400-051: CCIE Collaboration Exam - Cisco

A.

E.164 defines a general format for international telephone numbers.

Plan-conforming numbers are limited to a maximum of 15 digits.

The presentation of numbers is usually prefixed with the character + (plus sign), indicating that the number includes the international country calling code (country code), and must typically be prefixed when dialing with the appropriate international call prefix, which is a trunk code to reach an international circuit from within the country of call origination.

ITU-T Recommendation E.164 defines the international public telecommunication numbering plan, which is used to assign unique telephone numbers to each telecommunications network worldwide. In this plan, a numeric geographic area address (NGAA) is a series of digits used to identify a geographic area within a country.

The maximum length of an NGAA in ITU-T Recommendation E.164 is 15 digits. This limit includes both the country code and the area code. The country code is typically one to three digits long, while the area code can be up to five digits long. The remaining digits are used for the local subscriber number.

For example, in the United States, the NGAA for New York City is 212, which is a three-digit area code. The local subscriber number for a specific telephone line within the 212 area code can be up to seven digits long, making the total length of the NGAA 10 digits.

It is important to note that the maximum length of an NGAA can vary depending on the country and the specific numbering plan in use. However, the limit of 15 digits specified in ITU-T Recommendation E.164 is widely recognized as a standard maximum length for NGAAs.