Performance of various input-buffered and output-buffered ATM switch design principles under bursty traffic: simulation study

Abstract

This paper investigates the packet loss probabilities of several alternative input-buffered and output-buffered switch designs with finite amounts of buffer space. The effects of bursty traffic, modeled by geometrically distributed active and idle periods, are explored. Methods for improving switch performance are classified, and their effectiveness for dealing with bursty traffic discussed. This work indicates that bursty traffic can degrade switch performance significantly and that it is difficult to alleviate the performance degradation by merely restricting the offered traffic load. Unless buffers are shared, or very large buffers provided, strategies that improve throughput under uniform random traffic are not very effective under bursty traffic. For input-buffered switches, our investigation suggests that the specific contention resolution scheme we use is a more important performance factor under bursty traffic than it is under uniform random traffic. In addition, many qualitative results true for uniform random traffic are not true for bursty traffic. The work also reveals several interesting, and perhaps unexpected, results: 1) output queueing may have higher loss probabilities than input queueing under bursty traffic; 2) speeding up the switch operation could result in worse performance than having several output ports per output address under bursty traffic; and 3) if buffers are not shared in a fair manner, sharing buffers could make performance worse than not sharing buffers at high traffic loads. Simulation results and intuitive explanations supporting the above observations are presented. >