The End-to-End Communication Based On SIP In NAT Environment

The capability of integrated communication of Telecom Network has been improved very fastly in last few years. The network is facing more and more challenge than before because of more and more requirements of multimedia services, which is required by users. To meet such requirements, the Next Generation Network(NGN) based on SoftSwith comes into being. SIP is a important protocol in SoftSwith and has been paid lots of attention. As a growing protocol was submitted by IETF in 1999, the standard and application on SIP needs more improvement. There are many fields in SIP's research now. In this thesis, we focus on the SIP's application on end to end communication in NAT and firewall entironments.One major part of this thesis is about the essential issues in providing a successful solution of end to end communication based on SIP in NAT and firewall entironments. We list several solutions such as solution based on NAT device rebuild, SIP systm rebuild and solution based on SIP application gateway. We focus on the solution of SIP application gateway and the implement in the thesis.Another point in this paper is the implement frame of SIP applicatiom gateway and SALG under linux which based on the attribute of SIP.There has been some researches on SIP application gateway and the implement, but it is not enough to build a gateway. Most of the corresponding drafts always only provided some advice about the message fixing. In this thesis, we discussed the SIP and NAT, and provide a uniform implement frame of SIP applicatiom gateway. In this frame, we difined the criterion and flow of implement a basic SIP application gateway.We implement a SIP application gateway based on linux followed the frame which is named SALG. SALG support the travels pass through the NAT of multi media communication based on SIP, can relizd most of the SIP terminal and servers automatically, and it also support the basic end to end communication based on SIP. It is a effective and low cost solution to end to end SIP communication based on SIP.