ENUM WG J. Peterson
Internet-Draft NeuStar
Expires: August 25, 2003 February 24, 2003
Enumservice Registration for Presence Services
draft-peterson-enum-pres-00
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document registers an ENUM service for presence services (as
described in RFC2778 [3]) pursuant to the guidelines in RFC2916bis
[2]. Specifically, this document focuses on provisioning pres URIs
in ENUM.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. ENUM Service Registration . . . . . . . . . . . . . . . . . . . 3
3. Presence for E.164 numbers . . . . . . . . . . . . . . . . . . . 4
4. The 'E2U+pres' enumservice . . . . . . . . . . . . . . . . . . . 4
5. Example of E2U+pres enumservice . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
A. To Do . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
ENUM (E.164 Number Mapping, RFC2916 [1]) is a system that uses DNS
(Domain Name Service, RFC1034 [9]) to translate telephone numbers,
like '+12025332600', into URIs (Uniform Resource Identifiers, RFC2396
[10]), like 'pres:user@host.com'. ENUM exists primarily to
facilitate the interconnection of systems that rely on telephone
numbers with those that use URIs to route transactions. ENUM is
currently under revision in RFC2916bis [2]; this document applies to
the revised version of ENUM described in the work-in-progress.
Presence is a service defined in RFC2778 [3] that allows users of a
communications service to monitor one another's availability and
disposition in order to make decisions about communicating. Presence
information is highly dynamic, and generally characterizes whether a
not a user is online or offline, busy or idle, away from
communications devices or nearby, and the like.
The IMPP WG of the IETF has a defined a generic URI used to identify
a presence service for a particular resource: the 'pres' URI scheme
(defined in CPP [5]). This document describes an enumservice for
advertising presence information associated with an E.164 number.
2. ENUM Service Registration
As defined in [2], the following is a template covering information
needed for the registration of the enumservice specified in this
document.
Service Name: "E2U+pres"
URI Scheme(s): "pres:"
Functional Specification: see Section 4
Security considerations: see Section 6
Intended usage: COMMON
Author: Jon Peterson (jon.peterson@neustar.biz)
Any other information that the author deems interesting: See
Section 3
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3. Presence for E.164 numbers
This document specifies an enumservice field that allows presence
information to be provided for an E.164 number. This may include
presence states associated with telephones, or presence of non-
telephony communications services advertised by ENUM.
Endpoints that participate in a presence architecture are known
(following the framework in RFC2778 [3]) as watchers and
presentities. Watchers subscribe to the presence of presentities,
and are notified when the presence of a presentity changes. Watchers
generally monitor the presence of a group of presentities with whom
they have an ongoing association. As an example, consider a way that
this might apply a telephony service. Most cellular telephones today
have an address-book like feature, a small database of names and
telephone numbers. Such a telephone might act as a watcher,
subscribing to the presence of some or all of the telephone numbers
in its address book. The display of the telephone might then show
its user, when a presence-enabled telephone number is selected, the
availability of the destination. With this information, user might
change their calling habits to correspond better to the availability
of their associates.
The presence information that is shared varies by communications
service. The IETF IMPP WG has defined a Presence Information Data
Format (or PIDF [7]) for describing the presence data associated with
a presentity. The baseline PIDF specification declares only two
presence states: OPEN and CLOSED (these terms are defined in RFC2778
[3]); the former suggests that the destination resource is able to
accept communication requests, the latter that it is not. These two
states provide useful but rudimentary insight into the communications
status of a presentity; for that reason, PIDF is an extensible
format, and new sorts of status can be defined for specific
communications services. For example, a telephony-based presence
service might define a status corresponding to 'busy'. Extending
PIDF for telephony services is however outside the scope of this
document.
4. The 'E2U+pres' enumservice
Traditionally, the services field of a NAPTR record (as defined in
[14]) contains a string that is composed of two subfields: a
'protocol' subfield and a 'resolution service' subfield. ENUM in
particular defines an 'E2U' (E.164 to URI) resolution service. This
document defines an 'E2U+pres' enumservice for presence.
The scheme of the URI that will appear in the regexp field of a NAPTR
record using the 'E2U+pres' enumservice will be the 'pres' URI
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scheme. There are, however, other URI schemes that can be used to
identify presence services. The purpose of a pres URI is to provide
a generic way of locating a presence service. Techniques for
dereferencing the pres URI scheme to locate a presence service are
given in [6].
The 'pres' URI scheme does not identify any particular protocol that
will be used to handle presence operations (such as subscriptions and
notifications). Rather, the mechanism in [6] details a way to
discover whether or not the presence protocol(s) supported by the
watcher is/are also supported by the presentity. SIP [8] is one
protocol that can be used to convey presence information and manage
subscriptions/notifications.
5. Example of E2U+pres enumservice
The following is an example of the use of the enumservice registered
by this document in a NAPTR resource record.
$ORIGIN 0.0.6.2.3.3.5.2.0.2.1.e164.arpa.
IN NAPTR 100 10 "u" "E2U+pres" "!^.*$!pres:jon.peterson@neustar.biz!" .
6. Security Considerations
DNS does not make policy decisions about the records that it shares
with an inquirer. All DNS records must be assumed to be available to
all inquirers at all times. The information provided within an ENUM
record set must therefore be considered to be open to the public -
which is a cause for some privacy considerations.
However, revealing a pres URI in and of itself is unlikely to
introduce many privacy concerns (although depending on the structure
of the URI, it might reveal the full name or employer of the target).
There are more serious privacy concerns associated with the
unauthorized distribution of presence information. For that reason,
presence protocols have a number of security requirements (detailed
in RFC2779 [4]) that call for authentication of watchers, integrity
and confidentiality properties, and similar measures to prevent abuse
of presence information. Any presence protocol that is used in
conjunction with the 'pres' URI scheme is required to meet these
requirements by the work in the IETF IMPP WG.
Unlike a traditional telephone number, the resource identified by a
pres URI may require that callers provide cryptographic credentials
for authentication and authorization before presence information is
returned. In this respect, ENUM in concert with presence protocols
can actually provide far greater protection from unwanted callers
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than the existing PSTN, despite the public availability of ENUM
records.
7. IANA Considerations
This document registers the 'E2U+pres' enumservice under the
enumservice registry described in the IANA considerations in
RFC2916bis. Details of the registration are given in Section 2.
References
[1] Faltstrom, P., "E.164 number and DNS", RFC 2916, September
2000.
[2] Faltstrom, P. and M. Mealling, "The E.164 to URI DDDS
Application", draft-ietf-enum-rfc2916bis-03 (work in progress),
January 2003.
[3] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[4] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[5] Crocker, D. and J. Peterson, "A Model for Presence and Instant
Messaging", draft-ietf-impp-pres-02 (work in progress),
February 2003.
[6] Crocker, D. and J. Peterson, "Address Resolution for Instant
Messaging and Presence", draft-ietf-impp-srv-02 (work in
progress), February 2003.
[7] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and
J. Peterson, "CPIM Presence Information Data Format", draft-
ietf-impp-cpim-pidf-07 (work in progress), August 2001.
[8] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, May 2002.
[9] Mockapetris, P., "Domain Names - Concepts and Facilities", RFC
1034, November 1987.
[10] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[11] International Telecommunications Union, "Recommendation E.164:
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The international public telecommunication numbering plan", May
1997, <http://www.itu.int>.
[12] Vaha-Sipila, A., "URLs for Telephone Calls", RFC 2806, April
2000.
[13] Mealling, M. and R. Daniel, "The Naming Authority Pointer
(NAPTR) DNS Resource Record", RFC 2915, September 2000.
[14] Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
Three: The Domain Name System (DNS) Database", RFC 3403,
October 2002.
Author's Address
Jon Peterson
NeuStar, Inc.
1800 Sutter St
Suite 570
Concord, CA 94520
USA
Phone: +1 925/363-8720
EMail: jon.peterson@neustar.biz
URI: http://www.neustar.biz/
Appendix A. To Do
This document cannot proceed until RFC2916bis has passed.
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