ENUM is Dynamic Delegation Discovery System (DDDS) application that maps E.164 numbers into Uniform Resource Identifiers. In other words, it is a means of using DNS in order to translate a phone number into an IP address.

However, ENUM goes further than simply mapping a phone number into an IP address. ENUM allows a phone number to be mapped to multiple services. For example, a search in DNS for a phone number may return services for certain services (e.g., H.323, SIP, and e-mail). The number and types of services are not restricted and new services may be defined in the future.

ENUM does not presently provide users with the ability to direct calls or queries to different locations based on the time of the day. However, it does have a means of providing a preferred order of contact. For example, if one prefers to be reached by e-mail, rather than phone, it is possible to indicate that preference.

ENUM is defined in RFC 3761 and relies on DDDS, which is defined in RFC 3401, RFC 3402, RFC 3403, RFC 3404, and RFC 3405. ENUM also utilizes DNS records called NAPTR records, as defined in RFC 2915.

Resources: ENUM Forum, ITU

See Also: Voice over IP (VoIP), H.323, Session Initiation Protocol (SIP)