Design And Implemention Of NAT Traversal Based On SIP Trunk Gateway

Recently,with the massive deployment of the IP-PBX which support the SIP, and the increasing number of ITSP who provide voice communication infrastructure for SIP, enterprises in desperately need a kind of SIP relay technology which can provide the similar service of the traditional PSTN relay line. The internal network of the enterprise is IP networks, all the external communication are through ITSP. This technology is called SIP TRUNK.Firstly, this article gives the basic concept of SIP and SDP, introduces their application background and analyses their basic principles which provide sufficient theoretical basis and practical foundation for the realization of SIP Trunk gateway. Secondly, this article gives an introduction of the relevant knowledge of NAT/FW and analyses the current problem of NAT/FW. Through extensive reading of literature, this article analyses the advantages and disadvantages of the current solutions, and proposes the general design thought of SIP Trunk gateway.This paper pays attention to the following two points: first, no need to make any alteration of the existing communication equipments; Second,It will not bring any software or hardware auxiliary equipment cost when upgrading the system. Based on these two points, this paper expounds how SIP Trunk gateway traverses the NAT/FW successfully. The advantages of SIP Trunk are as follows: the communication between the internal and external network of the enterprises are entirely realized by SIP Trunk gateway. It does not need any software and hardware auxiliary equipment.Finally, the paper puts forward the test plan of the whole system and analyses the test result which completely meet the design requirements and can exchange with other companies'equipments . It has very good application prospect.