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Knowledge document #124

Callers do not hear busy signal when a call is already being conducted via FRITZ!Box

Callers hear a ringing tone instead of a busy signal if a telephone call is already being conducted over the FRITZ!Box. The caller therefore assumes that the line is free.

Note:All instructions on configuration and settings given in this guide refer to the latest FRITZ!OS for the FRITZ!Box.

Simply proceed as described below. After each measure, check whether the problem is solved.

1 IP telephones do not support the function

The "Busy on busy" function is not supported when making calls with IP telephones (for example FRITZ!App Fon). If you are using an IP telephone to conduct a call, it is therefore not possible to give the caller a busy signal.

2 Configuring the FRITZ!Box

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Telephony Devices" in the "Telephony" menu.
  3. Click the (Edit) button for the respective telephone.
  4. Click on the "Telephony Device Features" or "Properties" tab.
  5. Enable the option "Call rejection on busy (busy on busy)".
  6. Disable the option "Call waiting". With ISDN telephones, you must disable the option directly in the ISDN telephone. Refer to the manufacturer of the device for information on how to set it up, for example consult the manual.
  7. Click "OK" to save the settings.

3 Configuring an ISDN NT with integrated analog converter

The analog extensions of ISDN NTs with integrated A/B converters (analog converters, terminal adapters) are often configured to react to all incoming calls. As a result, callers hear a ringing tone even if you are already conducting a call over the FRITZ!Box. You do not notice that you are being called if there is no telephone connected to the analog extensions of the converter:

  1. Configure the analog converter so that its analog extensions do not react to calls.

4 Configuring other ISDN devices

If you are using the FRITZ!Box on an ISDN line and other ISDN devices (for example telephones, a telephone system) are also connected to the ISDN line, those devices must not be allowed to react to calls. Otherwise, the caller hears a ringing tone because another ISDN device could accept the call:

  1. Either:Use an ISDN distributor to connect all of the ISDN devices to the "FON S0" socket of your FRITZ!Box. You can connect up to eight ISDN devices to the "FON S0" socket.
    • Or: Configure the ISDN devices so that they do not to react to calls.
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