H3C Technologies H3C SecPath F1000-E - Manual (Page 5)

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• Routers or Layer 3 switches that support Layer 3 multicast are called multicast routers or Layer 3
multicast devices. In addition to providing the multicast routing function, a multicast router can also
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 assimilate multicast transmission to the
transmission of TV programs, as shown in Table 1 .
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
Two notations are commonly used in multicast:
• (*, 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.
• (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.
NOTE:
For more information about the concepts RPT and SPT, see PIM Configuration or IPv6 PIM Configuration
in the IP Multicast Volume.
Advantages and Applications of Multicast
Advantages of multicast
Advantages of the multicast technique include:
• 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
Applications of the multicast technique include: