Adding local scheduling mechanisms to FDDI for time critical communications

More and more distributed manufacturing applications use field busses at their lower level as the communication system for their message exchanges, with or without real-time constraints. These applications can be qualified hard real-time or time critical. The general purpose real-time LAN FDDI can be considered an attractive alternative for these applications due to its high speed and user controllable bounded channel access delay. The parameters of FDDI for guaranteeing the transmission of the real-time messages before their deadlines, and for providing a high throughput for the nonreal-time messages, must be found. We discuss parameter setting when used for transmitting periodic and aperiodic traffics. A local scheduling mechanism for each FDDI station is given, with performance improvements. Several scheduling mechanisms have been examined by means of simulation. A simulator is developed which allows us to carry out not only a performance comparison of modified FDDI using the above scheduling mechanisms but also the fine tuning of the values of the synchronous allocation timers for an efficient implementation. So this simulator can be used as a practical tool for the FDDI configuration knowing the time constraints of the supported application