| 摘要 |
PURPOSE:To facilitate detection of malicious call subscriber's number by using a circuit that transmits and receives AC signals of inaudible high frequency for retrieving malicious call subscriber's number in a telephone set and control circuit holding function of the telephone set by reception of the AC signals. CONSTITUTION:When a telephone set SUBB of a malicious call subscriber discriminates that the call is incoming call from a telephone set SUBA of a malicious call subscriber, a dial circuit 2 generates the dial signal by button operation of SUBB. A malicious call detecting operation discriminating circuit 6 detects this, and transfers malicious call information to an AC signal receiving circuit 3 and sends out inaudible high frequency AC signals to SUBA through channels A, B via a speech train. On the other hand, SUBA receives AC signals from SUBB by the AC signal transmitting and receiving circuit 3 and transfers the information to a circuit holding control circuit 1, and makes the service circuit final subscriber restoring state. when SUBA hooks on after completion of talking, a hook switch (hks) is restored. However, as the circuit holding control circuit section 1 holds the speech circuit, closed state of the speech train is maintained irrespective of on-hook of SUBA.
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