Operation Manual – MulticastH3C S5500-EI Series Ethernet Switches Chapter 1 Multicast Overview1-6z Any other point-to-multiple-point data distribution application.1.2 Multicast ModelsBased on how the receivers treat the multicast sources, there are two multicast models:I. ASM modelIn the ASM model, any sender can send information to a multicast group as a multicastsource, and numbers of receivers can join a multicast group identified by a groupaddress and obtain multicast information addressed to that multicast group. In thismodel, 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 modelIn the practical life, users may be interested in the multicast data from only certainmulticast sources. The SSM model provides a transmission service that allows users tospecify 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 SSMmodel, receivers already know the locations of the multicast sources by some othermeans. In addition, the SSM model uses a multicast address range that is different fromthat of the ASM model, and dedicated multicast forwarding paths are establishedbetween receivers and the specified multicast sources.1.3 Multicast ArchitectureIP multicast addresses the following questions:z Where should the multicast source transmit information to? (multicast addressing)z What receivers exist on the network? (host registration)z Where is the multicast source from which the receivers need to receive multicastdata? (multicast source discovery)z How should information be transmitted to the receivers? (multicast routing)IP multicast falls in the scope of end-to-end service. The multicast architecture involvesthe following four parts:1) Addressing mechanism: Information is sent from a multicast source to a group ofreceivers through a multicast address.2) Host registration: Receiver hosts are allowed to join and leave multicast groupsdynamically. This mechanism is the basis for group membership management.3) Multicast routing: A multicast distribution tree (namely a forwarding path tree formulticast data on the network) is constructed for delivering multicast data from amulticast 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
