H3C Technologies H3C S3100 Series Switches - Manual (Page 230)

Operation Manual – Multicast
H3C S3100-52P Ethernet Switch Chapter 1 Multicast Overview
1-3
Server
Multicast
User A
User B
User D
User E
Server
Multicast
Server
Multicast
User A
User B
User D
User E
Figure 1-3
Information transmission in the multicast mode
Assume that users B, D and E need the information. To transmit the information to the
right users, it is necessary to group users B, D and E into a receiver set. The routers on
the network duplicate and distribute the information based on the distribution of the
receivers in this set. Finally, the information is correctly delivered to users B, D, and E.
The advantages of multicast over unicast are as follows:
z
No matter how many receivers exist, there is only one copy of the same multicast
data flow on each link.
z
With the multicast mode used to transmit information, an increase of the number of
users does not add to the network burden remarkably.
The advantages of multicast over broadcast are as follows:
z
A multicast data flow can be sent only to the receiver that requires the data.
z
Multicast brings no waste of network resources and makes proper use of
bandwidth.
In the multicast mode, network components can be divided in to the following roles:
z
An information sender is referred to as a multicast source.
z
Multiple receivers receiving the same information form a multicast group. Multicast
group is not limited by physical area.
z
Each receiver receiving multicast information is a multicast group member.
z
A router providing multicast routing is a multicast router. The multicast router can
be a member of one or multiple multicast groups, and it can also manage
members of the multicast groups.
For a better understanding of the multicast concept, you can assimilate a multicast
group to a TV channel. A TV station is a multicast source. It sends data to the channel.
The audiences are the receivers. After turning on a TV set (a computer), they can select
a channel to receive a program (namely join a group) and then watch the program.
Therefore, a multicast group should be an agreement between the sender and the
receivers, like the frequency of a channel.