What is Enum? > How it works

The "ENUM" standard links telephone numbers with internet addresses using the DNS (Domain Name System). For this purpose a globally unique domain name is assigned to each telephone number as follows:

1. +353 1 2365400 (Specification of the complete telephone number)
2. 35312365400 (Removal of all characters except numbers)
3. 00456321353 (Reversal of the number order)
4. 0.0.4.5.6.3.2.1.3.5.3 (Insertion of dots between the numbers)
5. 0.0.4.5.6.3.2.1.3.5.3.e164.arpa (Adding the global ENUM domain e164.arpa)

Special DNS entries ("NAPTR-Records") are stored for this domain name, which specify the services available for a telephone number. According to the above example the DNS query returns the following entries:

0.0.4.5.6.3.2.1.3.5.3.e164.arpa NAPTR 100 10 "u" "E2U+smtp" "!^.*$!mailto:info@enum.ie!" .
0.0.4.5.6.3.2.1.3.5.3.e164.arpa NAPTR 100 10 "u" "E2U+web:http" "!^.*$!www.enum.ie!" .

In the example above, the telephone number +353 1 2365400 is linked with the email address mailto:info@enum.ie as well as the web address http://www.enum.ie/. Both addresses represent an alternative communication possibility in addition to the "classical" phone call. This information allows an email message to be sent using the specified telephone number and in addition, the specified website can be displayed on the hardware device (as long as this is supported). As a matter of course, the procedure as shown above is not performed manually by the user. Similar to conventional telephones the user only enters the phone number, and the necessary technical processes are carried out "in the background" by the end device or by the service provider.