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:

zHost registration: What receivers reside on the network?

zTechnologies of discovering a multicast source: Which multicast source should the receivers receive information from?

zMulticast addressing mechanism: Where should the multicast source transports information?

zMulticast 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:

zAddressing mechanism: Information is sent from a multicast source to a group of receivers through multicast addresses.

zHost registration: A receiving host joins and leaves a multicast group dynamically using the membership registration mechanism.

zMulticast routing: A router or switch transports packets from a multicast source to receivers by building a multicast distribution tree with multicast routes.

zMulticast 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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3Com WX3000 operation manual Multicast Architecture, ASM model, SFM model, SSM model