Local communication networks for industrial automation

The author presents a study of the physical and data link layers of the dynamic token-passing bus protocol. This protocol is a variant of the IEEE 802.4 token-passing bus protocol and can therefore be applied to communication systems which support industrial automation. Simulation results have been used for operational validation and extensive evaluation of the communication network´s performance. The complex process of allocating a portion of the channel bandwidth to scheduling control, in a completely distributed fashion, has been investigated. The protocol is capable of efficient operation for the full range of channel utilization, while its dual-phase behaviour provides for a reliable and flexible channel assignment scheme. Thresholds have been determined for switching between the modes, and a hardware unit has been proposed which monitors the bus activities and, using existing signals, generates the switch-over command. Two recommendation for modifications of the existing 802.4 standard are also proposed which increase the reliability and reduce the overheads of the logical ring maintenance functions.