85.27.10 ROUTER ROUTER ROUTER ROUTER ROUTER ROUTER ROUTER 138.85.27.10 The Internet Multimedia Conferencing Architecture involved in a n-party conference, a host would have to transmit n-1 IP pack- ets, each containing the IP address of one of the hosts designated to receive the data. Obviously, systems with these mathematics don't scale well for a large number of users. As soon as the number of hosts involved increases at all, traffic in the network increases dramatically, straining the processing power of the hosts. Every host needs to register the IP addresses of all receivers and build n-1 IP packets with exactly the same information- the only difference being the destination address. Many of these packets tra- verse a common set of nodes until they finally are routed to their destina- tions, requiring links in the network to transport the same information multiple times (Figure 3-7). In Figure 3-7, packets from 131.160.112 to 138.85.27.10 and packets from 131.160.1.112 to 153.88.251.19 follow the same path to arrive at the router R. Therefore, all the links from 131.160.112 to R are loaded twice as much as they ought to be. Figure 3-7 Sending the same data to different hosts using unicast. 131.160.1.112 Destination IP address: 153.88.251.19 138.85.27.10 Destination IP address: 153.88.251.19 ROUTER ROUTER ROUTER ROUTER ROUTER ROUTER ROUTER 138.85.27.10 Chapter 3 Multicast routing resolves these issues by providing many-to-many com- munication scaling to groups with a large number of participants. These routers collaborate to forward IP packets destined for a multicast address towards their several destinations. A multicast address represents a group of hosts willing to receive the IP packets that will be transmitted, and by the same token, hosts receiving data from a multicast address are members of a particular multicast group. Any host in the network can send data to a multicast address, but it must belong to the multicast group in order to receive data. (In IP version 4 [RFC 791], addresses between 224.0.0