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Network Working Group
Request for Comments: 5509
Category: Standards Track
S. Loreto
Ericsson
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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Copyright © 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.

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

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 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.

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).

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