Network Working Group S. Loreto
Request for Comments: 5509 Ericsson
Category: Standards Track April 2009
Internet Assigned Numbers Authority (IANA) Registration
of Instant Messaging and Presence DNS SRV RRs
for the Session Initiation Protocol (SIP)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
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Provisions Relating to IETF Documents in effect on the date of
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Abstract
This document registers with IANA two new DNS SRV protocol labels for
resolving Instant Messaging and Presence services with SIP.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DNS SRV Usage of SIP with 'im' and 'pres' URIs . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Instant Messaging SRV Protocol Label Registration . . . . . 5
5.2. Presence SRV Protocol Label Registration . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
The Service Record (SRV) [RFC2782] identifies the host(s) that will
support particular services. The DNS is queried for SRV RR in the
general form:
_Service._Proto.Name
Service: the symbolic name of the desired service
Proto: the protocol of the desired service
Name: the domain name for which this record is valid
"Address Resolution for Instant Messaging and Presence" [RFC3861]
provides guidance for locating the services associated with URIs that
employ the following two URI schemes [RFC3986]: 'im' for INSTANT
INBOXes [RFC3860] and 'pres' for PRESENTITIES [RFC3859].
In order to ensure that the association between "_im" and "_pres" and
their respective underlying services are deterministic, the IANA has
created two independent registries: the Instant Messaging SRV
Protocol Label registry and the Presence SRV Protocol Label registry.
This document defines and registers the "_sip" protocol label in both
registries so that computer programs can resolve 'im:' and 'pres:'
URIs down to SIP addresses.
Moreover, this document explains how the use of SIP for Presence and
Instant Messaging uses SRV.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. DNS SRV Usage of SIP with 'im' and 'pres' URIs
Although there are standard procedures for resolving 'im' and 'pres'
URIs (Section 3 of [RFC3861]), the labels for SIP are not registered.
Section 5 of [RFC3428] states that if a user agent (UA) is presented
with an IM URI (e.g., "im:fred@example.com") as the address for an
instant message, it SHOULD resolve it to a SIP URI, and place the
resulting URI in the Request-URI of the MESSAGE request before
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sending.
Following the procedures defined in [RFC3861], in order to resolve
the IM URI, the UA performs a SRV lookup for:
_im._sip.example.com
Assuming that the example.com domain offers a SIP service for instant
messaging at simple.example.com, this will result in a resolution of
_im._sip.example.com. to simple.example.com. Thus, the instant
messaging URI im:fred@example.com would resolve to a SIP URI of
sip:fred@simple.example.com.
SIP supports both pager [RFC3428] and session [RFC4975] IM mode.
However, a DNS SRV lookup does not specify which SIP IM mode a domain
offer. If the user agent client (UAC) supports both session mode and
pager mode, it is then suggested to try session mode first; if that
mode is rejected, the UAC has to be ready to fall back to pager mode.
Section 5 of [RFC3856] states that procedures defined in [RFC3861]
are also used to resolve the protocol-independent PRES URI for a
presentity (e.g., "pres:fred@example.com") into a SIP URI.
Following the procedures defined in [RFC3861], in order to resolve
the PRES URI, the UA performs a SRV lookup for:
_pres._sip.example.com
Assuming that the example.com domain offers a SIP presence service at
simple.example.com, this will result in a resolution of
_pres._sip.example.com. to simple.example.com. Thus, the protocol-
independent PRES URI pres:fred@example.com would resolve to a SIP URI
of sip:fred@simple.example.com.
4. Security Considerations
This document merely serves for the registration of DNS SRV labels in
the appropriate IANA registry. The document does not specify a
protocol; therefore, there are no security issues associated with it.
5. IANA Considerations
This specification registers a new SRV protocol label in both the
Instant Messaging SRV Protocol Label registry and the Presence SRV
Protocol Label registry.
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5.1. Instant Messaging SRV Protocol Label Registration
"Address Resolution for Instant Messaging and Presence" [RFC3861]
defines an Instant Messaging SRV Protocol Label registry for
protocols that can provide services that conform to the "_im" SRV
Service label. Because SIP is one such protocol, IANA registers the
"_sip" protocol label in the "Instant Messaging SRV Protocol Label
Registry", as follows:
Protocol label: _sip
Specification: RFC 5509
Description: Instant messaging protocol label for the use of SIP for
Presence and Instant Messaging protocol as defined by
[RFC3428].
Registrant Contact: Salvatore Loreto
5.2. Presence SRV Protocol Label Registration
"Address Resolution for Instant Messaging and Presence" [RFC3861]
defines a Presence SRV Protocol Label registry for protocols that can
provide services that conform to the "_pres" SRV Service label.
Because the use of SIP for Presence and Instant Messaging is one such
protocol, the IANA registers the "_sip" protocol label in the
"Presence SRV Protocol Label Registry", as follows:
Protocol label: _sip
Specification: RFC 5509
Description: Presence protocol label for the use of SIP for Presence
and Instant Messaging protocol as defined by [RFC3856].
Registrant Contact: Salvatore Loreto
6. Acknowledgments
The need for this registration was discussed with Jon Peterson and
Peter Saint-Andre.
Miguel Garcia reviewed this document on behalf of the Real-time
Applications and Infrastructure (RAI) Area Review Team (ART).
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7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3428] Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C.,
and D. Gurle, "Session Initiation Protocol (SIP) Extension
for Instant Messaging", RFC 3428, December 2002.
[RFC3856] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004.
[RFC3859] Peterson, J., "Common Profile for Presence (CPP)",
RFC 3859, August 2004.
[RFC3860] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, August 2004.
[RFC3861] Peterson, J., "Address Resolution for Instant Messaging
and Presence", RFC 3861, August 2004.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975, September 2007.
Author's Address
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Salvatore.Loreto@ericsson.com
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RFC, FYI, BCP