SSM requires that the receiver specify the source address and explicitly excludes the use of the (*,G) join for all multicast groups in RFC 3376, which is possible only in IPv4's IGMPv3 and IPv6's MLDv2.
In the ASM service model a receiver expresses interest in traffic to a multicast address.
Interest in multicast traffic from a specific source is conveyed from hosts to routers using IGMPv3 as specified in RFC 4607.
For IPv6 current allowed SSM destination addresses are specified by ff3x::/96, where the hexadecimal digit x represents the scope.
[1] Note however that the allocation may be extended in the future so receivers and network equipment should treat any ff3x::/32 address as SSM.