3Com Switch 8800 Advanced Software V5 Configuration Guide

492 CHAPTER 37: MULTICAST OVERVIEW
Assume that Hosts B, D and E need this information. The information source
establishes a separate transmission channel for each of these hosts.
In unicast transmission, the traffic over the network is proportional to the number
of hosts that need the information. If a large number of users need the
information, the information source needs to send a copy of the same information
to each of these users. This means a tremendous pressure on the information
source and the network bandwidth.
As we can see from the information transmission process, unicast is not suitable
for batch transmission of information.
Broadcast
In broadcast, the information source sends information to all hosts on the
network, even if some hosts do not need the information, as shown in
Figure 156.
Figure 156 Broadcast transmission
Assume that only Hosts B, D, and E need the information. If the information
source broadcasts the information, Hosts A and C also receive it. In addition to
information security issues, this also causes traffic flooding on the same network.
Therefore, broadcast is disadvantageous in transmitting data to specific hosts;
moreover, broadcast transmission is a significant usage of network resources.
Multicast
As discussed above, the unicast and broadcast techniques are unable to provide
point-to-multipoint data transmissions with the minimum network consumption.
The multicast technique has solved this problem. When some hosts on the
network need the information, the multicast source (namely, the information
source) sends only one copy of the information. With tree-type routes established
Source
Server
Receiver
Receiver
Receiver
Host A
Host B
Host C
Host D
Host E
Packets for all the network