Operation Manual – MulticastH3C S3100-52P Ethernet Switch Chapter 1 Multicast Overview1-3SourceServerReceiverReceiverReceiverHost AHost BHost CHost DHost EPackets for all the networkFigure 1-2 Information transmission in the broadcast modeAssume that Hosts B, D, and E need the information. The source server broadcasts thisinformation through routers, and Hosts A and C on the network also receive thisinformation.As we can see from the information transmission process, the security and legal use ofpaid service cannot be guaranteed. In addition, when only a small number of users onthe same network need the information, the utilization ratio of the network resources isvery low and the bandwidth resources are greatly wasted.Therefore, broadcast is disadvantageous in transmitting data to specific users;moreover, broadcast occupies large bandwidth.1.1.3 Information Transmission in the Multicast ModeAs described in the previous sections, unicast is suitable for networks with sparselydistributed users, whereas broadcast is suitable for networks with densely distributedusers. When the number of users requiring information is not certain, unicast andbroadcast deliver a low efficiency.Multicast solves this problem. When some users on a network require specifiedinformation, the multicast information sender (namely, the multicast source) sends theinformation only once. With multicast distribution trees established for multicast datapackets through multicast routing protocols, the packets are duplicated and distributedat the nearest nodes, as shown in Figure 1-3:
