An Research And Implementation Of Solution For NAT Traversal On VoIP

This thesis deeply analyzes current solutions of NAT traversal on the VoIP. However, these solutions present obvious advantages VoIP is a technology that mostly utilized in IP phone, and relevant value-added services. The most advantage of VoIP is that can make use of the global IP internetworking environment, to provide the more and more the better and better services than traditional PSTN network. It is also the hot research field of Internet. The widely application of VoIP increases the requirement of a large number of IP addresses. VoIP mainly uses NAT to solve this. Accompanied by the matter of NAT traversal .The VoIP application based on H.323 and SIP uses the IP address and port in the message body of signaling to route. So besides transforming the TCP/UDP layer port and IP layer address, VoIP NAT traversal needs to transform parts of the payload of IP packages. NAT traversal is the biggest drawback of VoIP application and it should be solved soon. This thesis deeply analyzes current solutions of NAT traversal on the VoIP. However, these solutions present obvious advantages and disadvantages depending on the topological conditions of the network. So we need a complete solution that is flexible enough to through most of NAT in different network topology. The innovation of this thesis lies in adopt a method named port predict to obtain next port allocated by symmetric NAT. It brings that STUN can traverse most of symmetric NAT and other all types of NAT. This solution doesn't require changing existing NAT devices. It benefits the problem that STUN can't traverse symmetric NAT by oneself. Research and practice indicate that this solution can solve efficiently the problem of typical SIP traverse NAT. It will be a good drive for widely usage of VoIP applications.