What does E.164 phone number format mean?

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The E.164 phone number format refers to an international standard set by the International Telecommunication Union (ITU-T), specifically outlined in its Recommendation E.164, titled "The international public telecommunication numbering plan." This standard defines a global numbering plan for the worldwide public switched telephone network (PSTN) and other data networks, ensuring that every telephone number is unique and globally recognizable. The primary purpose of E.164 is to enable seamless and accurate routing of calls and messages across different countries and telecommunication networks.


An E.164 compliant phone number is structured to be unambiguous for automated systems and typically consists of three main parts:

The Plus Sign (+): This is the mandatory prefix that signals an international number. It instructs the dialing system that the digits immediately following constitute the country code for an international call, replacing the specific International Direct Dialing (IDD) prefixes that vary from country to country (e.g., '00' in much of Europe, '011' in North America). While the plus sign is crucial for representation, it's the signaling system that internally handles the conversion to the appropriate IDD prefix.


Country Code (CC): This is a 1 to 3 digit numerical code that chinese overseas australia data uniquely identifies a specific country or an integrated numbering plan area. For example, '1' is used for the North American Numbering Plan (including the US and Canada), '44' for the United Kingdom, and '880' for Bangladesh. The ITU-T is responsible for assigning these country codes.



National Significant Number (NSN): This is the remaining part of the phone number after the country code. The NSN identifies a specific subscriber within that country's telecommunication network. It often comprises a National Destination Code (NDC) – which might be an area code, city code, or mobile network code – followed by the Subscriber Number (SN) itself. A critical rule for the NSN when converting from a domestic format is to omit any leading zeros that are typically used for national long-distance dialing. For instance, if a number in Germany is dialed domestically as 030 12345678 (where 0 is the national prefix), its E.164 format would be +493012345678, with the leading '0' removed.


Key characteristics and benefits of E.164 format include:

Global Uniqueness: Each E.164 number is globally unique, preventing conflicts and ensuring that a call or message reaches its intended recipient anywhere in the world.
Standardized Length: An E.164 number, including the country code, has a maximum length of 15 digits. This consistent length aids in system design and database management.
Machine Readability: For optimal processing by telecommunication systems, E.164 numbers are ideally represented without any spaces, hyphens, parentheses, or other non-digit characters after the plus sign. While humans might add these for readability, they should be stripped for automated use.
Interoperability: By providing a common numbering plan, E.164 ensures seamless interoperability between different national and international telecommunication networks and services, including Voice over IP (VoIP), SMS, and over-the-top (OTT) communication apps like WhatsApp.
Scalability: The design allows for the growth of numbering plans within countries and the introduction of new services without breaking the international dialing framework.
In essence, the E.164 format is the backbone of international telecommunications, enabling accurate and efficient routing of communications across borders by providing a clear, unique, and machine-readable identification for every phone line globally.