Performance evaluation of congestion phenomena in the rate based flow control mechanism for ABR

We investigate the performance of the EFCI-based (explicit forward congestion indication) and ER-based (explicit rate; EPRCA in particular) algorithms for the rate-based flow control of the ABR (available bit rate) traffic in an ATM network. We consider the case of multiple switches in tandem. We present several definitions of a bottleneck, and provide conditions that determine which queue is the bottleneck. We show that it is not necessarily the queue with the slowest transmission rate that is the first to notify congestion, and that queues with faster transmission rates can increase considerably the congestion. Moreover, a queue may build up in a faster node before it builds in a slower one. We derive analytic formulas for the maximum queue length. We compare our results to those obtained by approximating a network by a simpler one, containing only the bottleneck switch. We show that the maximum queue lengths under the approximating approach may largely underestimate the ones obtained in the real network