ALCOMFT-TR-02-85

Fabrice Guillemin, Philippe Robert and Bert Zwart
Performance of TCP in the presence of correlated packet loss
INRIA. Work package 2. May 2002.

Abstract: We study in this paper the performance of a single persistent TCP connection, which experiences packet loss occurring in clumps. More precisely, the transmission of packets is altered by several packet losses during some time periods, which can span over several round trip time intervals. In spite of multiple packet loss, we assume that TCP remains in the congestion avoidance regime. We perform, by properly rescaling time, an exact analysis of the behavior of TCP when the loss rate becomes arbitrarily small. In particular, we investigate by means of elementary q-calculus the stationary distribution of the congestion window size embedded at the finishing times of loss periods. This allows us to exactly compute the mean throughput of the TCP connection. Then, by using stochastic ordering arguments, we investigate the impact of correlations on the mean throughput. Surprisingly, for a same loss rate, the mean throughput in the case of correlated losses is greater than that obtained under independent loss conditions. We conclude the paper by discussing how the results could be extended to account for additional features of TCP. In particular, we show that the slow start algorithm and variable round trip times have no impact on the asymptotic results of this paper. Finally, timeouts could easily be introduced in the model.

Postscript file: ALCOMFT-TR-02-85.ps.gz (96 kb).