Cycle time properties of the PROFIBUS timed-token protocol

A recent trend in distributed computer-controlled systems (DCCS) is to interconnect the distributed elements by means of a multi-point broadcast network. As the network bus is shared between a number of network nodes, there is an access contention, which must be solved by the medium access control (MAC) protocol. Usually, DCCS impose real-time constraints. In essence, by real-time constraints we mean that 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 with MAC protocols that guarantee bounded access and response times to message requests. PROFIBUS is a fieldbus network with a MAC protocol based on a simplified version of the timed token protocol. In this paper, we analyse PROFIBUS MAC’s cycle time properties, as they are crucial to guarantee a real-time behaviour of DCCS supported by this type of fieldbus networks.