Multicast Distribution Trees
Multicasts use two different ways to distribute data between a server and hosts:
�¡ A source-based tree is the simplest kind. Its root is the server, and it
forms branches throughout the network to all the members of the
multicast group. A source tree is identified by (S,G) where S is the IP
address of the server and G is the group multicast address. It creates
optimal paths between the server and the hosts, but takes more router
resources. Every router along the path must maintain path information
for every server.
�¡ A shared tree selects a common root called a rendezvous point (RP).
The server sends traffic to the RP, which forwards it to hosts belonging
to the group. The tree is identified by (*,G) where * means any source
and G is the group multicast address. Shared trees use less router
resources, but can result in suboptimal paths.