H3C Technologies H3C S10500 Series Switches - Manual (Page 19)

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manage multicast group memberships on stub subnets with attached group members. A multicast
router itself can be a multicast group member.
For a better understanding of the multicast concept, you can compare multicast transmission to the
transmission of TV programs.
Table 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
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.
NOTE:
For more information about the concepts RPT and SPT, see the chapters “PIM configuration” and “IPv6 PIM
configuration.”
Advantages and applications of multicast
Advantages of multicast
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
Applications of multicast
The scenarios in which the multicast technique can be effectively applied are:
• Multimedia and streaming applications, such as web TV, web radio, and realtime video/audio
conferencing