Patent ID: 7535914

Claim:
A method a of operating a datagram network comprising at least three nodes having respective external links to a subnetwork, said datagrams being constructed in accordance with a protocol that specifies a first set of predetermined locations in said datagram to represent a source address, said method comprising: (a) operating each of a group of two or more of said nodes as a sender node to transmit one or more datagrams with a common group identifier in said first set of predetermined locations to one of said nodes which is operating as a recipient node, the transmission taking place via the sender node's external link to said subnetwork, the subnetwork and the recipient node's external link to said subnetwork; (b) operating said subnetwork to forward said datagram over the external link leading to a recipient node selected in dependence upon said common group identifier value in said first set of predetermined locations; said subnetwork including, for each of said groups, stored data representing one or more routing trees associated with said group, said stored data comprising, for each routing tree, routing tree data identifying one of said external links as a root-bound external link in relation to said routing tree and a plurality of others of said external links as leaf-bound external links in relation to said routing tree; said selected one of said external links comprising the external link defined as the root-bound external link in relation to the routing tree that corresponds to the group identifier value in said first set of predetermined locations; and said protocol further defining a second set of predetermined locations to represent a destination address; (c) operating one of said nodes to send one or more datagrams with said common group identifier in said second set of predetermined locations; and (d) operating said subnetwork, on receipt of a datagram with said common group identifier in said second set of predetermined locations, to forward said datagram over the leaf-bound external links associated with said routing tree for said group.