On Use of 802.4 Token Bus in Distributed Control Systems

IEEE 802.4 broadband channel access scheme has been widely accepted as the standard for factory Local-Area Networks. The priority option of the 802.4 standard supports multiple classes of traffic by using a set of timers to control information exchange. A timer assignment technique is presented for factory LANs using the 802.4 priority option. The timers are set to satisfy the worst case access delay requirements of real-time control applications. Other applications that are not time constrained can be supported simultaneously. In fact, under certain conditions, such applications can also be guaranteed a minimum bandwidth allocation. The results given here can be used during network design stage to ensure that the network can support the requirements of the devices connected to the network. Simulation results are used to evaluate the timer assignment scheme.