Instant Messaging and Presence Purpose for the Call-Info Header Field in the Session Initiation Protocol (SIP)
draft-saintandre-impp-call-info-03

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

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This Internet-Draft will expire on November 15, 2013.

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Table of Contents

• 1. Introduction
• 2. Security Considerations
• 3. IANA Considerations
• 4. References
• 4.1. Normative References
• 4.2. Informative References
• Appendix A. Acknowledgements
• Author's Address

1. Introduction

To improve interoperability among real-time communication endpoints that support the combined use of the Session Initiation Protocol (SIP) [RFC3261] and the Extensible Messaging and Presence Protocol (XMPP) [RFC6120] (so-called "CUSAX" endpoints [I-D.ivov-xmpp-cusax]), it can be helpful to communicate the endpoint's SIP address over XMPP and the endpoint's XMPP address over SIP to provide hints about the endpoints communication capabilities. 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 TLS.

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 can complete 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:

  Header Field: Call-Info
  Parameter Name: purpose
  Predefined Values: Yes
  Reference: [this document]
        

4. References

4.1. Normative References

4.2. Informative References

Appendix A. 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, and Glen Zorn completed reviews on behalf of the General Area Review Team, Applications Area Directorate, and Security Directorate, respectively. Thanks to Yana Stamcheva for her helpful comments and for shepherding the document.

Author's Address