Multicast Models; Asm Model; Sfm Model; Ssm Model - HP A6600 Configuration Manual

Multicast models

Multicast models, including ASM, SFM, and SSM, determine how receivers treat multicast sources.

ASM model

In the ASM model, any sender can send information to a multicast group as a multicast source, and
receivers can join a multicast group (identified by a group address) and obtain multicast information
addressed to that multicast group. In this model, receivers do not determine 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 model. To a sender, the two models appear to 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. To a
receiver, not all multicast sources are valid because they are filtered.

SSM model

Users are sometimes 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 they
prefer.
The primary difference between the SSM model and the ASM model is that in the SSM model, receivers
have already determined 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 is an end-to-end service with architecture that involves several key areas, including:
• Addressing mechanism—A multicast source sends information to a group of receivers through a
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
•
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
conferencing, must be installed on multicast sources and receiver hosts. The TCP/IP stack must
support reception and transmission of multicast data.
5