Information Transmission In The Multicast Mode - H3C S3100 8C SI Operation Manual

Operation Manual – Multicast
H3C S3100 Series Ethernet Switches

1.1.3 Information Transmission in the Multicast Mode

As described in the previous sections, unicast is suitable for networks with sparsely
distributed users, whereas broadcast is suitable for networks with densely distributed
users. When the number of users requiring information is not certain, unicast and
broadcast deliver a 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 multicast distribution trees established for multicast data
packets through multicast routing protocols, the packets are duplicated and distributed
at the nearest nodes, as shown in
Source
Server
Figure 1-3 Information transmission in the multicast mode
Assume that Hosts B, D and E need the information. To transmit the information to the
right users, it is necessary to group Hosts 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 Hosts 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 of the number of
users does not add to the network burden remarkably.
The advantages of multicast over broadcast are as follows:
A multicast data flow can be sent only to the receiver that requires the data.
Figure
Packets for the multicast group
1-3:
Host A
Receiver
Receiver
Receiver
Host E
1-3
Chapter 1 Multicast Overview
Host B
Host C
Host D