Applications of multicast, Multicast models, Asm model – H3C Technologies H3C S7500E Series Switches User Manual
Page 23: Sfm model, Ssm model, Multicast architecture
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Applications of multicast
Applications of the multicast technique include:
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Multimedia and streaming applications, such as Web TV, Web radio, and real-time video/audio
conferencing.
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Communication for training and cooperative operations, such as distance learning and
telemedicine.
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Data warehouse and financial applications (stock quotes).
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Any other point-to-multipoint data distribution application.
Multicast Models
Based on how the receivers treat the multicast sources, there are three multicast models:
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 as a multicast source, and
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 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. From the view of a sender, the two models 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. 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 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:
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Where should the multicast source transmit information to? (multicast addressing)
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What receivers exist on the network? (host registration)
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Where is the multicast source the receivers need to receive multicast data from? (multicast
source discovery)
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How should information be transmitted to the receivers? (multicast routing)