Switch off FON lines


Neuer User
Mitglied seit
29 Jan 2012
Punkte für Reaktionen
Dear forum,
I'd like to configure my FRITZ!Box Fon WLAN 7170 Annex A so that it puts completely off the FON output lines when the ADSL is not connected.

My telephone line is pure ADSL (no POTS/PSTN) so I can make telephone calls through Fritz!Box only if ADSL is connected.

On FON2 port I have connected a GSM/PSTN box. This box has a telephone line input (where I connected an analog telephone device), a telephone line output (connected to FON2 of Fritz!Box) and a GSM SIM card with modem and antenna.

Normally the calls originated from the telephone device are routed from the input to the output line of the box and correctly managed by the Fritz that uses the VoIP over ADSL connection.
When the box detects a failure telephone line (low voltage) on its output line (FON2), the box automatically switches to GSM connection as a backup line and calls will be routed through GSM network, until the output telephone line voltage is fixed.
In this way I can continue making calls even if ADSL is down.

If I disconnect the ADSL line cable from Fritz, I noticed the box continues insisting to route the calls through telephone line. This is because the voltage at FON1/FON2 ports doesn't change, even if the ADSL line is not connected. So the box can't detect the problem on fixed telephone line (VoIP over ADSL) and doesn't change to GSM.

I'm finding a way, even with a custom firmware, that switch completely off the FON1/FON2 ports when the ADSL is not connected.

Any help?