E.164 is an international standard (ITU-T Recommendation), titled The international public telecommunication numbering plan, that defines a numbering plan for the worldwide public switched telephone network (PSTN) and some other data networks.
|the international public telecommunication numbering plan|
|Committee||Study Group 2|
|Related standards||E.123, E.163|
As defined by the ITU-T, the E.164 general format must contain only digits split as follows:
- Country code (1 to 3 digits)
- Subscriber number (max 12 digits)
Alternative formats (with area codes and country specific numbers) are available.
The title of the original version and first revision of the E.164 standard was Numbering Plan for the ISDN Era
The E.164 recommendation provides the telephone number structure and functionality for three categories of telephone numbers used in international public telecommunication:
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.
|National Destination Code||National (significant)|
|cc = 1 to 4 digits||maximum = 15 − cc = 11 to 14 digits|
|International public telecommunication number for geographic areas (maximum 15 digits)|
|Country Code||Global Subscriber Number|
|cc = 3 digits||maximum 12 digits|
|International public telecommunication number for global services (maximum 15 digits)|
 Figure 2
|Country Code||Identification Code||Subscriber Number|
|cc = 1 to 3 digits||x = 1 to 4 digits||maximum = 15 − (cc + x) = 8 to 13 digits|
|International public telecommunication number for networks (maximum 15 digits)|
Groups of countries
|Group Identification Code|
|cc = 1 to 3 digits||gic = 1 digit||maximum = 15 − (cc + gic) = 11 digits|
|International public telecommunication number for groups of countries (maximum 15 digits)|
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.
This recommendation describes the procedures and criteria for the reservation, assignment, and reclamation of E.164 country codes and associated identification code (IC) assignments. The criteria and procedures are provided as a basis for the effective and efficient utilization of the available E.164 numbering resources.
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 for the purpose of conducting an international non-commercial trial.
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. 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.
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 prefixing numbers with a plus sign (+) and including visual separators like hyphen (-). As the PSTN evolved a number of standards have been adopted that incorporate the ITU-T E.164 standard.
SIP Usage of E.164 Numbers
With the evolution of the Public switched telephone network from TDM Circuit Switching to IP Data Networks using Voice over IP, the IETF SIP protocol defined in the Internet Engineering Task Force RFC 3261 was introduced to setup sessions between users for voice, video, and multi-media.
The presentation of a number at the called (B-party) device is usually prefixed with the plus sign (+), indicating that the number includes the country calling code. Prefixing of the number with "+" is called the globalized format of an E.164 number and is defined in the Internet Engineering Task Force RFC 2806.
This is done by the B-party subscriber's network by usually looking at the NOA (Nature Of Address) field of the signaling messages or through other pattern based number analysis using rules derived from E.164. When dialing, the number must typically be prefixed with the appropriate international call prefix (in place of the plus sign), which is a trunk code to reach an international circuit from within the country of call origination.
DNS Mapping of E.164 Numbers
Some national telephone administrations and telephone companies have implemented an Internet-based database for their numbering spaces. E.164 numbers may be used 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 phone number may be mapped into a domain name using a reverse sequence of subdomains for each digit. For example, the telephone number +19995550123 translates to the domain name 18.104.22.168.22.214.171.124.9.9.1.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 addresses are similar in format (user@domain...) to e-mail addresses.
This allows a direct, end-to-end Internet connection without passing to the public switched telephone network (and back) and without incurring PSTN tolls.
As this is effectively a free call, there is little incentive for carriers to promote e164 DNS service. The e164.arpa domain is in production status as of 2013[update] only in a few European nations (Austria, Czech Republic, Finland, Germany, Ireland, Lithuania, Poland, Romania, Netherlands, United Kingdom). Australia conducted a trial in 2007 but then abandoned further support of .1.6.e164.arpa. Many nations have no .e164.arpa implementation active.
- "E.164 : The international public telecommunication numbering plan". www.itu.int. p. 11. Archived from the original on 2019-11-06. Retrieved 2019-11-12.
- "E.163 : Numbering plan for the international telephone service". www.itu.int. Archived from the original on 2019-07-29. Retrieved 2019-11-12.
- "E.164.1 : Criteria and procedures for the reservation, assignment and reclamation of E.164 country codes and associated identification codes (ICs)". www.itu.int. Archived from the original on 2019-11-12. Retrieved 2019-11-12.
- "E.164.2 : E.164 numbering resources for trials". www.itu.int. Archived from the original on 2019-11-12. Retrieved 2019-11-12.
- "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". www.itu.int. Archived from the original on 2019-11-12. Retrieved 2019-11-12.
- SIP: Session Initiation Protocol. IETF. June 2002. doi:10.17487/RFC3261. RFC 3261. Retrieved January 11, 2021.
- URLs for Telephone Calls. IETF. April 2000. sec. 2.2. doi:10.17487/RFC2806. RFC 2806. Retrieved January 11, 2021.
- Olsen, Chris (2011-08-01). Implementing Cisco Unified Communications Manager, Part 2 (CIPT2) Foundation Learning Guide: (CCNP Voice CIPT2 642-457). Cisco Press. p. 172. ISBN 9780132312141.
- "RIPE ENUM Working Group: Progress Matrix". Enumdata.org. Retrieved 26 October 2013.
- Russell Bryant; Leif Madsen; Jim Van Meggelen (2013-05-10). Asterisk: The Definitive Guide. p. 312. ISBN 9781449332464. Retrieved 2019-11-12.
- Text of the Recommendation, Amd. 1 and supplement 6 (E.164)
- Numbering plan for the international telephone service (E.163) (incorporated in E.164)
- World Telephone Numbering Guide