2-5
For a better understanding of the multicast concept, you can assimilate multicast transmission to the
transmission of TV programs, as shown in
Table 1-1
.
Table 1-1
An analogy between 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
Two notations are commonly used in multicast:
z
(*, G): Indicates a rendezvous point tree (RPT), or a multicast packet that any multicast source
sends to multicast group G. Here “*” represents any multicast source, while “G” represents a
specific multicast group.
z
(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, while “G” represents a specific
multicast group.
Advantages and Applications of Multicast
Advantages of multicast
Advantages 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 network
resources.
Applications of multicast
Applications of the multicast technique include:
z
Multimedia and streaming applications, such as Web TV, Web radio, and real-time video/audio
conferencing.
z
Communication for training and cooperative operations, such as distance learning and
telemedicine.
z
Data warehouse and financial applications (stock quotes).
z
Any other point-to-multipoint data distribution application.
Multicast Models
Based on how the receivers treat the multicast sources, there are three multicast models: any-source
multicast (ASM), source-filtered multicast (SFM), and source-specific multicast (SSM).
