Effect of the token holding timer on MAP performance

Expressions are obtained for the mean excess token holding time for general service time distributions. They were used in the mean message delay approximations for both homogeneous token holding timer (THT) networks and nonhomogeneous THT and token rotating timer networks. Comparisons with simulation results indicated that these approximate formulas are quite accurate. The nonhomogeneous case considered here is only one of many possible mixes of low- and high-priority stations in a network. However, for the purpose of planning manufacturing automation protocol networks, only approximate and worst-case analyses are needed to determine the size of the network and the traffic characteristics for certain performance specifications. The formulas derived here can be used to provide guidance in the choice of timer settings for meeting various priority service requirements