| 摘要 |
PURPOSE:To detect the communication unable state of an opponent station distinctively from the in-use state by using network controllers in a couple on an origination and a termination side. CONSTITUTION:A relay 204 switches a circuit to the side of a modulator and demodulator by an indication from the modulator and demodulator after an answer is detected by an answer detecting circuit 23 during origination. A network controller 15' detects a specific communication unable display signal which is superposed through the circuit when the circuit is switched to the modulator and demodulator side by the relay 204 to obtain a visible, an audio, and other outputs. The network controller 15', on the other hand, operates an incoming detecting circuit 26 by a ringing tone from a line 205 during termination to output a signal CI to the modulator and demodulator. When everything is normal, the relay 204 operates to accept an incoming call and the circuit is switched to the side of the modulator and demodulator. When this time is long, a communication unable setting circuit 27 judges that a data terminal device or the modulator and demodulator is unable for communication. |
