Methods and apparatus for routing packets in packet transmission networks

A packet communications system provides for point-to-point packet routing and broadcast packet routing to limited subsets of nodes in the network, using a routing field in the packet header which is processed according to two different protocols. A third protocol is provided in which a packet can be broadcast to the limited subset even when launched from a node which is not a member of the subset. The routing field includes a first portion which contains the route labels necessary to deliver the packet to the broadcast subset. A second portion of the routing field contains the broadcast subset identifier which can then be used to deliver the packet to all of the members of the broadcast subset. Provision is made to backtrack deliver the packet to the last node identified before the broadcast subset if that last node is itself a member of the subset.