Modified SIP NAT Traversal via Pre-established Media Sessions

The patent applies preliminary action by performing NAT type detection and address prediction before actual voice communication. The system detects NAT types (full-cone, restricted-cone, port-restricted, symmetric) during the SIP signaling phase and pre-calculates the mapping relationships between private and public IP addresses and ports. This preliminary preparation enables subsequent direct media transmission without requiring proxy servers for voice packets.

The patent uses the SIP proxy server as an intermediary only for signaling messages, not for media transmission. The proxy server facilitates the exchange of NAT traversal information (IP addresses, ports, NAT types) between endpoints during the call setup phase, then allows endpoints to communicate media directly. This selective intermediary approach resolves the contradiction by using the proxy only where necessary (signaling) while enabling direct communication where possible (media).

The patent applies parameter changes by dynamically determining and utilizing different NAT traversal methods based on detected NAT types. The system changes communication parameters (IP addresses, ports, mapping rules) according to the specific NAT configuration of each endpoint. For full-cone NAT, direct addressing works; for symmetric NAT, the system adjusts to use the established mapping relationships. This adaptability to different parameter configurations enables SIP communication across various NAT firewall types while maintaining security.

The patent implements dynamics by making the SIP communication protocol adaptive to different NAT environments. The system dynamically detects NAT types during call setup and adjusts the media transmission parameters accordingly. Rather than using a static communication method, the protocol becomes flexible and responsive to the actual network conditions, enabling compatibility with various NAT firewall configurations without compromising security policies.