BLOCKING AND NONBLOCKING MULTIRATE CLOS SWITCHING-NETWORKS

This paper investigates in detail the blocking and nonblocking behavio r of multirate Clos switching networks at the connection/virtual conne ction level. The results are applicable to multirate circuit and fast- packet snitching systems, Necessary and sufficient nonblocking conditi ons are derived analytically. Based on the results, an optimal bandwid th partitioning scheme is proposed to reduce switch complexity while m aintaining the nonblocking property. The blocking behavior of blocking switches supporting multicast connections is investigated by means of simulation. We propose a novel simulation model that filters out exte rnal blocking events without distorting the bandwidth and fanout (for multicasting) distributions of connection requests. In this way, the i nternal blocking statistics that truly reflect the switch performance can be gathered and studied. Among many simulation results, we have sh own that for point-to-multipoint connections, a heuristic routing poli cy that attempts to build a narrow multicast tree can have relatively low blocking probabilities compared with other routing policies. In ad dition, when small blocking probability can he tolerated, our results indicate that situations with many large-fanout connection requests do not necessarily require a switch architecture of higher complexity co mpared to that with only point-to-point requests.