Performability Analysis and Validation of a Large Scale Fieldbus System by Formal Methods

The complexity of large scale fieldbus systems is two-fold: message-sending concurrency and emergent bus behavior. On the one hand, an increase in the number of accumulating nodes within one fieldbus system expands its message-sending concurrency; on the other hand, the growth of emergent bus behavior causes a temporary or lasting message burst on the fieldbus channel. The message sequences in turn have an increased burst behavior, aggravating the traffic density. Therefore, this dissertation evaluates the performability of large scale fieldbus systems by presenting a busload validation procedure by formal methods. The model concept is conceptualized and formulated by UMLCD and OSI Model. Furthermore, the validation procedure is formalized and structurally specified by applying the attribute hierarchy and BMW principle. Based on sorting the message-sending occurrences from the log data of a real fieldbus-based building automation system, the validation procedure is thus quantified with the real system timed-parameters. In addition, the stochastic distributions of message transmissions are determined by the goodness of fit method. The entire work is based on DSPN as formal means of descriptions and models. The corresponding Petri net communication model is hierarchically constructed, which has been further parameterized, integrated and simulated. The analysis of system complexity is provided by the programming-based extension of the Petri net communication model. In addition, the results of Monte-Carlo-Simulation have been sorted, analyzed and evaluated regarding the validation aspects of system performability. Finally, the emergent message burst generated from the function interrelations has also been observed and evaluated. The result of this work will make a formal contribution to the improvement the fieldbus specification.