Direct inward dial

An extension or Austrian flap allows to reach an extension on a telephone system via public telephone networks directly, instead of being taught at the polling place. The extension marks the end of a phone number.

English names for dial are direct dial in (DDI ) and direct inward dial (DID).

The assignment of extensions to extensions is done by programming the telephone system. In German-speaking dial 0 is used for the query space in the rule. If you can forgive multi-digit extensions, is dispensed with each digit extension, however, to all multi-digit extensions that start with the corresponding digit.

In Germany each system connection is (for example, 1234) assigned a base number and a phone number block with at least ten one-to five -digit extensions ( for example, 0 to 29). DIN is written extensions often discontinued following 5008 with a hyphen from the rest of the number. In this notation, the extension can be clearly seen, for example, in 1234-14 the number dial 14 International is not this spelling usual. After the Recommendation E.123 of the International Telecommunication Union no symbols should be used to highlight extensions.

In Austria an extension in the telephone exchange is also referred to as a flap. The term comes from the optical signaling at a switchboard. In contrast to Germany no number blocks are assigned, the number and length of extensions are the responsibility of the end user, which can make its numbering plan so flexible. Only by Directive E.164 the entire length of the telephone number, including area code is limited to 13 digits (without the access code 0) and ext. For a Primary Rate Interface usually a shortened number is assigned ( by 2 points ), so that more extensions are possible according to.

In the Czech Republic all DDI-capable extensions have the same number length in a telephone system. The switching is achieved by selecting appropriate number of ones. For example: four digit extension numbers are used in a telephone system, the agency has the number 1111.