In SSM, Source-Specific Multicast, things are done differently from standard multicast forwarding. SSM is specifying a group of hosts that are receiving same multicast stream using group IP address and additionally using stream unicast source IP.
In this article it is shown how to configure Source Specific Multicast on Cisco and Juniper equipment.
In standard multicast, forwarding is done using group IP address which is an IP from multicast dedicated range 188.8.131.52/4 (184.108.40.206 – 220.127.116.11) or FF00::/8 in IPv6. Each multicast group IP address is a single address which specifies all hosts receiving a specific stream, streamed towards that group IP address from multicast source. In standard multicast everybody can start to stream with some IP multicast group IP, becoming in that way, the multicast source.