| NGN(Next Generation Network)is a packet-based network able to provide telecommunication services and meet people's demand for various new services. Providing the real-time voice communication and multimedia services on NGN are the hotspot of the current research.At the same time, it is noticed that global IP-address resources are more and more deficient. The way adopted to solve the problem of IP-address deficiency include CIDR, NAT technology and IPv6 and NAT technology is mostly widely used. When a node in the LAN is communicating with the Internet, in the process of IP package from source address reaching destination address, NAT modify the source, destination address and port, translate the internal IP address into legal public IP address. Multimedia communication based 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 TCP/UDP 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. As the NGN is used more and more in business, it is meaningful to study the traversal of NAT in the SIP protocol, which is one of the most useful protocols.Firstly, the paper introduced the SIP protocol systemically, and analyzed the mechanism of NAT, presented the in-depth study of the SIP traversal of NAT, and three categories of solutions for SIP traversal of NAT are investigated: the solutions at the user agent, the solutions at the routers, the solutions at the servers.Based on the investigation, it is decided to use STUN to resolve the problem of SIP traversal. With the purpose of cross-plantform, it is implemented that discoverying the presence of NAT and its type for the device in the LAN, as well as the lifetime of binding allocated by NAT by java language. |
