A Study On NAT Traversing Solutions For SIP Protocol

In this thesis, author firstly introduces the basic concepts of SIP and NAT, gives a brief reminder of how NAT affects SIP, and explains the principle of some common NAT traversing solutions.In open source community, there is a more innovative NAT traversing solution named MediaProxy which is developed exclusively for SER. To show what a good solution MediaProxy is, author gives a very detailed description of the architecture and pricinple of MediaProxy, and tests MediaProxy together with SER.Unforturenally, ther are two main disadvantages of MediaProxy: the reliance on DNS service and the lack of compatibility with other SIP proxy. To improve this solution, author reads and rewrites parts of source code of MediaProxy to discard the reliance on DNS, and proposes a new NAT traversing solution named NTP by modifying the architecture of MediaProxy. NTP not only inherits the advantages of MediaProxy, but also overcomes the shortcomings of MediaProxy and can be compatible with any standard SIP Proxy.This article focuses on improvements of MediaProxy, introduces how author modify the source code and the architecture of MediaProxy, and gives a detailed verification of the pricinple of NTP.