E2U
E.164 to URI
The ENUM (Electronic Number) working group of the IETF defined a name space in which E.164 format telephone numbers may be resolved into URI (Uniform Resource Indicator) for use in IP environments. E2U is a NAPTR (Naming Authority Pointer Record) standardized resolution service, often encountered as part of the “E2U+SIP” enumservice for SIP (Session Initiation Protocol).