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rfc:rfc5509

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.

Copyright Notice

 Copyright (c) 2009 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents in effect on the date of
 publication of this document (http://trustee.ietf.org/license-info).
 Please review these documents carefully, as they describe your rights
 and restrictions with respect to this document.

Abstract

 This document registers with IANA two new DNS SRV protocol labels for
 resolving Instant Messaging and Presence services with SIP.

Loreto Standards Track [Page 1] RFC 5509 IANA SRV Label for SIP April 2009

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

Loreto Standards Track [Page 2] RFC 5509 IANA SRV Label for SIP April 2009

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

Loreto Standards Track [Page 3] RFC 5509 IANA SRV Label for SIP April 2009

 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.

Loreto Standards Track [Page 4] RFC 5509 IANA SRV Label for SIP April 2009

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 <salvatore.loreto@ericsson.com>

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 <salvatore.loreto@ericsson.com>

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).

Loreto Standards Track [Page 5] RFC 5509 IANA SRV Label for SIP April 2009

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

Loreto Standards Track [Page 6]

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