Multicast Models; Multicast Architecture - HP 6125XLG Ip Multicast Configuration Manual

Multicast models

Based on how the receivers treat the multicast sources, the multicast models include 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. Receivers
can join a multicast group identified by a group address and get multicast information addressed to that
multicast group. In this model, receivers do not know 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. 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, multicast
sources are not all valid, but 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 at the client side the multicast sources in
which they are interested.
In the SSM model, receivers have already determined the locations of the multicast sources. This is the
main difference between the SSM model and the ASM model. In addition, a different multicast address
range than the ASM/SFM model is used in the SSM model. Dedicated multicast forwarding paths are
established between receivers and the specified multicast sources.

Multicast architecture

IP multicast addresses the following issues:
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 that will provide data to the receivers? (Multicast source discovery.)
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How should information be transmitted to the receivers? (Multicast routing.)
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IP multicast is an end-to-end service. The multicast architecture involves the following parts:
Addressing mechanism—A multicast source sends information to a group of receivers through a
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multicast address.
• Host registration—Receiver hosts can join and leave multicast groups dynamically. This mechanism
is the basis for management of group memberships.
Multicast routing—A multicast distribution tree (a forwarding path tree for multicast data on the
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network) is constructed for delivering multicast data from a multicast source to receivers.
Multicast applications—A software system that supports multicast applications, such as video
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conferencing, must be installed on multicast sources and receiver hosts. The TCP/IP stack must
support reception and transmission of multicast data.
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