FRITZ!Fon C4 Service - Knowledge Base

FRITZ!Fon C4 Service

Callers do not hear busy signal when 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 then assumes that the line is available.

Important:Some of the settings described here are only displayed if the advanced view is enabled in the user interface. The configuration procedure and notes on functions given in this guide refer to the latest FRITZ!OS

Simply proceed as described below. After each measure, check whether the issue persists.

1 Configuring the FRITZ!Box

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Telephony Devices" in the "Telephony" menu.
  3. Click the button (Edit) for the relevant telephone.
  4. Click on the "Telephony Device Features" tab.
  5. Enable the option "Call rejection on busy (busy on busy)".
  6. Disable the option "Call Waiting".
  7. Click "OK" to save the settings.

2 Configuring an ISDN NT with an integrated analog converter

In the case of ISDN NTs with integrated A/B converters (analog converters, terminal adapters), the analog ports are often configured to react to all incoming calls. This means that 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 you did not connect a telephone to the analog ports of the converter:

  • Configure the analog converter so that its analog ports do not react to incoming calls.

3 Configuring other ISDN devices

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

  • Connect all ISDN devices to the "FON S0" port of your FRITZ!Box by means of an ISDN hub. You can connect up to eight ISDN devices to the "FON S0" port on the FRITZ!Box. The FRITZ!Box can provide power to one ISDN telephone. The other ISDN devices must use their own power supply.
    • or, if other ISDN devices are connected to the ISDN line in addition to the FRITZ!Box:
  • Configure the ISDN devices so that they do not to react to incoming calls.