Research And Implementation Of SIP Traversal NAT

Over the years, the issue that SIP(Session Initiation Protocol) traversals NAT (Network Address Translation) has handicaped the large-scale applications of SIP. Under many conditions, the deployment of NAT prevents the end-to-end communication procedure between equipments on private networks and equipments on public networks. Thus, in this paper, a novel NAT Traversal Solution based on STUN(Simple Traversal of UDP Through Network Address Translators) is put forward named as PSTUN(Prediction based STUN) to traversal the Symmetric NAT.This thesis firstly analyzes the SIP protocol and its hierarchical structure deeply, and analyses the impact of NAT to SIP. Then we compare the major five NAT Traversal Solutions deeply in performance, scalability and security. But these solutions have their own disadvantages respectively. As STUN can not provide the solution to Symmetric NAT Traversal Which is used in many private networks requiring high level of security. A novel NAT Traversal Solution based on STUN is put forward to traversal the Symmetric NAT. We make a design from three aspects: SIP UA, PSTUN client and interface. PSTUN client is embedded in SIP UA. The system effectively guarantees the voice quality and provide the most types of NAT (include symmetric NAT) traversal functions. So the system meets the needs that SIP traversals NAT.The testing result shows that the PSTUN has fulfilled the requirement that SIP traversals NAT. It will be a good help to wide usage of VoIP applications.