Patent ID: 6999452

Claim:
A packet-switched network system comprising a multiplicity of multi-port network units each of which has first and second ports and other ports; and transmission links coupling the first and second ports of said units in a closed ring, said first and second ports and said transmission links supporting duplex transmission of data packets; wherein each unit transmits from said first and second ports packets including selected information enabling on reception of a packet at any of the units a determination of a number of hops from unit to unit around said ring said packet has made, each unit has a forwarding database and in response to the said selected information controls the transmission of said packets in two directions around said ring, and each unit causes discard of packets which have according to said selected information circumnavigated the ring; and wherein each unit includes means responsive to said selected information (i) to determine the number of hops from unit to unit around the ring a received packet has made; (ii) when the number is less than half the total number of hops around the ring, to learn a source address of the packet as that one of the said first and second ports at which the packet was received; (iii) when the number is greater than half the total number of hops around the ring, to learn a source address for the packet as that one of the first and second ports other than that at which the packet was received; and (iv) when the number is equal to the total number of hops around the ring, to cause discard of the packet.