Performability of a token bus network under transient fault conditions

Local area networks are representative of a growing class of distributed systems which demand more sophisticated methods and tools to evaluate system behavior in the presence of faults. In particular, since they are likely to exhibit degradable performance, the concept of performability can provide more re ned assessments of their ability to perform under fault and error conditions. This paper presents the results of a detailed performability evaluation of a network employing the IEEE 802.4 protocol. In particular, a 30-station IEEE 802.4 token bus network operating in a hostile factory environment is evaluated using stochastic activity networks. Stochastic activity networks, a generalization of stochastic Petri nets, provide a convenient representation for computer networks and are formal enough to permit solution by both analysis and simulation. The evaluation results show 1) that stochastic activity networks are an appropriate model type for evaluating the performability of local area networks and 2) that the protocol is extremely tolerant to transient faults such as token losses and noise bursts under moderate network loads.