Delay-Based False Congestion Detection on Groups of TCP Flows

By opening a number of concurrent parallel TCP flows, a node can achieve high utilization of available link bandwidth in high-bandwidth long-delay network without modification of TCP itself. However, parallel TCP flows are inherently unfair with respect to normal TCP flows. There have been several proposals to improve performance of parallel TCP flows. CM, COCOON, Fractional/Combined TCP, and TCP-P are some examples. In this paper, we first assess fairness of these schemes with extensive experiments. Then, we propose TCP-P, which augments TCP-P with a delay-based false congestion detection mechanism to improve performance in high bandwidth-delay product networks where non-congestion related packet losses are the limiting factor for TCP performance. The proposed scheme effectively utilizes available bandwidth in random, systemic packet loss situations while maintaining fairness, i.e., without stealing bandwidth from normal TCP flows. We implemented TCP-P as part of Linux and experimental results show that the proposed scheme indeed achieves high utilization without penalty to single flows.