Patrick Thiran , EPFL

Location :

The next seminar of TREC will take place at ENS, Salle S16, Aile Rataud: http://www.di.ens.fr/AccesDI.html

Abstract :

How can we locate congested links in the Internet from end-to-end measurements
using active probing mechanisms? As IP multicast is not widely deployed, we
want to use only IP unicast probes and avoid relying on tight temporal
synchronization between beaconing nodes, which is difficult to achieve between
distant sites. Like other problems in network tomography or traffic matrix
estimation, this inverse problem is ill-conditioned: the end-of-end measurement
outcomes do not allow to uniquely identify the variables representing the
status of the IP links.


To overcome this critical problem, current methods use the unrealistic
assumption that all IP links have the same prior probability of being
congested. We find that this assumption is not needed: spatial correlations are
sufficient to either learn these probabilities, or to identify the variances
of the link loss rates. We can then use the learned probabilities or variances
as priors to find rapidly the congested links at any time, with an order of
magnitude gain in accuracy over existing algorithms. These solutions scale well
and are therefore applicable in today's Internet, as shown by the results
obtained  both by simulation and real implementation using the PlanetLab
network over the Internet.

Host :