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Instant Messaging and Presence Purpose for the Call-Info Header Field in the Session Initiation Protocol (SIP)
RFC 6993

Document Type RFC - Informational (July 2013)
Author Peter Saint-Andre
Last updated 2015-10-14
RFC stream Internet Engineering Task Force (IETF)
IESG Responsible AD Gonzalo Camarillo
Send notices to (None)
RFC 6993
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)


   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

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
   Provisions Relating to IETF Documents
   ( 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.

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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) [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: <> ;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.

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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: [RFC3261][RFC5367][RFC6910][RFC6993]

4.  References

4.1.  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, RFC
              3986, 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.

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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

   Phone: +1-303-308-3282

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