E164numerojärjestelmä

E164numerojärjestelmä, often referred to as the E.164 standard, is an international numbering plan for public telecommunication networks. It defines a uniform structure for international telephone numbers, ensuring that each number is unique worldwide. The primary purpose of E.164 is to facilitate seamless international call routing and to prevent numbering conflicts between different countries.

The E.164 standard specifies that an international telephone number can have a maximum of 15 digits. This number is composed of a country code, followed by a national destination code (NDC), and finally a subscriber number (SN). The country code is assigned by the International Telecommunication Union (ITU) and can range from one to three digits. The NDC and SN are assigned by national telecommunication authorities within each country. Together, the NDC and SN form the subscriber's full national number.

For example, in the United States, the country code is 1. The NDC for New York City is 212, and a specific subscriber number would follow. When dialing internationally, a user first dials an international access code (e.g., 00 in many European countries, 011 in North America), then the country code, and finally the national number. The E.164 standard is crucial for the interoperability of global telecommunication systems, including traditional telephone networks and Voice over IP (VoIP) services. It provides a common framework that allows all connected networks to interpret and route calls correctly.