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SCS

Seminar

Locating Congested Links in the Internet with Unicast Probes

Thiran, P (EPFL)
Friday 25 June 2010, 16:45-17:30

Seminar Room 1, Newton Institute

Abstract

How can we locate congested IP (Internet Protocol) links from end-to-end measurements using active probing mechanisms? For practical reasons, we want to avoid using IP multicast protocols, which are not widely deployed, and to 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 often 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.

This joint work with Hung X. Nguyen (Univ. of Adelaide), Denisa Ghita, Katerina Argyrak, and Maciej Kurant (EPFL).

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