| The development of packet switch network technology and digital transmission technology has greatly boosted the communication technology to be digital and intelligent. The new communication technology integrates the advantages of data network and multimedia technology. This makes it possible to realize multi-services such as audio, video, etc. on a single network platform. The VoIP technology emerged in such a background and has developed fast to be a competitive technology in voice communication field. Apart from those advantages such as packet switching, effectively utilization of the bandwidth and cost-effective, VoIP takes uncomparable advantages of audio technology in PSTN. This is the key factor for it competitiveness and its prospective market. Although currently the quality of the voice of VoIP telephone is not good, it is paid high attention by the communication practitioner. Many international standard organization such as ITU-T, ETSI, IETF, IMTC, etc. are proposing new related standards.SIP (Session Initiation Protocol) is one of application-layer control signaling protocols proposed by IETF(Internet Engineering Task Force). It has became an important protocol in VoIP architecture. Based on SIP, the simple request/response model can make the establishment of VoIP session easy. The traditional voice and its added service can be integraed, and some new real time service over IP network can be provided. The architecture of SIP protocol based on distributed design supplies high flexiblity and scalablity to the mobile devices. This can offer a standard and highly scalable platform for more added services providers and advance the development of VoIP technology.This thesis focuses on the key technologies of VoIP multimedia application based on SIP protocol on mobile phone terminal. The thesis first introduces the technical background and architecture of the VoIP, then elaborates three key technologies. Next, it has described the important protocol SIP in VoIP architecture.The definition, functionalities, components, message and protocol architecture of SIP is introduced. According to the function of the VoIP terminal, SIP protocol stack is designed to implement voice over Internet protocol functionality. The necessary functional modules are designed, incnluding the user agent in SIP architecture, the transmission of real-time data and the processing of the audio data, among which the user agent module is paid more attention. Then, on the basis of modular software development concept, the software is developed, the related data structures such as classes and functions are defined and the functional modules are implemented.At last, the developed system is tested under local area network with SIP proxy server. The test result shows that the functions of SIP model in mobile phone terminal can be implemented. The effect of time delay, jittering and packet loss on voice quality is assessed according to the tested results. |
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