Using E.164 numbers with the Session Initiation Protocol (SIP)
RFC 3824

Network Working Group                                        J. Peterson
Request for Comments: 3824                                        H. Liu
Category: Informational                                            J. Yu
                                                                 NeuStar
                                                             B. Campbell
                                                             dynamicsoft
                                                               June 2004

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

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   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.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Handling Telephone Numbers in SIP  . . . . . . . . . . . . . .  3
   4.  Design Principles  . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Authoring NAPTR Records for SIP  . . . . . . . . . . . . . . .  6
       5.1.  The Service Field  . . . . . . . . . . . . . . . . . . .  6
       5.2.  Creating the Regular Expression: Matching  . . . . . . .  6
       5.3.  Creating the Regular Expression: The URI . . . . . . . .  7
       5.4.  Setting Order and Preference amongst Records . . . . . .  8
       5.5.   Example of a Well-Formed ENUM NAPTR Record Set for SIP.  8
   6.  Processing ENUM Records  . . . . . . . . . . . . . . . . . . .  8
       6.1.  Contending with Multiple SIP records . . . . . . . . . .  8

Peterson, et al.             Informational                      [Page 1]
RFC 3824                     SIPPING E.164                     June 2004

       6.2.  Processing the Selected NAPTR Record . . . . . . . . . .  9
   7.  Compatibility with RFC 3761. . . . . . . . . . . . . . . . . . 10
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
       9.1.  Normative References . . . . . . . . . . . . . . . . . . 11
       9.2.  Informative References . . . . . . . . . . . . . . . . . 12
   A.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15
       Full Copyright Statement . . . . . . . . . . . . . . . . . . . 16

1.  Introduction

   ENUM (E.164 Number Mapping, RFC 3761 [1]) is a system that uses DNS
   (Domain Name Service, RFC 1034 [4]) in order to translate certain
   telephone numbers, like '+12025332600', into URIs (Uniform Resource
   Identifiers, RFC 2396 [9]), like 'sip:user@sipcarrier.com'.  ENUM
   exists primarily to facilitate the interconnection of systems that
   rely on telephone numbers with those that use URIs to route
   transactions.  E.164 [10] is the ITU-T standard international
   numbering plan, under which all globally-reachable telephone numbers
   are organized.

   SIP (Session Initiation Protocol, RFC 3261 [2]) is a text-based
   application protocol that allows two endpoints in the Internet to
   discover one another in order to exchange context information about a
   session they would like to share.  Common applications for SIP
   include Internet telephony, instant messaging, video, Internet
   gaming, and other forms of real-time communications.  SIP is a
   multi-service protocol capable of initiating sessions involving
   different forms of real-time communications simultaneously.

   The most widespread application for SIP today is Voice-over-IP
   (VoIP).  As such, there are a number of cases in which SIP
   applications are forced to contend with telephone numbers.
   Unfortunately, telephone numbers cannot be routing in accordance with
   the traditional DNS resolution procedures standardized for SIP (see
   [14]), which rely on SIP URIs.  ENUM provides a method for
   translating E.164 numbers into URIs, including potentially SIP URIs.
   This document therefore provides an account of how SIP can handle