Delay analysis of networked control systems based on 100 M switched Ethernet.

Ming Li

doi:10.1155/2014/751491

Abstract

For the delay may degrade the performance of networked control systems, networked control systems based on 100 M switched Ethernet are proposed in this paper. According to the working principle of Ethernet switch, the formulas of the upper bound delay of the single-level switched Ethernet and the multiple-level switched Ethernet are deduced by the timing diagram method, and the values of the upper bound delay are also given. The key factors that influence the upper bound delay of switched Ethernet are analyzed; then, the characteristics of the upper bound delay are presented, which show that the delay induced by the single-level 100 M switched Ethernet has little effect on the performance of control systems, while the delay induced by the multiple-level 100 M switched Ethernet may meet the time requirements of all classes of control systems if the numbers of levels and the numbers of nodes connecting to switches are set properly. Finally, the performance of networked control systems is simulated by TrueTime, and the results further show the feasibility and superiority of 100 M switched Ethernet based networked control systems without modification of the network protocols.

Highlights

Networked control systems (NCSs) are feedback control systems wherein the control loops are closed through real-time control networks
Single level and multiple levels is analyzed by the timing diagram in order to show how the delay induced by switched Ethernet affects the performance of an NCS
The characteristics of the single-level 100 M switched Ethernet can be concluded as follows: the upper bound delay is only affected by the numbers of the data frames in the buffer of a switch and has nothing to do with the network loads; more than one NCS can be established by only one 100 M Ethernet switch; and each NCS has no effect on others if the source port and the destination port in each control loop are completely different

Summary

Introduction

Networked control systems (NCSs) are feedback control systems wherein the control loops are closed through real-time control networks. Current researches are mainly focused on 10 M shared Ethernet, and the network protocols must be modified to some extent in order to obtain real-time data transmission; the conclusions obtained from 10 M shared Ethernet cannot be directly applied to 100 M switched Ethernet. Aiming at the performance degradation of control systems caused by the network-induced delay, the 100 M commercial switched Ethernet is presented to establish an NCS without any modification of the network protocols in this paper. Single level and multiple levels is analyzed by the timing diagram in order to show how the delay induced by switched Ethernet affects the performance of an NCS. Through a case, the tool TrueTime is used to simulate the performance of an NCS based on 100 M commercial switched Ethernet to show the feasibility and superiority of this class of NCSs. we present our conclusions

Delay Description of an NCS

Upper Bound Delay of 100 M Switched Ethernet

Simulation Analysis

10 M Ethernet CAN

Conclusions