Telephone numbering plan

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A telephone numbering plan is a plan for allocating telephone number ranges to countries, regions, areas and exchanges and to non-fixed telephone networks such as mobile phone networks. A typical dialed telephone number comprises digits that need not always be dialed (codes) and digits that must always be dialed (local number).

Contents

[edit] Structure

The structure is:

  • Access code (either international or national) - only necessary when dialing international and "national" (non-local domestic) calls. The national access code is often quoted as if it were part of the telephone number. One of these access codes must be dialed from mobile phones. The most common national access code is "0", and the most common international access code "00"; in the United States and Canada, however, "1" and "011" are used, respectively.
  • Country code - only necessary when dialing to phones in other countries. 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"). In international usage, telephone numbers are typically quoted with the country code preceded by a "+", and spaces in place of hyphens (e.g. "+XX YYY ZZZ ZZZZ"). (On GSM networks, "+" is an actual character that may be used internally as the international access code, rather than simply being a convention.)
  • Area code - only necessary dialed from outside the code area, from mobile phones, and (especially within North America) from within overlay plans. Area codes usually indicate geographical areas within one country that are covered by perhaps hundreds of telephone exchanges. It must usually be preceded in the dial string by either the national access code or the international access code and country code. Non-geographical numbers, as well as mobile telephones outside of the United States and Canada, do not strictly speaking have an area code even though they are usually written as if they do.
  • Local number - must always be dialed in its entirety. The first few digits in the local number typically indicate smaller geographical areas or individual telephone exchanges. In mobile networks they indicate the (original) network provider. Callers from a number with a given area/country code usually do not need to include this particular area/country code in the number dialed, which enables shorter 'dial strings' to be used. This is an issue when the number must be keyed by hand, but where the dialing is automated (increasingly common) it is not an issue - and it is arguably better to include the full number with access codes in devices that dial automatically.

[edit] Standards

Although the International 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 the United States, Canada, and other countries and territories participating in the North American Numbering Plan.

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

Generally the area codes determine the cost of a call. Calls within an area code and often a small group of adjacent or overlapping area codes are normally charged at a lower rate than outside the area. Special area codes are generally used for free, 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. Israel), calls are charged at the same rate regardless of area and in others (e.g. the UK) an area code is occasionally treated as two parts with different rates.

[edit] Open dialing plans

An open dialing plan is one in which there are different dialing arrangements for local and long distance telephone calls. This means that to call another number within the same city or area, callers need only dial the number, but for calls outside the area, an area code is required. 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 Amsterdam in the Netherlands for example:

xxx xxxx (within Amsterdam- no area code required)
(020) xxx xxxx (outside Amsterdam)  
+31 20 xxx xxxx (outside the Netherlands)

In the United States, Canada, and other countries or territories using the North American Numbering Plan (NANP), the trunk code is '1', which is also (by coincidence) the country calling code. To call a number in San Francisco, the dialing procedure will vary:

xxx xxxx (local calls, no area code required)
1 415 xxx xxxx (outside San Francisco)
415 xxx xxxx (mobile phones within NANP)
+1 415 xxx xxxx (outside NANP)

However, in parts of North America, especially where a new area code overlays an older area code, dialing 1 + 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 that the trunk code is not necessary. (Most mobile phones today can be programmed to automatically prepend 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.)

Open and closed dialing plan 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.

[edit] Closed dialing plans

A closed numbering plan is one in which the subscriber's number is a standard length, and a closed dialing 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 in Norway before 1992, 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, eg:

22xx xxxx     (within Norway - including Oslo)   
+47 22xx xxxx (outside Norway)

In other countries, such as France, Belgium, Switzerland, and South Africa, the trunk code is retained for domestic calls, whether local or national, eg:

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)

While the use of full national dialing is less user-friendly than only using 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 in Prague Czech Republic can now be displayed as:

+420 2xx xxx xxx
formerly:[1]
02/xx xx xx xx  (inside Czech Republic) 
+420 (0)2/xx xx xx xx (outside Czech Republic)

[edit] 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 codes +870 through +874, while Iridium satellite phones are issued with codes +881 6 and +881 7. Some satellite phones are issued with ordinary phone numbers, such as Globalstar satellite phones issued with U.S. telephone numbers.

+870: SNAC (Single Network Access Code)
+871: Atlantic Ocean Region – East (AOR-E),
+872: Pacific Ocean Region (POR)
+873: Indian Ocean Region (IOR)
+874: Atlantic Ocean Region – West (AOR-W)

[edit] Special services

Some country calling codes are issued for special services, or for international/inter regional zones.

  • +388 – shared code for groups of nations
+388 3 – European Telephony Numbering Space - Europe-wide services

[edit] Numbering plans by global regions

[edit] References

  1. ^ (25 September 2000) "Číslovací plán veřejných telefonních sítí" (PDF). Telekomunikační věstník 9/2000. ISSN 0862-724X. Retrieved on 2006-10-13. (in Czech language)
    Numbering Plan for Public Telephone Networks - annotation of the article in English

[edit] External links

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