Development Of Videophone Software System Based On IP Set Top Box

STB(Set Top Box) ,which is designed to extend function of TV set, can provide multiple services since it has powerful capability of multimedia processing and enough IP network access bandwidth. Videophone is one of these kinds of software service.The research and development of videophone terminal software involves many technologies, such as signaling protocol in IP network, packet-based voice technology, video code/decode technology and media stream transportation, etc. Nowadays, the most videophone system is based on H.323. However, SIP will play an important role in the process of evolution of NGN. After comparisons between H.323 and SIP, SIP is adopted as our videophone's signaling protocol. Consequently a comprehensive study of SIP is given. Quality of service (QoS) is an important issue in IP multimedia communication system. In this thesis the QoS is dynamically estimated by RTP/RTCP, and an adaptive dynamic QoS adjustment policy is devised. According to the network payload status determined by media packet lose rate, the terminal dynamically adjusts its send code rate of media stream. The policy can decrease the likelihood of network congestion, reduce the delay of packet transportation, increase the bandwidth utilization, and so obtain an acceptable QoS.Based on the research of key technologies of videophone terminal system, the thesis discusses the software architecture of videophone software system. Then the implementations of two software modules are investaged. The two modules resolve the problem of resource management and control, which arises from the coexistence of IPTV/VOD and videophone services.