Performance of split routing algorithm for three-stage multicast networks

This paper studies three-stage Clos (1953) switching networks for multicast communications in terms of their blocking probabilities on a random traffic model. Even though the lack of multicast capability in input-stage switches requires a prohibitively large number of middle switches to provide compatible requests with nonblocking paths, the probabilistic model gives an observation that the blocking probability decreases drastically and then approaches zero as the number of middle switches is far less than the theoretical bound. The S-shaped curves of blocking probability versus degree of fanout indicate that high fanout requests are mostly blocked at some given reference network utilization. A split routing algorithm and its blocking probability are introduced to enhance the routability of the high fanout requests. We also corroborate the analytic model by performing network simulations based on a random request generator and a random routing strategy.