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Table 1 Comparing TV transmission and multicast transmission
TV transmission
Multicast transmission
A TV station transmits a TV program through a
channel.
A multicast source sends multicast data to a multicast
group.
A user tunes the TV set to the channel.
A receiver joins the multicast group.
The user starts to watch the TV program
transmitted by the TV station via the channel.
The receiver starts to receive the multicast data that the
source is sending to the multicast group.
The user turns off the TV set or tunes to another
channel.
The receiver leaves the multicast group or joins another
group.
Common notations in multicast
The following notations are commonly used in multicast transmission:
•
(*, G)—Indicates a rendezvous point tree (RPT), or a multicast packet that any multicast source
sends to multicast group G. Here the asterisk represents any multicast source, and "G"
represents a specific multicast group.
•
(S, G)—Indicates a shortest path tree (SPT), or a multicast packet that multicast source S
sends to multicast group G. Here, "S" represents a specific multicast source, and "G"
represents a specific multicast group.
Advantages and applications of multicast
Advantages of multicast
The multicast technique has the following advantages:
•
Enhanced efficiency—Reduces the CPU load of information source servers and network
devices.
•
Optimal performance—Reduces redundant traffic.
•
Distributed application—Enables point-to-multipoint applications at the price of minimum
network resources.
Applications of multicast
The multicast technique has the following applications:
•
Multimedia and streaming applications, such as web TV, web radio, and real-time video/audio
conferencing
•
Communication for training and cooperative operations, such as distance learning and
telemedicine
•
Data warehouse and financial applications, such as stock quotes
•
Any other point-to-multipoint applications for data distribution
Multicast models
Multicast models—any-source multicast (ASM), source-filtered multicast (SFM), and source-specific
multicast (SSM)—determines how the receivers treat the multicast sources.