Hard Real-Time Communications in Fieldbus Networks: a Survey
Ref: HURRAY-TR-9923 Publication Date: 1, Aug, 1999
Hard Real-Time Communications in Fieldbus Networks: a SurveyRef: HURRAY-TR-9923 Publication Date: 1, Aug, 1999
Fieldbus networks are widely used as the communication support for distributed computer-controlled systems (DCCS), in applications ranging from process control to discrete manufacturing. Usually, DCCS impose real-time requirements; that is, traffic must be sent and received within a bounded interval, otherwise a timing fault is said to occur. This motivates the use of communication networks within which the MAC protocol is able to schedule messages according to their real-time requirements. Therefore, a potential leap towards the use of fieldbuses in such time-critical applications lies on the accurate characterisation of the temporal behaviour of its MAC protocol. For typical factory-floor DCCS applications, the communication profiles encompassed in the EN 50170 fieldbus standard (P-NET, PROFIBUS and WorldFIP) are strong contenders, since they all offer deterministic access and thus are able to schedule messages according to their real-time requirements. Another strong contender is the CAN protocol which, in spite of originally developed as an in-vehicle network, has an interesting priority resolution scheme which makes it also appealing for DCCS applications. In this paper, we describe the main characteristics of four different fieldbus networks: CAN, P-NET, PROFIBUS and WorldFIP, with a special emphasis on the temporal behaviour of their MAC protocols. Importantly, we survey some of the most recent results concerning the analysis on the ability of such fieldbus networks to support real-time communications.