Performance effects of two-way FAST TCP

In this paper we study the performance of delay-based congestion control in the presence of queueing in the reverse path. Specifically, we consider FAST TCP in a single-bottleneck network by considering two scenarios, each corresponding to an equilibrium where a different direction of the bottleneck link is saturated. We argue that the local stability properties of FAST are unchanged by reverse traffic, and present expressions for the throughput of each flow and link. Finally, we consider the effect of bidirectional traffic on the dynamics of the number of flows in the network. We find conditions on the traffic loads under which the bottleneck shifts between the forward and reverse links, and conditions under which a given direction is always the bottleneck.