3. Terminology
To reduce confusion when talking about the any-source and source-specific multicast models, we use different terminology when discussing them.
We use the term "channel" to refer to the service associated with an SSM address. A channel is identified by the combination of an SSM destination address and a specific source, e.g., an (S,G) pair.
We use the term "host group" (used in RFC 1112) to refer to the service associated with "regular" ASM multicast addresses (excluding those in the SSM range). A host group is identified by a single multicast address.
Any host can send to a host group, and similarly, any host can send to an SSM destination address. A packet sent by a host S to an ASM destination address G is delivered to the host group identified by G. A packet sent by host S to an SSM destination address G is delivered to the channel identified by (S,G). The receiver operations allowed on a host group are called "join(G)" and "leave(G)" (as per RFC 1112). The receiver operations allowed on a channel are called "Subscribe(S,G)" and "Unsubscribe(S,G)".
The following table summarizes the terminology:
| Service Model | any-source | source-specific |
|---|---|---|
| Network Abstraction | group | channel |
| Identifier | G | S,G |
| Receiver Operations | Join, Leave | Subscribe, Unsubscribe |
We note that, although this document specifies a new service model available to applications, the protocols and techniques necessary to support the service model are largely a subset of those used to support ASM.