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Knowledge document #50

Cannot send or receive faxes with an external fax machine

Although the fax machine was configured according to our guide and you can conduct calls over the FRITZ!Box, you are either sometimes or never able to send or receive faxes. Faxes cannot be transmitted or transmission is aborted. One of the following error messages may be displayed in the event log of the FRITZ!Box:

  • "Not Acceptable Here (488)"
  • "Unsupported Media Type (415)"
  • "Not Acceptable Here (606)"

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 for the FRITZ!Box

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

2 Checking the event log of the FRITZ!Box

  1. Click "System" in the FRITZ!Box user interface.
  2. Click "Event Log" in the "System" menu.
  3. Select "Telephony" from the drop-down list.
  4. Check whether one of the following error messages is displayed for the fax that failed. If so, note the information that correspond to the message.
  5. If the message "Unsupported Media Type (415) is displayed, your provider does not support the requested codec or does not allow you to send faxes.
    • If the message "Not Acceptable Here (488 or 606)" is displayed, your provider does not support the T.38 standard. Without T.38, reliable fax transmission over the internet is not possible.

      Note:In this case, you can either use a telephone number from a provider that supports T.38 or disable T.38 again for fax reception. T.38 may not be necessary for fax transmission.

3 Setting your fax machine to tone dialing

  1. Set your device to "tone dialing" (DTMF) and not "pulse dialing". Pulse dialing is no longer state of the art and can lead to dialing problems on a telephone system. We therefore cannot guarantee that devices with pulse dialing will operate correctly with the FRITZ!Box. With tone dialing, you hear a tone when you press a number key; with pulse dialing, you hear clicking sounds. Refer to the manufacturer of the device for information on how to set it up, for example consult the manual.

4 Reconfiguring the fax machine

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Telephony Devices" in the "Telephony" menu.
  3. If the fax machine is already displayed in the list of telephony devices, click the (Delete) button for the fax machine.
  4. Reconfigure the fax machine: Click the "Configure New Device" button and follow the instructions.
  5. If you cannot select the socket the fax machine is connected to when configuring it, another telephony device was already configured for that socket. Delete that device.

5 Testing different remote sites

  1. Test fax transmission to or from different fax machines on different telephone lines.
  2. If fax transmission only fails with a particular remote site, the fax machine at the remote site is either not ready to receive faxes or incorrectly configured.

6 Testing different transmission speeds

Many fax machines allow you to select from various transmission speeds (4800, 7200, 9600, 14400 and 36600 baud):

  1. If your fax machine supports it, test the different transmission speeds one after the other. The FRITZ!Box supports transmission speeds of up to 14400 baud.

    Note:For instructions on configuring the transmission speed, refer to the device's manual or consult the manufacturer directly.

7 Enabling the error correction mode (ECM)

Using the error correction mode (ECM) on your fax machine can significantly improve the faxing results, as long as the remote machine also supports ECM. In some cases, however, the results may be worse:

  1. Enable the error correction mode (ECM) on your fax machine for testing purposes. Refer to the manufacturer for information on how to configure ECM, for example consult the manual.

8 Checking the protocol for fax transmission

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Telephone Numbers" in the "Telephony" menu.
  3. Click on the "Voice Transmission" tab.
  4. Look for the aborted faxes under "Details on Completed Calls" and check whether "T.38" is displayed in the "Coding" column for these faxes:
  5. If "T.38" is displayed, T.38 was used for the fax transmission.
    • If "T.38" is not displayed, T.38 was not used. Without T.38, reliable fax transmission over the internet is not possible.

      Note:If your internet telephony provider does not support T.38, for the fax you can use an internet number from an internet telephony provider that supports T.38.

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