The Research And Implementation Of SIP Protocol Traversal NAT

Along with the rapid development of Internet, the requirements of subscribers for new services are increasing. The integration of the traditional telecom and the IP network becomes the trend of the network development. The next generation network (NGN) that is based on the Softswitch technology can implement the integration smoothly and becomes the hotspot of the current research. The Softswitch technology can help utilize the existing investment in the telecom networks to the most and provide more and better services so as to promote the smooth evolution of the telecom networks to the next generation networks.Due to the large-scale application, the requirements for IP addresses increase. The way adopted to solve the problem of IP-address deficiency include CIDR, NAT technology and IPV6 and NAT technology is mostly widely used. NAT technology is a process that when a internal pot communicate with a internet, in the process of ip package from source addresses reaching destination addresses NAT change the source ,destination addresses and port to turn internal ip address into legal public ip addresses.The NGN, which complies with the H.323 and SIP protocols, supports routing through IP addresses and ports specified by signaling messages in the application layer. Not only the port information based on the TCPAJDP protocol and the source addresses and destination addresses based on the IP protocol, but also the related address information carried by the IP payloads must be converted. Above all, the NAT technology is the most essential factor in the application of NGN. Because the SIP protocol is among the most significant ones used by the Softswitch, to which more and more attention is paid, the focus of this thesis is placed on the implementation of SIP protocol traversal NAT.The thesis consider from the problem of SIP protocol traversal NAT and the features of the NAT and SIP and analyzes the most common solutions of NAT. On this basis, a SIP ALG solution is put forward. Currently, the research on the SIP application layer gateway (ALG) and the implementation of it is far from being complete. The related drafts have only made some recommendation on themodification part of SIP messages or other parts. Based on related materials, this thesis puts forward a uniform framework for implementing the SIP-based ALG. Both the researches and applications show that the SIP ALG solution can solve the problems of SIP NAT. This thesis can provide a reference for large-scale application ofNGN.