Using Virtual Network Card To Implement Firewall And NAT Traversal Of VoIP Application

The NAT and Firewall are the problems that must be solved in the SIP application. NAT and Firewall would cause SIP address failure or bad quality of communication, the solution is NAT traversal and Firewall traversal.There are two main ways to solve NAT traversal problem: the one is to update NAT server, the other is to modify the client. The solutions to Firewall traversal have same point: packets deception to Firewall traversal.Existing solutions to NAT and Firewall traversal have the same drawback: they have to modify server or client, so they are named not-transparent-traversal. The thesis addresses a new traversal solution: NAT and Firewall traversal by virtual network card, and it is transparent-traversal because you need not change anything.There are two core technologies of NAT and Firewall traversal by virtual network card: the virtual network card and the virtual network card protocol. To achieve transparent-traversal is by the virtual network and to achieve NAT and Firewall traversal is by the virtual network protocol. The thesis discusses the solution from following aspects:Chapter I is about the firewall and NAT issues: discussed the background: the firewall and NAT, then studies the classification of the firewall and NAT.Chapter II is about the design of the firewall and NAT traversal: analyzes the prototype system: OpenVPN, and gives the definition of network environment value and conception of the communication channels, also discusses the virtual network protocol.Chapter III is about the implement of the firewall and NAT traversal: mainly discusses the implement of the virtual network card, client software and server software.