TUNNEL DEVICE, RELAY DEVICE, TERMINAL DEVICE, CALL CONTROL SYSTEM, IP TELEPHONE SYSTEM, CONFERENCE DEVICE, AND THEIR CONTROL METHOD AND PROGRAM

摘要

For communications between terminals in different FWs, tunnel devices (T1 and T3) in the individual FWs perform a call control and a voice packet transmission via a relay device (T2) outside of the FWs, so that communications can be made by the transmissions of voice packets and so on between the terminals even in the case of a Symmetric NAT. A voice packet transmission route such as an RTP between the terminals is set not via the tunnel devices but as a direct route (i.e., a straight route) so that bottlenecks in the tunnels can be resolved. It is possible through the tunnels to provide the technique of an IP telephone for transmitting the voice packets even in the case of the Symmetric NAT.