Scheme And Implement For SIP To Traverse NAT

Internet apply in more and more new fields accompanied with the development of network and communication technology. SIP protocol is a typical example. It get widely used because this protocol has many good characters, such as simple message, flexible architector and easy to expand. But it consumes large numbers of IP address when many applications are deployed on the Internat and IP address is not enough gradually. This problem is mainly resolved by NAT technology. NAT cause another problem. That is public user can not visit a internal user. SIP protocol also face this problem. It will be a bottle-neck in the development of SIP if we can not resolve it. Many companies pay more attension on how to traverse NAT in SIP protocal.This task bases on the SIP project of AltiGen Communications Ltd. In order to resolve NAT problem in the SIP system, it use several technoloy, such as register periodically, Record-Route, Medea consult later and media stream relay. SIP can traverse all kind of NAT gateway by this method. SIP terminal ane AltiGateway can be deploye on NAT environment freely and need not complex configuration.This design works well in testing environment and customer site. This docoment also talk about potential limitations and some expectation.