Evaluation of ABR congestion control protocols for ATM LAN and WAN

This paper evaluates and compares six rate-based congestion control protocols for the ABR (available bit rate) traffic over the ATM (asynchronous transfer mode) networks. They include: the EFCI-bit setting, the EFCI-bit setting with separate RM queues, the CI-bit setting in the backward direction, the CI-bit setting in the backward direction with separate RM queues, the CAPC2 ER (explicit rate) scheme, and the EFCI-bit setting with utilization-based congestion indication. Each scheme is simulated and compared in the LAN, WAN, and GFC (general fairness configuration) environments specified by the ATM Forum. The effects of varying the VC (virtual circuits) number and changing the endsystem-switch distance has been investigated. Their fairness is also compared using the GFC configuration. For each simulation run, we measure the average queueing delay, maximum queue length, and network utilization. Traces of the ACR (allowed cell rate) and buffer queue length are also examined. We have found that the ER control scheme performs significantly better than the other five binary control schemes by its faster response to congestion, smoother regulation of bit rates, lower queueing delay, shorter buffer queue length, and fairness. Among the other five schemes, the CI-bit setting scheme performs better than the EFCI (explicit forward congestion indication) bit setting scheme. Providing separate RM queues has significantly improved the EFCI scheme in the WAN environment, but has little effect on the CI scheme. Link utilization-based congestion detection has suffered from either low utilization or an excess cell loss which is unacceptable in most data applications.