| 摘要 |
PROBLEM TO BE SOLVED: To attain a speech with an external line at the same time even when an extension speech is made by adopting a half-duplex extension speech using a B channel. SOLUTION: ISDN telephone terminals 5-1, 5-2 are connected to two B channels 3, 4 connected to extension sides of a master set 2 using an ISDN interface for an extension speech in the ISDN telephone system 1, and the master set 2 discriminates whether a call sent from the ISDN telephone terminals 5-1, 5-2 is an external line speech or an extension speech and discriminates whether or not the extension speech is an extension speech between conventional ISDN telephone terminals, or between the conventional ISDN telephone terminal and an exclusive ISDN telephone terminal adopting a half duplex extension speech, and between the exclusive ISDN telephone terminals when the discrimination indicates the extension speech. In the case of the extension speech between the exclusive ISDN telephone terminals, a transmission reception loopback control section 9 controls loopback of a transmission channel of a corresponding B channel to a reception channel of the B channel.
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