Abstract-This work concerns the control, the observation and then, the implementation principles of a remote system (Master and Slave parts) through the Internet network. This communication link introduces variable delays that have to be taken into account in the control-observation loop. The data-sampling effects will also be considered, even in the aperiodic case. The Slave part is considered to be a linear system. But, since its computation power is supposed to be limited, the control complexity (which, here, is an observerbased state feedback) has to stay in the Master part. The global system must ensure speed performance whatever the delay variation. Such a performance is obtained by showing the robust, exponential stability property, which is proven by using adequate Lyapunov-Krasovskii functionals. This makes possible to compute the controller and observer gains by using LMI optimization. The technical solution we propose is based on a GPS system, which guarantees the Master and Slave clocks to be synchronized. Then, the control and measurement packets are sent together with time-stamps that allow for reconstructing a non-symmetric delay information. It means that Master-to-Slave and Slave-to-Master delays are separately reconstructed by the system (and not only the global RTT, round-trip-time). The last part of the paper provides an example where the Slave is a second-order system.
In an industrial or technical context, some of the communications are strongly time-constrained. Our objective is to evaluate the service offered by a switched Ethernet architecture. We have chosen the network calculus theory because it gives a good representation of the exchanges and enables to determine the maximum end to end delays. Previous models implementing a strict priority policy presented in [7] are improved in order to take into account the Weighted Fair Queueing mechanism which enables to balance the allocation of the network to the different traffics regarding the time contraints they have to respect. This paper also presents the new analytical formulas which upper bound the maximum end-to-end delays of the time-critical messages over the whole network. This enables to determine the optimal bandwith dedicated to both critical and best effort traffics. On an industrial scenario, Strict Priority and Weighted Fair Queueing policies are finally compared.
SUMMARYThe Ethernet network is more and more used to interconnect industrial devices. The objective of this paper is to study the performances of such a network to support real-time communications. For this, first we propose a general representation to model a switched Ethernet network by using a sequence of elementary components such as buffers, multiplexers, etc. Second, we aggregate the individual temporal properties of each component given in the Cruz' survey to obtain a global formula enabling one to calculate the maximum end-to-end delay for any industrial communication scenarios. Finally, we deduce the limits of the switched Ethernet network regarding the number of input/output cards connected to the network and to the sizes of periodic and aperiodic messages.
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