Analysis of control parameters on ABR rate-based control mechanisms
L.E. Hester, C. Luna, Sonu Kumar · 2002
We show that by adjusting the rate decrease factor (RDF) and the rate increase factor (RIF) of the switches in an explicit forward congestion indication (EFCI) ATM network, we are better able to implement available bit rate (ABR) services via improved flow and congestion control. First, we find that adjusting the RDF while keeping the RIF constant reduces the amount of time a network remains in a congested state. Increasing the RIF while keeping the RDF constant, on the other hand, causes longer periods of congestion in a network. Second, if single-hop (SH) sources are given larger RDF values than multi-hop (MH) sources in a heterogeneous network environment, then smaller periods of congestion and larger throughputs will result. Moreover, this scheme also provides for bandwidth fairness among the various ABR sources, thus also reducing the "beat-down" problem for multi-hop virtual channels (MH VCs). Thus, an optimal combination of RDF and RIF is needed to minimize congestion, while achieving higher throughput and bandwidth fairness. We describe a simple analytical model which combines MH and SH sources. With this model, we explore the choice of appropriate parameters. From observations of the simple model, we expand our analysis to the creation of a more intricate analytical model. By fine tuning the switching mechanisms through the proper selection of control parameters, we can provide better estimates of the amount of bandwidth available to users, and thus enrich the implementation of ABR services.