Abstract: An improved timed deterministic bus access method and system for a bidirectional linear bus, a unidirectional linear bus, a star and a tree type of bus structure. The method employs a master timing reference signal and discrete values of time delay at each node together with a cycle start signal to provide orderly deterministic access by a number of nodes to a shared bus structure. The master timing reference signal is generated by a polling node which can also transmit messages. The time delays in the nodes can correspond to their physical order from the polling node when this is located at one end. Alternatively values of timing delays can be chosen to make the physical location of the polling node of the other nodes unimportant. The method provides for prioritised access to the bus structure using a reservation hold.

Abstract: A LAN priority control system is described which uses an interrupt priority control structure which suspends transmission of a packet from a lower priority node and allows a higher priority interrupting node, which desires to transmit a higher priority message, to obtain rapid access to the transmission medium and to transmit the message. The message is interrupted using a within packet interrupt which is taken to include any command which results in the transmission of a packet onto a common-medium being halted before the complete packet has been transmitted. In addition, the priority of nodes can be adjusted by a centralized network manager or by intelligent terminals distributed among the nodes, allowing priorities to be adjusted at nodes to correspond to the relative priorities of messages currently at these nodes rather than having a fixed allocation of priorities. In a token ring implementation, suspension of the message causes a busy token to be released which recirculates round the ring.