A linked numbering scheme (LNS) is a dialing procedure in effect in a service area within which call routing between adjacent exchanges does not require a dialing code. The term is only used in the United Kingdom, but not in the

North American Numbering Plan The North American Numbering Plan (NANP) is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the international calling ...

United Kingdom

The largest linked numbering scheme in the UK is that for the

London telephone area 020 is the national dialling code for London in the United Kingdom. All subscriber numbers within the area code consist of eight digits and it has capacity for approaching 100 million telephone numbers. The code is used at 170 telephone exch ...

, formerly known as the London Director area. Within the area, several million subscribers can call each other by dialing a uniform code. For example, anyone calling from an (020) number can reach Transport for London travel enquiries by dialing 7222 1234. Smaller schemes apply outside London.

Uxbridge Uxbridge () is a suburban town in west London and the administrative headquarters of the London Borough of Hillingdon. Situated west-northwest of Charing Cross, it is one of the major metropolitan centres identified in the London Plan. Uxb ...

, for example, has the subscriber trunk dialing (STD) code 01895. Uxbridge exchange is the parent for Denham,

Harefield Harefield is a village in the London Borough of Hillingdon, England, northwest of Charing Cross near Greater London's boundary with Buckinghamshire to the west and Hertfordshire to the north. The population at the 2011 Census was 7,399. Haref ...

Ruislip Ruislip ( ) is an area in the London Borough of Hillingdon in West London, and in the historic county of Middlesex. Ruislip lies west-north-west of Charing Cross, London. The manor of Ruislip appears in the Domesday Book, and some of the ear ...

and

West Drayton West Drayton is a suburban town in the London Borough of Hillingdon. It was an ancient parish in the county of Middlesex and from 1929 was part of the Yiewsley and West Drayton Urban District, which became part of Greater London in 1965. Th ...

; anyone connected to any of those exchanges can call any of the others without having to prefix the number with 01895. This is achieved by giving subscriber lines on each exchange different prefix numbers, thus: all numbers are six-figure; Denham numbers start with 83, Harefield with 82, Ruislip with 6 and West Drayton with 4. Uxbridge numbers start with 2 or 81. All calls must have all six digits dialled - even if a subscriber is on Denham exchange and is calling another subscriber on Denham exchange, they must still dial 83xxxx. Incoming calls from any other exchange for a subscriber on any of the five exchanges must all be prefixed with the same 01895 code.

North America

The terminology ''linked numbering scheme'' is not used in the

(NANP). A local call in this scheme, standardized in 1948 for the introduction of direct-dial long-distance calling, was originally dialled as a fixed-length seven-digit number and did not require an area code. In some cases, a local call to a number just across an area code boundary could be seven digits if an

exchange code protection In the administration of the North American Numbering Plan, central office code protection is a numbering policy for maintaining local seven-digit dialing in communities that extend on both sides of the boundary line between multiple numbering plan ...

scheme prevented the same prefixes being assigned to local numbers in the other area code. A long-distance

trunk call In telecommunications, trunking is a technology for providing network access to multiple clients simultaneously by sharing a set of circuits, carriers, channels, or frequencies, instead of providing individual circuits or channels for each clie ...

within the same area code used to be dialable as ''1'' followed by seven digits, without the area code. This no longer possible everywhere in the NANP by 1995. In areas using toll alerting, where long-distance calls are identified by a

trunk prefix A trunk prefix is a digit sequence to be dialed before a telephone number to initiate a telephone call for the purpose of selecting an appropriate telecommunications circuit by which the call is to be routed. Making a domestic (national) telephone ...

(a leading 1-) to be distinguishable from flat-rate local calls, all toll calls must be dialled with the area code. Some local calls require

ten-digit dialling Ten-digit dialing is a telephone dialing procedure in the countries and territories that are members of the North American Numbering Plan (NANP). It is the practice of including the area code of a telephone number when dialing to initiate a telep ...

, either across area code boundaries in a

split plan Split(s) or The Split may refer to: Places * Split, Croatia, the largest coastal city in Croatia * Split Island, Canada, an island in the Hudson Bay * Split Island, Falkland Islands * Split Island, Fiji, better known as Hạfliua Arts, entertai ...

or within the same community in an

overlay plan Overlay may refer to: Computers * Overlay network, a computer network which is built on top of another network * Hardware overlay, one type of video overlay that uses memory dedicated to the application *Another term for exec, replacing one proce ...

. This may mean that no standard numbers are reachable without dialling an area code in some localities.

References

{{DEFAULTSORT:Linked Numbering Scheme Telephone numbers