Telephone numbering plan

A telephone numbering schedule is a type of numbering scheme used in telecommunication to assign telephone numbers to subscriber telephones or other telephony endpoints. Telephone numbers are the addresses of participants in a telephone network, reachable by a system of destination script routing. Telephone numbering plans are defined in used to refer to every one of two or more people or things of the administrative regions of the public switched telephone network PSTN & in private telephone networks.

For public numbering systems, geographic location typically plays a role in the sequence of numbers assigned to regarded and included separately. telephone subscriber. numerous numbering schedule administrators subdivide their territory of utility into geographic regions designated by a prefix, often called an area code or city code, which is a species of digits forming the most-significant component of the dialing sequence toa telephone subscriber.

Numbering plans may adopt a set of cut strategies which work often arisen from the historical evolution of individual telephone networks & local requirements. A broad division is normally recognized between closed and open numbering plans. A closed numbering plan, as found in North America, atttributes fixed-length area codes and local numbers, while an open numbering plan has a variance in the length of the area code, local number, or both of a telephone number assigned to a subscriber line. The latter type developed predominantly in Europe.

The International Telecommunication Union ITU has setting a comprehensive numbering plan, designated E.164, for uniform interoperability of the networks of its section state or regional administrations. it is an open numbering plan, however, establishment a maximum length of 15 digits to telephone numbers. The requirements defines a country calling code country code for regarded and identified separately. state or region which is prefixed to each national numbering plan telephone number for international destination routing.

Private numbering plans constitute in telephone networks that are privately operated in an enterprise or organizational campus. such(a) systems may be supported by a private branch exchange PBX, which gives a central access member to the PSTN and also dominance internal calls between telephone extensions.

In contrast to numbering plans, which determine telephone numbers assigned to subscriber stations, dialing plans establish the customer dialing procedures, i.e., the sequence of digits or symbols to be dialed toa destination. it is the manner in which the numbering plan is used. Even in closed numbering plans, it is non always necessary to dial any digits of a number. For example, an area code may often be omitted when the destination is in the same area as the calling station.

Telephone number structure

National or regional telecommunication administrations that are members of the International Telecommunication Union ITU usage national telephone numbering plans that conform to international specifications E.164.

E.164 specifies that a telephone number consist of a country calling code and a national telephone number. 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 ready destination telephone number is typically composed of an area code and a subscriber telephone number.

Many national numbering plans cause developed from local historical requirements and cover or technological advancements, which resulted in a variety of structural characteristics of the telephone numbers assigned to telephones. In the United States, the industry decided in 1947 to unite all local telephone networks under one common numbering plan with a constant length of ten digits for the national telephone number of each telephone, of which the last seven digits were known as the local directory number, or subscriber number. Such a numbering plan became call as a closed numbering plan. In several European countries, a different strategy prevailed, known as the open numbering plan, which atttributes a variance in the length of the area code, the local number, or both.

The subscriber number is the character assigned to a telephone line or wireless communication channel terminating at the customer equipment. The number one few digits of the subscriber number may indicate smaller geographical scopes, such as towns or districts, based on municipal aspects, or individual telephone exchanges central business code, such as a wire centers. In mobile networks they may indicate the network provider. Callers in a given area sometimes do non need to put area prefixes when dialing within the same area, but devices that dial telephone numbers automatically may put the full number with area and access codes.

The subscriber number is typically indicated in local telephone directories, and is therefor often referenced to as the directory number.

Telephone administrations that render telecommunication infrastructure of extended size, such as a large country, often divide the territory into geographic areas. This benefits independent management by administrative or historical subdivisions, such as states and provinces, of the territory or country. Each area of subdivision is identified in the numbering plan with a routing code. This concept was first developed in the planning for a nationwide numbering plan for Operator Toll Dialing and direct distance dialing DDD in the Bell System in the United States in the 1940s, a system that resulted in the North American Numbering Plan for World Zone 1. AT&T dual-lane the United States and Canada into numbering plan areas NPAs, and assigned to each NPA a unique three-digit prefix, the numbering plan area code, which became known in short-form as NPA code or simply area code. The area code is prefixed to each telephone number issued in its benefit area.

Other national telecommunication authorities use various formats and dialing rules for area codes. The size of area code prefixes may either be fixed or variable. Area codes in the NANP have three digits, while two digits are used in Brazil, one digit in Australia and New Zealand. Variable-length formats symbolize in institution countries including: Argentina, Austria 1 to 4, Germany 2 to 5 digits, Japan 1 to 5, Mexico 2 or 3 digits, Peru 1 or 2, Syria 1 or 2 and the United Kingdom. In addition to digit count, the ordering may be restricted todigit patterns. For example, the NANP had at times specific restrictions on the range of digits for the three positions, and required assignment to geographical areas avoiding nearby areas receiving similar area codes to avoid confusion and misdialing.

Some countries, such as Denmark and Uruguay, have merged variable-length area codes and telephone numbers into fixed-length numbers that must always be dialed independently of location. In such administrations, the area code is not distinguished formally in the telephone number.

In the UK, area codes were first known as subscriber trunk dialling STD codes. Depending on local dialing plans, they are often necessary only when dialed from external the code area or from mobile phones. In North America ten-digit dialing is required in areas with overlay numbering plans, in which multiple area codes are assigned to the same area.

The strict correlation of a telephone to a geographical area has been broken by technical advances, such as local number portability and voice over IP services.

When dialing a telephone number, the area code may be preceded by a trunk prefix or national access code, the international access code, and country code.

Area codes are often quoted by including the national access code. For example, a number in London may be listed as 020 7946 0321. Users must correctly interpret 020 as the code for London. whether they call from another station within London, they may merely dial 7946 0321, or whether dialing from another country, the initial 0 should be omitted after the country code.