-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.
a b s t r a c tIn this paper, we present an approach to evaluate end-to-end delays in packets switching networked automation systems. Since Client-Server paradigm is considered for communication between the field devices, the existing methods of network delays evaluation are hardly applicable to assess realistic upper bounds of these delays. In an effort to enhance these delays evaluation, we propose an alternative method. Two algorithms, usually used for optimization problems, exhaustive and genetic algorithms, are then developed to achieve this purpose. While a formal proof about the capacity of the former one to ensure the worst delay overestimation is given, the latter proves to provide faster and more accurate results at the same time. This is shown on a practical case study while comparing the results of the two methods.
In this paper, an approach to evaluate time performances of networked control systems (NCS) is presented. Switched-Ethernet with Client/Server protocol is considered for communication. As a result, the reactivity of these NCS is not only affected by the network delays but also by the field devices due delays. Obviously, all of them have to be taken into account to evaluate efficiently the NCS reactivity. So, by including some preliminary results, we propose an overall study in an effort to achieve this aim. First, we model the traffic of the NCS and provide formal proofs to characterize the scenarios leading to the worst delays. Subsequently, we develop a virtual queuing based algorithm (VQA) to search these scenarios and deduce the corresponding delays. Through a practical case study, it is shown how VQA fits experimental observations both quantitatively and qualitatively.
Abstract-In this paper, a new approach to evaluate the response time in Ethernet-based automation systems using client server protocols, is presented. It is based on modeling the behaviour of the system using timed event graphs and the resulting state representation in Max-Plus algebra. First, an algorithm for tracking the frames in the architecture and giving the response time relative to any occurring event is explicated. Subsequently, analytical formulas for direct calculus of this delay are obtained. Finally, experimental measurements taken on a laboratory platform are used to check the validity of the method. Hence, the interest and effectiveness of our results become obvious. They can be used a posteriori to assess the delays in an existing architecture or a priori during the design phase to fulfill the time requirements of a control system.
-In this paper, we present an analytic approach to evaluate the reactivity of client-server networked automation systems (NAS). Both deterministic and probabilistic analyses are provided while modeling the NAS using Timed Event Graphs (TEG). Since many results with regard to the deterministic approach have already been published, we recall only its main steps that prove useful while exposing the probabilistic method. Thereby, we provide the density of probability distribution of the response time (or reactivity) using the probability densities of the local delays, experienced at the different stages of the NAS. Furthermore, a case study is presented to compare the results of the study to measures taken from a real platform.Note to Practitioners-As a matter of fact, client-server networked automation systems are largely used in industry and therefore the efforts to deal with their performances evaluation are necessary. In the current work, we propose an analytic approach to evaluate their reactivity. Analytic formulae are provided to calculate directly and deterministically the bounds of response time along with others to assess its probability density distribution. Moreover, the results of these formulae turn out to be complying with a lot of experimental measurements carried out under different circumstances.
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