A delay model for priority classes of FDDI based on M/G/1 with vacations

The classical M/G/1 system with vacations has been used to estimate the mean waiting time of individual priority classes of homogeneous FDDI networks. To faithfully model the FDDI network using M/G/1 system, the vacation interval of the server (token) as seen by individual priority classes must be evaluated. The expressions for the mean waiting time of individual priority classes are functions of first and second moments of the vacation intervals of that class. It can be shown that the expression derived for the first and second moments of the vacation intervals of the respective classes are functions of the mean and variance of number of messages transmitted by each priority class per token rotation. These expressions are evaluated using an iterative procedure that utilizes the prior knowledge of the throughput characteristics of the FDDI network. Simulation results show that the model provides accurate estimates for the mean waiting time of individual priority classes of a homogeneous FDDI network.