H3C Technologies H3C S3600 Series Switches - Manual (Page 377)

1-3
Figure 1-2 Information transmission in the broadcast mode
Assume that Hosts B, D, and E need the information. The source server broadcasts this information
through the routers, reaching the targets, but also Hosts A and C on the network receive this
information.
This is an efficient way to send the same content to densely distributed users. However, as we can see
from the information transmission process, security and restricted use of paid services cannot be
guaranteed. In addition, when only a small number of users on the same network need the information,
the utilization ratio of the network resources is very low and the bandwidth resources are greatly
wasted.
Therefore, broadcast is disadvantageous in transmitting data to specific users, and is more bandwidth
intensive.
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 not efficient.
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 Figure 1-3 :