1-11 Multicast OverviewMulticast OverviewWith development of networks on the Internet, more and more interaction services such as data, voice,and video services are running on the networks. In addition, highly bandwidth- and time-critical services,such as e-commerce, Web conference, online auction, video on demand (VoD), and tele-educationhave come into being. These services have higher requirements for information security, legal use ofpaid services, and network bandwidth.In the network, packets are sent in three modes: unicast, broadcast and multicast. The followingsections describe and compare data interaction processes in unicast, broadcast, and multicast.Information Transmission in the Unicast ModeIn unicast, the system establishes a separate data transmission channel for each user requiring thisinformation, and sends a separate copy of the information to the user, as shown in Figure 1-1:Figure 1-1 Information transmission in the unicast modeSourceServerReceiverReceiverReceiverHost AHost BHost CHost DHost EPackets for Host BPackets for Host DPackets for Host EAssume that Hosts B, D and E need this information. The source server establishes transmissionchannels for the devices of these users respectively. As the transmitted traffic over the network is indirect proportion to the number of users that receive this information, when a large number of usersneed this information, the server must send many pieces of information with the same content to theusers. Therefore, the limited bandwidth becomes the bottleneck in information transmission. Thisshows that unicast is not good for the transmission of a great deal of information.
