Common Notations In Multicast - 3Com 5500-EI PWR Install Manual

All receivers interested in the same information form a multicast group. Multicast groups are not
subject to geographic restrictions.
A router that supports Layer 3 multicast is called multicast router or Layer 3 multicast device. In
addition to providing multicast routing, a multicast router can also manage multicast group
members.
For a better understanding of the multicast concept, you can use the analogy of a transmission of TV
programs, as shown in
Table 1-1 An analogy between TV transmission and multicast transmission
Step
A TV station transmits a TV program
1
through a television channel.
2 A user tunes the TV set to the channel.
The user starts to watch the TV program
3 transmitted by the TV station via the
channel.
4 The user turns off the TV set.
A multicast source does not necessarily belong to a multicast group. Namely, a multicast source is
not necessarily a multicast data receiver.
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:
(*, 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.
For details about the concepts RPT and SPT, see
Table 1-1.
TV transmission Multicast transmission
A multicast source sends multicast data to a
multicast group.
A receiver joins the multicast group.
The receiver starts to receive the multicast
data that the source sends to the multicast
group.
The receiver leaves the multicast group.
"PIM Configuration".
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