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Telephone numbering plan

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A telephone numbering plan is a type ofnumbering scheme used intelecommunications to allocate and routetelephone numbers in a telephone network. A closednumbering plan,such as found in North America,features fixed length area codes and local numbers. An open numbering plan features variance in length of area code or local number,or both.

A dial plan establishes the expected number and pattern of digits for atelephone number. This includescountry codes,access codes,area codes and all combinations of digits dialed. For instance,theNorth Americanpublic switched telephone network (PSTN) uses a 10-digit dial plan that includes a 3-digit area code and a 7-digit telephone number. MostPBXs support variable-length dial plans that use 3 to 11 digits. Dial plans must comply with thetelephone networks to which they connect.

History

In early telephone systems,connections were made in the central office bytelephone operators usingpatch cords to connect one party to another. If a person wanted to make a phone call,he or she would pick up a phone and wind a crank on the side. The crank was a small generator that would light a lamp at the central office. An operator would see the light and insert their patch cord into a socket and assist the customer with the call connection. The operator would use patch cords to connect the caller to the person being called. If the party being called was in another exchange,the operator would use a patch cord to connect to another exchange where an operator elsewhere would finish the connection. As technology advanced,electro-mechanical switches were introduced and calls were made usingrotary dials.

Initial use of area codes in the United States began in the 1950s with large cities. By 1966,the system was nationwide.

Area codes were assigned based on the length of time arotary dial phone took to dial the area code. Densely populated areas like New York City,Chicago,Los Angeles,and Detroit had huge incoming call volume and were assigned numbers (212,312,213,313) that could be quickly dialed from a rotary dial phone. On a rotary dial phone low digits (1,2,3,4) could dial quickly as the time the rotary dial took to return to the home position was minimal. High digit numbers (7,8,9,0) on rotary dial phones took much longer to return to the home position and were usually used in less densely populated areas like rural Texas (915). This numbering strategy became unnecessary whentouch-tone phones arrived,as the tone allowed instant entry of digits.

Structure

Most telephone numbers belong to theE.164 numbering plan,though somePABXs have internal extensions.

TheE.164 numbering plan fortelephone numbers includes:

Country calling codes
  • Regional numbering plans,such as:
  • theEuropean Telephony Numbering Space
  • theNorth American Numbering Plan
  • Various national numbering plans,such as:
    Telephone numbers in the United Kingdom
    Apart from the use of numbering plans for telephone numbers,they are also used in routing ofSS7 signalling messages as part of theGlobal Title. Inpublic land mobile networks,theE.212 numbering plan is used for subscriber identities (e.g. stored in theGSMSIM) whileE.214 is used for routing database queries acrossPSTN networks.

    Country code

    Country code - necessary only when dialing to phones in other countries. In international usage,telephone numbers are quoted with the country code preceded by a "+",and with spaces in place of hyphens (e.g.,"+XX YYY ZZZ ZZZZ"). This allows the reader to choose which Access Code (also known as International Dialing Digit) they need to dial from their location. However,it is often quoted together with the international access code which must precede it in the dial string,especially in the United States and Canada (e.g.,"011-XX-YYY-ZZZ-ZZZZ"). This can cause confusion as "011" may not be a valid Access Code where the reader is located. OnGSM networks,"+" is an actual character that may be used internally as the international access code,rather than simply being a convention.

    Area code

    Area codes are also known as Numbering Plan Areas (NPAs). These are necessary (for the most part) only when dialed from outside the code area,from mobile phones,and (especially within North America) from withinoverlay plans. Area codes usually indicate geographical areas within one country that are covered by perhaps hundreds of telephone exchanges,although the correlation to geographical area is becoming obsolete.[ 2 - It must usually be preceded in the dial string by either the national access code or the international access code and country code. For non-geographical numbers,as well as mobile telephones outside of the United States and Canada,the "area code" does not correlate to a particular geographic area.

    Area codes were introduced in the United States by theBell System,in 1951,with the first direct dial long distance call.[ 3 -

    Local number

    The local number (or subscriber number) must always be dialed in its entirety. The first few digits in the local number typically indicate smaller geographical areas or individualtelephone exchanges. In mobile networks they may indicate a network provider in case the area code does not. Callers from a number with a given area/country code usually do not need to (but optionally may) include the particular area/country code in the number dialed,which enables shorter "dial strings" to be used. Devices that dial phone numbers automatically can include the full number with area and access codes,since there is no additional annoyance related to dialing extra digits.

    Standards

    Although theInternational Telecommunication Union (ITU) has attempted to promote common standards among nation states,numbering plans take different formats in different parts of the world. For example,the ITU recommends that member states adopt 00 as their international access code. However,as these recommendations are not binding on member states,some have not,such as theUnited States,Canada,and other countries and territories participating in theNorth American Numbering Plan.

    The international numbering plan establishescountry codes,that is,area codes that denote nations or groups of nations. TheE.164 standard regulatescountry codes at the international level and sets a maximum length limit on a full international phone number (15 digits). However,it is each country's responsibility to define the numbering within its own network. As a result,regional area codes may be:

    A fixed length,e.g.,three digits in theUnited States andCanada; two digits inBrazil; one digit inAustralia andNew Zealand,
  • A variable length,e.g.,between 2 and 5 inGermany,Argentina,United Kingdom and inAustria; between 1 and 5 inJapan; 1 or 2 inSyria andPeru,or
  • Incorporated into the subscriber's number,as is the case in many countries,such asSpain orNorway. This is known as a "closed" telephone numbering plan. In some cases a trunk code (usually 0 ) must still be dialed,as inBelgium,Italy,Switzerland,South Africa and some locations within theNANP.
  • Generally the area codes determine the cost of a call. Calls within an area code and often a small group of adjacent oroverlapping area codes are normally charged at a lower rate than outside the area code. (This is often not the case in the United States where rates to call within a state [regulated by that state's public utilities commission] are often higher than rates to call across the country [generally determined by competition]. In some United States locations where area codes cover more territory,different rates will apply within a single area code depending on the distance to the number called. Rates are determined from rate centers,and rates are set in zones of zero to six miles,six to twelve miles,and so on. This has changed dramatically with the deregulation of local phone services.)dubious Each year,more customers switch to a fixed rate,"all-you-can-dial" plan covering the state,the United States,and/or all North America generally (as of May 2008 and exclusive of taxes) for approximately $30 per month. Competition withcable telephony andVoice over Internet Protocol services have helped drive the cost of service down for residential and business customers.

    Special area codes are generally used forfree,premium rate,mobile phone systems (in countries where the mobile phone system is caller pays) and other special rate numbers. There are however some exceptions,in some countries (e.g.,Egypt),calls are charged at the same rate regardless of area and in others (e.g.,theUK) an area code is occasionally treated as two parts with different rates.

    Dialing plans

    Example

    In theU.S.,some typical dial plans include:

    Internal extension numbers of two,three,or four digits
  • Local numbers of seven or ten digits
  • Long distance numbers of eleven digits,consisting of a 1,then a three-digit area code,then a seven-digit number
  • International numbers of any length starting with 011
  • Within internal phone systems,a code (typically the number 9) is generally required to obtain an outside line.

    Open dialing plans

    An opendialing plan is one in which there are different dialing arrangements for local andlong distance telephone calls. This means that to call another number within the same city or area,callers need dial only the number,but for calls outside the area,an area code is required. In this situation it is customary to show the area code in parentheses,signifying that in some cases the area code is optional or is not required,as suggested byITU-T RecommendationE.123. The area code is prefixed by a trunk code (usually "0"),which is omitted when calling from outside the country.

    To call a number in Sydney,Australia for example:

    xxxx xxxx (withinSydney and other locations withinNew South Wales - no area code required )
  • (02) xxxx xxxx (outsideNew South Wales - the area code is required )
  • +61 2 xxxx xxxx (outsideAustralia; notice the dropped 0
  • Note that the "+" is not dialed,it signifies that first theinternational access code must be dialed,followed by the country code,in this case 61,followed by the number. When using a mobile telephone to place a call,many models do allow the + to be entered and this is internally converted to the correct access code,based on caller location,as the call is made.

    New Zealand has a special case of an open dialing plan. While most nations require the area code to be dialed only if it is different,in New Zealand,one needs to dial the area code if the phone is outside the local calling area. For example,to call a phone number inDunedin:

    xxx xxxx - within Dunedin
  • (03) xxx xxxx - within the 03 area code,but not within Dunedin (e.g. fromChristchurch orQueenstown
  • (03) xxx xxxx - within New Zealand,outside the 03 area code
  • +64 3 xxx xxxx - outside New Zealand
  • In theUnited States,Canada,and other countries or territories using theNorth American Numbering Plan (NANP),the trunk code is '1',which is also (by coincidence) thecountry calling code. The same rule also applies in many parts of the NANP,including all areas of Canada that still have an open dialing plan. This is not universal,as there are locations within the United States that allow long distance calls within the same area code to be dialed as seven digits. In Canada,the trunk code (also known as the long distance access code ) must also be dialed along with the area code for long distance calls even within the same area code. For example,to call a number inRegina:
    xxx xxxx (withinRegina,Lumsden and other local areas)
  • 1 (306) xxx xxxx (within the 306 area code,but not within the Regina local calling area (e.g.,Saskatoon))
  • 1 (306) xxx xxxx (anywhere within the NANP outside the 306 area code)
  • +1 (306) xxx xxxx (outside NANP
  • To call a number inSan Francisco,California the dialing procedure will vary:
    xxx xxxx ( local calls,no area code required )
  • 1 (415) xxx xxxx (outside San Francisco,and within the U.S.,Canada,and other countries in the NANP)[ 4 -
  • +1 (415) 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 + the area code,is now required even for local calls,which means that the NANP is now closed in certain areas and open in others. 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 today can be programmed 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 such asPennsylvania served byVerizon Communications,the full 10-digit number must be dialed. If the call is not local,the call will not complete unless the dialed number is preceded by a 1 . In this situation,where the area code is not optional,the area code is not enclosed in parentheses. Thus:

    610 xxx xxxx (local calls,area code required; one of two completion options for mobile phones within the U.S.)
  • 1 610 xxx xxxx (intra-area code charged calls; second of two completion options for mobile phones within the U.S.)
  • +1 610 xxx xxxx (outside the NANP
  • In areas served byAT&T inCalifornia,pre-recorded messages instruct customers that use of the local area code within the area code is not permissible and that only the xxx xxxx format is permitted.

    Many organizations haveprivate 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 "feature" 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 thepublic switched telephone network.

    Open and closed dialing plans should not be confused with open and closed numbering plans. A closed numbering plan,such as found in North America,features fixed length area codes and local numbers. An open numbering plan,as found in assorted countries that have not yet standardized,features variance in length of area code or local number,or both. Closed dialing plans are rare where numbering plans are open.

    Closed dialing plans

    Mergefrom.svg - It has been suggested thatClosed telephone numbering plan bemerged into this article or section. (Discuss
    Aclosed numbering plan is one in which the subscriber's 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 inNorway before1992,one would dial:
    xxx xxx (within Oslo - no area code required )
  • (02) xxx xxx (within Norway - outside Oslo )
  • +47 2 xxx xxx (outside Norway
  • After 1992,this changed to a closed eight-digit numbering plan,e.g.:
    22xx xxxx (within Norway - including Oslo )
  • +47 22xx xxxx (outside Norway
  • In other countries,such asFrance,Belgium,Switzerland,South Africa and some parts of North America where the dialing plan is closed,the trunk code is retained for domestic calls,whether local or national,e.g.,
    Paris 01 xx xx xx xx (outside France +33 1 xxxx xxxx)
  • Brussels 02 xxx xxxx (outside Belgium +32 2 xxx xxxx)
  • Geneva 022 xxx xxxx (outside Switzerland +41 22 xxx xxxx
  • Cape Town 021 xxx xxxx (outside South Africa +27 21 xxx xxxx)
  • New York 1 212 xxx xxxx (outside the North American Numbering Plan +1 212 xxx xxxx
  • while some,like Italy,require the initial zero to be dialled,even for calls from outside the country,e.g.,
    Rome 06 xxxx xxxx (outside Italy +39 0 6 xxxx xxxx
    Further,there are locations with closed dialing plans in the NANP that require the full phone number including area code to be dialed for all calls,but the trunk code is required for only long distance calls,even in the same area code.

    While the use of full national dialing is less user-friendly than using only a local number without the area code,the increased use of mobile phones,which require full national dialing and can store numbers,means that this is of decreasing importance. It also makes easier to display numbers in the international format,as no trunk code is required—hence a number inPrague,Czech Republic,can now be displayed as:

    2xx xxx xxx (inside Czech Republic)
  • +420 2xx xxx xxx (outside Czech Republic
  • as opposed to before September 21,2002:[ 5 -
    02 / xx xx xx xx (inside Czech Republic)
  • +420 2 / xx xx xx xx (outside Czech Republic
  • Satellite phone numbering plans

    Satellite phones are usually issued with numbers in a special country calling code. For example,Inmarsat satellite phones are issued with code +870,whileGlobal Mobile Satellite System providers,such asIridium,issue numbers in country code +881 ("Global Mobile Satellite System") or +882 ("International Networks"). Some satellite phones are issued with ordinary phone numbers,such asGlobalstar satellite phones issued with NANP telephone numbers.

    Inmarsat:+870: SNAC (Single Network Access Code
    ICO Global: +881 0,+881 1.
  • Ellipso: +881 2,+881 3.
  • Iridium: +881 6,+881 7.
    Globalstar: +881 8,+881 9.
  • Emsat: +882 13.
  • Thuraya: +882 16.
    ACeS: +882 20.
    Special services

    Somecountry 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
  • +800 – International Freephone (UIFN)
  • +808 – reserved forShared Cost Services
  • +878 –Universal Personal Telecommunications services
  • +881 –Global Mobile Satellite System
  • +882 – International Networks
  • +979 –International Premium Rate Service
  • +991 – International Telecommunications Public Correspondence Service trial (ITPCS)
  • +999 – reserved for potential disaster relief service
  • Numbering plans by global regions
    Telephone numbers in the Americas
    Telephone numbers in Oceania
    Telephone numbers in Europe
    Telephone numbers in Asia
    Telephone numbers in Africa
    Dial plan syntax

    The following syntax used to identify a dial plan in a digit map is adapted from [RFC 2705]page needed ].

    Dial Plan Syntax
    To specify a - Enter the following - Result
    Digit - 0 1 2 3 4 5 6 7 8 9 * - Identifies a specific digit (do not use #
    Range - [digit-digit] - Identifies any digit dialed that is included in the range
    Range - [digit-digit,digit] - Specifies a range as a comma separated list
    Wild card - x - x matches any single digit that is dialed
    Wild card - . - . matches an arbitrary number of digits
    Timer - T - Indicates that an additional time out period of 4 seconds should take place before automatic dialing starts
    Some dial plan examples using the above syntax look as follows:

    Dial Plan Syntax Examples
    For calls to - Users dial - Dial plan
    Internal Extension - a two digit number - xx
    Local Number - 9 (if required for an outside line) and then a seven digit number - 9xxxxxxxT
    Emergency - 911 - 911
    Local Operators - 9 (if required for an outside line) then 0 - 90T
    Long Distance - 9 (if required),1,area code and local number - 91xxxxxxxxxx
    International - 9 (if required),011,any number of additional digits - 9011x.T
    Numbering Plan Indicator

    The Numbering Plan Indicator (NPI) is a number which is defined in the ITU standardQ.713,paragraph 3.4.2.3.3,indicating the numbering plan of the attached telephone number. NPIs can be found inSCCP andSMS messages. As of 2004update - the following numbering plans and their respective Numbering Plan Indicator values have been defined:

    NPI - Description - Standard
    0 - unknown
    1 - ISDN Telephony - E.164
    2 - generic
    3 - data - X.121
    4 - telex - F69
    5 - maritime mobile - E.210 andE.211
    6 - land mobile - E.212
    7 - ISDN/mobile - E.214
    Closed telephone numbering plan
    List of North American Numbering Plan area codes for the U.S.,Canada,Caribbean,and Pacific Ocean islands
    List of United Kingdom dialling codes
    List of ITU-T Recommendation E.164 assigned country codes as of 15 April 2009
    List of ITU-T Recommendation E.164 Dialling Procedures as of 1 March 2010
    World Telephone Numbering Guide
    References
    Lincmad.com
  • Saunders,Amy (2009-05-16)."Cell-phone age turns the 614 into just numbers".The Columbus Dispatch . dispatch.com/live/content/local_news/stories/2009/05/16/0_AREA_CODES.ART_ART_05-16-09_A1_5JDSM84.html.
  • Note: From mobile phones the initial 1 is not required,but is recommended.
  • "Číslovací plán veřejných telefonních sítí" (in Czech) (PDF). Telekomunikační věstník (Czech Telecommunication Office) 9/2000 . 2000-09-25. ISSN 0862-724X. ctu.cz/1/download/cislovaci-plan-verejnych-telefonnich-siti_1114435245.pdf .Numbering Plan for Public Telephone Networks - annotation of the article in English - References from Telephone_numbering_plan"
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