Impact of fairness policies on slow links and long thin networks

Abstract

Various alternative congestion avoidance policies have been proposed to overcome the bias of TCP congestion avoidance mechanism against connections with long round trip times (RTT). The policies attempt to provide a fair share of the bottleneck bandwidth for long RTT connections by enabling them to open up their congestion window at a relatively faster rate. However, in this paper, it is shown that in cases where connections are traversing slow links or long thin networks (LTNs), such methods can cause excess probing, leading to degradation of performance for that connection. In an attempt to mitigate the detrimental effect of such policies, studies were conducted with limited receiver window and increased last hop router buffer sizes for connections traversing slow links and LTNs. The effect of using the standard congestion avoidance policy on slow links and LTNs, and using alternate policies on competing connections, was also studied. Finally, methods are suggested to reduce the impact of such policies on connections traversing slow links or LTNs. In this paper, experiments were conducted on a testbed setup 1 to study the effect of such fairness policies on slow links and LTNs.