Showing papers by "Nathalie Mitton published in 2005"

Self-stabilization in self-organized multihop wireless networks

Abstract: In large scale multihop wireless networks, flat architectures are not scalable. In order to overcome this major drawback, clusterization is introduced to support self-organization and to enable hierarchical routing. When dealing with multihop wireless networks, the robustness is a main issue due to the dynamicity of such networks. Several algorithms have been designed for the clustering process. As far as we know, very few studies check the robustness feature of their clustering protocols. In this paper, we show that a clustering algorithm, that seems to present good properties of robustness, is self-stabilizing. We propose several enhancements to reduce the stabilization time and to improve stability. The use of a directed acyclic graph ensures that the self-stabilizing properties always hold regardless of the underlying topology. These extra criterion are tested by simulations.

Analysis of the Multi-Point Relay Selection in Olsr and Implications

Abstract: OLSR is a promising routing protocol for multi-hop wireless networks, recently standardized by the IETF. It intensively uses the concept of MPR to minimize the routing messages and limit the harmful effects of the broadcasting in such networks. In this article, we are interested in the performances of the Multi-Point Relay selection. We analyze the mean number of selected MPR per node and their spatial distribution with a theoretical approach and simulations. Then, we discuss the implications of these results on the efficiency of a broadcasting and on the reliability of OLSR when links between nodes may fail.

An analysis of the Multi-Point Relays selection in OLSR

Abstract: OLSR is a recent routing protocol for multi-hop wireless ad-hoc networks standardized by the IETF. It uses the concept of Multi-Point Relays (MPR) to minimize the overhead of routing messages and limit the harmful effects of broadcast in such networks. In this report, we are interested in the performance evaluation of Multi-Point Relays selection. We analyze the mean number of selected MP= R in the network and their spatial distribution.

On Fast Randomized Colorings in Sensor Networks

Abstract: We present complexity analysis for a family of self-stabilizing vertex coloring algorithms in the context of sensor networks. First, we derive theoretical results on the stabilization time when the system is synchronous. Then, we provide simulations for various schedulings and topologies. We consider both the uniform case (where all nodes are indistinguishable and execute the same code) and the non-uniform case (where nodes make use of a globally unique identifier). Overall, our results show that the actual stabilization time is much smaller than the upper bound provided by previous studies. Similarly, the height of the induced DAG is much lower than the linear dependency to the size of the color domain (that was previously announced). Finally, it appears that symmetry breaking tricks traditionally used to expedite stabilization are in fact harmful when used in networks that are not tightly synchronized.

Distributed node location in clustered multi-hop wireless networks

Abstract: Wireless routing protocols in MANET are all flat routing protocols and are thus not suitable for large scale or very dense networks because of bandwidth and processing overheads they generate. A common solution to this scalability problem is to gather terminals into clusters and then to apply a hierarchical routing, which means, in most of the literature, using a proactive routing protocol inside the clusters and a reactive one between the clusters. We previously introduced a cluster organization to allow a hierarchical routing and scalability, which have shown very good properties. Nevertheless, it provides a constant number of clusters when the intensity of nodes increases. Therefore we apply a reactive routing protocol inside the clusters and a proactive routing protocol between the clusters. In this way, each cluster has O(1) routes to maintain toward other ones. When applying such a routing policy, a node u also needs to locate its correspondent v in order to pro-actively route toward the cluster owning v. In this paper, we describe our localization scheme based on Distributed Hashed Tables and Interval Routing which takes advantage of the underlying clustering structure. It only requires O(1) memory space size on each node.

An analysis of the MPR selection in OLSR and consequences

Abstract: Optimized Link State Routing protocol (OLSR) is a promising routing protocol for multi-hop wireless ad-hoc networks, recently standardized by the IETF as a RFC. OLSR uses intensively the concept of Multi-Point Relays (MPR) to minimize the overhead of routing messages and limit the harmful effects of broadcasting in such networks. In this article, we are interested in the performance evaluations of the Multi-Point Relay selection. We analyze the mean number of selected MPR in the network and their spatial distribution with a theoretical approach and simulations. Then, we discuss the implications of these results on the efficiency of a broadcasting in OLSR and on the reliability of OLSR when links between nodes may fail.

Efficient broadcasting in self-organizing multi-hop wireless networks

Abstract: Multi-hop wireless networks (such as ad-hoc or sensor networks) consist of sets of mobile nodes without the support of a pre-existing fixed infrastructure. For the purpose of scalability, ad-hoc and sensor networks may both need to be organized into clusters and require some protocols to perform common global communication patterns and particularly for broadcasting. In a broadcasting task, a source node needs to send the same message to all the nodes in the network. Some desirable properties of a scalable broadcasting are energy and bandwidth efficiency, i.e., message retransmissions should be minimized. In this paper, we propose to take advantage of the characteristics of a previous clustered structure to extend it to an efficient and scalable broadcasting structure. In this way, we build only one structure for both operations (organizing and broadcasting) by applying a distributed clustering algorithm. Our broadcasting improve the number of retransmissions as compared to existing solutions.

Auto-stabilisation dans les réseaux ad hoc.

Abstract: Les réseaux sans-fil multi-sauts sont des réseaux radio mo biles sans aucune infrastructure fixe. Leur fonctionnement est basé sur les principes d’auto-organisatio n et d’auto-stabilisation. Les protocoles actuels proposés pour un contexte multi-sauts fonctionnent corre tement sur des réseaux de taille moyenne mais deviennent beaucoup trop coûteux sur de grands réseaux. U n défi majeur actuellement dans ce domaine concerne l’élaboration de solutions qui ”passent à l’éc helle”, i.e. qui fonctionnent correctement sur de grands réseaux. Pour les protocoles de routage multi-saut s, une des solutions proposées pour tenter de résoudre ce problème de passage à l’échelle est d’organ iser le réseau en regroupant géographiquement des nœuds proches en clusters(on parle alors declusterisation) et en utilisant des approches différentes au sein des clusters et entre les clusters [KVCP97]. Dans la majorit é des techniques de clusterisation proposées, chaque nœud choisit localement un chef. Tous les nœuds ayant choisi le même chef appartiennent au même cluster et le chef est appelé cluster-head. L’élection de ce chef peut se faire en se basant sur un crit` ere d’identité (p.ex.le plus petit identifiant), sur un critère de connexité ( p.ex.le degré ou le diamètre) ou sur un critère mixte identité/connexité. La maintenance de ces clusters repose elle aussi sur des critères fixes comme un diamètre ou rayon fixe ou un nombre constant de nœuds par cluster. Cependant, ces solutions ne sont pas adaptées aux grands réseaux puisque d’une part el les p uvent générer un nombre inutilement élevé de clusters et que d’autre part une toute petite modification de la topologie (comme le mouvement d’un nœud par exemple) peut conduire à de nouveaux calculs et rec onstructions. Dans [MBF04], un nouveau critère de densité est proposé. Les auteurs montrent que cette métrique permet de limiter les reconstructions de clusters inutiles et se révèle plus stable que d’autres métriques face à la mobilité des nœuds.

Broadcast in Self-Organizing Multi-hop Wireless Networks

Abstract: Multi-hop wireless networks (MWN) consist of sets of mobile wireless nodes without the support of a pre-existing fixed infrastructure. Each host/node acts as a router and may arbitrary appear or vanish. This feature is a challenging issue for protocol design since protocols must adapt to frequent changes of network topologies. When dealing with sensor networks, the scalability also becomes a crucial aspect. In such large networks, we need not only to be able to route messages from any node to any other node but also to spread some information over the whole network. Till nowadays, it seems that these two properties have only been studied separately. In this report, we propose to use our existing cluster formation algorithm also to perform the broadcast operation.