A nonpreemptive priority delay model with modified-vacation intervals for homogeneous FDDI networks

A closed-form analytical expression is derived for the individual priority classes of FDDI based on a nonpreemptive priority delay model. To faithfully model the FDDI network using the nonpreemptive priority delay model, we use a concept of modified-vacations. The expressions for the mean waiting time of individual priority classes are functions of first and second moments of the modified-vacation intervals of that class. It can be shown that the expression derived for the first and second moments of the modified-vacation intervals of the respective classes are functions of mean and variance of the number of messages transmitted by each priority class per token rotation. These variables are evaluated using an iterative procedure that utilizes the prior knowledge of the throughput characteristics of the FDDI network. Simulation results show that the nonpreemptive priority delay model provides accurate estimates for the mean waiting time of individual priority classes of a homogeneous FDDI network