où la connexité ne s'établit qu'à travers le temps et l'espace (e.g. DTNs).

08 mars 2013 à 09h26 par 85.68.151.221 -
Lignes 12-20 ajoutées:

Lundi 18 Mars 2013 : "Vers une classification des réseaux dynamiques en fonction des problèmes qu'on peut y résoudre." - Arnaud Casteigts (Labri)
'Abstract: Derrière les notions de "graphe dynamique" ou de "réseau dynamique" se cache une très grande diversité de scénarios et d'hypothèses, allant de réseaux semi-statiques où la connexité est toujours assurée à des réseaux complètement mobiles, où la connexité ne s'établit qu'à travers le temps et l'espace (e.g. DTNs). Dans cet exposé, résolument transversal, je présenterai l'état d'avancement de nos recherches autour de la question suivante : quel lien existe-t-il entre la "faisabilité" de tâches distribuées et la dynamique du réseau. Les hypothèses résultantes sur la dynamique peuvent être vues comme autant de classes de graphes (ou alternativement, comme autant de puissances possibles pour un adversaire qui contrôlerait la topologie). Nous avons à ce jour caractérisé et/ou recensé une petite vingtaine de classes de ce type.

Certains de ces travaux ont été menés en collaboration avec Serge Chaumette et Afonso Ferreira. D'autres avec Paola Flocchini et Nicola Santoro.

24 février 2013 à 20h22 par 85.68.151.221 -
Lignes 12-17 ajoutées:

Lundi 25 Février 2013 : "Sur les 1001 modèles en algorithmique distribuée." - Yves Metivier (Labri)
Abstract: Le but de cet "exposé-discussion" est de présenter quelques modèles en algorithmique distribuée et d'échanger sur leurs liens et leurs mérites.

13 février 2013 à 15h54 par 85.68.151.221 -
Lignes 12-22 ajoutées:

Lundi 18 Février 2013 : "Distributed Calculation of Graph Diameter" - Mike Robson (Labri)
Abstract: We consider the problem of calculating the diameter of a graph given that there is a single vertex "Leader" and neighbouring vertices can exchange messages of a single bit at each round. We show that this can be achieved in the same O(n) time complexity as well known algorithms without this bound on message length. The techniques used can be applied to a number of other graph computations. We consider briefly how the algorithm behaves if applied in a situation where more than one vertex considers itself the Leader.

This is joint work with Yves Métivier and Akka Zemmari.

06 février 2013 à 14h02 par 85.68.151.221 -
Lignes 12-19 ajoutées:

Lundi 11 Février 2013 : "Bounds for Communication in Wireless Grids" - Joseph Peters (Simon Fraser University)
Abstract: In a wireless network, a transmission can be received by a node if it is close enough to the sender. However, transmissions can interfere with each other and the interference distance is typically greater than the reception distance. Efficient communication protocols in these networks minimize the time to move information without interference. In this talk, I will describe optimal protocols for the problem of collecting information into a central node of a two-dimensional square or hexagonal grid graph. The optimality of the protocols is proved using a new lower bound technique that is an adaptation to a discrete environment of a method based on linear programming duality for continuous flows.

This is joint work with Jean-Claude Bermond, CNRS-INRIA-University of Nice.

23 janvier 2013 à 12h23 par 147.210.8.81 -
Lignes 13-17 ajoutées:

Lundi 04 Février 2013 : "Distributed Detection of Clone Attacks in Wireless Sensor Networks" - Mauro Conti (University of Padua, Italy)
Abstract: Wireless Sensor Networks (WSNs) are often deployed in hostile environments where an adversary can physically capture some of the nodes, first can reprogram, and then, can replicate them in a large number of clones, easily taking control over the network. A few distributed solutions to address this fundamental problem have been recently proposed. However, these solutions are not satisfactory. First, they are energy and memory demanding: A serious drawback for any protocol to be used in the WSN-resource-constrained environment. Further, they are vulnerable to the specific adversary models that we introduced. The contributions of our work are threefold. First, we analyze the desirable properties of a distributed mechanism for the detection of node replication attacks. Second, we show that the known solutions for this problem do not completely meet our requirements. Third, we propose a new self-healing, Randomized, Efficient, and Distributed (RED) protocol for the detection of node replication attacks, and we show that it satisfies the introduced requirements. Finally, extensive simulations show that our protocol is highly efficient in communication, memory, and computation; is much more effective than competing solutions in the literature; and is resistant to the new kind of attacks introduced in our work, while other solutions are not.

Ligne 23 supprimée:
21 janvier 2013 à 10h43 par 147.210.204.186 -
Ligne 21 modifiée:

Abstract: A destination des cabinets de propritété industrielle et des services juridiques, Keep Alert propose des surveillances de marque parmi les noms de domaine, les régies publicitaires et les réseaux sociaux. Anthony DON, directeur technique chez Keep Alert, présentera au groupe de travail, le fonctionnement global de la plateforme, puis abordera les problématiques actuelles et les perspectives de développement relatives à l'algorithmique distribuée.

en:

Abstract: A destination des cabinets de propriété industrielle et des services juridiques, Keep Alert propose des surveillances de marque parmi les noms de domaine, les régies publicitaires et les réseaux sociaux. Anthony DON, directeur technique chez Keep Alert, présentera au groupe de travail, le fonctionnement global de la plateforme, puis abordera les problématiques actuelles et les perspectives de développement relatives à l'algorithmique distribuée.

18 janvier 2013 à 15h38 par 147.210.8.81 -
Lignes 20-21 modifiées:

Lundi 21 Janvier 2013 : "Autour de quelques problèmes en fouille de données distribuées" - Nicolas Hanusse (Labri) \\

en:

Lundi 21 Janvier 2013 : "Présentation de Keep Alert, une solution pour la surveillance de marques sur Internet" - Anthony Don (Keep Alert)
Abstract: A destination des cabinets de propritété industrielle et des services juridiques, Keep Alert propose des surveillances de marque parmi les noms de domaine, les régies publicitaires et les réseaux sociaux. Anthony DON, directeur technique chez Keep Alert, présentera au groupe de travail, le fonctionnement global de la plateforme, puis abordera les problématiques actuelles et les perspectives de développement relatives à l'algorithmique distribuée.

06 janvier 2013 à 12h13 par 85.68.151.221 -
Ligne 31 ajoutée:
06 janvier 2013 à 11h59 par 85.68.151.221 -
Lignes 12-23 ajoutées:

Lundi 28 Janvier 2013 : "Distributed Exclusive Graph Searching in Trees" - Janna Burman (LRI-Université Paris-Sud)
Abstract: We consider a version of the well known graph searching problem, where a team of robots aims at clearing the contaminated edges of a graph. We study graph searching in the model of mobile computing where autonomous deterministic robots move between the graph nodes when operating in asynchronous cycles of Look-Compute-Move. Moreover, motivated by physical constraints, following some recent works, we consider the exclusivity property, stating that no two or more robots can occupy a same node at the same time. In addition, we assume that all the graph elements and the robots are anonymous. Robots are oblivious and have no sense of direction. Our objective is to characterize for a graph $G$, the set of integers $k$ such that graph searching can be achieved by a team of $k$ robots starting from any $k$ distinct nodes in $G$. Our main result consists in a full characterization for any asymmetric tree. Towards providing a characterization in the general case, including trees with non-trivial automorphisms, we provide a set of positive and negative results, including a full characterization for any line. All our positive results are based on the design of algorithms enabling perpetual graph searching to be achieved with the desired number of robots. We prove that, in addition to the distributed nature of our setting, the exclusivity property has a significant impact on the nature of the graph searching problem. Hence, the design of the algorithms requires to invent new methods.

Lundi 21 Janvier 2013 : "Autour de quelques problèmes en fouille de données distribuées" - Nicolas Hanusse (Labri)

21 novembre 2012 à 14h21 par 147.210.64.24 -
Ligne 12 modifiée:

Lundi 10 Décembre 2012 : "Two Monte-Carlo Election Algorithms for Anonymous Graphs without any Initial Knowledge" - Akka Zemmari (Labri) \\

en:

Lundi 14 Janvier 2013 : "Two Monte-Carlo Election Algorithms for Anonymous Graphs without any Initial Knowledge" - Akka Zemmari (Labri) \\

Lignes 17-19 ajoutées:

Lundi 10 Décembre 2012 : pas de seminaire. Soutenance de thèse-Florent Foucaud. \\

19 novembre 2012 à 12h08 par 147.210.8.81 -
Lignes 20-23 modifiées:

Lundi 3 Décembre 2012 : Cyril Gavoille (Labri) \\

en:

Lundi 3 Décembre 2012 : "Progress and Challenges for Labeling Schemes" - Cyril Gavoille (Labri)
Abstract: A fundamental question in Distributed Computing is to understand how localized and how much information are required to solve a task on a network. Typically, if the distance between any pair x,y of nodes in a network is asked, we would like to know which minimal information about x and y in the network are needed. The goal in labeling schemes is precisely to understand how much information must be attached to the nodes (formalized as labels) to solve a graph problem assuming the answer can be determined solely on the basis of the labels of the nodes invoked in the query. In this talk, I give a survey on labeling schemes, present some recent results with their techniques, and highlight new challenges.

15 novembre 2012 à 12h15 par 85.171.223.215 -
Ligne 18 modifiée:
en:

15 novembre 2012 à 12h12 par 85.171.223.215 -
Lignes 12-18 ajoutées:

Lundi 10 Décembre 2012 : "Two Monte-Carlo Election Algorithms for Anonymous Graphs without any Initial Knowledge" - Akka Zemmari (Labri)
Abstract: The paper proposes and analyses two Monte Carlo election algorithms for anonymous graphs without any initial knowledge. Both have a time complexity equal to $O(D)$, where $D$ is the diameter of the graph. The first is correct with probability $1-o(n^{-1})$ (where $n$ is the size of the graph). The size of messages is $O(\log n)$ with probability $1-o(n^{-1})$ and the expected value of the size of messages is also $O(\log n)$. The second is correct with probability $1-o(n^{-c})$ for any $c\geq 1$. The size of messages is $O\left((\log n)(\log^* n)^2 \right)$ with probability $1-o(n^{-c})$ for any $c\geq 1$; their expected size is $O\left((\log n)(\log^* n) \right)$.

This is a joint work with Y. Métivier and J. M. Robson

13 novembre 2012 à 20h32 par 85.171.223.215 -
Lignes 19-23 modifiées:

Lundi 19 Novembre 2012: Olivier Beaumont (Labri)\\

en:

Lundi 19 Novembre 2012: " Reliable Service Allocation in Clouds"- Lionel Eyraud-Dubois, Olivier Beaumont (Labri)
Abstract: We consider several reliability problems that arise when allocating applications to processing resources in a Cloud computing platform. More specifically, we assume on the one hand that each computing resource is associated to a capacity constraint and to a probability of failure. On the other hand, we assume that each service runs as a set of independent instances of identical Virtual Machines, and that the Service Level Agreement between the Cloud provider and the client states that a minimal number of instances of the service should run with a given probability. In this context, given the capacity and failure probabilities of the machines, and the capacity and reliability demands of the services, the question for the cloud provider is to find an allocation of the instances of the services (possibly using replication) onto machines satisfying all types of constraints. In this paper, our goal is to assess the impact of the reliability constraint on the complexity of resource allocation problems. We consider several variants this problem, depending on the number of services (one or many) and if their reliability demand is individual or global. We prove several fundamental complexity results ($\#$P and NP-completeness results) and we provide several optimal and approximation algorithms. In particular, we prove that a basic randomized allocation algorithm, that is easy to implement, provides optimal or quasi-optimal results in several contexts, and we show through simulations that it also achieves very good results in more general settings.

11 novembre 2012 à 20h15 par 85.171.223.215 -
Ligne 15 modifiée:

Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we should how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.

en:

Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we showed how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.

09 novembre 2012 à 12h08 par 85.171.223.215 -
Lignes 15-18 modifiées:

Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we should how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.\\

en:

Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we should how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.

09 novembre 2012 à 12h07 par 85.171.223.215 -
Lignes 13-14 modifiées:

Lundi 3 Décembre 2012 : ? -
Lundi 26 Novembre 2012: Prosenjit Bose (Carleton University)\\

en:

Lundi 3 Décembre 2012 : Cyril Gavoille (Labri)
Lundi 26 Novembre 2012: "Competitive Routing on a Variant of the Delaunay Triangulation" - Prosenjit Bose (Carleton University)
Abstract: A subgraph H of a weighted graph G is a t-spanner of G provided that for every edge xy in G, the weight of the shortest path between x and y in H is at most t times the weight of xy. It is known that the Delaunay triangulation of a point set P (where the empty region is an equilateral triangle) is a 2-spanner of the complete Euclidean graph. We present a new and simple proof of this spanning ratio that allows us to route competitively on this graph. Specifically, we present a deterministic local routing scheme that is guaranteed to find a short path between any pair of vertices in this Delaunay triangulation. We guarantee that the length of the path is at most 5/sqrt(3) times the Euclidean distance between the pair of vertices. Moreover, we show that no local routing scheme can achieve a better competitive spanning ratio thereby implying that our routing scheme is optimal. This is somewhat surprising since the spanning ratio is 2. Finally, we should how this routing scheme can be extended to route on some bounded degree subgraphs of this Delaunay triangulation.\\

07 novembre 2012 à 11h06 par 147.210.8.81 -
Ligne 17 modifiée:

Abstract:' In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

en:

Abstract: In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

07 novembre 2012 à 11h06 par 147.210.8.81 -
Lignes 17-18 modifiées:

'Abstract: 'In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

en:

Abstract:' In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

Lignes 23-26 modifiées:

Lundi 15 Octobre 2012: Ralf Klasing (LaBRI)
Lundi 8 Octobre 2012 : pas de séminaire
----

en:
Ligne 28 modifiée:
en:

Lundi 8 Octobre 2012 : pas de séminaire\\

07 novembre 2012 à 11h03 par 147.210.8.81 -
Ligne 16 modifiée:

Lundi 12 Novembre 2012 : Dominik Pająk (LaBRI)\\

en:

Lundi 12 Novembre 2012 : "MAXIMUM MATCHING IN MULTI-INTERFACE NETWORK"- Dominik Pająk (LaBRI)\\

Lignes 18-20 ajoutées:

07 novembre 2012 à 11h01 par 147.210.8.81 -
Ligne 17 ajoutée:

'Abstract: 'In heterogeneous networks, devices can communicate by means of multiple wireless interfaces. By choosing which interfaces to switch on at each device, several connections might be established. That is, the devices at the endpoints of each connection share at least one active interface. In this paper, we consider the standard matching problem in the context of multi-interface wireless networks. The aim is to maximize the number of parallel connections without incurring in interferences.

05 novembre 2012 à 15h22 par 147.210.8.81 -
Ligne 13 modifiée:

Lundi 3 Décembre 2012 : ? - Dominik Pająk (LaBRI)\\

en:

Lundi 3 Décembre 2012 : ? - \\

Lignes 15-16 modifiées:

Lundi 19 Novembre 2012: Cours sur Visidia
Lundi 12 Novembre 2012 : Session Logiciels (LaBRI)\\

en:

Lundi 19 Novembre 2012: Olivier Beaumont (Labri)
Lundi 12 Novembre 2012 : Dominik Pająk (LaBRI)\\

04 novembre 2012 à 15h41 par 85.171.223.215 -
Ligne 17 modifiée:

Lundi 5 Novembre 2012 : Thomas Morsellino (LaBRI)\\

en:

Lundi 5 Novembre 2012 : pas de séminaire \\

17 octobre 2012 à 10h28 par 147.210.8.81 -
Lignes 19-22 modifiées:

Lundi 5 Novembre 2012 : ? - Thomas Morsellino (LaBRI)
Lundi 22 Octobre 2012 : "?" - Christian Glacet (LaBRI)
Lundi 15 Octobre 2012: "?" - Ralf Klasing (LaBRI)
Lundi 8 Octobre 2012 : ? - pas de séminaire\\

en:

Lundi 5 Novembre 2012 : 'Thomas Morsellino (LaBRI)
Lundi 22 Octobre 2012 : Christian Glacet (LaBRI)
Lundi 15 Octobre 2012: Ralf Klasing (LaBRI)
Lundi 8 Octobre 2012 : pas de séminaire\\

15 octobre 2012 à 14h00 par 147.210.8.81 -
Lignes 35-36 modifiées:

Abstract: We address the problem of verifying the accuracy of a map of a network by making as few measurements as possible on its nodes. This task can be formalized as an optimization problem that, given a graph G=(V,E), and a query model specifying the information returned by a query at a node, asks for finding a minimum-size subset of nodes of G to be queried so as to univocally identify G. This problem has been faced w.r.t. a couple of query models assuming that a node had some global knowledge about the network. Here, we propose a new query model based on the local knowledge a node instead usually has. Quite naturally, we assume that a query at a given node returns the associated routing table, i.e., a set of entries which provides, for each destination node, a corresponding (set of) first-hop node(s) along an underlying shortest path. First, we show that any network of n nodes needs Omega(log log n) queries to be verified. Then, we prove that there is no o(log n)-approximation alg

 orithm for the problem, unless P=NP, even for networks of diameter 2. On the positive side, we provide an O(log n)-approximation algorithm to verify a network of diameter 2, and we give exact polynomial-time algorithms for paths, trees, and cycles of even length.

en:

Abstract: We address the problem of verifying the accuracy of a map of a network by making as few measurements as possible on its nodes. This task can be formalized as an optimization problem that, given a graph G=(V,E), and a query model specifying the information returned by a query at a node, asks for finding a minimum-size subset of nodes of G to be queried so as to univocally identify G. This problem has been faced w.r.t. a couple of query models assuming that a node had some global knowledge about the network. Here, we propose a new query model based on the local knowledge a node instead usually has. Quite naturally, we assume that a query at a given node returns the associated routing table, i.e., a set of entries which provides, for each destination node, a corresponding (set of) first-hop node(s) along an underlying shortest path. First, we show that any network of n nodes needs Omega(log log n) queries to be verified. Then, we prove that there is no o(log n)-approximation algorithm for the problem, unless P=NP, even for networks of diameter 2. On the positive side, we provide an O(logn)-approximation algorithm to verify a network of diameter 2, and we give exact polynomial-time algorithms for paths, trees, and cycles of even length.

15 octobre 2012 à 14h00 par 147.210.8.81 -
Lignes 37-38 ajoutées:
15 octobre 2012 à 13h59 par 147.210.8.81 -
Ligne 22 modifiée:

Lundi 8 Octobre 2012 : ? - pas de séminaire (fête du LaBRI)\\

en:

Lundi 8 Octobre 2012 : ? - pas de séminaire\\

Lignes 33-36 ajoutées:

Lundi 15 Octobre: " NETWORK VERIFICATION VIA ROUTING TABLE QUERIES" - Ralf Klasing (LaBRI)
Abstract: We address the problem of verifying the accuracy of a map of a network by making as few measurements as possible on its nodes. This task can be formalized as an optimization problem that, given a graph G=(V,E), and a query model specifying the information returned by a query at a node, asks for finding a minimum-size subset of nodes of G to be queried so as to univocally identify G. This problem has been faced w.r.t. a couple of query models assuming that a node had some global knowledge about the network. Here, we propose a new query model based on the local knowledge a node instead usually has. Quite naturally, we assume that a query at a given node returns the associated routing table, i.e., a set of entries which provides, for each destination node, a corresponding (set of) first-hop node(s) along an underlying shortest path. First, we show that any network of n nodes needs Omega(log log n) queries to be verified. Then, we prove that there is no o(log n)-approximation alg

 orithm for the problem, unless P=NP, even for networks of diameter 2. On the positive side, we provide an O(log n)-approximation algorithm to verify a network of diameter 2, and we give exact polynomial-time algorithms for paths, trees, and cycles of even length.

05 octobre 2012 à 11h22 par 81.56.255.99 -
Ligne 22 modifiée:

Lundi 8 Octobre 2012 : ? - pas de séminaire (LaBRI)\\

en:

Lundi 8 Octobre 2012 : ? - pas de séminaire (fête du LaBRI)\\

05 octobre 2012 à 11h21 par 81.56.255.99 -
Ligne 16 modifiée:

Lundi 26 Novembre 2012: Prosenjit Bose \\

en:

Lundi 26 Novembre 2012: Prosenjit Bose (Carleton University)\\

05 octobre 2012 à 11h20 par 81.56.255.99 -
Ligne 15 modifiée:
en:

Lundi 3 Decembre 2012 : ? - Dominik Pająk (LaBRI)\\

Ligne 22 modifiée:

Lundi 8 Octobre 2012 : ? - Dominik Pająk (LaBRI)\\

en:

Lundi 8 Octobre 2012 : ? - pas de séminaire (LaBRI)\\

05 octobre 2012 à 10h13 par 81.56.255.99 -
Ligne 16 ajoutée:

Lundi 26 Novembre 2012: Prosenjit Bose \\

01 octobre 2012 à 14h40 par 147.210.129.249 -
Lignes 15-17 ajoutées:

Lundi 19 Novembre 2012: Cours sur Visidia
Lundi 12 Novembre 2012 : Session Logiciels (LaBRI)\\

01 octobre 2012 à 14h28 par 147.210.129.249 -
Lignes 15-18 ajoutées:

Lundi 5 Novembre 2012 : ? - Thomas Morsellino (LaBRI)
Lundi 22 Octobre 2012 : "?" - Christian Glacet (LaBRI)
Lundi 15 Octobre 2012: "?" - Ralf Klasing (LaBRI)
Lundi 8 Octobre 2012 : ? - Dominik Pajak (LaBRI)\\

01 octobre 2012 à 12h01 par 147.210.8.180 -
Lignes 22-23 ajoutées:
• enseignement: état des lieux des enseignements locaux
• stages X, ENS, ...
01 octobre 2012 à 11h57 par 147.210.8.180 -
Ligne 17 modifiée:

Lundi 1er Octobre : Réunion de rentrée du thème - Nicolas Hanusse (LaBRI)\\

en:

Lundi 1er Octobre 2012 : Réunion de rentrée du thème - Nicolas Hanusse (LaBRI)\\

01 octobre 2012 à 11h57 par 147.210.8.180 -
Lignes 20-21 modifiées:
• organisation du groupe de travail: exposé à venir (projets à long terme, discussion sur les modèles, logiciels, ...)
en:
• organisation du groupe de travail: exposé à venir (projets à long terme, discussion sur les modèles, logiciels, ...), vitrine
• mise-à-jour site web
01 octobre 2012 à 11h56 par 147.210.8.180 -
Ligne 20 modifiée:
• organisation du groupe de travail: exposé à venir (projets à long terme, logiciels, ...)
en:
• organisation du groupe de travail: exposé à venir (projets à long terme, discussion sur les modèles, logiciels, ...)
01 octobre 2012 à 11h55 par 147.210.8.180 -
Lignes 11-12 ajoutées:
Lignes 14-23 ajoutées:

Lundi 1er Octobre : Réunion de rentrée du thème - Nicolas Hanusse (LaBRI)
Abstract: L'ordre du jour:

• projets: thèse, région, ingénieur, conférence
• organisation du groupe de travail: exposé à venir (projets à long terme, logiciels, ...)

14 juin 2010 à 21h36 par 88.170.241.129 -
Lignes 17-18 modifiées:

containing $1$ bit, its bit complexity per channel is $O(log n)$.

en:

containing $1$ bit, its bit complexity per channel is $O(log n)$.\\

Lignes 21-22 modifiées:

$O(log n)$ with probability $1-o(n^{-1}).$

en:

$O(log n)$ with probability $1-o(n^{-1}).$\\

Lignes 25-26 modifiées:

or the radius of trees of the spanning forest.

en:

or the radius of trees of the spanning forest.\\

Lignes 29-30 modifiées:

on the size) of graphs is known.

en:

on the size) of graphs is known.\\

14 juin 2010 à 21h36 par 88.170.241.129 -
Lignes 12-36 ajoutées:

Lundi 21 Juin : "ABOUT RANDOMISED DISTRIBUTED GRAPH COLOURING AND GRAPH PARTITION ALGORITHMS" - Akka Zemmari (LaBRI)
Abstract: We present and analyse a very simple randomised distributed vertex colouring algorithm for arbitrary graphs of size $n$ that halts in time $O(log n)$ with probability $1-o(n^{-1}).$ Each message containing $1$ bit, its bit complexity per channel is $O(log n)$.

From this algorithm, we deduce and analyse a randomised distributed vertex colouring algorithm for arbitrary graphs of maximum degree $Delta$ and size $n$ that uses $Delta+1$ colours and halts in time $O(log n)$ with probability $1-o(n^{-1}).$

We also obtain a partition algorithm for arbitrary graphs of size $n$ that builds a spanning forest in time $O(log n)$ with probability $1-o(n^{-1})$. We study some parameters such as the number, the size or the radius of trees of the spanning forest.

We assume that graphs are anonymous; we only assume that each vertex distinguishes between its neighbours by locally known channel names. Furthermore we do not assume that the size (or an upper bound on the size) of graphs is known.

Joint work with Y. Métivier, N. Saheb and J.M. Robson

10 juin 2010 à 10h03 par 147.210.129.51 -
Lignes 13-14 modifiées:

Lundi 14 Juin : Almost optimal asynchronous rendezvous in infinite multidimensional grids - Arnaud Labourel (LaBRI)

en:

Lundi 14 Juin : Almost optimal asynchronous rendezvous in infinite multidimensional grids - Arnaud Labourel (LaBRI)\\

10 juin 2010 à 10h03 par 147.210.129.51 -
Ligne 14 ajoutée:
09 juin 2010 à 09h38 par 147.210.129.51 -
Lignes 14-17 modifiées:

Abstract: Dans cet exposé, je montrerais comment deux agents mobiles peuvent se rencontrer dans une grille infinie de dimension supérieure à 2. On considère le modèle asynchrone. C'est-à-dire que la durée de traversée de chaque sommet par un agent est déterminée par un adversaire omniscient qui essaye d'empêcher le rendez-vous. On supposera que chaque agent connait sa position dans la grille mais pas celle de l'autre agent. Cette connaissance permet d'avoir un algorithme de rendez-vous ayant un coût, mesuré en terme de distance parcourue par les agents, quasiment optimal.

en:

Abstract: Dans cet exposé, je montrerais comment deux agents mobiles peuvent se rencontrer dans une grille infinie de dimension supérieure à 2. On considère le modèle asynchrone. C'est-à-dire que la durée de traversée de chaque sommet par un agent est déterminée par un adversaire omniscient qui essaye d'empêcher le rendez-vous. On supposera que chaque agent connait sa position dans la grille mais pas celle de l'autre agent. Cette connaissance permet d'avoir un algorithme de rendez-vous ayant un coût, mesuré en terme de distance parcourue par les agents, quasiment optimal.

09 juin 2010 à 09h37 par 147.210.129.51 -
Lignes 4-5 ajoutées:

Les exposés ont lieu le Lundi de 14h à 15h, en salle 178.

Lignes 9-10 modifiées:

(:if:)

en:

Talks are scheduled on Mondays from 2 to 3PM, in room 178.

(:if:)

Lundi 14 Juin : Almost optimal asynchronous rendezvous in infinite multidimensional grids - Arnaud Labourel (LaBRI) Abstract: Dans cet exposé, je montrerais comment deux agents mobiles peuvent se rencontrer dans une grille infinie de dimension supérieure à 2. On considère le modèle asynchrone. C'est-à-dire que la durée de traversée de chaque sommet par un agent est déterminée par un adversaire omniscient qui essaye d'empêcher le rendez-vous. On supposera que chaque agent connait sa position dans la grille mais pas celle de l'autre agent. Cette connaissance permet d'avoir un algorithme de rendez-vous ayant un coût, mesuré en terme de distance parcourue par les agents, quasiment optimal.

09 juin 2010 à 09h34 par 147.210.129.51 -
Lignes 1-8 ajoutées:

(:if userlang fr:) (:title Exposés à venir:)

(:if userlang en:) (:title Coming talks:)

(:if:)

Group

GT

Positions