Comparison of congestion control schemes for ABR service in ATM local area networks

Abstract

High speed LAN architecture has begun to migrate from shared media technologies to switch based solutions, and ATM based switch architectures are at the forefront of this development. With this radical change in mind, the ATM Forum has defined a new service class for data applications known as the available bit rate service (ABR). If ABR service has to achieve the same level of performance as the best effort service offered by current LAN technologies, then appropriate traffic control mechanisms are necessary. The ATM Forum is currently in the process of evaluating several competing traffic control schemes. In this contribution we propose a reference network model and a reference traffic model for evaluation of competing traffic control schemes. We also present detailed simulation results on the effectiveness of the back pressure (BP), backward explicit congestion notification (BECN), forward explicit congestion notification (FECN), and combination of BECN and BP, and FECN and BP controls. These results indicate that with pure BP, BECN or FECN, severe network performance degradation can occur under overload. A combination of BECN and BP or FECN and BP averts such degradation in LANs. On the other hand, BP alone or in combination leads to significant performance degradation in WANs. The performance in WANs however can be substantially improved by giving priority to network transit traffic over traffic entering the network.