A Study Of NAT Traversal Technology Based On The STUN Protocol

With the rapid development of the network technology and the popularization of computers, currently the Internet users are rapidly increasing. The web is running out of the “IPv4” addresses, and cannot meet humans’ need. So the researchers proposed the IPv6 protocol which can solve the shortage of IP addresses completely. But it’s not easy for the change from IPv4 to IPv6, because some network devices can not support the IPv6 protocol well. So the Network Address Translation technology has been proposed to relieve the shortage of IP addresses.The NAT devices can relieve the shortage of IPv4 address, but the NAT devices hide the internal network, and limit the P2 P communications. Now the NAT devices have been widely used in the network environments. The NAT device makes the hosts cannot communicate effectively, and hampers the development of the P2 P application seriously. It has become one of the key problems of the P2 P development.Firstly, this paper describes the current situation of the NAT traversal technology, such as the ALG technology and the Middle-box technology.Then describes the NAT device’s type, principle and some technologies of the NAT traversal. And I analyzed various methods of the NAT traversal, and compared the STUN protocol, TURN protocol and ICE frame. Then found that the NAT traversal based on the STUN protocol is reasonable.Secondly, this paper analyzes some NAT devices deeply and proposes a method to detect a NAT device’s type. Then introduces some different scenes according to NAT device’s type, and uses different method of NAT traversal to solve the problem. And I focused on the symmetric NAT which is the difficulty of the NAT traversal, and proposed a method to solve the symmetric NAT traversal. For instance, the port prediction technology can be used to solve the symmetric NAT traversal which the port can be predicted. And the port guess technology is used to solve the symmetric NAT traversal which the port can’t be predicted. I also proposed a method to avoid the delay caused by the hairpin method, to improve the communication efficiency.Then, according to the solution, I gave the framework and design of the system. The system uses a combination of client and server model, and the communication between clients is the major, and the server assists the work. The system also has an interaction module, a type detection module, a port prediction module and a NAT traversal module. After the type detection, clients need to select different NAT traversal solutions to establish communication between clients.Finally, I tested the system’s functional and performance under the existing experimental conditions, then gave the results of the analysis, and achieved the desired effects.