Multicast Architecture - 3Com WX3000 Series Operation Manual

ASM model
In the ASM model, any sender can become a multicast source and send information to a multicast
group; numbers of receivers can join a multicast group identified by a group address and obtain
multicast information addressed to that multicast group. In this model, receivers are not aware of the
position of a multicast source 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. From the view of a sender, the two models have the
same multicast group membership architecture.
Functionally, the SFM model is an extension of the ASM model. In the SFM model, the upper layer
software checks the source address of received multicast packets so as to permit or deny multicast
traffic from specific sources. Therefore, receivers can receive the multicast data from only part of the
multicast sources. From the view of a receiver, multicast sources are not all valid: they are filtered.
SSM model
In the practical life, users may be interested in the multicast data from only certain multicast sources.
The SSM model provides a transmission service that allows users to specify the multicast sources they
are interested in at the client side.
The radical difference between the SSM model and the ASM model is that in the SSM model, receivers
already know the locations of the multicast sources by some means. In addition, the SSM model uses a
multicast address range that is different from that of the ASM model, and dedicated multicast forwarding
paths are established between receivers and the specified multicast sources.

Multicast Architecture

The purpose of IP multicast is to transmit information from a multicast source to receivers in the
multicast mode and to satisfy information requirements of receivers. You should be concerned about:
Host registration: What receivers reside on the network?
Technologies of discovering a multicast source: Which multicast source should the receivers
receive information from?
Multicast addressing mechanism: Where should the multicast source transports information?
Multicast routing: How is information transported?
IP multicast is a kind of peer-to-peer service. Based on the protocol layer sequence from bottom to top,
the multicast mechanism contains addressing mechanism, host registration, multicast routing, and
multicast application:
Addressing mechanism: Information is sent from a multicast source to a group of receivers through
multicast addresses.
Host registration: A receiving host joins and leaves a multicast group dynamically using the
membership registration mechanism.
Multicast routing: A router or switch transports packets from a multicast source to receivers by
building a multicast distribution tree with multicast routes.
Multicast application: A multicast source must support multicast applications, such as video
conferencing. The TCP/IP protocol suite must support the function of sending and receiving
multicast information.
Multicast Address
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