Design And Implementation Of A Mechanism For Supporting VPN And Web Proxy Used By SIP Terminal

In order to ensure the security of private network, many enterprises have adopted Firewall/NAT between private network and Internet. However, if the SIP client needs to communicate with the client of Internet or other private network, it must resolve the problem of Firewall/NAT traversal. There are some problems to be resolve:1. NAT mapping problem. There are many methods to resolve this problem, such as STUN, TURN and ICE. However, it's very difficult for client behind firewall to set up communication only by resolving NAT mapping problem.2. Firewall restricting problem. Firewall has many safe strategies, such as only permitting TCP connection, restricting the outing port or only permitting the 80 port. However, SIP sets up communication by using dymanic ports. Consequently, it's very difficult for SIP packet to traverse the firewall to set up communication.There are several solutions to traverse Firewall/NAT. But each solution has its own limitations. Some solutions are adapted to one kind of firewall; some solutions need to upgrade the firewall. This paper proposes a method from reality, which combines HTTP and tunnel traversing technique, Http Tunnel. The system can resolve all the aforementioned problems. The main works of the paper include the following parts:1. This paper analyzes several solutions to traverse Firewall/NAT, and proposes a method which combines HTTP and tunnel traversing technique—Http Tunnel.2. This paper designes the main function of Tunnel Client and Tunnel Server. Then this paper emphatically expatiates the basic theories, the frame of the Http Tunnel traversing solution and how the Tunnel Client and Tunnel Server coordinate to work.3. Base on the designs before, this paper demonstrates the implementation of Tunnel Client and Tunnel Server. And the paper gives the flow chats for some importment methord, such as receiving thread and senging thread.4. This paper evaluates the rough performance of the Http Tunnel traversing solution through two applications, and brings forth the proposition for continue study.