Using E.164 numbers with the Session Initiation Protocol (SIP)

There are a number of contexts in which telephone numbers are employed by Session Initiation Protocol (SIP) applications, many of which can be addressed by ENUM. Although SIP was one of the primary applications for which ENUM was created, there is nevertheless a need to define procedures for integrating ENUM with SIP implementations. This document illustrates how the two protocols might work in concert, and clarifies the authoring and processing of ENUM records for SIP applications. It also provides guidelines for instances in which ENUM, for whatever reason, cannot be used to resolve a telephone number. This memo provides information for the Internet community.