Petri net-based performance evaluation of asynchronous traffic management in fieldbus

The paper deals with the problem of asynchronous traffic management in FieldBus systems. A FieldBus is a digital communication bus able to interconnect field devices with control systems in a process control environment. In FieldBus systems the management of the asynchronous flow, made up above all of alarms and of processing results, is particularly critical on account of the difficulty to foresee its communication requirements (i.e. the bandwidth required for the transmission) a priori. Efficient policies for the management of the asynchronous information flow are needed. Actually the IEC/ISA FieldBus represents the only international standard for process control communication systems. The standard is composed of only three levels: Application, Data Link and Physical. In particular the Data Link provides for two policies for the management of the asynchronous information flow. Both policies are based on a centralized management of the physical medium. The paper compares and discusses the performances of both the policies through modelling and simulation, using Transition Time Petri Nets (TTPN).