Strictly speaking, SSM is a subset/simplification of ASM and this is naturally the case for its implementation. The specification of PIM-SSM is now included in the PIM-SM specification, so from now on we will call PIM-SSM the behaviour of PIM-SM with SSM addresses (the FF3x::/32 prefix), and PIM-SM the behaviour with ASM addresses.

The additional components needed for inter-domain ASM are used for the in-band automatic source discovery function and for group address allocation. These functions are not needed with SSM because S from (S,G) is supposed to be previously known by each receivers and because (S,G) is supposed to be globally unique in the Internet as S has been allocated by IANA.

We have seen that with PIM-SM, Embedded-RP is a candidate solution for large scale multicast deployment as it resolves partially the multicast group address allocation and the rendezvous point discovery issues. With this solution, the IPv6 ASM multicast Internet is a unique “PIM” domain where multiple PIM-RPs are configured. SSM does not need any rendezvous point and address allocation scheme, and relies on a subset of PIM-SM to function. The IPv6 SSM multicast Internet is still a unique “PIM” domain, possibly not congruent with the unicast one with the help of MBGP but a lot easier to debug compared to PIM-ASM.