1-3Figure 1-2 Information transmission in the broadcast modeSourceServerReceiverReceiverReceiverHost AHost BHost CHost DHost EPackets for all the networkAssume that Hosts B, D, and E need the information. The source server broadcasts this informationthrough routers, and Hosts A and C on the network also receive this information.As we can see from the information transmission process, the security and legal use of paid servicecannot be guaranteed. In addition, when only a small number of users on the same network need theinformation, the utilization ratio of the network resources is very low and the bandwidth resources aregreatly wasted.Therefore, broadcast is disadvantageous in transmitting data to specific users; moreover, broadcastoccupies large bandwidth.Information Transmission in the Multicast ModeAs 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 usersrequiring information is not certain, unicast and broadcast deliver a low efficiency.Multicast solves this problem. When some users on a network require specified information, themulticast information sender (namely, the multicast source) sends the information only once. Withmulticast 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:
