Loss-resilient window-based congestion control

This paper addresses the problem of fair allocation of bandwidth resources on lossy channels in hybrid heterogeneous networks. It discusses more particularly the ability of window-based congestion control to support non-congestion related losses. We investigate methods for efficient packet loss recovery by retransmission, and build on explicit congestion control mechanisms to decouple the packet loss detection from the congestion feedback signals. For different retransmission strategies that respectively rely on conventional cumulative acknowledgments or accurate loss monitoring, we show how the principles underlying the TCP retransmission mechanisms have to be adapted in order to take advantage of an explicit congestion feedback. A novel retransmission timer is proposed in order to deal with multiple losses of data segments and, in consequence, to allow for aggressive reset of the connection recovery timer. It ensures significant benefit from temporary inflation of the send-out window, and hence the fair share of bottleneck bandwidth between loss-prone and lossy connections. Extensive simulations analyze the performance of the new loss monitoring and recovery strategies, when used with two distinct explicit congestion control mechanisms. The first one relies on a coarse binary congestion notification from the routers. The second one, introduced in [D. Katabi, M. Handley, C. Rohrs, Internet congestion control for high bandwidth-delay product environments, ACM SIGCOMM (2002) 89–102], exploits accurate and finely-tuned router feedbacks to compute a precise congestion window adjustment. For both congestion control mechanisms, we observe that retransmissions triggered based on a precise monitoring of losses lead to efficient utilization of lossy links, and provide a fair share of the bottleneck bandwidth between heterogeneous connections, even for high loss ratios and bursty loss processes. Explicit window-based congestion control, combined with appropriate error control strategies, can therefore provide a valid solution to reliable and controlled connections over lossy network infrastructures.