Patent ID: 7376138

Claim:
A communications system including a communications network, the communications network comprising: a ring topology with at least two duplicate ring transmission paths; a plurality of nodes connected to the plural ring network, each node being arranged to output onto one of the ring transmission paths packets addressed to one or more other nodes on the network using a packet address field containing a node address unique to the ring transmission path being used; and, a switch bridging the at least two transmission paths, and arranged in the event of a failure in one of the transmission paths, to divert packets from the said one of the ring transmission paths onto another of the ring transmission paths, each node being assigned a different network address for each of the plural transmission paths, and one or more of the nodes being arranged to remove a packet from the network when the packet carries a node address corresponding to anyone of said plural different network addresses for said one or more of the nodes, wherein at least one of the nodes has: (a) an input arranged to receive packets from the network, (b) an output arranged to output packets onto the network, (c) a switch arranged selectively to remove packets from the network, and to insert the packets into the network, and (d) a control structure arranged to determine a priority assigned to a transit packet arriving at the node, and arranged to control the switch to remove a transit packet determined to have a low priority, and to insert in the vacancy created by removing said packet another packet determined to have a high priority.