Scheduling combined unicast and multicast traffic in broadcast WDM networks

This paper studies the performance of various strategies for scheduling a c ombined load of unicast and multicast traffic in a broadcast WDM network. T he performance measure of interest is schedule length, which directly affec ts both aggregate network throughput and average packet delay. Three differ ent scheduling strategies are presented, namely: separate scheduling of uni cast and multicast traffic, treating multicast traffic as a number of unica st messages, and treating unicast traffic as multicasts of size one. A lowe r bound on the schedule length for each strategy is first obtained. Subsequ ently, the strategies are compared against each other using extensive simul ation experiments in order to establish the regions of operation, in terms of a number of relevant system parameters, for which each strategy performs best. Our main conclusions are as follows. Multicast traffic can be treate d as unicast traffic, by replicating all multicast packets, under very limi ted circumstances. On the other hand, treating unicast traffic as a special case of multicast traffic with a group of size 1, produces short schedules in most cases. Alternatively, scheduling and transmitting each traffic com ponent separately is also a good choice.