Research And Implementation Of Traversing NAT Based On Peer-to-peer Network

Peer-to-peer network technologies is one of hotspot network applications, which has achieved great success in File-Sharings , distributed computation and distributed storage and etc. aspects. However, the network address translation technology which is raised to solve the problems of IP address lackness and network security causes the p2p network communication problem. How to solve the problem of traverse NAT for signaling and mediastream efficiently will become the key technology for implementation and extension of P2P network. In this paper, the principle and traverse method of NAT technique are mainly discussed, combining with the feature of P2P network to solve the NAT traverse problem of UDP and TCP, and one scheme is designed for P2P network traversing communication .Comparing with traditional the module of C/S , P2P network module has the features of strong extensibility and high automation netting mode, as for the security consideration , many terminals that behind the NAT, or even after multiple NATs , the outside network cannot access the internal computers directly , which brings great difficulties to resource sharing . Among the existing traverse schemes, some need to remark the current equipments, and few are fit for the P2P network, such as: STUN, TRUN and etc. Among them, STUN is better for UDP traversing, but cannot traverse symmetrical NAT. Though TRUN can traverse symmetrical NAT, it causes network delay because packet needs to transmit through TRUN server. These schemes are not fit for the NAT traverse problem of UDP and TCP in P2P network.In this paper, the hole punching scheme is raised and the signaling transfer and packet transmit are departed in structure. Signaling is transmitted through united servers, so as to implement punching in NAT, and thus the packet can pass through the "hole" to traverse NAT easily without servers' retransmitting, and finally implements NAT traversing of UDP and TCP.The hole puching scheme must set up the Public Network Rendezvous Server. Relaying,Connection Reversal and ect technology is used to implement punching a hole in the single NAT and multiple NAT. In this way, the scheme implements the UDP communication. As for TCP communication,Considering TCP is a kind of multidirection connection server, the scheme implements the TCP traversing by this way that client imitate the SYN&ACK packet and the Rendezvous Server control message forwarding. The scheme implements symmetrical NAT traversing by port predicting technology. In this scheme, the Rendezvous Server only transmit signaling while the packet can traverse NAT transparently ,and thus it can reduse the network delay caused by Packet Forwarding of the server.Finally, the functionality of scheme is tested and whose result explains that this scheme can implement multiple styles of NAT traversing through UDP and TCP, and makes little time-delay.