RFC 5509

Ayy, RFC 5509 🎀✨

Okay bestie, so this is RFC 5509 💖, and it's called "Internet Assigned Numbers Authority (IANA) Registration of Instant Messaging and Presence DNS SRV RRs for the Session Initiation Protocol (SIP)" 🧚. Salvatore Loreto from Ericsson wrote it. It's a Standards Track doc, dated April 2009 📅. The header doesn't list anything it obsoletes or updates, so there's no drama there 🫶.

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Status of This Memo 📜

This document is an Internet standards track protocol for the Internet community, and it's asking everyone for discussion and suggestions for improvements 💅. If you want to check where this protocol stands, look at the current edition of the "Internet Official Protocol Standards" (STD 1) 🔥. 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, as they were in effect on the date of publication 📚. Please actually read those, bestie, because they explain your rights and restrictions for this document 🙈 (http://trustee.ietf.org/license-info).

Abstract 🌸

This document registers two brand new DNS SRV protocol labels with IANA, so you can resolve 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

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1. Introduction 🧚‍♀️

Okay so the Service Record (SRV) [RFC2782] tells you which host(s) support a particular service 💁‍♀️. To ask DNS for an SRV RR, you use this 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] is the guide for finding the services behind URIs that use two URI schemes [RFC3986]: im for INSTANT INBOXes [RFC3860] and pres for PRESENTITIES [RFC3859] 🦋.

To keep the link between "_im" and "_pres" and their underlying services predictable, IANA made two separate 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 programs can turn im: and pres: URIs into SIP addresses 🫶. It also explains how SIP for Presence and Instant Messaging uses SRV, so yes, it's a whole plan 💅.

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 💌

Even though there are standard procedures for resolving 'im' and 'pres' URIs (Section 3 of [RFC3861]), the labels for SIP are not registered yet 😭.

Section 5 of [RFC3428] says that if a user agent (UA) gets an IM URI (like "im:fred@example.com") as the address for an instant message, it SHOULD resolve it to a SIP URI, and put that URI in the Request-URI of the MESSAGE request before sending 💖.

Following the procedures in [RFC3861], the UA does an SRV lookup for:

_im._sip.example.com

Say example.com offers a SIP service for instant messaging at simple.example.com. Then _im._sip.example.com. resolves to simple.example.com., and the IM URI im:fred@example.com turns into the SIP URI sip:fred@simple.example.com ✨.

SIP supports two IM modes: pager [RFC3428] and session [RFC4975] 🍓. The catch is that a DNS SRV lookup doesn't tell you which SIP IM mode a domain offers 🙈. So if the user agent client (UAC) supports both session mode and pager mode, it's suggested to try session mode first. If that gets rejected, the UAC has to be ready to fall back to pager mode 🔥.

Section 5 of [RFC3856] says the procedures in [RFC3861] are also used to turn the protocol-independent PRES URI for a presentity (like "pres:fred@example.com") into a SIP URI 💜.

Following the procedures in [RFC3861], the UA does an SRV lookup for the PRES URI:

_pres._sip.example.com

Assume example.com offers a SIP presence service at simple.example.com. Then _pres._sip.example.com. resolves to simple.example.com., and the protocol-independent PRES URI pres:fred@example.com resolves to the SIP URI sip:fred@simple.example.com 🦋.

4. Security Considerations 🔐

This document just does the registration of DNS SRV labels in the right IANA registry 💅. It doesn't specify a protocol, so 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] sets up an Instant Messaging SRV Protocol Label registry for protocols that can provide services conforming to the "_im" SRV Service label. SIP is one of those protocols, so IANA registers the "_sip" protocol label in the "Instant Messaging SRV Protocol Label Registry", like this:

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 🌸

[RFC3861] also sets up a Presence SRV Protocol Label registry, for protocols that can provide services conforming to the "_pres" SRV Service label. SIP for Presence and Instant Messaging is one of those protocols, so IANA registers the "_sip" protocol label in the "Presence SRV Protocol Label Registry", like this:

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 🙌

Big thanks to Jon Peterson and Peter Saint-Andre, because the need for this registration was discussed with them 👑.

Miguel Garcia reviewed this document for 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

That's the whole thing, bestie! 🌈💖 Main character energy, no cap 💅