| 摘要 |
PURPOSE:To prevent the ineffective holding of a common channel and the waste of a battery and to increase the larm tone as requested by detecting a permanent call of a telephone set. CONSTITUTION:When a permanent call elapses by a prescribed time, an exchange 1 sends a howler tone to a telephone line 3. A master device 2 uses a detection circuit 6 to detect a howler tone, a howler detection signal from a transmission circuit 7 is sent to a talking channel in use. An identification circuit 8 of a telephone set at a terminal device side detects the howler signal, sends the signal to a control section to cut off forcibly the talking channel during connection. Further, the identification circuit 8 amplifies the detection signal to send the alarm tone at high level. |
