Multicast models
Based on how the receivers treat the multicast sources, the multicast models include any-source multicast (ASM), source-filtered multicast (SFM), and source-specific multicast (SSM).
ASM model
In the ASM model, any sender can send information to a multicast group. Receivers can join a multicast group and get multicast information addressed to that multicast group from any multicast sources. In this model, receivers do not know the positions of the multicast sources in advance.
SFM model
The SFM model is derived from the ASM model. To a sender, the two models appear to have the same multicast membership architecture.
The SFM model functionally extends the ASM model. The upper-layer software checks the source address of received multicast packets and permits or denies multicast traffic from specific sources. The receivers can receive the multicast data from only part of the multicast sources. To a receiver, multicast sources are not all valid, but are filtered.
SSM model
The SSM model provides a transmission service that enables users to specify at the client side the multicast sources in which they are interested.
In the SSM model, receivers have already determined the locations of the multicast sources. This is the main difference between the SSM model and the ASM model. In addition, the SSM model uses a different multicast address range than the ASM/SFM model. Dedicated multicast forwarding paths are established between receivers and the specified multicast sources.