The ability to support multicast connections is a necessary component of emerging high speed networks, including SONET/SDH switching networks. Nonblocking capability, in which multicast connections never block, comes at the expense of considerable network complexity. Savings in complexity can be obtained by sacrificing the nonblocking property and designing algorithms to rearrange existing connections in the event a new connection is blocked. The authors consider multicast routing in the three stage Clos network, with particular interest in rearrangement algorithms that efficiently find a small set of connections to rearrange. They consider three rearrangement algorithms, an exhaustive flooding algorithm, a least used middle switch algorithm and a most used middle switch algorithm, The algorithms are evaluated for blocking probability and rearrangement length. The results indicate that the less complex algorithms give reasonably good performance in most cases, however the worst case rearrangement length can be quite long for the non-exhaustive algorithms.
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