3Com 4510G Configuration Manual page 384

Figure 1-2 Broadcast transmission
Assume that only Host B, Host D, and Host E need the information. If the information is broadcast to
the subnet, Host A and Host C also receive it. In addition to information security issues, this also
causes traffic flooding on the same subnet.
Therefore, broadcast is disadvantageous in transmitting data to specific hosts; moreover, broadcast
transmission is a significant waste of network resources.
Multicast
As discussed above, unicast and broadcast techniques are unable to provide point-to-multipoint data
transmissions with the minimum network consumption.
Multicast can well solve this problem. When some hosts on the network need multicast information, the
information sender, or multicast source, sends only one copy of the information. Multicast distribution
trees are built through multicast routing protocols, and the packets are replicated only on nodes where
the trees branch. Figure 1-3 shows the delivery of a data stream to receiver hosts through multicast.
2-3