4
Table 1 Comparing TV program 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 through 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)
—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)
—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.
For more information about the concepts RPT and SPT, see "
Multicast advantages and applications
Multicast advantages
Advantages of the multicast technique include the following:
•
Enhanced
efficiency
—Reduces the processor 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.
Multicast applications
The scenarios in which the multicast technique can be effectively applied are:
•
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 (stock quotes)
•
Any other point-to-multipoint application for data distribution
Multicast models
Based on how the receivers treat the multicast sources, the multicast models include any-source
multicast (ASM), source-filtered multicast (SFM), and source-specific multicast (SSM).
