E.164 is an

international standard international standard is a technical standard developed by one or more international standards organizations. International standards are available for consideration and use worldwide. The most prominent such organization is the International Or ...

(

ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...

Recommendation), titled ''The international public telecommunication numbering plan'', that defines a

numbering plan A telephone numbering plan is a type of numbering scheme used in telecommunication to assign telephone numbers to subscriber telephones or other telephony endpoints. Telephone numbers are the addresses of participants in a telephone network, reac ...

for the worldwide

public switched telephone network The public switched telephone network (PSTN) provides Communications infrastructure, infrastructure and services for public Telecommunications, telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that ...

(PSTN) and some other data

networks Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...

. E.164 defines a general format for international

telephone number A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices f ...

s. Plan-conforming telephone numbers are limited to only digits and to a maximum of fifteen digits. 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. Alternative formats (with area codes and country specific numbers) are available. Any country-specific

international call prefix An international call prefix, international dial-out code or international direct dial code (IDD code) is a trunk prefix that indicates an International call, international phone call. In the dialling sequence, the prefix precedes the country call ...

es are not contained in the specification. The title of the original version and first revision of the E.164 standard was ''Numbering Plan for the ISDN Era''

Recommendations

E.163

E.163 was the former

recommendation for describing

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

numbers for the

(PSTN). In the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

, 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.

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. 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 for the purpose of conducting an international non-commercial trial.

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. 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 (

), 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

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

. For each of the categories, it details the components of the numbering structure and the digit analysis required for successful

routing Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone netw ...

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 Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Wo ...

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

Global services

Figure 2

Networks

Groups of countries

Trials

Uses of E.164 Numbers

E.164 numbers were originally defined for use in the worldwide

(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 E.123 is an international standard by the standardization union (ITU-T), entitled ''Notation for national and international telephone numbers, e-mail addresses and Web addresses''. It provides guidelines for the presentation of telephone numbers, e ...

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 ( +) and including visual separators such as the hyphen ( -). The presentation of a telephone number with the plus sign ( +) indicates that the number should be dialed with an international calling prefix, in place of the plus sign. The number is presented starting the

country calling code Country calling codes or country dial-in codes are telephone number prefixes for reaching telephone subscribers in the networks of the member countries or regions of the International Telecommunication Union (ITU). The codes are defined by the ...

. This is called the ''globalized'' format of an E.164 number, and is defined in the Internet Engineering Task Force RFC 2806. The international calling prefix is a

trunk code A trunk prefix is a digit sequence to be dialed before a telephone number to initiate a telephone call for the purpose of selecting an appropriate telecommunications circuit by which the call is to be routed. Making a domestic (national) telephone ...

to reach an international circuit in the country of call origination.

DNS Mapping of E.164 Numbers

Some national telephone administrations and telephone companies have implemented an

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

-based database for their numbering spaces. E.164 numbers may be registered in the

Domain Name System The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned to ...

(DNS) of the

in which the second-level domain e164.arpa has been reserved for

telephone number mapping Telephone number mapping is a system of unifying the international telephone number system of the public switched telephone network with the Internet addressing and identification name spaces. Internationally, telephone numbers are systematically ...

(ENUM). In the system, any telephone number may be mapped into a

domain name A domain name is a string that identifies a realm of administrative autonomy, authority or control within the Internet. Domain names are often used to identify services provided through the Internet, such as websites, email services and more. As ...

using a reverse sequence of subdomains for each digit. For example, the telephone number translates to the domain name . 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 The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating communication sessions that include voice, video and messaging applications. SIP is used in Internet telephony, in private IP telepho ...

(SIP), a call-signaling

VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

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 through the public switched telephone network.

References

{{Reflist

External links

Text of the Recommendation, Amd. 1 and supplement 6 (E.164)

List of ITU-T Recommendation E.164 assigned country codes as of 15 December 2016
*
List of ITU-T Recommendation E.164 Dialling Procedures as of 15 December 2011

Numbering plan for the international telephone service (E.163) (incorporated in E.164)

World Telephone Numbering Guide
Telephone numbers Identifiers ITU-T E Series Recommendations