ITU-T Recommendation E.164
E.164 defines a general format for international telephone numbers
. Plan-conforming numbers are limited to a maximum of 15 digits, excluding the international call prefix
The presentation of a number at the B-party device is usually prefixed with the plus sign (+
), indicating that the number includes the country calling code
. This is done by the B-party subscribers network by usually looking at the NOA (Nature Of Address) field of the signaling messages. 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.
As described in by the ITU, 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+966502001668
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.
International public telecommunication number for geographic areas (maximum 15 digits)
International public telecommunication number for global services (maximum 15 digits)
International public telecommunication number for networks (maximum 15 digits)
Groups of countries
This recommendation describes the procedures and criteria for the reservation, assignment, and reclamation of E.164 country codes and associated identification code
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.
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 126.96.36.199.188.8.131.52.9.9.1.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 only in a few European nations (Austria
, Czech Republic
, United Kingdom
conducted a trial in 2007, but then abandoned further support of .1.6.e164.arpa
. Many nations have no .e164.arpa
- ^ a b "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.
- ^ 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.
- ^ "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.
- ^ "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.
Last edited on 18 June 2021, at 02:56
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