Patrick Thiran, EPFL

Location :

Thomson Paris Lab
46, Quai A. Le Gallo
92648 Boulogne Cedex
Nearest metro station: "Boulogne Pont de Saint Cloud" (line 10).
Look for  directions  with mappy.fr.

Please register in advance!
All are welcome to attend the sessions and stay for lunch, but we would like to know in advance to help organizing the event.
Please contact augustin.chaintreau@thomson.net or venus.apovo@thomson.net to announce that you are coming. 
Thank you.

Abstract :

Joint work with Mathilde Durvy (Cisco) and Olivier Dousse (Nokia).
IEEE 802.11 is probably the most widely used Medium Access Control protocol in
current wireless networks. In the single-hop setting (wireless LAN), its performance
is quite well understood. In the multi-hop setting however, there is, to date, no widely
accepted model that captures rigorously all the essential features of the protocol
while staying simple enough to provide insight. Consequently, when confronted
with experimental results, people often find it hard to interpret them.
We use a continuous-time Markovian loss network to model protocols ``à la 802.11''
in the context of multi-hop ad hoc networks. It enables us to explore systematically
the trade-off between spatial reuse and fairness, which is inherent to these decentralized
CSMA/CA MAC protocols. We show in particular that the widely observed unfairness of
the protocol in small network topologies does not always persist in large topologies.
In large 1-dim. networks, nodes sufficiently far away from the border of the network
have equal access to the channel. In 2-dim. networks, we observe a phase transition,
linked to the existence of multiple Gibbs measures in the Markov Random Field model.
If the access intensity of the protocol is small, border effects remain local and the
protocol is long term fair as in 1-dim. networks. However, for a large enough access
intensity, the border effects persist independently of the size of the network and
the protocol is strongly unfair. 

Host :

The Thomson Team