ISDN frame relay and its congestion control

Abstract

Frame relay is a new ISDN (integrated services digital network) packet mode bearer service which is expected to provide an efficient means of information transport using high‐speed transmission media. Several new applications requiring high bandwidth, such as file transfer, video and packetized voice, are suitable candidates to use this streamlined protocol. However, as there are no control frames present within the network for traffic flow management, congestion may arise during periods of peak offered loads. Efficient congestion control mechanisms are needed to make the frame relay effective. In this paper, after a brief discussion of the frame relay protocol, we consider the congestion problem in networks using this protocol and evaluate the performance. Specifically, we consider static and dynamic window flow control methods and develop models to determine the throughput under various load conditions. The throughput of the static window flow control model is determined by computing the frame loss probability and the virtual retransmission time, which is the time between arrivals of retransmitted frames at the destination. The frame loss probability is calculated by modelling the bottleneck resource as a finite state Markov chain. The results are validated by simulation. Furthermore, to analyse the dynamic interactions between the virtual circuits and their effect on the throughput and delay characteristics, we develop a simulation model which incorporates a dynamic window congestion control mechanism. It is shown that when the offered load is high, the performance of dynamic window flow control is superior to that of static window flow control.