Real-time Communication using Foundation Fieldbus

Local area networks (LANs) are becoming popular in industrial computer-controlled systems increasingly. Broadcast LANs aimed at the interconnection of sensors, actuators and controllers are commonly known as fieldbus networks. Recently, the vendor-specific fieldbus has being substituted by vendor-independent standardized fieldbus, which supports the open system concept and has started to be used commonly. Particular relevance must be given to the IEC 61158 (1999), which encompasses eight widely used fieldbuses: FF H1, ControlNet, PROFIBUS, P-NET, FF HSE, SwiftNet, WorldFIP and Interbu (Xiuju 2000; Xiong 2000) known that time constraints are more stringent as we go down in the automation hierarchy. In this charter, we consider time constraints or deadlines as the maximum allowable time span between a message transfer request and its transmission on the bus. In fact, the total message cycle delay results from multiple factors, such as the access and queuing delays, the transmission time (frame length / transmission rate) and the protocol processing time. As we are dealing with real-time communication across a shared transmission medium, we focus our analysis on the access delay and queuing delay factors. These factors depend on the MAC (Medium Access Control) mechanism used by the fieldbus network