Italy, September streaming for networks with varying [15] E. Setton. Congestion-Aware Video 2004. delay. In Proceedings of the IEEE Streaming over Peer-to-Peer Networks. [17] E. Setton, J. Noh, and B. Girod. International Conference on Ph.D. dissertation, Stanford Congestion-distortion optimized Multimedia and Expo 2002, University, Electrical Engineering, peer-to-peer video streaming. In Proc. Lausanne, Switzerland, August 2006. IEEE International Conference on 2002. [16] E. Setton and B. Girod. Congestion- Image Processing, ICIP-2006, distortion optimized scheduling of Atlanta, GA, October 2006. Chapter 3.6 Real-time communication over networks Yi Liang, Yen-Chi Lee, and Andy Teng 3.6.1 Introduction transport. In Section 3.6.3, we will address QoS issues, especially minimizing latency, combating loss, adapting to Internet protocol (IP)-based real-time communication, available bandwidth, and audio-video synchronization. including voice-over IP (VoIP), video telephony, and teleconferencing, has been gaining popularity in recent 3.6.2 Architecture and years. One example is VoIP, which has been competing fundamentals with the traditional public switched telephone network (PSTN) for years and now enjoys increased market share. This is due to the many advantages of IP-based com- 3.6.2.1 Systems munication, including lower cost as well as the capability of providing integrated data, voice, and video, a larger Figure 3.6-1 shows the setup of a typical VoIP system. An variety of features, and more value-added services. IP phone or a sufficiently equipped PC connects to the Despite rapid expansion and improvement of the un- Internet to be able to make VoIP calls. For traditional derlying infrastructure, quality-of-service (QoS) is still phones in the PSTN network, a gateway is needed for the one of the major challenges of real-time communication interoperation between the PSTN and the Internet. After over IP networks. The unreliable and stateless nature of introducing signaling and transport protocols later in this today