H3C Technologies H3C S3100V2 Series Switches - Manual (Page 13)

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Multicast models
Multicast models—any-source multicast (ASM), source-filtered multicast (SFM), and source-specific
multicast (SSM)—determines how the receivers treat the multicast sources.
ASM model
In the ASM model, any sender can send information to a multicast group as a multicast source, and
numbers of receivers can join a multicast group—which is identified by a group address, and can obtain
multicast information addressed to that multicast group. In this model, receivers do not determine the
positions of the multicast sources in advance. However, they can join or leave the multicast group at any
time.
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. In the SFM model, the upper layer software checks
the source address of received multicast packets and permits or denies multicast traffic from specific
sources. Therefore, receivers can receive the multicast data from only part of the multicast sources. To a
receiver, not all multicast sources are valid because they are filtered.
SSM model
Users might be interested in the multicast data from only certain multicast sources. The SSM model
provides a transmission service that enables users to specify the multicast sources that they are interested
in at the client side.
The main difference between the SSM model and the ASM model is that in the SSM model, receivers
have already determined the locations of the multicast sources by some other means. In addition, the
SSM model uses a multicast address range that is different from that of the ASM/SFM model, and
dedicated multicast forwarding paths are established between receivers and the specified multicast
sources.
Multicast architecture
IP multicast addresses the following questions:
• Multicast addressing—Where should the multicast source transmit information to?
• Host registration—What receivers exist on the network?
• Multicast source discovery—Where is the multicast source that will provide data to the receivers?
• Multicast routing—How should information be transmitted to the receivers?
IP multicast is an end-to-end service. The multicast architecture involves the following parts:
1. Addressing mechanism—A multicast source sends information to a group of receivers through a
multicast address.
2. Host registration—Receiver hosts can join and leave multicast groups dynamically. This
mechanism is the basis for management of group memberships.
3. Multicast routing—A multicast distribution tree—a forwarding path tree for multicast data on the
network—is constructed for delivering multicast data from a multicast source to receivers.