E.164

What Does E.164 Mean?

E.164 is an International Telecommunications Union for Telecommunications (ITU-T) recommendation, which defines international public telecommunication numbering plans used in public switched telephone networks and other data networks. They also define the telephone number formats. E.164 numbers have a maximum of 15 digits and are written with a + prefix. An international call prefix is used to dial this numbers from normal fixed line phones.

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Techopedia Explains E.164

E.164 is an international public numbering plan developed by the ITU. It is developed for telephone systems in which each assigned number has country codes, national destination code and a subscriber number. There are up to 15 digits in an E.164 number.

The E.164 number is designed to include the necessary information to successfully route calls to individual subscribers on nation’s public telephone network. The conditions involved in E.164 numbering plan are:

  • The telephone numbers can hold maximum of 15 digits.
  • The first part of telephone numbers are country codes.
  • The second part is a national destination code.
  • The last part includes the subscriber number.
  • The second and third parts together are called the national number.

The combined length of significant numbers cannot exceed 15-n where n is the number of digits in the country code. This permits every country to decide the number of digits to be present in their national destination code and subscriber number. The 15 digit numbers allow an estimated 100 trillion permutations.

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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.