TUNNEL DEVICE, RELAY DEVICE, TERMINAL DEVICE, CALL CONTROL SYSTEM, IP TELEPHONE SYSTEM, CONFERENCE DEVICE AND METHOD AND PROGRAM FOR CONTROLLING THEM

摘要

PROBLEM TO BE SOLVED: To provide a technique of an IP telephone by which a voice packet is transmitted via a tunnel, even in the case of symmetric NAT.

SOLUTION: With respect to telephone calls among terminals inside different firewalls (FW), call control and voice packet transmission are performed between tunnel devices T1 and T3 inside their firewalls via a relay device T2 outside the firewalls. In this way, telephone calls by transmission of voice packets between terminals are made possible, even in the case of the symmetric NAT. By setting a voice packet transmitting path, such as a real-time transport protocol(RTP) between terminals as a direct path instead of via a tunnel device, bottleneck in the tunnel can be eliminated.

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