Loss synchronization, router buffer sizing and high-speed TCP versions: Adding RED to the mix

Adapting router buffer sizing rules and TCP´s congestion control to Gbit/s link speeds has been the subject of many studies and proposals. In a previous work (Hassayoun and Ros, 2008), we found that high-speed versions of TCP may be prone to strong packet-loss synchronization between flows. Given that synchronized losses may lead to oscillatory behavior in router queues, a relatively large amount of buffering may be needed to sustain an adequate TCP performance. In this paper, we are interested in evaluating the potential impact of the Random Early Detection (RED) queue management algorithm, in the context of high-speed TCP versions. In principle, under mild congestion RED should tend to reduce loss synchronization between flows. Hence, we wanted to test in particular whether RED would allow to use moderately-sized buffers, while ensuring good performance. Simulation results are used to assess the effect of RED on goodput, link utilization and fairness among high-speed flows, for a wide range of buffer sizes and several high-speed TCP variants.