Multicast routing using core based trees

A method for enabling a particular node to join a particular multicast group of nodes in a network, said multicast group having a multicast tree including a core node, said method comprising the steps of:

• transmitting a join request control packet containing a multicast address of said core node from said particular node to a node already on said multicast tree using unicast routing,
• at said node already on said multicast tree, writing an address of the node from which said join request control packet was received in an entry of a forwarding table maintained at said node already on said multicast tree, which entry is indexed by said multicast address of said core node, and
• transmitting a join acknowledgement control packet to said particular node.

A method for transmitting a data packet to a multicast group of nodes in a network using a multicast tree of nodes associated with said group comprising the steps of:

• at each node on a multicast tree corresponding to said multicast group, retrieving an entry from a forwarding table maintained at each node and indexed by a multicast address of a core node indicated by said data packet, and transmitting a copy of said data packet to each node indicated by said retrieved entry except a node from which said packet was received.,
• said multicast tree having been constructed by the steps of:
• transmitting from a particular node wishing to join said particular multicast group a join request control packet indicating a multicast address of said core node, receiving said join request control packet at another node, writing an address of the node from which said join request was received in an entry of a forwarding table maintained at said other node, which entry is indexed by said multicast address of said core node, and if said other node is not already on said multicast tree of said particular multicast group, writing an address of a next node on a path to said core node in said forwarding table entry indexed by said multicast address of said core node and retransmitting said packet form said other node to said next node.

A method for transmitting a data packet from a source node which is not a member of a multicast group of nodes to a multicast group of nodes in a network using a multicast tree of nodes associated with said group comprising the steps of:

• transmitting said data packet containing a multicast address of a core node on said multicast tree from said source node to a node on said multicast tree using unicast routing,
• said packet being transmitted on said multicast tree by the steps of:
• at each node on a multicast tree corresponding to said multicast group, retrieving an entry from a forwarding table maintained at each node and indexed by a multicast address of a core node indicated by said data packet, and transmitting a copy of said data packet to each node indicated by said retrieved entry except a node from which said packet was received.