Switched Ethernet-Based Real-Time Networked Control System with Multiple-Client–Server Architecture

This paper experimentally verifies that a multiple-client-server architecture based on switched Ethernet can be used as a real-time communication standard for possible applications in factory automation, by observing the effects of packet delays, network congestion, and packet loss on the performance of a networked control system (NCS). The NCS experimental setup used in this research involves real-time feedback control of multiple plants connected to one or more controllers over the network. A multiclient-multiserver (MC-MS) architecture on a local area network (LAN) was developed using user datagram protocol as the communication protocol. In the single-client-single-server (SC-SS) system, as the Ethernet link utilization increased over 82%, the average packet delays and steady-state error of a dc motor speed-control system increased by 2231% and 304%, respectively. As the link utilization increased beyond the threshold, employing an additional server in the NCS reduced average packet delays and also overcame the negative effects of Ethernet's flow control mechanism. The MC-MS architecture is tested with artificially generated random packet loss. The standard deviation of steady-state error (SSE) at 80% utilization with packet loss is found to be 70.2% less than SC-SS and 200% less than multiclient-single-server architecture. The MC-MS architecture remained stable till 70% of control or measurement packet loss.