A
source tree
—A path from a multicast source (the
root of the tree) through the network to the receivers in the multicast
group. The source tree is the shortest path that a multicast packet
can take from source to receiver, so it is also known as the
shortest-path
tree (SPT)
. The sender and receiver are annotated as a source
and multicast group pair, shortened to (S, G); for example, (192.168.1.1,
225.9.2.6). The following figure illustrates three shortest-path
trees from the source to three receivers.