Analytic Calculus of Response Time in Networked Automation Systems

This paper presents a novel approach to evaluate the response time in networked automation systems (NAS) that use a client/server protocol. The developments introduced are derived from modeling the entire architecture in the form of timed event graphs (TEGs), as well as from the resulting state representation in Max-Plus algebra. The various architectural stages are actually modeled in a very abstract pattern, which yields just those TEG models where local delays are sufficient to perform the overall evaluation. In this manner, linear Max-Plus equations are obtained. A thorough analysis of these equations has led to analytical formulas for direct calculus of NAS response time. As a final step, experimental measurements taken on a laboratory facility have been used to verify the validity of the results. In conclusion, the benefit and effectiveness of this novel method have been demonstrated. Note to Practitioners-In this work, we present an overall study of networked automation systems working according to client/server paradigm. Unlike systems where a global scheduling of the shared resources is available and the delays well handled, in such systems it is not the case and the investigations to evaluate their real-time performances are required. Actually, these systems are very present in industry but the efforts to deal with this issue are rare and often informal, based on simulation of particular cases. In our work, we assess a major criterion of their time performances, the response time. We give a formal evaluation of this feature through an analytic approach. The results we present are generic and fit the experimental observations in different cases.