Interference Resistance

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When the DSL connection is established, specific connection parameters are negotiated between the exchange and the FRITZ!Box. Under some circumstances it may not be possible to take into consideration interference caused at peak load times or by electrical devices in the household.

Adjusting Interference Resistance

In order to increase stability against interference pulses, you can change the settings of your FRITZ!Box as far toward "Maximum stability" as possible. Do not change the preconfigured settings if your DSL connection is stable.

  1. Move the control toward "Maximum stability" step by step until the DSL connection is stable again.

    Keep in mind that the data throughput of the DSL connection is reduced accordingly.

  2. Click "Apply" to submit your settings to the FRITZ!Box. The DSL connection then will be established anew using the changed parameters.

    These settings are not supported by all remote stations. If the problems with the DSL connection cannot be resolved in this way, change the setting back to "Maximum performance".

Intended signal-to-noise ratio The signal-to-noise ratio is a value for the quality of the DSL signal. The higher the ratio, the more stable the DSL connection. The signal-to-noise ratio cannot be influenced.
Impulse Noise Protection (INP) The electronic immunity of the DSL connection to sources of interference can be increased by means of Impulse Noise Protection. When you move this control step by step toward "Maximum stability", the FRITZ!Box negotiates the DSL connection by applying such technologies to increase the electromagnetic immunity of the connection.
Identification of radio frequency interference (RFI) Under some circumstances radio transmitters located nearby can interfere with DSL communication (RFI: Radio Frequency Interference). This normally will be detected automatically by the FRITZ!Box. If this identification does not work correctly or if an additional source of interference appears, you can move this control step by step toward "Maximum stability" to improve the DSL connection.

Use previous DSL version

The DSL version is part of FRITZ!OS. The DSL version of the FRITZ!Box is developed further with each FRITZ!OS. Installing the the latest FRITZ!OS brings your FRITZ!Box up to date with the latest DSL technology.

In individual cases (for example on DSL lines with outdated DSLAMs) the FRITZ!Box may only be able to establish a stable DSL connection with certain DSL versions.

With the "Use previous DSL version" feature you can enable the previous version of DSL in the FRITZ!Box:

  1. Enable "Use previous DSL version".
  2. Click on "Apply".

The previous DSL version is enabled and then the FRITZ!Box is restarted. This will take about two minutes.

Send feedback if you were able to resolve the issue by using the previous DSL version. To do this, switch to the "Feedback" tab.

With your feedback you assist AVM in optimizing the DSL performance of the FRITZ!Box.

Limit DSL sync rate to the available bit rate

Deutsche Telekom and some other DSL providers generally provide the DSL connection with the highest possible data rate. For customers who contract a lower data rate with their DSL provider, the DSL provider implements the reduction of the data rate on the IP connection layer rather than the DSL connection layer. The FRITZ!Box, however, always establishes the DSL connection with the data rate offered by the DSL provider. So the higher the data rate, the more susceptible to interference the DSL connection is.

The "Limit DSL sync rate to the available bit rate" setting is displayed only if the two following points apply to your DSL provider:

  • The DSL provider transmits the value of the contracted data rate to the FRITZ!Box.
  • The DSL provider does not reduce the data rate of the DSL connection to the contracted data rate.

When you enable the "Limit DSL sync rate to the available bit rate" setting, then the data rate is reduced on the DSL connection layer to make the DSL connection stable.

Remedying Malfunctions due to Powerline


DSL connections can be disrupted by powerline connections. The "Detect and Resolve Malfunctions" function can minimize disruptions of the VDSL connection that may be caused by powerline products.


  • The "Detect and Resolve Malfunctions" function is available only if VDSL interference was detected that could have been caused by a FRITZ!Powerline product.
  • The FRITZ!Box has an active DSL connection.
  • Powerline products are connected with the FRITZ!Box.

Detecting Malfunctions

  1. Click on the "Detect and Resolve Malfunctions" button.

    This process of checking and adjusting can take up to ten minutes. During this time, the load on the powerline connection may affect the network quality and internet connection.

  2. The process of checking and adjusting can be repeated to optimize the interaction of VDSL with a high-performance powerline installation step by step.

Avoiding Malfunctions

See our tips on how to Avoid Disruptions and Improve Powerline Connections.

Reset Powerline Settings

With the "Reset Powerline Settings" button you can reverse any adjustment to the settings.