| SIP has gained a lot of attention over the last few years. The decision to use SIP as the signaling protocol to provide IP multimedia services in the third generation of mobile systems has dramatically increased the number of people interested in knowing about SIP. SIP is the protocol that will merge together the cellular and the Internet worlds. With the development of network technology, SIP protocol will play the most important and the most crucial roles in the near future. This paper study on media communication using SIP has enormous practicability.In the paper, I first explained technological background and significance of this paper and then make a detail introductory about functions and characteristics of SIP protocol. Summarily this paper completes the work as follows:(1) Have a detailed introduction about the function structure, realization principle, message mechanism and signaling flow of SIP protocol, and the advantage of SIP-based mobility management. And then I proposed an improved frame of SIP mobility before calling about time delay and jitter which caused by high frequency of register.(2) I used some open sources, such as OSIP,eXosip,JRTPLIB,SDL and V4Linux to implement a system. Based on SIP protocol, this system can establish a media communication session. In order to increase the speed of video capture I used a method named memory mapping.In the module of media transmission, I implement arithmetic to partition vedio frame, so that these data's sum is smaller than the number that one RTP can bring.(3) I use Asterisk SIP server as registrar and proxy to simulate register and calling signaling setup after terminal mobility.I implement this paper on the platform of Linux, use C/C++.Captured video data can be transmitted fluently between point to point terminals because of transmitting in local area network.As Asterisk server supports SIP registration and proxy function, and it has excellent management in user authority, the simulation of UA registration is consistent with signaling flowing regulated by SIP protocol. |
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