3Com MSR 50 Series, Руководство по настройке

Страница: 1088 / 2443

1088 C
HAPTER
67: M
ULTICAST
O
VERVIEW
n
■
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.
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.
■
Distributive application: Enables point-to-multiple-point applications at the
price of the minimum network resources.
Applications of multicast
Applications of the multicast technique include:
■
Multimedia and streaming applications, such as Web TV, Web radio, and
real-time video/audio conferencing.
■
Communication for training and cooperative operations, such as distance
learning and telemedicine.
■
Data warehouse and financial applications (stock quotes).
■
Any other point-to-multiple-point data distribution application.
Multicast Models
Based on how the receivers treat the multicast sources, there are two multicast
models:
ASM model
In the ASM model, any sender can send information to a multicast group as a
multicast source and numbers of receivers can join a multicast group identified by
a group address and obtain multicast information addressed to that multicast
group. In this model, receivers are not aware of the position of multicast sources in
advance. However, they can join or leave the multicast group at any time.
Table 43 An analogy between TV transmission and multicast transmission
Step TV transmission Multicast transmission
1 A TV station transmits a TV
program through a 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 or
tunes to another channel. The receiver leaves the multicast group or
joins another group.