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{{short description|ITU-T Recommendation for telephone numbering}}
{{For|the food additive E164|Saffron}}

{{Infobox technology standard
| title             = Recommendation ITU-T E.164
| long_name         = The international public telecommunication numbering plan
| status            = In force
| year_started      = 1984
| version           = (06/20)
| version_date      = June 2020
| organization      = [[ITU-T]]
| committee         = Study Group 2
| related_standards = [[E.123]], [[E.163]]
| domain            = [[telephony]]
| website           = https://www.itu.int/rec/T-REC-E.164/
}}
[[File:Phone_number_setup.png|thumb|right]]

'''E.164''' is an [[international standard]] ([[ITU-T]] Recommendation), titled ''The international public telecommunication numbering plan'', that defines a [[Telephone numbering plan|numbering plan]] for the worldwide [[public switched telephone network]] (PSTN) and some other data [[telecommunications network|networks]].

E.164 defines a general format for international [[telephone number]]s. Plan-conforming telephone numbers are limited to only digits and to a maximum of fifteen digits.<ref name=":0">{{Cite web|url=https://www.itu.int/rec/T-REC-E.164/|title=E.164 : The international public telecommunication numbering plan|website=www.itu.int|page=11|url-status=live|archive-url=https://web.archive.org/web/20191106122855/https://www.itu.int/rec/T-REC-E.164/|archive-date=2019-11-06|access-date=2019-11-12}}</ref> The specification divides the digit string into a country code of one to three digits, and the subscriber telephone number of a maximum of twelve digits.

==History==
Recommendation E.164 is part of a series of standards (E.160–E.169, ''Numbering plan of the international telephone service'') that represent a redefinition of the earlier specifications in Recommendation E.29 in the Red Books of 1960 and 1964. In 1960, an international numbering plan was defined for Europe and parts of western Asia, and some Mediterranean countries.<ref>{{cite book
|title=Recommendation E.29
|publisher=ITU
|author=C.C.I.T.T. IInd Plenary Assembly 1960
|location=New Delhi
|edition=Red Book Volume IIbis
|page=43
|date=September 1960
}}</ref> In 1964, E.29 was expanded with a global code system based on [[world numbering zones]]. In the 1968 White Book, the definition of country codes was relegated to ITU Recommendation E.161.  The first issue of E.164 was published in 1988 in Blue Book Fascicle II.2, under the title ''Numbering Plan for the ISDN Era''.

==Recommendations==
===E.163===
E.163 was the former [[ITU-T]] recommendation for describing [[telephone]] numbers for the [[public switched telephone network]] (PSTN). In the United States, this was formerly referred to as a ''directory number''. E.163 was withdrawn, and some recommendations were incorporated into revision 1 of E.164 in 1997.<ref>{{Cite web|url=https://www.itu.int/rec/T-REC-E.163|title=E.163 : Numbering plan for the international telephone service|website=www.itu.int|url-status=live|archive-url=https://web.archive.org/web/20190729130203/https://www.itu.int/rec/T-REC-E.163|archive-date=2019-07-29|access-date=2019-11-12}}</ref>

===E.164.1===
This recommendation describes the procedures and criteria for the reservation, assignment, and reclamation of E.164 country codes and associated ''identification code'' (IC) assignments.<ref>{{Cite web|url=https://www.itu.int/rec/T-REC-E.164.1|title=E.164.1 : Criteria and procedures for the reservation, assignment and reclamation of E.164 country codes and associated identification codes (ICs)|website=www.itu.int|url-status=live|archive-url=https://web.archive.org/web/20191112172208/https://www.itu.int/rec/T-REC-E.164.1|archive-date=2019-11-12|access-date=2019-11-12}}</ref> The criteria and procedures are provided as a basis for the effective and efficient utilization of the available E.164 numbering resources.

===E.164.2===
This recommendation contains the criteria and procedures for an applicant to be temporarily assigned a three-digit identification code within the shared E.164 country code [[+991|991]] for the purpose of conducting an international non-commercial trial.<ref>{{Cite web|url=https://www.itu.int/rec/T-REC-E.164.2|title=E.164.2 : E.164 numbering resources for trials|website=www.itu.int|url-status=live|archive-url=https://web.archive.org/web/20191112172324/https://www.itu.int/rec/T-REC-E.164.2|archive-date=2019-11-12|access-date=2019-11-12}}</ref>

===E.164.3===
This recommendation describes the principles, criteria, and procedures for the assignment and reclamation of resources within a shared E.164 country code for groups of countries.<ref>{{Cite web|url=https://www.itu.int/rec/T-REC-E.164.3|title=E.164.3 : Principles, criteria and procedures for the assignment and reclamation of E.164 country codes and associated identification codes for groups of countries|website=www.itu.int|url-status=dead|archive-url=https://web.archive.org/web/20191112172813/https://www.itu.int/rec/T-REC-E.164.3|archive-date=2019-11-12|access-date=2019-11-12}}</ref> These shared country codes will coexist with all other E.164-based country codes assigned by the ITU. The resource of the shared country code consists of a ''country code'' and a ''group identification code'' (CC + GIC) and provides the capability for a group of countries to provide telecommunication services within the group. The Secretariat of the ITU Standardization Sector ([[ITU-T]]), the Telecommunication Standardization Bureau (TSB) is responsible for the assignment of the CC + GIC.

==Numbering formats==
The E.164 recommendation provides the telephone number structure and functionality for five categories of telephone numbers used in international public [[telecommunications]].

For each of the categories, it details the components of the numbering structure and the digit analysis required for successful [[routing]] of calls. Annex A provides additional information on the structure and function of E.164 numbers. Annex B provides information on network identification, service parameters, calling/connected line identity, dialing procedures, and addressing for Geographic-based [[ISDN]] calls. Specific E.164-based applications which differ in usage are defined in separate recommendations.

The number categories are all based on a fifteen-digit numbering space. Before 1997, only twelve digits were allowed. The definition does not include any [[international call prefixes]], necessary for a call to reach international circuits from inside the country of call origination.

===Geographic areas===
{| class="wikitable"
|-
! Country Code
! National Destination Code 
! Subscriber Number
|- style="text-align:center;"
|| 1 to 3 digits
| colspan=2 | maximum 15 digits − number of digits in the country code
|-
| colspan="3" style="text-align:center;"| maximum 15 digits
|}

===Global services===
{| class="wikitable"
|-
! Country Code
! Global Subscriber Number
|- style="text-align:center;" 
|| 3 digits   
| maximum 12 digits
|- 
| colspan="2" style="text-align:center;"| maximum 15 digits
|} 

<ref name=":0" /> Figure 2

===Networks===
{| class="wikitable"
|-
! Country Code
! Identification Code
! Subscriber Number
|- style="text-align:center;" 
|| 3 digits
|| 1 to 4 digits
|| maximum 12 digits − number of digits in the identification code
|-
| colspan="3" style="text-align:center;"| maximum 15 digits
|}

===Groups of countries===
{| class="wikitable
! Country Code
! Group Identification Code
! Subscriber Number
|- style="text-align:center;" 
|| 3 digits
|| 1 digit
|| maximum 11 digits
|-
| colspan="3" style="text-align:center;"| maximum 15 digits
|}

===Trials===
{| class="wikitable"
|-
! Fixed code
! Trial Identification Code
! Subscriber Number
|- style="text-align:center;" 
|| 991
|| 1 digit
|| maximum 11 digits
|-
| colspan="3" style="text-align:center;"| maximum 15 digits
|}

==Uses of E.164 numbers==
E.164 numbers were originally defined for use in the worldwide [[public switched telephone network]] (PSTN). The early PSTN collected routing digits from users (e.g. on a dial pad), signaled those digits to each telephony switch, and used the numbers to determine how to ultimately reach the called party.

ITU-T [[E.123]] entitled ''Notation for national and international telephone numbers, e-mail addresses and web addresses'' provides guidance when printing E.164 telephone numbers. This format includes the recommendation of prefixing international telephone numbers with a plus sign ([[Plus and minus signs#Plus sign|+]]) and using only spaces for digit grouping.

The presentation of a telephone number with the plus sign ([[Plus and minus signs#Plus sign|+]]) indicates that the number should be dialed with an [[List of international call prefixes|international calling prefix]], in place of the plus sign. The number is presented starting with the [[telephone country code]]. This is called the ''globalized'' format of an E.164 number, and is defined in the Internet Engineering Task Force {{IETF RFC|2806}}.<ref>{{cite IETF|title=URLs for Telephone Calls|rfc=2806|section=2.2|date=April 2000|publisher=[[Internet Engineering Task Force|IETF]]|access-date=January 11, 2021}}</ref> The international calling prefix is a [[trunk code]] to reach an international circuit in the country of call origination.<ref>{{Cite book|url=https://books.google.com/books?id=iQBmBIBfWXEC&pg=PT172|title=Implementing Cisco Unified Communications Manager, Part 2 (CIPT2) Foundation Learning Guide: (CCNP Voice CIPT2 642-457)|last=Olsen|first=Chris|date=2011-08-01|publisher=Cisco Press|isbn=9780132312141|pages=172|language=en}}</ref>

===DNS Mapping of E.164 numbers===
{{main|Telephone number mapping}}
Some national telephone administrations and telephone companies have implemented an [[Internet]]-based database for their numbering spaces. E.164 numbers may be registered in the [[Domain Name System]] (DNS) of the [[Internet]] in which the second-level domain e164.arpa has been reserved for [[telephone number mapping]] (ENUM). In the system, any telephone number may be mapped into a [[domain name]] using a reverse sequence of subdomains for each digit. For example, the telephone number {{gaps|+1|999|555|0123}} translates to the domain name {{mono|3.2.1.0.5.5.5.9.9.9.1.e164.arpa}}. When a number is mapped, a DNS query may be used to locate the service facilities on the Internet that accept and process telephone calls to the owner of record of the number, using, for example, the [[Session Initiation Protocol]] (SIP), a call-signaling [[VoIP]] protocol whose [[SIP address]]es are similar in format (user@domain...) to e-mail addresses. This allows a direct, end-to-end Internet connection without passing through the public switched telephone network.

==See also==
*[[Carrier of record]]

==External sources==
* [https://www.itu.int/rec/T-REC-E.164/en ITU National Number Plans Reference]

==References==
{{Reflist}}

==External links==
* [https://www.itu.int/rec/T-REC-E.164 Text of the Recommendation, Amd. 1 and supplement 6 (E.164)]
* [https://www.itu.int/dms_pub/itu-t/opb/sp/T-SP-E.164D-2016-PDF-E.pdf List of ITU-T Recommendation E.164 assigned country codes as of 15 December 2016]
* [http://www.itu.int/dms_pub/itu-t/opb/sp/T-SP-E.164C-2011-PDF-E.pdf List of ITU-T Recommendation E.164 Dialling Procedures as of 15 December 2011]
* [https://www.itu.int/rec/T-REC-E.163 Numbering plan for the international telephone service (E.163) (incorporated in E.164)]
* {{usurped|1=[https://web.archive.org/web/20190626203635/http://www.wtng.info/ World Telephone Numbering Guide]}}


[[Category:Telephone numbers]]
[[Category:Identifiers]]
[[Category:ITU-T E Series Recommendations]]