Translating the Telephone Number

A telephone number is translated into an Internet address using the following steps:

1. The number is first stored in the following format, [phone]. 1 is the country code for the United States, Canada, and the seventeen other countries that make up the North American Numbering Plan (NANP). The + indicates that the number is a complete, international E.164 telephone number.
2. All characters are removed except for the digits. For example, 12025551234.
3. The order of the digits is reversed. For example, 43215552021. The telephone number is reversed because DNS reads addresses from right to left, from the most significant to the least significant character. Dots are placed between each digit. Example: 4.3.2.1.5.5.5.2.0.2.1. In DNS terms, each digit becomes a zone. Authority can be delegated to any point within the number.
4. A domain (for example, e164.arpa) is appended to the end of the numbers in order to create a FQDN. For example,4.3.2.1.5.5.5.2.0.2.1.e164.arpa.
5. The domain name is queried for the resource records that define URIs necessary to access SIP-based VoIP.

   Once the authoritative name server for that domain name is found, ENUM retrieves relevant records and uses that data to complete the call or service. For example, the number 12025551234 returns sip:[e-mail].