Research And Implementation Of A File Transfer Method Based On Media Streaming SIP IM System With NAT

In recent years, instant message application has become one of the most popular applications on the Internet. But unified communication protocol isn't used by most current IM platform. And system scalability isn't considered either. This situation can result in the problem that different platform can't communicate with others. And the protocol has to be redesigned when a new function need to be added. In this situation, the problem can be solved effectively by bringing SIP to current IM platform. But a new problem appears after that. In IM applications, file transfer is a vital function. But file transfer relay function can't be supported by most SIP server. File transfer function has to be implemented by TCP connection in most SIP IM. But, the TCP connection can't be established when one of the clients is in a private network. And the applications of SIP IM system are limited by this problem.It was found that RTP data packet relay is supported by most SIP server after a significant insight into the features of current SIP IM system. Besides, media streaming relay based on RTP can be supported by most SIP server. Thereby, combined with RTP and SIP technology, a new file transfer mechanism can be proposed in order to solve the NAT problem of file transfer function. This paper introduces the SIP and RTP technical features, describes and analyzes the types of NAT and current solutions. Combined with the SIP IM based on Winpidgin project in next generation wireless mobile internet application, file transfer technology based on media streaming is designed and implemented, which is used to solve NAT problem. And the performance of this technology is analyzed, a formula used to improve performance is proposed. This technology is used to solve the NAT file transfer issue without extra module on server and improve the adaptability of the network of SIP IM system. Furthermore, this technology maximizes the utilization of the server. Validity of this technology in solving NAT file transfer issue is proved from the perspective of the practical application, and a very significant formula for improving performance is provided from the view of theoretical research in this paper.