Supporting Multicast Communication in Clos-Type Switching Networks

Abstract

Multicast (or one-to-many) is a vital operation in both broadband integrated services digital networks (BISDN) and scalable parallel and distributed computing systems. There are broad ranges of applications for multistage networks which can realize multicast connection requests in a nonblocking manner in the sense that a request from an idle network input port to be connected to some set of idle network output ports can always be satisfied without any disturbance of existing multicast connections in the network. In this chapter, we overview the recent development in supporting multicast in a well-known multistage network called Clos network. Both nonblocking and almost nonblocking multicast networks are considered. We first present results that lead to the currently best available nonblocking multicast network, and describe a linear time routing algorithm for satisfying multicast connection requests in the network. Next, we will show that the sufficient nonblocking condition used in the network design is also a necessary condition under several typical routing strategies for a multicast network to be nonblocking, discuss the complexity of the control strategies used, and briefly describe the hardware implementation of the best control strategy, which further speeds up the routing process. Finally, we discuss the blocking behavior of the multicast network that does not satisfy the nonblocking condition. We present two analytical models for the blocking probability of the multicast network, and show the simulation results on the blocking behavior of the network under several routing strategies. The analytical and simulation results demonstrate that a Clos-type multicast network with a comparable cost to a permutation is almost nonblocking for multicast connections and can provide cost-effective support for multicast communication.