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Knowledge document #115

Diverting incoming calls via a particular number (call through)

With the "Call through" function, you can configure your FRITZ!Box so that certain calls are forwarded to any destination telephone number using a cheaper telephone connection. This saves costs compared to using your landline or mobile telephone to call the number directly, for example.

Example:
You are on the road and want to call somebody abroad using your mobile telephone. You can either make an international call, or you can call your FRITZ!Box at home and have it forward the call to the extension abroad over the internet at a much less expensive rate.

Note:All instructions on configuration and settings given in this guide refer to the latest FRITZ!OS for the FRITZ!Box.

1 Configuring call through

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Call Handling" in the "Telephony" menu.
  3. Click on the "Call Through" tab.
  4. Enable the option "Enable call through".
  5. From the drop-down list "Incoming number", select the number that you want to enable call through for.
  6. From the drop-down list "Number for outgoing calls", select the number the FRITZ!Box should use for forwarding calls.
  7. Enter a four-digit number in the "PIN" field in the section "Security Settings". Callers must enter this PIN on their telephone in order for their call to be forwarded via the FRITZ!Box.
  8. If only certain callers should be allowed to use the call through function, enable the option "Only accept calls from the following numbers" and enter their telephone numbers including the area code.

    Important:Authorized callers must transmit their caller ID; otherwise, they cannot use call through.

  9. Click "Apply" to save the settings and on the FRITZ!Box, confirm that the procedure may be executed, if you are asked to do so.

2 Using call through

  1. Call the telephone number that you configured call through for.
  2. After the signal tone, enter the PIN on the telephone.
  3. If you want to have a call routed via the FRITZ!Box:
    1. Enter 0, because outside line access is disabled for the call through function.
    2. As soon as you hear the ringing tone, enter the destination telephone number and include the area code.
    • If you want to call a telephone connected to the FRITZ!Box, enter the internal number of the telephone you want to call.

      Note:You can find the internal numbers of the telephony devices under "Telephone Book > Internal Numbers" in the FRITZ!Box user interface.

3 Problems with establishing a call through connection

If there was a problem with establishing the call through connection, proceed as follows:

Own caller ID is not transmitted

If you have configured "call through" in the FRITZ!Box and then use this function to make a call, your caller ID will not be transmitted automatically. However, you can transmit the telephone number of the telephone line that your FRITZ!Box is connected to on an individual basis (only for one call):

  1. Enter the prefix #31# before entering the telephone number you want to be routed to.

    Important:The number of the telephone line you are calling the FRITZ!Box from cannot be transmitted.

Cannot hear prompt to enter your PIN

If you do not hear the prompt to enter the PIN, call through was only configured for particular telephone numbers. The telephone number being transmitted to the FRITZ!Box does not match a telephone number you enabled call through for, or your caller ID is not being transmitted. Check the FRITZ!Box's call list to see which caller ID you are transmitting.

PIN entry is not accepted or digits are not / are not recognized correctly

If the PIN is not accepted or one or more digits are not recognized or are not recognized correctly, inband signaling is being used for the DTMF transmission. With this transmission method, the DTMF tones are transmitted within the voice data stream and not over a separate channel, which leads to errors in recognizing DTMF tones. Therefore, set the DTMF transmission to "SIP-INFO" or "RTP-Event" in the FRITZ!Box:

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Telephone Numbers" in the "Telephony" menu.
  3. Click the (Edit) button for the respective internet telephone number.
  4. Select "Other provider" from the drop-down list, even if you are using a preconfigured internet telephony provider.
  5. Select "INFO, RTP or in-band" for "DTMF transmission".
  6. Click "Apply" to save the settings.

One or more digit(s) is/are recognized twice

If certain digits are recognized twice, the SIP INFO method or RTP Event method is being used for the DTMF transmission. These are secure transmission methods, but your provider does not cleanly filter the original DTMF spectrum from the actual voice data stream. This causes the DTMF entry to be detected twice: once in-band and once as the separately transmitted DTMF event. Changing the DTMF transmission method to "In-band" may help:

  1. Click "Telephony" in the FRITZ!Box user interface.
  2. Click "Telephone Numbers" in the "Telephony" menu.
  3. Click the (Edit) button for the respective internet telephone number.
  4. Select "Other provider" from the drop-down list, even if you are using a preconfigured internet telephony provider.
  5. Select "In-band" for "DTMF transmission".
  6. Click "Apply" to save the settings.

Busy signal is heard after dialing the outside line access code or destination telephone number

Either calls are already being conducted over the FRITZ!Box or a call through connection is already active. This means that the maximum number of calls that can be conducted via the FRITZ!Box or are allowed by the telephony provider has been reached.

Long delay before calls are ended

The FRITZ!Box does not detect the busy signal from the party being called, or it detects it too late. Proceed as follows to clear the connection securely:

  1. Enter # or ## on your telephone. You will hear a tone when the call through connection is cleared; the connection to the FRITZ!Box remains intact. Now you can either hang up to completely terminate the connection, or you can have the FRITZ!Box forward your call again.
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