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
telephone numbers by making use of ENUM. Guidelines are proposed for
the authoring of the DNS records used by ENUM, and for client-side
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