Study Of Traversing NAT/Firewall Based On SIP And Implementation Of SBC

Voice over IP technology develops with the rapid development of network applications. However, NAT and firewall technologies, which are brought forward for the insufficiency of IP address and the network security, conduce to issue between end to end communication .Consequently, how to solve the problems mentioned above effectively will greatly affect the promotion and application of VoIP. In this paper, the author conducts the research on the traversal of NAT/ firewall. Different NATs use different processing mechanisms. Thus, in different applied environments, different solutions to the traversal of NAT/firewall are adopted, for example, ALG method, STUN method, RSIP method, TURN method, MIDCOM method and tunnel traversal method, etc. However, each of them has its own shortcomings. For example, STUN method doesn't adapt to symmetrical NAT and ALG method doesn't adapt to large-scale VoIP organized network. In this sense, Session Border Control (SBC), a new solution is introduced to realize NAT/firewall traversal and seamless network access. For the application of VoIP, the guarantee of security and QoS is necessary. When designing realization of SBC, this paper considers access security and QoS guarantee of SBC thoroughly. When it comes to the realization of it, differentiated service and controlled access are to be used to ensure QoS, while digest authentication mechanism, dynamic unfolding way for media passage, and VPN organized network are to be adopted to ensure connection security. In this paper, great emphasis is laid on the research of communication model and working principles in SBC solution. When it comes to the realization of it, SIP message is divided into register message and non-register message, and then processed by two different models . At the meantime, a model design is carried out hierarchically. Since maintenance policy of NAT mapping table has great effects on system performance, and it is a necessary method to ensure the traversal of signaling and media. This paper studies three solutions about the problem, and analyzes them. Through session states analysis, a finite state machine (FSM) is adopted to design of the signaling processing model. Since the loaded capacity is very important for SBC performance, the independently developed software MyPhone is used as a testing terminal to analyze and evaluate the load performance of SBC.