Patent ID: 7751387

Claim:
A modified NAT firewall traversal method for SIP communication comprising: (A) a NAT address prediction session comprising the steps of: (At) a calling host sending a request sequence for carrying out address prediction with a called host to an Interactive NAT Traversal (INT) server, and the INT server transferring the request sequence to the called host; (A2) the called host replying a response sequence to the calling host via the INT server after receiving the request sequence, the calling host knowing and recording IPs and communication ports that are used from the response sequence, and recording a time interval from sending out the request sequence till receiving the response sequence; (A3) the calling host repeating the steps (A1) and (A2) until obtaining the variation patterns of the IPs and the communication ports; (A4) the calling host predicting IPs and the communication ports that will be used for transmitting messages by the both hosts, and the calling host transmitting a connection request to the called host via the INT server according to the time interval; and (A5) the called host replying a connection response to the calling host via the INT server after receiving the connection request so that the calling host and the called host can build a pre-established media session; and (B) a direct data intercommunication session wherein the calling host sends out a request for building a call connection via a SIP proxy server, and the called host receives the request, and the calling host and the called host then activate the pre-established media session that has been built beforehand to make the pre-established media session become a formal media session.