A Study of Wide-Sense Nonblocking Multicast Clos Networks

Abstract

Clos networks is a well-known kind of multistage switching networks, and nonblocking multicast capacity in Clos networks is important for group communication to meet the rapid growing application demand. However, the cost of nonblocking multicast Clos networks is high due to the large number of middle stage switches required. In this paper, we investigate wide-sense nonblocking multicast in three stage Clos networks. The sufficient condition on the number of middle stage switches is provided which is based on the more general case in which both of the minimum fanout f ₁ and the maximum fanout f ₂ for each connection are considered. We denote it as ( f ₁ , f ₂ )-cast traffic, which covers the unicast traffic ( f ₁ = f ₂ = 1) and multicast traffic(1 ≤ f ₁ ≤ f ₂ ≤ r) as special cases. We also provide a multicast connection request balance strategy with linear time complexity which can evenly distribute all multicast connection requests among input stage switches. Then, we show that the number of middle stage switches required for nonblocking multicast Clos networks can be reduced.