A TELEPHONE NUMBERING PLAN 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 code routing. Telephone numbering plans are defined in each of administrative regions of the public switched telephone network (PSTN) and they are also present in private telephone networks.
Numbering plans may follow a variety of design strategies which have often arisen from the historical evolution of individual telephone networks and local requirements. A broad division is commonly recognized, distinguishing open numbering plans and closed numbering plans. A closed numbering plan imposes a fixed number of digits assigned to every telephone, while an open numbering plan features a variable length of telephone numbers assigned to stations. An open plan permits the expansion of the total numbering capacity of the plan by addition of more digits to a subset of numbers. Many numbering plans subdivide their territory of service into geographic regions designated by a special prefix, often called AREA CODE, which is a set of digits forming the most-significant part of the dialing sequence to reach a telephone subscriber. For example, the North American Numbering Plan , which is a closed numbering plan, prescribes ten digits for each complete destination routing code, including a three-digit area code. Other countries with open numbering plans use variable-length numbers; in some, such as Finland , subscriber numbers may vary in length even within an exchange.
Private numbering plans exist in telephone networks that are privately operated in an enterprise or organizational campus. Such systems may be supported by a private branch exchange (PBX) which controls internal communications 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 required to reach a destination. Even in closed numbering plans, it is not always necessary to dial all 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.
North American Numbering Plan
* 6 Subscriber dialing procedures
* 6.1 Variable-length dialing * 6.2 Full-number dialing
* 7 International numbering plan
* 7.1 Satellite telephone systems
* 8 Numbering plan indicator * 9 Private numbering plan * 10 See also * 11 References * 12 External links
NORTH AMERICAN NUMBERING PLAN
In early telephone systems, connections were made in the central office by switchboard operators using patch cords to connect one party to another. A telephone call was initiated by operating a magneto hand generator, usually integral to the customer telephone, to alert the central office operator by the ringing of a switchboard bell or the activation of a drop. In response, the operator inserted a patch cord into the corresponding line jack and assisted the customer by voice. The other end of the patch cord connected the caller to the destination telephone line. If the destination party belonged to another exchange, the operator established a connection to that exchange where another operator completed the call setup. As technology advanced, automatic electro-mechanical switches were introduced and telephones were equipped initially with rotary dials for pulse-dialing and then Touch-Tone key pads in the 1960s, which increased the speed of dialing and enabled other vertical telephone features.
The Bell System organized the numbering plan to minimize the cost of providing automatic dialing to large population centers, as calls crossing numbering plan area boundaries were required to be switched by special toll switching systems. Thus, it was avoided to cut heavily used toll routes by area boundaries. Tributary routes were placed into the same area as the major toll center. States that foreseeably required more than ca. 500 central offices, a technical limitation of the number plan, were split into multiple areas, receiving a code with the middle digit being _1_, while area codes that covered an entire state, had the digit _0_ in the middle. In contrast to the area code, the second digit of the three-digit exchange code was never _0_ or _1_, thus affording a simple rule for recognition of whether a user was dialing a full ten-digit telephone number or merely dialing within the local area code using seven-digit dialing . Toll operators were able to differentiate between the two types of areas from the middle digit of the area code when a routing operator had to be consulted.
By the 1990s, the electromechanical central office switches were replaced with electronic switching system (ESS) equipment and the previous area code logic was no longer necessary. The demand for telephone numbers was increasing rapidly, and the remaining n0n and n1n combinations were insufficient to sustain growth. This area code scheme was abandoned, with the result that area codes and central office codes could not necessarily be automatically distinguished by the switching equipment. The solution was to require the dialing of a preceding 1 for calls across area codes, in which case the equipment expected 10 more digits. If the first digit dialed was not a "1", only 7 digits were expected and the area code was inferred from the originating subscriber's area code. For a short while, in some area codes, one could enter the full 11 digits for a call within their own neighborhood or just enter the last 7 digits, and the call would be routed and billed identically.
The rising popularity of fax machines and pagers required far more telephone numbers than were anticipated in the design of the numbering system. As a remedy, the restrictions on the format of area codes were eased. Since 1995, over 380 new area codes were added to the North American Numbering Plan. Some areas used area code splits, by which an existing numbering plan area (NPA) was split into multiple divisions each assigned a new area code. Thus, many businesses were required to reprint business stationery, catalogs, and directories. Area code splits were often contested as to which area could keep the existing code, which usually fell to the largest city. For example, 305 was split in 1995, and had served both the Miami and Fort Lauderdale area. Dade County (Miami-Dade) kept 305 and Broward County (Fort Lauderdale area) had to change to 954. Another method was using area code overlays, which avoided renumbering existing stations. An overlay is a new area code that covers the same geographical area as an existing code. Over 75 overlays have been introduced since 1995.
Area code overlays invariably require ten-digit dialing of telephone
numbers in the numbering plan area.
Most national telephone administrations issue telephone numbers that
conform to the
numbers 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
Numbering plans also decide on the routing of Signaling System 7
(SS7) signaling messages as part of the
Global Title. In public land
mobile networks , the
E.212numbering plan is used for subscriber
identities, e.g., stored in the
In general, the structure of telephone numbers issued within a national telephone numbering plan follows both the international formats and the national standards. Within the international system administered by the ITU, each national plan has a unique country code.
Within the national numbering plan, a complete destination telephone number is composed of an area code and a subscriber telephone number.
The subscriber number is the number assigned to a line connected to customer equipment. It must always be dialed in its entirety. The first few digits of the subscriber number typically indicate smaller geographical areas or individual telephone exchanges . In mobile networks they may indicate the network provider. Callers in a given area or country usually do not need to include the particular area prefixes when dialing within the same area. Devices that dial telephone numbers automatically may include the full number with area and access codes.
Country codes are necessary only when dialing telephone numbers in
other countries than the originating telephone. These are dialed
before the national telephone number. By convention, international
telephone numbers are indicated by prefixing the country code with a
plus sign (+), which is meant to indicate that the subscriber must
dial the international dialing prefix in the country from which the
call is placed. For example, the international dialing prefix or
_access code_ in all NANP countries is _011_, while it is _00_ in most
European countries. On
Many telephone numbering plans are structured based on divisions into
geographic areas of the service territory. Each area identified in the
plan is assigned a numeric routing code. This concept was first
Operator Toll Dialingof the Bell System in the early
1940s, which preceded the
North American Numbering Plan
National telecommunication authorities use various formats and dialing rules for area codes. In the initial design of the NANP, the three-digit format was _NBX_, where _N_ could be any digit from 2 through 9, _B_ either 0 or 1, and _X_ any digit, although no area code ended in _0_ until the code 800 was introduced for toll-free service. The pattern of assignment to geographical areas avoided nearby areas having similar area codes, to avoid confusion and misdialed numbers. In 1995, during the expansion of area codes the center-digit rule was relaxed, defining it as any digit except 9. 9 as the middle digit of an NPA is reserved in case the three-digit area code pool is exhausted and has to be augmented to four digits.
Other countries use a variety of either fixed-length or variable
length area codes. Area codes consist of two digits in Brazil , one
Some countries, such as Uruguay , have merged variable-length area codes and telephone numbers into fixed-length numbers that must always be dialed independently of location. In such closed dialing plans, also having a closed numbering plan, the area code is formally not distinguished 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 outside the code area or from mobile phones. In North America ten-digit dialing is required in areas with overlay plans .
The strict correlation of a telephone to a geographical area has been
broken by technical advances, especially
The area code is usually preceded in the dialing sequence by either
the national access code ("0" for many countries, "1" in USA and
Canada) or the international access code and country code. However,
this is not always the case, especially when 10-digit dialing is used.
For example, in
Area codes are often quoted by including the national access code.
For example, a number in
CALL PRICING BASED ON AREA CODES
In countries other than the
Therefore, calls between nearby rate centers in different area codes may be cheaper than calls to more distant rate centers in the same area code. Rates are set in zones of 0-6 mi, 6-12 mi, and so on, with these bands determined on a state-by-state basis for intrastate calls (calls within the same state) and determined by federal regulation for interstate calls (calls which cross a state line). As a specific example, callers in the Falls Church, Virginia, rate center, which is officially named "Washington Zone 17, VA"—example numbers begin with 703-534, V=5636, H=1600, may make unmetered local calls to 31 other nearby rate centers in Virginia, Maryland, and the District of Columbia in area codes 703, 571, 202, 301, and 240, while calls to distant locations in 703, such as Manassas and Haymarket, VA, are charged as long distance.
Calls within a state are often higher than rates to call more distant locations in some other state . The partial deregulation and introduction of competition for long-distance phone services has established other methods of determining call pricing that do not necessarily follow the traditional model. Each year, more customers switch to a fixed rate, "all-you-can-dial" plan covering the state, the United States, or all North America generally (as of May 2008 and exclusive of taxes) for approximately $30 per month. Competition with cable telephony and Voice over Internet Protocolservices has helped drive the cost of service down for residential and business customers.
Landline telephony operators in
SUBSCRIBER DIALING PROCEDURES
A dial plan establishes the expected sequence of digits dialed on subscriber premises equipment, such as telephones, in private branch exchange (PBX) systems, or in other telephone switches to effect access to the telephone networks for the routing of telephone calls, or to effect or activate specific service features by the local telephone company, such as 311 or 411 service.
A variety of dial plans may exist within a numbering plan and these often depend on the network architecture of the local telephone operating company.
Within the North American Numbering Plan, the administration defines standard and permissive dialing plans, specifying the number of mandatory digits to be dialed for local calls within the area code, as well as alternate, optional sequences, such as adding the trunk code 1 before the telephone number.
Despite a closed numbering plan, different dialing procedures exist in many of the territories for local and long distance telephone calls. This means that to call another number within the same city or area, callers need to dial only a subset of the full telephone number. For example, in the NANP, only the 7-digit number may need to be dialed, but for calls outside the area, the full number including the area code is required. In these situations, the ITU-TRecommendation E.123suggests to list the area code in parentheses, signifying that in some cases the area code is optional or is not required. Typically the area code is prefixed by a domestic trunk access code (usually 0) when dialing from inside a country, but is not necessary when calling from other countries, but there are exceptions, such as for Italian land lines .
To call a number in Sydney,
* xxxx xxxx (within
The plus character (+) in the markup signifies that the following digits are the country code, in this case 61. Some phones, especially mobile telephones, allow the + to be entered directly. For other devices the user must replace the + with the international access code for their current location.
* 306 xxx xxxx — within Regina , Lumsden and other local areas
* 1 306 xxx xxxx — within Saskatchewan, but not within the Regina
local calling area, e.g.,
* xxx xxxx — local or long-distance within area code 510, no area code required) * 1 510 xxx xxxx — local or long-distance outside of 510 but within the U.S., Canada, and other countries in the NANP. _1_ is the long-distance trunk code. * 1 510 xxx xxxx — outside the NANP. _1_ is the country code for the U.S.
However, in parts of North America, especially where a new area code overlays an older area code, dialing the area code, or 1 and the area code, is required even for local calls. Dialing from mobile phones is different in the U.S., as the trunk code is not necessary, although it is still necessary for calling all long distance numbers from a mobile phone in Canada. Most mobile phones can be configured to automatically add a frequently-called area code as a prefix, allowing calls within the desired area to be dialed by the user as seven-digit numbers, though sent by the phone as 10-digit numbers.
In some parts of the United States, especially northeastern states
* 610 xxx xxxx — local calls within the 610 area code and its overlay (484), as well as calls to or from the neighboring 215 area code and its overlay, 267. Area code is required; one of two completion options for mobile phones within the U.S. * 1 610 xxx xxxx — calls from numbers outside the 610/484 and 215/267 area codes; second of two completion options for mobile phones within the U.S.
Many organizations have private branch exchange systems which permit dialing the access digit(s) for an outside line (usually 9 or 8), a "1" and finally the local area code and _xxx xxxx_ in areas without overlays. This aspect is unintentionally helpful for employees who reside in one area code and work in an area code with one, two, or three adjacent area codes. 1+ dialing to any area code by an employee can be done quickly, with all exceptions processed by the private branch exchange and passed onto the public switched telephone network .
In small countries or areas, the full telephone number is used for
all calls, even in the same area. This has traditionally been the case
in small countries and territories where area codes have not been
required. However, there has been a trend in many countries towards
making all numbers a standard length, and incorporating the area code
into the subscriber's number. This usually makes the use of a trunk
code obsolete. For example, to call Oslo in
* xxx xxx (within Oslo - no area code required)
* (02) xxx xxx (within
After 1992, this changed to a closed eight-digit numbering plan, e.g.:
* 22xx xxxx (within
Therefore, in other countries, such as
while some, like
While dialing of full national numbers takes longer than a local
number without the area code, the increased use of phones that can
store numbers means that this is of decreasing importance. It also
makes it easier to display numbers in the international format, as no
trunk code is required—hence a number in
* 2xx xxx xxx (inside Czech Republic) * +420 2xx xxx xxx (outside Czech Republic)
as opposed to before September 21, 2002:
* 02 / xx xx xx xx (inside Czech Republic) * +420 2 / xx xx xx xx (outside Czech Republic)
Some countries already switched, but trunk prefix re-added with the closed dialing plan, for example in Bangkok, Thailand before 1997:
* xxx-xxxx (inside Bangkok) * 02-xxx-xxxx (inside Thailand) * +66 2-xxx-xxxx (outside Thailand)
has been switched in 1997:
* 2-xxx-xxxx (inside Thailand) * +66 2-xxx-xxxx (outside Thailand)
Trunk prefixhas re-added in 2001
* 02-xxx-xxxx (inside Thailand) * +66 2-xxx-xxxx (outside Thailand)
INTERNATIONAL NUMBERING PLAN
E.164standard of the
International Telecommunications Union
Within the system of country calling codes, the ITU has defined certain prefixes for special services and assigns such codes for independent international networks, such as satellite systems, spanning beyond the scope of regional authorities.
SATELLITE TELEPHONE SYSTEMS
Satellite phones are usually issued with numbers with a special
country calling code. For example,
* Inmarsat: +870: SNAC (Single Network Access Code)
* ICO Global : +881 0, +881 1.
* Ellipso: +881 2, +881 3.
* Iridium : +881 6, +881 7.
Some country calling codes are issued for special services, or for international/inter regional zones.
* +388 5 – shared code for groups of nations * +388 3 – European Telephony Numbering Space– Europe-wide services (discontinued) * +800 – International Freephone (UIFN ) * +808 – reserved for Shared Cost Services * +878 – Universal Personal Telecommunicationsservices * +881 – Global Mobile Satellite System * +882 and +883 – International Networks * +888 - international disaster relief operations * +979 – International Premium Rate Service * +991 – International Telecommunications Public Correspondence Service trial (ITPCS) * +999 – reserved for future global service
NUMBERING PLAN INDICATOR
The numbering plan indicator (NPI) is a number which is defined in the ITU standard Q.713 , paragraph 18.104.22.168.3, indicating the numbering plan of the attached telephone number. NPIs can be found in Signalling Connection Control Part (SCCP) and short message service (SMS) messages. As of 2004 , the following numbering plans and their respective numbering plan indicator values have been defined:
NPI DESCRIPTION STANDARD
1 ISDN Telephony E.164
3 data X.121
4 telex F69
5 maritime mobile E.210 and E.211
6 land mobile E.212
7 ISDN/mobile E.214
PRIVATE NUMBERING PLAN
Like a public telecommunications network, a private telephone network in an enterprise or within an organizational campus may implement a _private_ numbering plan for the installed base of telephones for internal communication. Such networks operate a private switching system or a private branch exchange (PBX) within the network. The internal numbers assigned are often called _extension numbers_, as the internal numbering plan extends an official, published main access number for the entire network. A caller from within the network only dials the extension number assigned to another internal destination telephone.
A private numbering plan provides the convenience of mapping station telephone numbers to other commonly used numbering schemes in an enterprise. For example, station numbers may be assigned as the room number of a hotel or hospital. Station numbers may also be strategically mapped to certain keywords composed from the letters on the telephone dial, such as 4357 (_help_) to reach a help desk .
The internal number assignments may be independent of any direct inward dialing (DID) services provided by external telecommunication vendors. For numbers without DID access, the internal switch relays externally originated calls via an operator, an automated attendant or an electronic interactive voice response system. Telephone numbers for users within such systems are often published by suffixing the official telephone number with the extension number, e.g., 1-800-555-0001 x2055.
Some systems may automatically map a large block of DID numbers
(differing only in a trailing sequence of digits) to a corresponding
block of individual internal stations, allowing each of them to be
reached directly from the public switched telephone network . In some
of these cases, a special shorter dial-in number can be used to reach
an operator who can be asked for general information, e.g. help
looking up or connecting to internal numbers. For example, individual
Universität des Saarlandescan be dialed directly from
outside via their four-digit internal extension +49-681-302-xxxx,
whereas the university's official main number is +49-681-302-0 (49 is
the country code for
Callers within a private numbering plan often dial a trunk prefix to reach a national or international destination (_outside line_) or to access a leased line (or _tie-line_) to another location within the same enterprise. A large manufacturer with factories and offices in multiple cities may use a prefix (such as '8') followed by an internal routing code to indicate a city or location, then an individual four- or five-digit extension number at the destination site. A common trunk prefix for an outside line on North American systems is the digit 9, followed by the outside destination number.
Additional dial plan customisations, such as single-digit access to a hotel front desk or room service from an individual room, are available at the sole discretion of the PBX owner.
* Category:Telephone numbers by country
National conventions for writing telephone numbers
List of country calling codes
* ^ Nunn W.H., _Nationwide Numbering Plan_, BSTJ 31(5), 851 (1952).
* ^ _A_ _B_ AT&T. _Notes on the Network_, Section 10, p.3 (1980).
* ^ "World Telephone Numbering Guide Glossary".
* ^ "Area Code History". _area-codes.com_.
* ^ "LincMad\'s Area Codes of the 1970s". _lincmad.com_.
* ^ AT&T (1955) _Notes on Nationwide Dialing_
* ^ W. H. Nunn (1952-05-15). "Nationwide Numbering Plan". _Bell
System Technical Journal_. AT&T. 31 (5): 856.
* ^ "GreatData.com and NANPA.com". Retrieved 5 February 2013.
Joseph Steinberg(June 22, 2015). "US area codes are no longer
area codes – but they can still be used for scamming".
_BusinessInsider_. Retrieved June 25, 2015.
* ^ J.J. Pilliod, H.L. Ryan, _Operator Toll Dialing—A New Long
Distance Method_, Bell Telephone Magazine, Volume 24, p.101–115
* ^ Saunders, Amy (2009-05-16). "Cell-phone age turns the 614 into
just numbers". _
The Columbus Dispatch
* List of ITU-TRecommendation E.164