Multicast Models; Multicast Architecture - H3C S5500-EI Series Operation Manual

Operation Manual – Multicast
H3C S5500-EI Series Ethernet Switches
Any other point-to-multiple-point data distribution application.

1.2 Multicast Models

Based on how the receivers treat the multicast sources, there are two multicast models:
I. 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.
II. 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 model, and dedicated multicast forwarding paths are established
between receivers and the specified multicast sources.

1.3 Multicast Architecture

IP multicast addresses the following questions:
Where should the multicast source transmit information to? (multicast addressing)
What receivers exist on the network? (host registration)
Where is the multicast source from which the receivers need to receive multicast
data? (multicast source discovery)
How should information be transmitted to the receivers? (multicast routing)
IP multicast falls in the scope of end-to-end service. The multicast architecture involves
the following four parts:
1) Addressing mechanism: Information is sent from a multicast source to a group of
receivers through a multicast address.
2) Host registration: Receiver hosts are allowed to join and leave multicast groups
dynamically. This mechanism is the basis for group membership management.
3) Multicast routing: A multicast distribution tree (namely a forwarding path tree for
multicast data on the network) is constructed for delivering multicast data from a
multicast source to receivers.
4) Multicast applications: A software system that supports multicast applications,
such as video conferencing, must be installed on multicast sources and receiver
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Chapter 1 Multicast Overview