Claude Chaudet

Optimal positioning of active and passive monitoring devices

Network measurement is essential for assessing performance issues, identifying and locating problems. Two common strategies are the passive approach that attaches specific devices to links in order to monitor the traffic that passes through the network and the active approach that generates explicit control packets in the network for measurements. One of the key issues in this domain is to minimize the overhead in terms of hardware, software, maintenance cost and additional traffic.In this paper, we study the problem of assigning tap devices for passive monitoring and beacons for active monitoring. Minimizing the number of devices and finding optimal strategic locations is a key issue, mandatory for deploying scalable monitoring platforms. In this article, we present a combinatorial view of the problem from which we derive complexity and approximability results, as well as efficient and versatile Mixed Integer Programming (MIP) formulations.

Bandwidth Estimation for IEEE 802.11-Based Ad Hoc Networks

Since 2005, IEEE 802.11-based networks have been able to provide a certain level of quality of service (QoS) by the means of service differentiation, due to the IEEE 802.11e amendment. However, no mechanism or method has been standardized to accurately evaluate the amount of resources remaining on a given channel. Such an evaluation would, however, be a good asset for bandwidth-constrained applications. In multihop ad hoc networks, such evaluation becomes even more difficult. Consequently, despite the various contributions around this research topic, the estimation of the available bandwidth still represents one of the main issues in this field. In this paper, we propose an improved mechanism to estimate the available bandwidth in IEEE 802.11-based ad hoc networks. Through simulations, we compare the accuracy of the estimation we propose to the estimation performed by other state-of-the-art CoS protocols, BRulT, AAC, and CoS-AODV.

Performance issues with IEEE 802.11 in ad hoc networking

Although 802.11 is initially designed for infrastructure-based networks, the distributed coordination function allows mobiles to access the radio medium without the need for a base station. Thus, studies in wireless multihop networks, also called ad hoc networks, often rely on the use of IEEE 802.11 for the physical and MAC layers. However, for a couple of years the use of 802.11 in ad hoc networks has been discussed. Different scenarios show serious performance issues. The performance offered by 802.11 is often low and directly impacts the performance of higher-layer protocols. In this article we provide a summary of the different performance issues extracted so far. We classify basic situations according to the main effects. We then present a quick survey of the possible solutions to these problems. This classification is intended to help design appropriate MAC protocols dedicated to ad hoc networks.

Study of the impact of asymmetry and carrier sense mechanism in IEEE 802.11 multi-hops networks through a basic case

This article presents a theoretical modeling of a small but basic scenario that shows a great inequity in medium access between nodes using the IEEE 802.11 DCF mode. In this configuration, two terminals evolve independently and are almost never synchronized, which results in a serious performance issue for a third emitter in between. The results are compared to simulation results and a discussion on the different performance loss causes follows.

A node-based available bandwidth evaluation in IEEE 802.11 ad hoc networks

We propose a new technique to estimate the available bandwidth of wireless nodes and by extension of one-hop links in IEEE 802.11-based ad hoc networks. Our technique exploits the fact that a node can estimate the channel occupancy by monitoring its environment. It provides a non-intrusive estimation meaning that it doesnt generate additional traffic to perform the evaluation. We show by simulations that our technique provides an accurate estimation of available bandwidth on wireless links in mobile ad hoc environment

Impact of interferences on bandwidth reservation for ad hoc networks: a first theoretical study

This paper presents a theoretical study on the bandwidth reservation problem for ad hoc networks. The proposed model is based on the spatial reuse and the existence of interferences. We show that in that case, the bandwidth reservation problem is NP-complete and we provide some bounds that compare solutions of the problems derived with greedy heuristics with an optimal one. We conclude with a discussion on the practical aspect of this model and its potential use in a practical protocol.

A Distributed Algorithm for Bandwidth Allocation in Stable Ad Hoc Networks

We propose a distributed algorithm for allocating bandwidth in stable ad hoc networks. After having discussed the problem of bandwidth allocation in such networks, we define a sequence of feasible solutions to this problem. This sequence has the property to be an increasing sequence in terms of overall used bandwidth. After a theoretical analysis of the sequence, we design a distributed algorithm based on this sequence. We test our algorithm by simulations on different topologies. Results obtained on geometric random graphs are presented here. We compare our solutions with the optimal solution in terms of global bandwidth allocation that presents the smallest standard deviation and with the the fairest solution regarding to max-min fairness. The simulations show that the global used bandwidth is less than 25% from optimality in the worst case and the standard deviation is the smallest of the three.

Routage QoS et réseaux ad hoc : De l'état de lien à l'état de noeud

Lengouement suscite par la telephonie cellulaire laisse a penser que lutilisateur va devenir de plus en plus mobile. Les reseaux ad-hoc repondent a ce besoin en eliminant le besoin dinfrastructure fixe pour communiquer. Lactivite du groupe IETF Manet cree en 1996 montre que le developpement de ces reseaux sans fil et sans infrastructure est en plein essor. Paralleleme- nt a ce phenomene, on assite a un deploiement des services multimedia aussi bien dans les reseaux dits grand public que dans les reseaux professionn- els. Ce type dapplications est exigeant en terme de qualite de la transmission et lon voit apparaitre un reel besoin de garanties sur la qualite du service offert. Toutefois, les reseaux ad-hoc introduisent un grand nombre de contraintes dont il faut tenir compte lors de lelaboration dun protocole de qualite de service. Dans cet article, apres avoir defini ce que nous entendions par qualite de service et avoir presente les specificites des reseaux ad-hoc et leur impact sur les protocoles cherchant a offrir des garanties aux applications, nous presenterons une solution au probleme du routage avec qualite de service basee sur letat des mobiles dans le reseau.

A Managed Bandwidth Reservation Protocol for Ad Hoc Networks

In this paper we present a bandwidth reservation protocol called BRuIT designed to operate in mobile ad hoc networks. The protocol is provided together with a policy-based outsourcing model enabling context-aware reservation authorization.