Petri Net based Fault Tolerance Evaluation of IEC 61158 FieldBus Standard

The aim of the paper is to evaluate the impact of the occurrence of faults on the IEC 61158 type 1 FieldBus protocol. This communication system was developed for use in process control environment, where robustness to the occurrence of a fault is an important requirement. After a survey of the protocol's main features, certain types of failures are defined, the occurrence of which may be critical for the communication system. It will be shown that for some of the failures considered, the IEC 61158 type 1 protocol doesn't foresee any recovery procedure. When other failures occur, the fault states caused by them, may be not recovered by the fault recovery procedures provided for by the IEC 61158 type 1 standard. In particular it will be shown that the standard provides for procedures aimed to recover faults caused by some kind of failures, but these procedures are unable to perform their goal. The evaluation of the effect of these faults on the performance of the communication system seems to be an important issue. For this reason, the paper presents a performance evaluation of the fault recovery mechanisms, foreseen by the IEC protocol, but unable to recover some faults. The evaluation is based on Petri Net model simulation, and is aimed to evaluate the impact on the recovery procedures on the information flow between control processes.