The Research On Travers Of NAT Based On Soft Switch Soft Switch SIP Protocol

With the development of computer science and the tele-communication, it has been agreed by most of the carriers that the voice, data, even video can be transported by public packet networks. Under the tendency of service-driven and network-integration, the next generation networks (NGN) was born which can carry voice, data, video with the distributed architecture in the packet network (IP network). As the core technology of NGN, the development of Softswitch has gathered more and more attention, the Softswitch devices are the kernel equipment of next generation packet network.The NGN is facing a series of problem as carried on IP layer, the traditional NAT device breaking-off the RTP media flow becomes the bottleneck of VOIP fast development, as the SIP protocol acts as the main application of multimedia transportation on the network largely deployed the NAT devices.From aspect of theory, the systemic research has been operated on the NGN topology, the application of soft switch in NGN, and relative tele-communication protocol. Here I give brief introduction of HUAWEI NGN solution: U-SYS, which was based on my intern working experience in huawei core-net department soft switch product line. Besides that, system theory, system structure and environment supervision of soft switch is accordingly discussed here.The research of traversing of NAT based on SIP protocol is the emphases of the paper. SIP protocol application on NGN topology is analyzed, besides I give particular study on the SIP message structure, SDP message, and SIP call/register process based on the RFC3261 standard. The NAT devices are largely deployed today for the short of IPV4 addresses, which given impact on the traversing of RTP media flow of SIP protocol. From the aspect of IP and port mapping, the NAT types are expatiated, then usual solutions have given on the settle the problem of SIP media flow traversing of NAT.STUN is the main research field of this paper, because it has very littleinfluence on the media message and the nowadays networks with its simple realization. Based on the STUN standard, I give thorough research on STUN, and design the realization of it. A stun simulated detecting system has build in WIN32 system. Last, some test of the system has been given, together with the analyzing of the test.