The big achievement of the Domain Name System (DNS) is that it greatly simplifies what would otherwise be a painstaking process using unwieldy IP numbers. By assigning each service to a domain, it is possible to address it through a meaningful name. The service for assigning names is available across networks. This has been by no means the least significant factor that has contributed to making the Internet so popular for broad sections of the population.
So why then should ENUM now bring numbers back to the setting up of communication links?
The first point to make is that that has so far been the usual way to make telephone calls! Modern VoIP communication protocols, such as the Session Initiation Protocol (SIP), do, however, use addresses that are similar to e-mail, which, in turn, are much easier to manage. If, however, the only device available for calling communication services is a simple telephone set (with the numeric keypad as its only input device) then there is no other choice than to use numeric addresses, i.e. telephone numbers. The function of ENUM is to provide a technology that enables Internet communication and conventional telephone services to be linked to one another. The use of ENUM makes it simple for a subscriber in the conventional telephone network to call another subscriber in the Internet.
Any user who happens to have a more sophisticated terminal device can also call their communication partner by means of a simple mnemonic address, such as sip:firstname.lastname@example.org.
In future, the simple way of addressing all individually allocated services via a single contact address might be through a domain with a format like firstname.surname.domain.TLD. An inquiry to the DNS would then return a NAPTR Resource Record. This would contain the user's telephone number as well as his/her other addresses for individual services. The application making the inquiry would then be able select one of these addresses and use it for the communication (telephone call, e-mail, http query and so on and so forth).