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Knowledge document #119

Parties cannot hear each other

When conducting calls, one of the following issues either occasionally occurs or always occurs. It either occurs right at the beginning of the conversation or sometime during the conversation, for example after five minutes:

  • You do not hear the other party.
  • The other party does not hear you.
  • The parties cannot hear each other.

This may give the impression that the telephone connection has been terminated. However, the connection is still active. You can see that it is because the telephony LED on the FRITZ!Box remains lit. The LED does not switch off until you end the call by hanging up.

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 Installing the latest FRITZ!OS

  1. Install the latest FRITZ!OS on the FRITZ!Box.

2 Restarting the FRITZ!Box

  1. Click "System" in the FRITZ!Box user interface.
  2. Click "Backup" in the "System" menu.
  3. Click on the "Restart" tab.
  4. Click the "Restart" button.

3 Configuring security software

The following steps are only necessary if the problem occurs when using FRITZ!App Fon:

  1. Briefly disable security software (for example Norton mobile Security) and VPN connections to any internet anonymization services (for example iCloud Privat-Relay, Nord VPN) on your telephone.
  2. Check whether you can now make calls with FRITZ!App Fon without any problems.
  3. If you can make calls now, then the security software was interfering with the voice connection. Re-enable the software and configure it so that it allows voice connections. Refer to the manufacturer for information on how to set it up, for example consult the manual.

4 Activating the microphone

The following steps are only necessary if the problem occurs with FRITZ!App Fon on an iOS device:

  1. Open the iOS settings.
  2. Tap "Privacy" and then "Microphone".
  3. Activate the microphone for FRITZ!App Fon.

5 Disabling expanded security functions and re-registering the telephone

The following steps are only necessary if the problem occurs with a cordless telephone from a different manufacturer:

Disabling expanded security functions

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "DECT" in the "Telephony" menu.
  3. Disable the expanded security functions in the section "Security".
  4. Click "Apply" to save the settings.

Re-registering the telephone

  1. Register the telephone with the FRITZ!Box.

6 Disabling support for CAT-iq 2.0 and re-registering the telephone

Disabling support for CAT-iq 2.0

The following steps are only necessary if the problem occurs with a cordless telephone from a different manufacturer:

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "DECT" in the "Telephony" menu.
  3. Disable the option "Support for CAT-iq 2.0-compatible devices enabled" in the section "Troubleshooting".
  4. Click "Apply" to save the settings.

Re-registering the telephone

  1. Register the telephone with the FRITZ!Box.

7 Entering a STUN server

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Telephone Numbers" in the "Telephony" menu.
  3. Click the (Edit) button for the respective internet telephone number.
  4. Check if the field "STUN server" is present under the fields for entering your login information.
  5. If the field is present and empty, enter the address of your internet telephony provider's STUN server and click "OK".
    • If the field is not present:
      1. Select "Other provider" from the drop-down list, even if you are using a preconfigured internet telephony provider.
      2. Check if the "STUN server" field is present now.
      3. If the field is present, enter the address of your internet telephony provider's STUN server and click "OK".
        • If the field is not present, click "Cancel". The STUN server is already preconfigured.

8 Setting up port forwarding for internet telephony

The following steps are only necessary if the FRITZ!Box does not establish its own connection to the internet, and uses the internet connection of another router in the network instead:

Setting up automatic port forwarding

If you enable port forwarding in the FRITZ!Box, the FRITZ!Box sends IP packets at regular intervals and the router's port forwarding automatically remains enabled:

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Telephone Numbers" in the "Telephony" menu.
  3. Click on the "Line Settings" tab.
  4. Click "Changing the Settings" in the "Telephony connection" section.
  5. Enable the option "Keep port sharing of the internet router enabled for telephony".
  6. Select a suitable time interval. Select "30 sec." if you do not know how long temporary port forwarding rules will be maintained.
  7. Click "Apply" to save the settings.

Setting up static port forwarding

The following steps are only necessary if the router does not support automatic port forwarding by the FRITZ!Box:

Note:Refer to the manufacturer of the router for information on setting it up; for example, consult the manual.

  1. On the router, configure port forwarding from UDP port 5060 to port 5060 on the FRITZ!Box.
  2. If your telephony provider supports encrypted telephone calls via TLS, for example Telekom, Easybell, dus.net, also configure port forwarding from TCP port 5061 to port 5061 on the FRITZ!Box.
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