1-5For a better understanding of the multicast concept, you can assimilate multicast transmission to thetransmission of TV programs, as shown in Table 1-1.Table 1-1 An analogy between TV transmission and multicast transmissionTV transmission Multicast transmissionA TV station transmits a TV program througha channel.A multicast source sends multicast data to amulticast group.A user tunes the TV set to the channel. A receiver joins the multicast group.The user starts to watch the TV programtransmitted by the TV station via the channel.The receiver starts to receive the multicast data thatthe source is sending to the multicast group.The user turns off the TV set or tunes toanother channel.The receiver leaves the multicast group or joinsanother group.Common Notations in MulticastTwo notations are commonly used in multicast:z (*, G): Indicates a rendezvous point tree (RPT), or a multicast packet that any multicast sourcesends to multicast group G. Here “*” represents any multicast source, while “G” represents aspecific multicast group.z (S, G): Indicates a shortest path tree (SPT), or a multicast packet that multicast source S sends tomulticast group G. Here “S” represents a specific multicast source, while “G” represents a specificmulticast group.Advantages and Applications of MulticastAdvantages of multicastAdvantages of the multicast technique include:z Enhanced efficiency: reduces the CPU load of information source servers and network devices.z Optimal performance: reduces redundant traffic.z Distributive application: enables point-to-multipoint applications at the price of minimum networkresources.Applications of multicastApplications of the multicast technique include:z Multimedia and streaming applications, such as Web TV, Web radio, and real-time video/audioconferencing.z Communication for training and cooperative operations, such as distance learning andtelemedicine.z Data warehouse and financial applications (stock quotes).z Any other point-to-multipoint data distribution application.Multicast ModelsBased on how the receivers treat the multicast sources, there are three multicast models: any-sourcemulticast (ASM), source-filtered multicast (SFM), and source-specific multicast (SSM).
