Implementing Time-Triggered Communication over a Standard Ethernet Switch

Cyber-physical systems in IIoT and Fog computing can use a variety of standards to guarantee real-time communication, based on enhanced switches with quality-of-service, audio-video bridging, time-triggered Ethernet and time-sensitive networking features. However, such real-time enabled network switches often come at a high design and maintenance cost. This paper explores the feasibility of source time-triggered communication over a standard Ethernet switch without enhanced capabilities and demonstrates the minimum requirements of a system needed to enable time-triggered communication. To achieve deterministic communication and synchronous operation of the tasks, the worst-case execution time of the tasks is analyzed and a static schedule is defined. We use the IEEE 1588 Precise Time Protocol to provide a global time reference for the network devices and time-triggered messages are scheduled at the source nodes. The communication is implemented and evaluated on a scalable synthetic cyber-physical system test-case composed of three nodes: a time server node and two application nodes that control a servo motor and exchange a time-triggered message containing the duty cycle of the pulse-width modulation signal.