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.