Using Server-Sent Events for Event-Based Control in Networked Control Systems

Server-Sent Events (or SSEs) is a standard HTTP technology used in many web applications nowadays. This protocol enables communication between a server and a client based on messages that are sent at the server's will. Different type of event triggers can be defined in the server and the client can subscribe to one or more of these event streams. Event-based control tries to optimize the communications between the plant and the controller while still performing an adequate control of the system. This is especially useful in networked control systems, where the plant and the controller are physically separated, and a network communication system is in between of them. Just like event-based control is a natural fit for networked control systems, this paper proposes the use of SSEs as a natural solution to implement event-based control strategies assigning the role of "server" to the plant and the role of "client" to the controller. The work presents the main advantages of using SSEs in this scenario, compares this technology to other possible solutions (such as WebSockets) and presents a communication workflow between client (controller) and server (plant) to define event triggers and subscribe to event streams that might be of interest to the controller. (C) 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.