Modeling and evaluating the DQDB protocol with stochastic timed Petri nets

The goal of the authors is to present a modeling methodology based on the stochastic timed Petri nets that allows an exhaustive analysis of the protocol DQDB. This methodology is based on structured models and abstraction concept. A new contribution to the analysis of the queue arbitrated (QA) mechanism is the determination by the modeling process of the time distribution function of the empty slots which arrive at a node (we take into account the correlation between the request arrival process and the empty slot arrival process). The study also points out: the unfairness of the QA mechanism; the control of this unfairness by introducing the BWB mechanism and also a counterpart of this mechanism (the bandwidth wastage can appear); and the increase of unfairness of the QA mechanism when the PA access is considered