Multicast Models - 3Com 4500 Configuration Manual

Distributive application: Multicast makes multiple-point application possible.
Application of multicast
The multicast technology effectively addresses the issue of point-to-multipoint data transmission. By
enabling high-efficiency point-to-multipoint data transmission, over an IP network, multicast greatly
saves network bandwidth and reduces network load.
Multicast provides the following applications:
Applications of multimedia and flow media, such as Web TV, Web radio, and real-time video/audio
conferencing.
Communication for training and cooperative operations, such as remote education.
Database and financial applications (stock), and so on.
Any point-to-multiple-point data application.

Multicast Models

Based on the multicast source processing modes, there are three multicast models:
Any-source multicast (ASM)
Source-filtered multicast (SFM)
Source-specific multicast (SSM)
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.
1-5