ltimedia Conferencing Architecture Advanced real-time services include several types of media (for example, videocon- ferencing includes video streams and audio streams) and are therefore referred to collectively as multimedia services. The IETF has developed a set of protocols specific to multimedia services. Applications will have to combine some of these protocols in order to attain the required functional- ity. Figure 3-5, taken from [draft-ietf-mmusic-confarch], shows how all these protocols fit together. SIP is part of the Internet multimedia conferencing architecture and is shown in real context in Figure 3-5. If you take the time to understand the role of each protocol in the architecture, you'll have a good functional explanation of why SIP was needed and what it is expected to deliver. Figure 3-5 Conference management Media Agents Internet multimedia conferencing Conference Setup Audio Shared Conference Course Control architecture. and Discovery Video Applications Distributed RTP and Reliable control multicast IP and IP multicast Integrated and Differentiated Services Forwarding Chapter 3 Multicast The Internet is designed for best-effort delivery of datagrams between hosts. A datagram contains a destination IP address and the routers in the network undertake the task of moving the datagram towards its destina- tion. An IP address typically identifies a network interface in a host (such as an Ethernet card). This mechanism enables two-party data exchange between any two hosts in the network, SO long as one host acts as sender and the other as receiver. It is also possible for the receiver to return data to the sender just by noting the sender's IP address. The kind of routing where one IP address identifies a single-host interface (Figure 3-6) is referred to as unicast. Routing Towards Many Receivers This simple scenario gets complicated when more than two parties wish to communicate. In order to send an IP packet to all of the hosts Figure 3-6 Unicast routing. 131.160.1.112 Destination IP address: 138.