Transforming Couloured Petri Nets to Counter Systems for Parametric Verification: A Stop-and-Wait Protocol Case Study
Résumé
Protocols may contain parameters that are chosen from a wide range. In some cases we would like our analysis results to apply to an arbitrary upper limit on a parameter value, such as the maximum number of retransmissions. In this case we have an infinite family of finite state systems. This makes their verification difficult. However, techniques and tools are being developed for the verification of parametric and infinite state systems. We explore the use of one such tool, fast, for verifying several properties of the stop-and-wait class of protocols, where the maximum number of retransmissions and the maximum sequence number are considered as parameters. We are also interested in using expressive languages for representing protocols such as Coloured Petri nets (CPNs). fast's foundation is counter systems, which are automata whose states are a vector of non-negative integers, with operations limited to Presburger arithmetic. We therefore also present some first steps in transforming CPNs to counter systems in the context of stop-and-wait protocols operating over unbounded FIFO channels.