15 MULTICAST OVERVIEWMulticast Overview With development of networks on the Internet, more and more interactionservices such as data, voice, and video services are running on the networks. Inaddition, highly bandwidth- and time-critical services, such as e-commerce, Webconference, online auction, video on demand (VoD), and tele-education havecome into being. These services have higher requirements for information security,legal use of paid services, and network bandwidth.In the network, packets are sent in three modes: unicast, broadcast and multicast.The following sections describe and compare data interaction processes in unicast,broadcast, and multicast.InformationTransmission in theUnicast ModeIn unicast, the system establishes a separate data transmission channel for eachuser requiring this information, and sends a separate copy of the information tothe user, as shown in Figure 55:Figure 55 Information transmission in the unicast modeAssume that Hosts B, D and E need this information. The source server establishestransmission channels for the devices of these users respectively. As thetransmitted traffic over the network is in direct proportion to the number of usersthat receive this information, when a large number of users need this information,SourceServerReceiverReceiverReceiverHost AHost BHost CHost DHost EPackets for Host BPackets for Host DPackets for Host E
