H3C S7500 Series Operation Manual page 427

Operation Manual – Multicast
H3C S7500 Series Ethernet Switches
users. When the number of users requiring information is not certain, unicast and
broadcast are both of low efficiency.
Multicast solves this problem. When some users on a network require specified
information, the multicast information sender (namely, the multicast source) sends the
information only once. With tree-type routes established for multicast data packets
through a multicast routing protocol, the packets are duplicated and distributed at the
nearest nodes to the destination as shown in
Source
Server
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:
No matter how many receivers exist, there is only one copy of the same multicast
data flow on each link.
With the multicast mode used to transmit information, an increase in the number of
users does not add to the network load significantly.
The advantages of multicast over broadcast are as follows:
A multicast data flow can be sent only to the receiver that requires the data.
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:
An information sender is referred to as a multicast source.
Packets for the multicast group
Figure 1-3:
Host A
Receiver
Receiver
R eceiver
Host E
1-3
Chapter 1 Multicast Overview
Host B
Host C
Host D