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Mobility causes frequent link failures in ad-hoc networks. This results in a severe degradation of performance specially in case of high mobility of nodes. This is because the routing protocols for ad-hoc networks are not equipped to handle high mobility. In this paper, we have presented a new link management algorithm to locally manage links. This new mechanism is based on signal strength measurements. Researchers over the years have presented approaches which use signal strength measurements but their focus has been on re-active protocols while our algorithm is aimed at pro-active protocols. Pro-active protocols are used since they provide greater flexibility to take advantage of the mesh configuration. We develop the hysteresis mechanism provided by OLSR, based on hello packets, to include signal strength measurements. The mechanism in OLSR uses Hello packets received/lost to decide to establish link or not. The problem with this approach arises when there is high mobility in which case the time to break the link and use a new path becomes significant. To overcome this, we propose to use signal strength to determine if the link-quality is improving or deteriorating. This combination of the two mechanisms, makes the link management more robust and also helps in anticipating link breakages thereby greatly improving performance.

In this article, we describe experiments with the multicast protocol MOST (Multicast Overlay minimum Spanning Tree) on a real testbed. The testbed is a wireless multi-hop network with nodes running a MANET protocol, the OLSRv2 routing protocol, and with IEEE 802.11g hardware. We present our specification and implementation of MOST for OLSRv2. Its main feature is to build an (unicast) overlay tree covering members of a group. Through different scenarios and applications such as voice and video, we evaluate MOST performance in term of average packet delivery ratio, jitter and pay a particular attention to the MAC layer statistics. We also evaluate qualitatively and quantitatively the improvements brought by MOST compared with MPR flooding (an optimization of a pure flooding proposed and used in OLSR).

In this paper, we study multicast protocols for Mobile Ad-Hoc Networks, and specifically OLSR networks. We describe and compare three multicast protocols, namely MOST (Multicast Overlay Spanning Tree), MOLSR (Multicast OLSR) and SMOLSR (Simple Multicast OLSR), with different approaches and properties with respect to scalability. Our approach is simulation-based: through different scenarios and configurations, we evaluate the performance of each protocol in terms of average packet delivery ratio and average packet retransmissions. We interpret the results in terms of key design properties and applicability of the protocols.

International audience; We study the benefits of multicast routing in the performance of wireless ad hoc networks. In particular we show that if a node wishes to communicate with n distinct destinations, multicast can reduce the overall network load by a factor , when used instead of unicast. One of the implications of this scaling property consists in a significant increase of the total capacity of the network for data delivery. Hence, we show that the aggregate multicast capacity of wireless ad hoc networks is larger than the unicast capacity, when the group size n is small compared to the total number of nodes in the network. We discuss how these information theoretic results can be taken into consideration in the operation of a multicast protocol for wireless mesh networks using Multicast Overlay Spanning Trees (MOST). We perform simulations of the MOST protocol to compare with the theoretical results, and we present a fully working implementation for real network environments.

Mobility causes frequent link failures in ad-hoc networks. This results in a severe degradation of performance specially in case of high mobility of nodes. This is because the routing protocols for ad-hoc networks are not equipped to handle high mobility. In this paper, we have presented a new link management algorithm to locally manage links. This new mechanism is based on signal strength measurements. We develop the hysteresis mechanism provided by OLSR based on hello packets to include signal strength measurements. The mechanism in OLSR uses Hello packets received/lost to decide to establish link or not. The problem with this approach arises when there is high mobility in which case the time to break the link and use a new path becomes significant. To overcome this, we propose to use signal strength to determine if the link-quality is improving or deteriorating. This combination of the two mechanisms, makes the link management more robust and also helps in anticipating link breakages thereby greatly improving performance.

In this paper we present an extension to the OLSR unicast routing protocol to support multicast routing in mobile ad hoc networks. The proposed protocol is based on Multicast Overlay Spanning Trees (MOST). The main benefits of this approach are twofold. Firstly, it implies that only nodes interested in taking part in the multicast communication need to participate in the protocol operation, which is transparent to other OLSR nodes. In addition, the MOST approach scaling properties achieve the theoretical performance bounds concerning the capacity of multicast communication in massive ad hoc networks. We perform simulations of the MOST protocol under the ns-2 simulator to compare with the theoretical results, and we present a fully working implementation for real network environments.

This paper addresses the problem of the evaluation of the delay distribution via analytical means in IEEE 802.11 wireless ad hoc networks. We show that the asymptotic delay distribution can be expressed as a power law. Based on the latter result, we present a cross-layer delay estimation protocol and we derive new delay-distribution-based routing algorithms, which are well adapted to the QoS requirements of real-time multimedia applications. In fact, multimedia services are not sensitive to average delays, but rather to the asymptotic delay distributions. Indeed, video streaming applications drop frames when they are received beyond a delay threshold, determined by the buffer size. Although delay-distribution-based routing is an NP-hard problem, we show that it can be solved in polynomial time when the delay threshold is large, because of the asymptotic power law distribution of the link delays.

In this paper we show that the CSMA IEEE 802.11 protocol (Wifi) provides packet access delays asymptotics in power law. This very feature allows us to specify optimal routing via polynomial algorithm while the general case is NP-hard.