TIMING PROPERTIES OF THE FDDI-M MEDIUM ACCESS PROTOCOL

The FDDI Standard specifies a 100 Mbits/s fibre-optic token ring netwo rk that has been implemented and widely installed, The FDDI medium acc ess control (MAC) protocol, however, has the inherent deficiency that, at most, one half of the bandwidth of a FDDI ring can be used to tran smit synchronous messages, In a recent paper, a modification to the FD DI MAC protocol, called FDDI-M, was proposed to overcome this deficien cy, It has been shown using simulation that FDDI-M doubles a ring's ab ility of supporting synchronous traffic while at the same time it achi eves a higher throughput for asynchronous traffic than standard FDDI, In this paper we present an analytical study of the timing properties of the FDDI-M protocol, The results presented in this paper complement those of the original paper. Using the worst-case achievable utilizat ion (WCAU) as the performance metric, we evaluate the performance of v arious synchronous bandwidth allocation (SBA) schemes in guaranteeing synchronous message deadlines, It is found that, in comparison with FD DI, the FDDI-M protocol results in a higher WCAU for the normalized pr oportional SBA scheme, However, for the local SBA schemes studied, the WCAU values remain at zero.