ABSTRACT
Nowadays, intelligent nodes, that is, microprocessor-based with communication capabilities, are extensively used in the lower layers of both process control and manufacturing industries [8]. In these environments, applications range from embedded command and control systems, to image processing, monitoring, human-machine interface, etc. Moreover, the communication between the different nodes has specific requirements [9] which are quite different from, and sometimes opposed to, those found in office environments. For instance, predictability is favored against average throughput, and message transmission is typically time and precedence constrained. Furthermore, the nonrespect of such constraints can have a significant negative impact on the quality of the control action in Distributed Computer Control Systems (DCCSs), or on the quality of the observation of the system state in Distributed Monitoring Systems (DMSs). Therefore, to deliver the adequate quality of service, special-purpose networks have been developed, essentially during the last two decades, which are generically called fieldbuses and are particularly adapted to support frequent exchanges of small amounts of data under time, precedence, and dependability constraints [8]. Probably, the most well-known examples existing today are Controller Area Network (CAN), DeviceNet, ProfiBus, WorldFip, P-Net, and Foundation Fieldbus.
