PIM-SSM does not use a Rendezvous Point to centralize the receivers and sources. A PIM-SSM router which has a receiver for a group multicast address in the SSM address range joins directly to a source for that group by sending an SG join toward the source, not a *G join toward the RP for the group. Because of this, MSDP is not required in order for the PIM Network to learn of an SSM range stream in the SPB network. However, in order for the SPB network to know where a PIM SSM source resides, it must statically configure S1,SSM-G1 at the controllers. In this way, a Gateway can be chosen for the stream, even in the absence of MSDP.
