Based on the control level for the multicast source, IP multicast can be classified into the following models:
ASM Model
SFM Model
SSM Model
In the Any-Source Multicast (ASM) model, any sender can act as the multicast source and send information to a multicast group address. Receivers join the multicast group to receive all the information sent to the group.
In the ASM model, receivers do not know the location of the multicast source. The receivers can join or leave the group at any time.
The Source-Filtered Multicast (SFM) model inherits some features of the ASM model. For the sender, the member relationship of the two models is the same.
The SFM model is an extension of the ASM model. The upper layer software checks the source address of the received multicast packets, permitting or denying packets from some multicast sources. The receivers receive data only from partial multicast sources because for them, only partial multicast sources are valid, and some multicast sources are filtered.
The SFM is basically an ASM with a multicast source filtering policy. The basic principles and configurations of ASM and SFM are the same.
In practice, users may be interested only in data sent by particular sources and may be unwilling to receive data sent by other sources. The Source-Specific Multicast (SSM) model provides a transmission service with which users can specify their preferred sources.
The main difference between the SSM model and the ASM model is that in the SSM model, receivers know the location of the multicast source. The SSM model uses a different address scope from that of the ASM model. The SSM model sets up a multicast distribution tree between receivers and the source.
