The Study And Implementation Of NAT Traversal Technology

Network Address Translation (NAT) technology is popularly applied to solve the depletion ofIPv4-address,but in the meantime,it is also an obstacle for the use of many P2P applications. Thecomplexity of NAT devices and the emergence of the latest STUN protocol make a lot of early NATtraversal techniques no longer apply. There is no single NAT traversal technique suitable for allNAT environments since the type of NAT devices is not standardized. Therefore, the effective NATtraversal is an issue of important practical significance.Firstly the dissertation elaborates on the current situation of NAT traversal, and gives anoverview of the relevant key technologies of NAT traversal for TCP. Then with the help of the latestSTUN protocol and TCP hole punching, a new TCP NAT traversal solution applied to differentscenes of new NAT type classification is proposed. The problem of TCP NAT traversal through theEndpoint-dependent Mapping NAT is solved based on port prediction, replacing the existingTURN technology with low efficiency. A method called port guessing is proposed to tackle theproblem of unpredictable NAT type. In addition, a private address sensing method is proposed tomake two peers behind the same NAT directly communicate with each other, getting rid of thehairpin operation associated with the NAT and being applicable to NAT devices without hairpinfunction.Furthermore the dissertation makes study on the issue of NAT traversal of SIP, includingsignaling traversal and media flow traversal. A completed solution is proposed applicable todifferent scenes of new NAT type classification. For the traversal of media flow, a port predictionmethod with STUN is proposed to solve the issue of traversal through Endpoint-dependentMapping NAT with predicable type. For the traversal of SIP signaling, a SIP protocol extensionbased method is proposed to allow new requests generated in the reverse direction by reusing theflow created between the client and the server during registration.Finally, the dissertation designes and implementes a simulation system for NAT traversal ofTCP with detailed simulation results and analysis provided.