Centralized versus distributed protocols for FieldBus applications

FieldBus communication systems provide a more efficient interconnection of field devices in factory automation environments than was possible with traditional point-to-point systems. A critical point in FieldBus communication systems, however, is represented by access to the distributed physical medium, and the use of one data link layer (DLL) access protocol rather than another may be decisive in order to reach optimal performance levels. The solutions adopted at this level may be subdivided into two categories: centralized (used in IEC/ISA FieldBus and FIP protocols) and distributed control protocol (used in Profibus protocol). In this paper the authors analyze the centralized and distributed approaches used in the IEC/ISA and Profibus protocols in order to assess the type of compatibility between them. Then, their performances are evaluated through simulation based on Petri net models of the protocols.