E.164

E.164
Maximilian Dörrbecker (Chumwa) · CC BY-SA 2.5 · source
Name	E.164
Caption	ITU-T recommendation for telephone numbering
Status	Active
Version	ITU-T E.164 (current)
Organization	International Telecommunication Union (ITU)
Domain	Public Switched Telephone Network, E.123

E.164 E.164 is an international telecommunication recommendation from the International Telecommunication Union that defines the international public telecommunication numbering plan used in the Public Switched Telephone Network and other networks. It prescribes a standardized numeric format for global telephone numbers to enable interoperability among national numbering plans such as those of the North American Numbering Plan, United Kingdom, Germany, France, Japan, and China. The recommendation underpins signaling systems including SS7, SIP, and interconnect arrangements used by carriers like AT&T, Vodafone, and Deutsche Telekom.

Overview

E.164 specifies a maximum length, structure, and allowed digits for international telephone numbers to ensure unique global reachability across operators including Telefónica, Orange S.A., T-Mobile, NTT, and Rogers Communications. It coordinates with regulatory authorities such as the Federal Communications Commission, Ofcom, ANATEL, BNetzA, and the European Commission on numbering resource administration. Implementations rely on signaling protocols developed by bodies like the Internet Engineering Task Force and the 3rd Generation Partnership Project. Major numbering databases and services such as ENUM, national numbering plans, and commercial numbering providers map E.164 addresses to services in frameworks used by companies like Google, Microsoft, and Twilio.

Numbering structure

E.164 numbers consist of a country code, national destination code, and subscriber number, aligning with numbering authorities such as the North American Numbering Plan Administration (NANPA) and national regulators like Ofcom and ANATEL. Country codes are allocated by the International Telecommunication Union and include codes for nations and regions such as United States, Canada, Russia, India, Brazil, and South Africa. National numbering plans by entities like Telekom Srbija, Telstra, BH Telecom, and MTN Group implement national destination codes and area codes consistent with E.164 constraints. The recommendation limits the international format to a maximum of 15 digits, a rule reflected in the numbering schemes of operators including Verizon Communications and Airtel.

Format and presentation

E.164 prescribes a presentation that commonly uses a leading plus sign followed by the international number, adopted by device manufacturers such as Nokia, Apple Inc., Samsung Electronics, and software platforms from Cisco Systems and Microsoft. The plus sign is processed by mobile networks and roaming systems administered by operators like Sprint Corporation and Vodafone to substitute appropriate international dialing prefixes like those used in United Kingdom or Australia. Standards documents such as E.123 and practices by organizations like GSMA and the 3GPP harmonize how E.164 numbers are displayed in user interfaces on devices from Motorola and Huawei Technologies.

International routing and dialing

Routing of E.164 numbers across international, national, and IP networks involves signaling systems including SS7, SIGTRAN, and SIP, and relies on interconnect agreements among carriers such as BT Group, Telefónica, China Mobile, and SK Telecom. Number portability regimes run by administrating bodies like Ofcom and Federal Communications Commission affect local routing and require coordination with clearinghouses and platforms like ENUM and national numbering databases. Emergency and roaming arrangements coordinate E.164 with services like E112 and international emergency standards followed in jurisdictions including European Union member states and Japan.

Implementation and compliance

Operators, regulators, and equipment vendors implement E.164 through number allocation, routing policies, and interoperability testing managed by organizations including ITU-T, GSMA, ETSI, and national regulators such as BNetzA and Anatel. Compliance processes involve audits, numbering resource management, and updates to interconnection frameworks used by carriers like CenturyLink, Tele2, and Claro. VoIP service providers and cloud communications platforms such as Vonage, Twilio, and RingCentral integrate E.164 into billing, fraud prevention, and lawful intercept systems coordinated with authorities like the Federal Bureau of Investigation and national communications commissions.

History and revisions

E.164 evolved from earlier international telephony coordination conducted by the International Telegraph and Telephone Consultative Committee and developments in the Post-World War II expansion of international services. Revisions and amendments have been issued by the ITU-T Study Group 2 and related working parties alongside contributions from major carriers and manufacturers including Bell Labs, Ericsson, and Alcatel-Lucent. The recommendation has been updated to address mobile telephony, VoIP, and ENUM mapping, reflecting technological shifts driven by entities such as 3GPP, IETF, and multinational operators including British Telecom and NTT Communications.

Category:Telecommunication standards