Hybrid scheduling for unicast and multicast traffic in broadcast WDM networks

Session length and group size are two most significant factors in achieving efficient scheduling for unicast and multicast traffic in single-hop wavel ength division multiplexing (WDM) local area networks (LANs). This paper pr esents a hybrid protocol to schedule both unicast and multicast traffic in broadcast WDM networks. The protocol makes an important assumption that uni cast traffic is the major portion of the overall traffic and is usually sch eduled with a pre-allocation-based protocol. On the other hand, multicast t raffic is a major portion of the overall traffic with multicast sessions an d multicast groups, and is scheduled with a reservation-based protocol. The concept of multicast threshold, a function of random variables including t he multicast session length and the multicast group size, is also proposed to partition the multicast traffic into two types. If the transmission thre shold of a multicast request is larger than the multicast threshold, the re quest is handled with a reservation-based protocol. Otherwise, the multicas t request is handled similar to unicast traffic; that is, each packet in th e multicast session is replicated and sent to the unicast queues of destina tions. The results show that the hybrid protocol can achieve better channel utilization efficiency and packet delay for unicast traffic under the mult icast scenarios with moderate session length and group size. However, separ ate scheduling or broadcasting will be more suitable for a multicast scenar io with very large session length and group size, which is not common on mo st realistic networks.