FRITZ!Box 6590 Cable Service - Knowledge Base

FRITZ!Box 6590 Cable Service
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Using an ISDN PBX with the FRITZ!Box

If you connect your ISDN PBX to the FRITZ!Box, the devices connected to the PBX can use all of the telephone numbers that were entered in the FRITZ!Box.

Requirements / Restrictions

  • The ISDN telephone system must be suitable for use on an ISDN point-to-multipoint line.

Note:The configuration procedure and notes on functions given in this guide refer to the latest FRITZ!OS for your FRITZ!Box.

1 Configuring telephone numbers in the FRITZ!Box

First, configure all of your telephone numbers in the FRITZ!Box:

2 Connecting the PBX to the FRITZ!Box

  • Connect the PBX to the "FON S0" port on your FRITZ!Box.

3 Configuring the PBX in the FRITZ!Box

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Telephony Devices" in the "Telephony" menu.
  3. Click the "Configure New Device" button.
  4. Enable the option "ISDN PBX", click "Next", and follow the wizard's instructions.

4 Configuring the extensions of your PBX

If you do not assign telephone numbers to the extensions of your PBX, then the main telephone number you configured in the FRITZ!Box is used to make outgoing calls. In addition, all of the extensions react to all incoming calls. Therefore, assign the desired telephone numbers to the extensions:

  • In the PBX, define which numbers the extensions should react to when you receive calls and which number should be used to make calls. Enter the numbers in the PBX the way they are displayed in the settings for the ISDN PBX in the FRITZ!Box user interface (see fig.).

    Note:Sometimes a number may be too long for you to enter the complete number in the ISDN device. If this is the case, do not enter the entire number. Instead, enter as many of the last digits as possible.

    Fig.: Settings for the ISDN PBX in the FRITZ!Box user interface

5 Disabling the energy-saving mode in the FRITZ!Box

The FRITZ!Box is equipped with a number of energy-saving mechanisms. For example, when idle, the internal S0 bus of the FRITZ!Box terminates communication between it and the ISDN device. Some ISDN devices have problems with this function. Therefore, disable this function in the FRITZ!Box if you experience problems when establishing connections with ISDN devices:


  • Configure the devices so that you can send keypad sequences (sequences of symbols and digits, such as *121#) and enter special characters such as * and # with them. With many telephones, you can use the menu "Operation at a PBX > Dialing options > Dial * and #" to configure this.

Disabling the energy-saving mode

  1. Enter #966*1* on your telephone and press the call key (lift the receiver).
  2. Hang up again after about 3 seconds.

    Note:You can re-enable this function by entering #966*0*.