The Study Of Voice Over IP Traversal Firewall

Voice over IP technology develops with the rapid development of network applications. Being cheap with flexible and powerful functions, VoIP has become the biggest challenge to the traditional PSTN. VoIP applications do not only provide the voice service, but video, data, fax and many other services. It is among the most promising technologies of the newly-born network era.However, NAT and firewall technologies, which are brought forward for the insufficiency of IP address and the network security, conduce to VoIP applications have greatly suffered communication obstacles. As a rule, FW/NATs are deployed at edges of networks to guarantee inner networks'security. Nowadays, even residential subscribers are bundled with FW/NATs in ADSL devices. FW(Firewall)/NATs have great influence on both business and residential users. Although FW/NATs can open fixed VoIP signaling ports, such as 5060 for SIP and 1720 for H.323, bidirectional voice and multimedia communications set up through the SDP description with the private ports and IP addresses will be blocked. The problem of VoIP's FW/NAT traversal slows down the business procedure. Consequently, how to solve the problems mentioned bove effectively will greatly affect the promotion and application of VoIP.Thoroughly research VoIP communication procedures with FW/NATs, analyse current leading solutions of VoIP FW/NAT traversal, We find the common characteristics:Networks need to be amended in the framework of the FW/NAT, or need new equipment to increase their services, different VoIP need to achieve a different way of traversal, They lead to the difficult of the deployment for FW/NAT, moreover they can not be achieved in point-to-point communication modes of communication. Based on defects analysis of the current traversing way, a new solution is introduced in this paper, RFC3519 for Mobile IP NAT traversal.is used to VoIP FW/ NAT traversal. The core idea of RFC3519 is using the tunnel to traversing Firewall/NAT. At the same time using the tunnel technology can be applied for high-level transparent transmission.Build experimental test platform to prove its feasibility by using PC,VoIP gateway,VoIP terminals,TornadoⅡ, VxWorks,Iptables,et. Intruduce the new solutions in both theory and realization and give the test results.