Common Notations In Multicast; Advantages And Applications Of Multicast - 3Com 4500 Configuration 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
1
2
3
4
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.

Advantages and Applications of Multicast

Advantages of multicast
Advantages of multicast include:
Enhanced efficiency: Multicast decreases network traffic and reduces server load and CPU load.
Optimal performance: Multicast reduces redundant traffic.
Table 1-1.
TV transmission
A TV station transmits a TV
program through a television
channel.
A user tunes the TV set to the
channel.
The user starts to watch the TV
program transmitted by the TV
station via the channel.
The user turns off the TV set.
1-4
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.