中文摘要：

SIP协议以其在开放性、扩展性以及与Intemet结合紧密的优势在VoIP应用中广泛采用，而NAT是主要用来通过防火墙或者路由器使多个局域网的私有IP共享一个共有的IP的技术。介绍了NAT的穿透原理，然后介绍了在SIPProxy系统中穿透NAT的方法，并且分析了这种方法如何和SIP的信令结合在一起。该方法可以大大地拓宽VoIP系统的应用范围，使得在目前IP地址资源非常紧缺的情况下有更多的用户可以享受到VoIP的服务，并已经在开发的VoIP系统得到了运用，系统稳定且有效。

英文摘要：

SiP is widely used in VolP system newly because of the advantage of degree of open , extension and connection with Interact. NAT is a technology most commonly used by firewalls and reuters to allow multiple devices on a LAN with private IP addreses to share a single public IP addre.ss. This paper introduces the concept of NAT traversal, then discusses the method of NAT traversal on SIP proxy system, and analyses how to combine this method and SIP signal together. The method discussed in the paper can enlarge the application seope of VoIP system, it makes more users can gain the service of VoIP in the case resource of IP address is lacking and it has used in the VoIP system the author developed, the system is stable and effective.