Analysis And Design Of NAT Traversal Based On P2P Network Application

The rapid development of the Internet, more and more users connected to the network, making the original IPv4 addresses increasingly scarce resources. In order to solve this problem, people made a variety of solutions, including the fundamental long-term effective solution which is to expand IP address resources, the conversion of IPv4 to IPv6 address resources, and effective short-term solution is to use Network Address Translation Technology (NAT), which addresses a very good ease the shortage. The current actual network has been deployed with a large number of NAT devices. NAT technology resolves on the one hand the emergence of the address shortage problem, but also hides internal network topology, to a certain extent, security. However, it has also brought a certain amount of negative issues and drawbacks. NAT technology breaks the IP connectivity model by preventing hosts outside the local network from initiating a connection with a host inside the local network.In recent years, the application based on P2P network technology has developed rapidly.The P2P download softwares represented by BT and Emule, the Internet chat softwares represented by QQ and GTalk and the audio and video streaming software represented by PPLive and Skypy have brought the Internet users tremendous convenience and efficiency, and they make full use of the network bandwidth, greatly increasing the bandwidth utilization. The P2P technology requires the equal peer-to-peer connectivity and communications. However NAT technology had seriously hindered the developments of P2P, because NAT technology has changed the address and port fields of network packets, making the peer-to-peer connection can not be successfully established, many P2P applications can not run in the private network environment connecting to Internet via NAT gateway devices.To solve this problem, the industry and scientific research institutions put forward the corresponding solutions, these solutions can be broadly divided into client intervention solution and NAT equipment functions update solution. The former solution has the representation of a STUN and TURN method, the latter has the representation of solutions including UPnP solution and ALG solution. These solutions have their own strengths and weaknesses.It is essential to take proper NAT Traversal Solutions according to different network situations and requirements which are network business, network quality and investment cost.This paper first discusses the principles and process of NAT technology, a STUNT their classification based on the behavior of NAT, and more in-depth analysis and research of each type of NAT devices.Then, the paper mainly discusses the current several more popular NAT traversal technologies and the differences between these NAT traversal solutions, and further choose the STUN solution to do some Research and Improvement. As one of client intervention type in the NAT traversal solutions, the STUN method has the merits of small burden of system, implementation easily, multi-level NAT management, and other advantages. However, the STUN method can not traverse the symmetric NAT equipments. In present, most enterprises which requirement higher security, usually use the symmertic NAT equipments.To solve this problem, we have proposed a new solution named as P-STUNT based on the STUNT method, which means port STUNT. This new method uses port prediction and port scan techniques.The client can predict the next port through obtaining enough information of NAT and then establish connection between the clients which locate in different local network.After that, the NAT traversal is accomplished. In this improved solution, the success rate is affected by many factors, which are analyzed. We have come up with the corresponding solutions to ensure the high success rate, such as minimizing the time length between t0 and t1, implementing a retry process as well as multiple port prediction. Finally, this paper put forward the detailed design of modules and system based on the novel STUNT solution, which further clarify the feasibility of this solution. Because this system is designed based modules, it makes it easy to expand. For each specific functional module gives a detailed design plan and recommendations. The paper also presented the results of testing and analysis.