The invention solves the problem of overloading intermediate routers with state
information as the number of multicast groups increases to millions of groups.
The invention places multicast delivery tree information in the header of an encapsulated
multicast packet, thereby relieving the routers from maintaining any state information
about the multicast groups. The encapsulated packet is referred to as a small group
multicast packet, or SGM packet. Routers which are neither branch points of the
delivery tree nor destination routers will also need to do no additional forwarding
processing other than that needed for standard unicast forwarding. A protocol designation
field in the Layer 3 header informs the router that the packet is a SGM packet,
and that the router is therefore instructed to parse the packet for route information.
The router parses the SGM packet header and determines the next hop address of
routers in the multicast delivery tree. The standard unicast forwarding tables
are then consulted to determine the next packet destination addresses, and the
router then rewrites the SGM packet and routes it to the next hop router. The routing
tables also instruct the router as to which outbound port to route the packet.