FRITZ!Box 3370 Service - Knowledge Base

FRITZ!Box 3370 Service

DSL connection drops frequently

The DSL connection between the FRITZ!Box and your DSL provider's exchange drops several times a day. When this occurs, the "Power" LED on the FRITZ!Box flashes and stays lit as soon as the Internet connection has been re-established.

If you have a DSL line with an additional analog landline, this issue may occur very often when you accept a call to your landline number or make a call from your landline.

The following error message is displayed in the event log of the FRITZ!Box:

  • "DSL not responding (no DSL synchronization)
    DSL synchronization starting (training)"


  • The stability of the DSL connection primarily depends on the length and quality of the access line. Faults in the cabling or problems with the Internet service provider's exchange (DSLAM) can also affect it.

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 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. Check whether there are events listed that occurred before and while the error occurred, or whether there are only events that occurred after the error occurred.
    • If events that occurred before and while the error occurred are also displayed:
      • Proceed with the following section.
    • If only events that occurred after the error are displayed:

2 Checking the cabling

It is often difficult to recognize mistakes in the cabling and they can remain unnoticed for a long time. Therefore, check the wiring in your home:

  • Make sure that the FRITZ!Box is connected correctly to your DSL line. Remove the following:
    • if you have an IP-based line: the DSL splitter,
    • all cable extensions,
    • unused cables and telephone jacks,
    • additional electrical components (for example surge protection, automatic extension outlets).

3 Installing the latest FRITZ!OS for the FRITZ!Box

Installing the latest FRITZ!OS makes your FRITZ!Box compatible with the latest DSL technology used by DSL providers in their DSL exchanges:

4 Increasing the interference resistance

Increase the interference resistance of your DSL connection; this reduces the number of interruptions of the DSL connection due to brief disturbances on the DSL line:

Note:Increasing the interference resistance of the DSL connection can slightly reduce the throughput of the DSL connection.

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "DSL Information" in the "Internet" menu.
  3. Click on the "Line Settings" tab.
  4. Next to "Intended signal-to-noise ratio" under "Receive direction", move the setting one step farther to the left towards "Maximum stability".

    Important:If you move the controls too far towards "Maximum stability", with some DSL lines you will no longer be able to establish a DSL connection. Therefore, do not select the setting "Maximum stability" right away. Instead, push the control gradually to the left in order to determine the best setting for your DSL line.

  5. Click "Apply" to save the settings.
    • If the DSL connection continues to drop frequently:
      • Repeat steps 4 - 5 until the DSL connection is stable.

5 Checking the DSL line

There may be a problem with the DSL line. Since it may take a while for your DSL provider to check your line, you may be charged for the service, and our experience shows that there is often a problem with DSL lines even if they have been checked by your provider, proceed as follows:

  1. Disconnect the FRITZ!Box from the DSL line.
  2. Connect a different DSL modem to the DSL line.
  3. Test whether the DSL connection remains stable when you use this DSL modem.
    • If the DSL connection continues to drop, there is a problem with your line:
      • Have the DSL provider check the DSL line.

        ATTENTION!Your DSL provider may charge you for checking your DSL line. Ask your DSL provider about charges in advance!