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Knowledge Base 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.

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

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

1 Configuring the FRITZ!Box

  1. Click on 'Telephony' in the FRITZ!Box user interface.
  2. Click on 'Telephony Devices' in the 'Telephony' menu.
  3. Click on the (Edit) button next to the phone to be configured.
  4. Click on the 'Telephony Device Features' or 'Properties' tab.
  5. Enable the 'Call rejection on busy (busy on busy)' option.
  6. Disable the 'Call waiting' option.

    Note: With an ISDN phone you disable the call waiting function directly on the phone. Find out from the manufacturer how to do this, e.g. in the manual for the ISDN phone.

  7. Click on 'Apply' to save the settings.

2 Function not supported by IP telephones and telephones connected to the Mesh Repeater

The 'Call waiting' and 'Busy on busy' functions are not supported for the following phones:

  • IP phones (e.g. FRITZ!App Fon)
  • Phones on a FRITZ!Box that is configured as a Mesh Repeater

If you are making a call with an IP phone or with a phone on a Mesh Repeater, a busy signal cannot be heard by other callers.

3 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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