Research And Application Of Key Technologies Of P2P Communication With TCP-Based Nat Traversal

Given the gradual depletion of IPv4addresses and the very slow transition to IPv6, Network Address Translation (NAT) technology has been widely used to solve the problem of insufficient network addresses. NAT translates private IP addresses into public IP addresses to provide a transparent routing solution to end hosts requiring communication to disparate address realms. Adapted by NAT, host with private IP addresses may access the Internet when needed, masquerading as having a public IP address to send and receive data. However, it is precisely the existence of NAT that has hindered many P2P-based applications to establish TCP connections. This is because that the NAT devices shield unauthorized packets from external network. An unauthorized packet is a packet that is coming to the local network without a host inside visiting it previously. Thus leading to the problem that hosts behind different NAT devices cannot communicate with each other, because both sides are unable to initiate a connection-all S YN request packet will be blocked by NATs.For this reason, how to traverse NAT devices to achieve broader P2P interconnecting has become an important research subject. For the non-standardized and diverse NAT devices, many kinds of NAT traversal protocols have been proposed, and different technical solutions have different application scope, complexity and success rate. In this paper, we introduce and compare the various NAT traversal protocols briefly, and then propose a new NAT traversal protocol-P2PNAT#2. In our protocol we take full use of simultaneous TCP open technology and solve the problem of exceedingly tight timings that hinders simultaneous TCP open from being widely used.