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The International Telecommunication Union (ITU) publishes a recommendation entitled Notation for national and international telephone numbers, e-mail addresses and Web addresses. Recommendation E.123 specifies the format of telephone numbers assigned to telephones and similar communication endpoints in national telephone numbering plans.
E.164 defines a general format for international telephone numbers. Plan-conforming telephone numbers are limited to only digits and to a maximum of fifteen digits. [ 1 ] The specification divides the digit string into a country code of one to three digits, and the subscriber telephone number of a maximum of twelve digits.
Microsoft canonical address format for telephone numbers [2] [3] derives from E.123 international notation by allowing explicit indication of area code with parentheses. The canonical format is used by the Telephony API (TAPI) , a Windows programming interface for dial-up fax, modem, and telephone equipment.
Country codes are defined by the International Telecommunication Union (ITU) in ITU-T standards E.123 and E.164. The prefixes enable international direct dialing (IDD). Country codes constitute the international telephone numbering plan. They are used only when dialing a telephone number in a country or world region other than the caller's.
National telephone numbers are defined by national or regional numbering plans, such as the European Telephony Numbering Space, the North American Numbering Plan (NANP), or the UK number plan. Within a national numbering plan, a complete destination telephone number is typically composed of an area code and a subscriber telephone number.
In the international telephone network, the format of telephone numbers is standardized by ITU-T recommendation E.164. This code specifies that the entire number should be 15 digits or shorter, and begin with an international calling prefix and a country prefix.
Telephone number mapping is a system of unifying the international telephone number system of the public switched telephone network with the Internet addressing and identification name spaces. Internationally, telephone numbers are systematically organized by the E.164 standard, while the Internet uses the Domain Name System (DNS) for linking ...
IDDD was implemented through extensive modifications in the switching systems to accommodate the international open numbering plan with seven to twelve digits in the national telephone numbers. [53] Access to the international network is facilitated by the dialing prefix 011, after which the country code and the national telephone number are ...