A delay-based approach for congestion avoidance in interconnected heterogeneous computer networks

Abstract

In heterogeneous networks, achieving congestion avoidance is difficult because the congestion feedback from one subnetwork may have no meaning to sources on other subnetworks. We propose using changes in round-trip delay as an implicit feedback. Using a black-box model of the network, we derive an expression for the optimal window as a function of the gradient of the delay-window curve.The problems of selfish optimum and social optimum are also addressed. It is shown that without a careful design, it is possible to get into a race condition during heavy congestion, where each user wants more resources than others, thereby leading to a diverging condition.It is shown that congestion avoidance using round-trip delay is a promising approach. The approach has the advantage that there is absolutely no overhead for the network itself. It is exemplified by a simple scheme. The performance of the scheme is analyzed using a simulation model. The scheme is shown to be efficient, fair, convergent, and adaptive to changes in network configuration.The scheme as described works only for networks which can be modeled with queueing servers with constant service times. Further research is required to extend it for implementation in practical networks. Several directions for future research have been suggested.