Research On High-Robustness NAT Traversal Technology Based On PPTP

The existing of NAT technology breaks the equality of network and limits the development of p2p communication. The forbidden of initiating connection from extranet causes that extranet can’t transferring data into intranet actively. To solve this problem, researchers have proposed various NAT traversal methods. Up to the present day, the common NAT traversal solutions contains tunnel mode, UPnP mode, "Hole Punching" mode. But because of the complexity of NAT types, none of them is accurate enough and can traverse all the NAT devices. So the research for high-robustness NAT traversal technique is of practical significance.This paper first studies the principle mechanism of TCP "Hole Punching" technology. Using the method of randomly selected client ports and determine whether the port is occupied and server set only one port to solve the problem of port occupation caused by port reuse.Then this paper analyzes the advantages and disadvantages of TCP "Hole Punching" technology. On this basis, we propose a high-robustness framework— HUP technology which combining UPnP protocol, PPTP VPN technology and TCP "Hole Punching" technology to traverse NAT network. This technology can remedy the shortcomings of respective NAT methods with following improvement: enhancing hole punching capacity, ensuring the robustness of the network, firming data transmission, relieving pressure on the server.After that, in this paper HUP technology will be applied to equipment’s communications. A solution for both real-time data transmission from GPRS/3 G/4G devices to server behind NAT and the converse real-time access controller from server to devices will be proposed.Finally, this paper presents the design and implementation in detail. We get the NAT traversal results in different network environment and give the analysis.