H3C Technologies H3C S3600 Series Switches - Manual (Page 379)

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Table 1-1 An analogy between TV transmission and multicast transmission
Step TV transmission Multicast transmission
1
A TV station transmits a TV program
through a television channel. A multicast source sends multicast data to a
multicast group.
2 A user tunes the TV set to the channel. A receiver joins the multicast group.
3
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 sends to the multicast
group.
4 The user turns off the TV set. The receiver leaves the multicast group.
z A multicast source does not necessarily belong to a multicast group. Namely, a multicast source is
not necessarily a multicast data receiver.
z A multicast source can send data to multiple multicast groups at the same time, and multiple
multicast sources can send data to the same multicast group at the same time.
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.
For details about the concepts RPT and SPT, see “ PIM Configuration ”.
Advantages and Applications of Multicast
Advantages of multicast
Advantages of multicast include:
z Enhanced efficiency: Multicast decreases network traffic and reduces server load and CPU load.
z Optimal performance: Multicast reduces redundant traffic.
z Distributive application: Multicast makes multiple-point application possible.