rs description control decoders control description control File format payload parser File system UMTS link layer UMTS link layer (a) Media streaming client (b) Media download client Figure 8.29 A streaming and a background application Service Implementation real transfer protocol (RTP), real-time control protocol (RTCP) and real-time streaming protocol (RTSP). Figure 7.14 gives also the relationships between adaptation protocols in IP and the underlying IP stack. Conversational Class Example of service implementation: Voice (VoIP, VoATM) - Voice has always been the cornerstone in telecommunications The class is real time, conversational, which is the most demanding class. The traditional network solution has been circuit-switched networks, initially fixed and then mobile. Today voice over IP and voice over ATM are installed in parallel with circuit-switched networks. For voice over packet short packets are used. See Figures 3.32 and 8.30. VoIP introduction - Strictly speaking, voice over IP or IP telephony is 'just another application' using a standard data network, which uses the TCP/IP suite of protocols (Figure 8.31). It is one of many other applications that use the basic application protocols TCP, UDP and IP. However, it is an application that is very demanding in relation to the original design goals of the TCP/IP technology. Both the telecom side and the datacom side have contributed with standards. Telecom- originated standards are H.323 and associated protocols. Datacom-originated standards are SIP and associated protocols. The voice over IP application will therefore suffer from the inherent shortcomings of packet networks, notably lack of QoS guarantees, and has to compensate these shortcom- ings within the service/adaptation layer. The basic IP telephony network (H.323) - VoIP has SO far been most successful in the enterprise sector, as a tool for a common or partly common network for LAN data and voice traffic. IP-PBX and IP-Centrex solutions are becoming increasingly common. See also Figure 8.13. 