Bandwidth allocation in fair distributed queue (FDQ) networks

Abstract

Fair distributed queue (FDQ) is a high speed metropolitan area network 3,5. It has been shown 3,5 that FDQ has fair throughput and delay characteristics and is a highly scalable protocol, in that its performance is little affected by growing network sizes and/or transmission speeds. FDQ allocates equal bandwidth to all active nodes. In this paper, we focus on dividing the capacity arbitrarily among the active nodes. Under heavy load, this results in nodes achieving throughput rates equal to their allocated bandwidths. Under normal load conditions, we aim to provide equal Quality of Service (QoS) to the nodes in terms of message delay, if their arrival rates turn out to be equal to their allocated bandwidths. We present the bandwidth allocation FDQ (BA-FDQ) protocol, which achieves this objective subject to propagation delays. The delay characteristics of BA-FDQ are compared via simulation with FDQ, DQDB and DQDB with BWB under symmetric load (an important special case in the absence of known arrival rates). We also consider arbitrary bandwidth allocations and study the delay characteristics of BA-FDQ by simulation. Our studies show that BA-FDQ makes the mean message delays of individual nodes close to each other (as intended) for transmission on one of the buses when the arrival rates match allocated bandwidth.