| VoIP (voice over IP) is a kind of communication technology which transmits the voicedata through IP networks. It converts voice signals into IP packets by quantizing, coding andcompressing for transmission over an IP network. With the rapid development of technology,VoIP phone and softswitch have become the mainstream technology of telecommunicationnetworks, which are related to the computer network, signaling protocols, DSP and manyother fields. It reflects the trend of network convergence, and ultimately brings diverse,inexpensive, simple and efficient real-time communication services for consumers.SIP (Session Initiation Protocol) is an application layer control protocol of VoIP and it issimple and highly scalable. It has been a great concern in the field of communication in recentyears. In the NGN (next generation network), SIP is mainly used between softswitchequipment and applications servers, different softswitch equipments, intelligent terminals andSIP servers, and different SIP servers. With the features of concise, open, compatible andscalable, SIP has become the key technology in the NGN of multimedia communication andsoftswitch. Currently SIP protocol has become the standard for3G mobile multimedianetworks.This paper analyzes the VoIP technology and a variety of key principles, and describesthe VoIP network protocols especially the principle and implementation of SIP signalingprotocol. And the writer proposed a design scheme of VoIP video phone. Under Windows+VS2008environment and based on an open-source SIP protocol stack PJSIP, added supportfor video capabilities, used interface development tool QT to complete a graphical userinterface. Eventually the writer developed a SIP-based VoIP video phone, and chievedregistration, voice and video calls and other basic functions. And also, the writer used thesoftware for functional testing, and analyzed protocol process and data. At last designed VoIPcomprehensive experimental platform to provide services for experimental teaching. |
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