Cell Delay Variation and Burst Expansion in ATM Networks: Results from a Practical Study Using Fairisle

Current interest in cell delay variation in ATM networks arises from the need to provide guarantees on loss and delay for traac with real time constraints. This study uses the Fairisle ATM LAN to measure the CDV experienced by CBR and periodic, bursty sources when multiplexed with Bernoulli, VBR video and LAN interconnection traac, in a network of non-blocking ATM switches. We nd that higher bitrate connections experience greater relative CDV for the same total load, and that larger ATM switches cause greater CDV. The Bernoulli model is a poor predictor of the performance using real traac. The CDV experienced by a CBR connection increases over successive switching stages, but is bounded above by an asymptote which depends on the source bitrate, the total load, and the type of background traac. Bursts become separated by background traac, causing a decrease in CDV. We study burst expansion by tracing individual cells in each burst, to determine the expansion rate, and relate the results to two analytical approximations. Finally, we study the performance of reference streams under static priority and rate-based scheduling, concluding that signiicant performance beneets can be achieved using non-FCFS queueing policies.