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Format of phone numbers for incoming calls

We show you what information is important when you set up the routing in your phone system.

For this purpose, you will have two different options to choose from in the customer portal as of 25.01.2022:

1. E.164-Format

Default for merged accounts and extensions of number blocks (DDI)

With the E.164 format, the international dialing code is specified without leading zeros (example 493012345).

If you use the E.164 format, the information for call number signaling is taken from the SIP-Invite. Here the complete dialed phone number is stored in the TO: header in E.164, i.e. without leading zeros.

This setting is easier to process for most telephone systems and allows more accurate routing than, for example, the international format.

We therefore strongly recommend to use E.164 instead of the international format.

2. International format

Default for trunks and single phonenumbers, as well as Cloud-Accounts

In the so-called international format, there are two zeros before the country code. For example 00493012345.

If you choose to use the international mode, the information to be signaled is taken from the so-called Contact header. This is automatically transmitted when a SIP trunk is registered and may be configured freely.

Possible problems when using the international format
  1. The information in the Contact header must be configured correctly. If you use the international format, your phone number should also be stored in the international format in the Contact header! Otherwise, error-free routing is not guaranteed.
    In some cases, especially with Asterisk-based systems, the formatting in the pre-settings In this case, please check the settings of the telephone system. This field is called differently depending on the phone system manufacturer, e.g. "Contact user" for FreePBX or "Auth user" for Askozia.
  2. Since a phone number block registers only once, i.e. sends only one Contact header with only one phone number, no unique routing can be guaranteed, especially with phone number blocks of unusual size. This is because it can happen that several phone numbers within this block are signaled with the same information from the Contact Header.

Attention!
If you use the international format, extensions of phone number blocks will still be signaled in E.164 for technical reasons.

Potential issues when using the international format

  1. The information in the Contact header must be configured correctly. If you use the international format, your phone number should also be stored in the international format in the Contact header! Otherwise, error-free routing is not guaranteed.
    In some cases, especially with Asterisk-based systems, the formatting may differ in the default setting. In this case, please check the configuration of the telephone system. This field is called differently depending on the phone system manufacturer, e.g. "Contact user" for FreePBX or "Auth user" for Askozia.
  2. Since a phone number block registers only once, i.e. sends only one contact header with only one phone number, it is not possible to guarantee unambiguous routing, especially for phone number blocks of unusual size. This is because it can happen that several phone numbers within this block are signaled with the same information from the Contact Header.

Attention!
If you use the international format, extensions of number blocks are still signaled in E.164 for technical reasons. You must therefore take two different formats into account in the routing settings of the telephone system.