On the ability of the FDDI-M protocol to support real-time traffic

Timed token networks such as FDDI networks have been widely deployed to support real-time traffic such as voice and video communications. However the medium access control (MAC) protocol of FDDI allows transmission of synchronous messages up to at most one half of the total bandwidth of the network. Shin and Zheng (1995) have proposed a modification to the FDDI MAC protocol, called FDDI-M, which can double a ring's ability in supporting synchronous traffic. We compare the ability of FDDI-M to support synchronous traffic under different SBA schemes with that of FDDI. We first propose a new taxonomy of SBA schemes based on the underlying strategy used to partition the synchronous bandwidth. Next we present an analysis of the timing properties of the FDDI-M protocol, using the Worst Case Achievable Utilization (WCAU) as the performance metric. Our analytical results show that while FDDI-M improves the WCAU values under one class of SBA schemes, its performance under the other category of SBA schemes is mixed. We also perform extensive simulation to study performance of FDDI-M for MPEG video traffic, and conclude FDDI-M does outperform FDDI significantly at heavy load. The effect of SBA schemes under overload conditions is also shown to be relatively minor.