What Is ENUM?
Electronic Numbering (ENUM), as defined in RFC 3761, is a relatively simple protocol involving two core concepts:
- the process of creating a domain name from a TN and resolving it to an Internet address (a uniform resource identifier, or URI) using DNS technology
- the hosting of ENUM domain names in the e164.arpa domain
For example, the telephone number +1 (202) 555-1212 will be converted into the ENUM domain name 2.1.2.1.5.5.5.2.0.2.1.e164.arpa. A DNS query to that domain name will ultimately resolve to one or more DNS records (NAPTR records), which will provide a URI. The domain name 2.1.2.1.5.5.5.2.0.2.1.e164.arpa may resolve to the SIP URI sip:12025551212@voipcarrier.net. The SIP proxy service will then use the URI to establish a session between the originating SIP user and the terminating SIP user.
Telephone country codes are delegated from the domain e164.arpa. Country Code 1 (the country code for the United States, Canada and 17 Caribbean countries) is designated by the domain 1.e164.arpa. Because the use of telephone numbers is regulated both globally and within each country, the process of creating and delegating these domains requires the involvement and approval of regulatory bodies.
