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Internet Engineering Task Force (IETF)                    P. Saint-AndreRequest for Comments: 6993                           Cisco Systems, Inc.Category: Informational                                        July 2013ISSN: 2070-1721Instant Messaging and Presence Purpose for theCall-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; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6993.Copyright Notice   Copyright (c) 2013 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   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 2013Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .22.  Security Considerations . . . . . . . . . . . . . . . . . . .23.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .34.  References  . . . . . . . . . . . . . . . . . . . . . . . . .34.1.  Normative References  . . . . . . . . . . . . . . . . . .34.2.  Informative References  . . . . . . . . . . . . . . . . .35.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .41.  Introduction   Some real-time communication endpoints support the combined use of   the Session Initiation Protocol (SIP) [RFC3261] and the Extensible   Messaging and Presence Protocol (XMPP) [RFC6120].  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 [RFC3261] 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) [RFC3986] 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 20133.  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: [RFC3261][RFC5367][RFC6910][RFC6993]4.  References4.1.  Normative References   [RFC3261]  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.   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform              Resource Identifier (URI): Generic Syntax", STD 66,RFC3986, January 2005.   [RFC6120]  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 20135.  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.comSaint-Andre                   Informational                     [Page 4]