"This document defines a new parameter ""enumdi"" for the ""tel"" Uniform Resource Identifier (URI) to support the handling of ENUM queries in Voice over Internet Protocol (VoIP) network elements. A VoIP network element may receive a URI containing an E.164 number@ where that URI contains an ""enumdi"" parameter. The presence of the ""enumdi"" parameter indicates that an ENUM query has already been performed on the E.164 number by a previous VoIP network element. Equally@ if a VoIP network element sends such a URI@ it asserts that an ENUM query has been carried out on this number."
RFC 4759-2006 history
2006RFC 4759-2006 "The ENUM Dip Indicator Parameter for the ""tel"" URI"