What is ENUM and what is it used for?

ENUM is a technology used to convert a traditional telephone number into a domain name that accords with the Internet DNS, namely an ENUM domain. By means of an ENUM domain, it is possible to provide various communications services to a number, such as Internet calls and e-mail. Even though ENUM supports different services, such as instant messaging and e-mail, it is primarily used for routing VoIP calls.

ENUM enables users to make Internet calls with traditional telephone numbers. This means that the call dialled by the user is routed to the recipient via the Internet instead of a fixed or mobile network. In practice, it is thus possible to make calls free of charge.

Calls are made just as before, that is, by dialling the desired telephone number (for instance, +358 40 730 6776). Then, the terminal equipment (or the network element of the telecommunications operator) transforms the dialled telephone number into an ENUM domain and contacts its own name server. The name server makes queries based on which it can give the VoIP address of the call recipient to the terminal equipment. Finally, the terminal equipment requests the recipient's IP address and, after receiving the address, contacts the call recipient directly.

ENUM technology also enables telecommunications operators to utilise the service efficiently in their own VoIP services.

ENUM has been defined in IETF's RFC 3761.