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.



















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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:[email protected]") 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:[email protected] would resolve to a SIP URI of
  sip:[email protected].

  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:[email protected]") 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:[email protected] would resolve to a SIP URI
  of sip:[email protected].


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 <[email protected]>

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 <[email protected]>


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: [email protected]









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