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

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/rfc6993.

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
   (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 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: <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]

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