Multicast - Source Specific Multicast (SSM)
Source Specific Multicast (SSM) involves a multicast implementation where receivers can be configured to accept multicast streams from specific sources, and similarly reject multicast streams from other sources.
This is in contrast to Any Source Multicast (ASM).
Using sparse mode, receivers require the RP (Rendezvous Point) to discover new sources in the network. SSM however requires IGMPv3 and lets hosts join multicast groups from specified source addresses.
Besides just joining any group, the receiver is able to receive the group from a specified source. When we use SSM / IGMPv3 there are no shared trees. We only build SPTs (Shortest Path Trees) towards our sources. This also means that we don’t use any RPs …you won’t need Auto-RP or Bootstrap in such an implementation.