Frequently Asked Questions

• What is ENUM?
• How does ENUM work?
• What are NAPTR records?
• What is e.164?
• What is e164.arpa?

What is ENUM?

ENUM is the convergence of communications technologies into one architecture. ENUM is a simple, but powerful protocol that maps numbers to Internet domain names.

By using the domain name system (DNS), a single number can be used for multiple communications technologies such as telephone, email, fax, text and voice messaging, web sites and more. ENUM promises easy and unified communication, no matter which network or device is used.

How does ENUM work?

ENUM routing can be broken into 4 steps as follows:

1. Remove all non-digit characters from the input string. Example: "+61.397831800" produces "61397831800"
2. Place dots (".") between each digit. Example: 6.1.3.9.7.8.3.1.8.0.0
3. Reverse the order of the digits. Example: 0.0.8.1.3.8.7.9.3.1.6
4. Append the string ".e164.arpa" to the input. Example: 0.0.8.1.3.8.7.9.3.1.6.e164.arpa

From this point, ENUM works in the same way as a domain name, using the DNS. When the communication request finds the authoritative name server for the ENUM domain, the associated zone file uses NAPTR records to direct the communication request to the appropriate service.

What are NAPTR records?

A NAPTR (Naming Authority Pointer Resource Record) is an entry in the Domain Name System (DNS) that contains rules for dealing with DNS requests. The result is returned to the application making the request.

For resolving ENUM, this means that a request about an ENUM domain is handled according to the appropriate rules and answered with a URI (Uniform Resource Identifier). This URI provides the output address and the protocol to be used for further communication.

By using the domain name system (DNS), a single number can be used for multiple communications technologies such as telephone, email, fax, text and voice messaging, web sites and more. ENUM promises easy and unified communication, no matter which network or device is used.

What is e.164?

E.164 is a recommendation issued by the ITU-T (E.164 02/05) for the international public telecommunication numbering plan. Recommendation E.164 provides the number structure and functionality of numbers used for international public telecommunication.

The section of the E.164 recommendation that relates to ENUM specifies that numbers can be used for communication only if it comprises of a one to three digit country code followed by an optional regional number, followed by the subscriber number. For example, Australia has the coutry code 61, and the number for Instra is +61 3 97831800.

What is e164.arpa?

e164.arpa is the designated root for ENUM domains and is operated by RIPE NCC. Within the e164.arpa root, all e164 country codes have a national-level domain relating to their code. For example:

.9.4.e164.arpa represents Germany (+49)
.1.6.e164.arpa represents Australia (+61)
.1.e164.arpa represents the United States of America (+1)

National-level e164 registries subsquently delegate zones under their country code to carriers, ENUM registrars, and other operators running DNS servers.