Revisiting TCP Congestion Control Using Delay Gradients

Abstract

AbstractTraditional loss-based TCP congestion control (CC) tends to induce high queuing delays and perform badly across paths containing links that exhibit packet losses unrelated to congestion. Delay-based TCP CC algorithms infer congestion from delay measurements and tend to keep queue lengths low. To date most delay-based CC algorithms do not coexist well with loss-based TCP, and require knowledge of a network path’s RTT characteristics to establish delay thresholds indicative of congestion. We propose and implement a delay-gradient CC algorithm (CDG) that no longer requires knowledge of path-specific minimum RTT or delay thresholds. Our FreeBSD implementation is shown to coexist reasonably with loss-based TCP (NewReno) in lightly multiplexed environments, share capacity fairly between instances of itself and NewReno, and exhibits improved tolerance of non-congestion related losses (86% better goodput than NewReno in the presence of 1% packet losses).KeywordsPacket LossTransmission Control ProtocolCongestion ControlCongestion WindowCongestion AvoidanceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.