Resarch On NAT Traversal In VoIP System Based On ICE And SIP

With the rapid development of the Internet, VoIP technology has been attracting more and more attention and interest from the society. Vo IP is an internet technology which converting voice signals into IP packets and transmitting via IP network. It has a high requirement with respect to real-time and fidelity for being a real-time service. Nowadays, due to the fact that more and more users have access to the Internet, IPv4 address space is facing depletion and an alternative method is required. So, IPv6 is developed. However, when upgrading IPv4 to IPv6, there exists many difficulties for upgrading Internet software and hardware devices, which involving many respects like terminals and transmission path. So, in order to alleviate the pressure of IP address allocation, the Network Address Translation(NAT) technology is coming into use and has been widely used in enterprises. While there is still not a mature and complete solution for traversing symmetric NAT, the research of this paper is focused on traverse symmetric NAT and shortening the amount of time for establishing the Peer to Peer(P2P) communication connection.An improved solution proposed by this paper is based on Session Initiation Protocol(SIP) and Interactive Connectivity Establishment(ICE). The first step is to explore further about SIP and ICE. Then, a detailed analysis about the limitations of a solution combined with SIP and ICE to traverse NAT is started. In order to overcome the limitations, a method is proposed to achieve the optimal communication connection establishment time by using the Address Resolution Protocol(ARP) and Internet Control Message Protocol(ICMP) to detect the topology of a terminal and saving it to a server for a client to accurately collect candidate addresses and to simplify the detected lists after a detailed analysis of all kinds of network topologies. Then, a lot of tests are done to research further about the allocation pattern of symmetric NAT, which can be divided into three categories. For each category, an algorithm is implemented to traverse NAT. Meanwhile, a solution of the server’s resource dispatch is presented with the consideration of cases which can affect the performance of each algorithm.First, three open-source SIP, Simple Traversal of UDP over NATs(STUN) and Traversal Using Relay NAT(TURN) servers are deployed in education network. Then, a server based on EPOLL and MYSQL is used to assist a client to traverse a symmetric NAT and optimize the connection establishment time. A client is based on an open-source project, pjproject, and is embedded with functions like port allocation, network topology detection and detected lists optimization, to implement the improved solution. After the above works are completed, a lot of tests and data collection are executed to show the fact that each function component is successfully accomplished. Moreover, by comparing and analyzing the collected test data and the performance difference of a system before improving and after improving, the improved solution is validated to be able to optimize the process of ICE address collection and connectivity detection.