Distributed Maintenance of Anytime Available Spanning Trees in Dynamic Networks

We address the problem of building and maintaining distributed spanning trees in highly dynamic networks, in which topological events can occur at any time and any rate, and no stable periods can be assumed. In these harsh environments, we strive to preserve some properties such as cycle-freeness or the existence of a root in each tree, in order to make it possible to keep using the trees uninterruptedly (to a possible extent). Our algorithm operates at a coarse-grain level, using atomic pairwise interactions in a way akin to recent population protocol models. The algorithm relies on a perpetual alternation of \emph{topology-induced splittings} and \emph{computation-induced mergings} of a forest of spanning trees. Each tree in the forest hosts exactly one token (also called root) that performs a random walk {\em inside} the tree, switching parent-child relationships as it crosses edges. When two tokens are located on both sides of a same edge, their trees are merged upon this edge and one token disappears. Whenever an edge that belongs to a tree disappears, its child endpoint regenerates a new token instantly. The main features of this approach is that both \emph{merging} and \emph{splitting} are purely localized phenomenons. In this paper, we present and motivate the algorithm, and we prove its correctness in arbitrary dynamic networks. Then we discuss several implementation choices around this general principle. Preliminary results regarding its analysis are also discussed, in particular an analytical expression of the expected merging time for two given trees in a static context.Comment: Distributed Maintenance of Anytime Available Spanning Trees in Dynamic Networks, Poland (2013

Applications et services DTN pour flotte collaborative de drones

Les travaux présentés dans cette thèse effectuée au LaBRI portent sur la mise en place d une flotte de drones et le portage sur celle-ci d applications collaboratives distribuées utilisant des communications asynchrones non sûres. Ces applications sont formalisées grâce au modèle de réétiquetage de graphes Asynchronous Dynamicity Aware Graph Relabeling System (ADAGRS) que nous proposons. Au delà des contributions théoriques, ces travaux ont débouché sur la mise en place du démonstrateur CARUS dans lequel cinq drones se partagent la surveillance d'une grille de 15 points d incidents potentiels (au sol).Lorsqu un drone détecte un incident, il s'en rapproche pour le traiter. Le reste de la flotte doit alors prendre en charge les points que ce drone ne traite plus.Les réorganisations nécessaires de la flotte se font en totale autonomie vis-à-vis du sol et sous hypothèse de perte éventuelle de drones et de messages.The work presented in this thesis, carried out at LaBRI, deals with the set up of a fleet of UAVs and the porting on it of distributed collaborative applications that use unsafe asynchronous communications. These applications are modeled with Asynchronous Dynamicity Aware Graph Relabeling System (ADAGRS), the formal model based on graph relabellings that we propose.Beyond the theoretical contributions, this work led to the development of the CARUS demonstrator in which five UAVs share the supervision of a grid of 15 points of potential ground incidents.When a UAV detects an incident, it comes close to it in order to deal with it. The rest of the fleet must then take care of the points that this UAV no longer visits.The necessary reorganizations of the fleet are done in total autonomy with respect to the ground and under the hypothesis of possible loss of UAVs and messages.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF