Achieving 100% throughput in a Two-Stage Multicast Switch

It is known that single-stage IQ based switch can provide 100% throughput guarantee for any admissible unicast traffic pattern. However, due to particular characteristics of multicast traffic, the performance of IQ switches in the case of general multicast traffic patterns is inferior to its performance in the case of unicast traffic, which motives us to find new architectures to provide better performance guarantee for multicast traffic. In this paper, we propose a two-stage multicast switch (TSMS) which is a serial combination of a multicast to unicast (MTU) switch to copy input cells from various sources simultaneously and a combined input and output queueing (CIOQ) switch to deliver copies of multicast cells to their final destinations. Based on MTU switch, we design a novel LFCNF-UMBA scheduling algorithm to determine how to copy multicast cells into unicast cells. By coordinately using maximal matching scheduling algorithm in CIOQ switch, we prove that speedup of 2 - 2 / (N + 1) is necessary and 2 is sufficient for a M times N TSMS to achieve 100% throughput under any admissible multicast traffic pattern, which is also verified by our simulation results.