On the Performance of the IEC 61158 Fieldbus

The IEC 61158 Fieldbus protocol merges two well-established medium access control techniques based respectively on a centralized arbitration method and on a token-passing distributed scheme. The first method is used to handle real-time (cyclic) traffic, while the second one allows to share out fairly the bandwidth left free by the cyclic traffic. This paper analyzes the behaviour of an IEC 61158 network to study how the acyclic message exchanges are affected by the selection of some relevant protocol parameters. In particular, two working conditions are considered in the paper. First case, a steady state situation is analyzed where the asynchronous requests for the system bandwidth are equally shared among the different nodes. Second, a transient condition is considered where the asynchronous message queues are temporarily overloaded and the offered load is higher than the available system bandwidth.