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Internet Engineering Task Force (IETF)                    P. Saint-Andre
Request for Comments: 6993                           Cisco Systems, Inc.
Category: Informational                                        July 2013
ISSN: 2070-1721

             Instant Messaging and Presence Purpose for the
    Call-Info Header Field in the Session Initiation Protocol (SIP)

Abstract

   This document defines and registers a value of "impp" ("instant
   messaging and presence protocol") for the "purpose" header field
   parameter of the Call-Info header field in the Session Initiation
   Protocol (SIP).

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/RFC 6993.

Copyright Notice

   Copyright (c) 2013 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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Saint-Andre                   Informational                     [Page 1]
RFC 6993 Call-Info Purpose: IMPP July 2013 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Security Considerations . . . . . . . . . . . . . . . . . . . 2 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 4. References . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.1. Normative References . . . . . . . . . . . . . . . . . . 3 4.2. Informative References . . . . . . . . . . . . . . . . . 3 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction Some real-time communication endpoints support the combined use of the Session Initiation Protocol (SIP) [RFC 3261] and the Extensible Messaging and Presence Protocol (XMPP) [RFC 6120]. To improve interoperability among such "CUSAX" endpoints [CUSAX], it can be helpful to advertise each endpoint's SIP address over XMPP and each endpoint's XMPP address over SIP, thus providing hints about the communication capabilities of the endpoints. The former feature is enabled by an XMPP extension protocol called Reachability Addresses [XEP-0152]. As to the latter feature, discussion in the SIP community led to the conclusion that it would be best to use the Call-Info header field [RFC 3261] with a value of "impp" ("instant messaging and presence protocol") for the "purpose" header field parameter. An example follows. Call-Info: <xmpp:juliet@example.com> ;purpose=impp Although CUSAX endpoints constitute the primary use case for the "impp" purpose, a Uniform Resource Identifier (URI) [RFC 3986] for an instant messaging and presence protocol other than XMPP could be included in the Call-Info header field. 2. Security Considerations Advertising an endpoint's XMPP address over SIP could inform malicious entities about an alternative attack vector. Because the "purpose" header field parameter could be spoofed, the receiving endpoint ought to check the value against an authoritative source such as a user directory. Clients can integrity protect and encrypt this header field using end-to-end mechanisms such as S/MIME or hop- by-hop mechanisms such as Transport Layer Security (TLS). This specification provides a new way to correlate otherwise possibly unconnected identifiers. Because such correlations can be privacy sensitive, user agents ought to provide a means for users to control whether or not these values are sent. Saint-Andre Informational [Page 2]
RFC 6993 Call-Info Purpose: IMPP July 2013 3. IANA Considerations This document defines and registers a new predefined value "impp" for the "purpose" header field parameter of the Call-Info header field. The IANA has completed this action by adding this RFC as a reference to the line for the header field "Call-Info" and parameter name "purpose" in the "Header Field Parameters and Parameter Values" section of the "Session Initiation Protocol (SIP) Parameters" registry as follows: Header Field: Call-Info Parameter Name: purpose Predefined Values: Yes Reference: [RFC 3261][RFC 5367][RFC 6910][RFC 6993] 4. References 4.1. Normative References [RFC 3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC 3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC 6120] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Core", RFC 6120, March 2011. 4.2. Informative References [CUSAX] Ivov, E., Saint-Andre, P., and E. Marocco, "CUSAX: Combined Use of the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP)", Work in Progress, June 2013. [XEP-0152] Saint-Andre, P. and J. Hildebrand, "Reachability Addresses", XSF XEP 0152, February 2013. Saint-Andre Informational [Page 3]
RFC 6993 Call-Info Purpose: IMPP July 2013 5. Acknowledgements Thanks to Gonzalo Camarillo, Keith Drage, Saul Ibarra, Emil Ivov, Cullen Jennings, Olle Johanssen, Paul Kyzivat, Gonzalo Salgueiro, Dean Willis, and Dale Worley for their input. Elwyn Davies, Salvatore Loreto, Glen Zorn, and Mehmet Ersue completed reviews on behalf of the General Area Review Team, Applications Area Directorate, Security Directorate, and Operations and Management Directorate, respectively. Stephen Farrell and Pete Resnick provided substantive feedback during IESG review. Thanks to Yana Stamcheva for her helpful comments and for shepherding the document. Author's Address Peter Saint-Andre Cisco Systems, Inc. 1899 Wynkoop Street, Suite 600 Denver, CO 80202 USA Phone: +1-303-308-3282 EMail: psaintan@cisco.com Saint-Andre Informational [Page 4]