Fibre-based local area network with priority access

A new-local area network based on a multiaccess unidirectional fibre bus is described. Communication between network stations is by means of objects and can be point-to-point, multicast or broadcast: Each communication object is unique, with an inherent priority embedded in its frame structure. It is impossible for objects of the same priority to attempt media access at the same time, and collisions between objects of different priority are always resolved in favour of the highest-ranked object without the need for a backoff interval. The access protocol is simple, robust and fair in as much as the physical position of stations does not adversely affect their probability of accessing the media or the station queueing delays. The network is ideal for real-time applications and electrically hostile environments, which are characteristic of manufacturing cells. Similar networks are briefly reviewed and the new distributed access protocol is described. It is shown that throughput is high, irrespective of the number of active nodes or the physical length of the media