CA-RTO: a contention-adaptive retransmission timeout

Abstract

We show that TCP timers, based solely on RTT estimations and measurements, cannot capture with precision the level of flow contention. We notice that increased contention may stabilize RTT variation, minimize the deviation and, in turn, shorten the timeout. We show that this behavior is undesirable indeed, since it leads to unfair resource utilization. We propose CA-RTO, an algorithm that incorporates a contention parameter and a randomization technique into the retransmission timeout. We report significant improvement in fairness, great reduction of retransmitted packets and slight improvements in application goodput.