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INTERNET-DRAFT                                            R. Shekh-Yusef
Intended Status: Informational                                     Avaya
Expires: April 12, 2014                                        M. Barnes
                                                                 Polycom
                                                         October 9, 2013


                Conference Focus Indicating CCMP Support
                draft-yusef-dispatch-ccmp-indication-07

Abstract

   The Centralized Conferencing Manipulation Protocol (CCMP) document
   defines a way for a client to discover a conference control server
   that supports CCMP. However, it does not define a way for a client
   involved in a conference to determine if the conference focus
   supports CCMP. This information would allow a CCMP-enabled client
   that joins a conference using SIP to also register for the
   centralized conferencing (XCON) conference event package and take
   advantage of CCMP operations on the conference.

   This document describes two mechanisms, depending upon the need of
   the User Agent (UA), to address the above limitation. The first
   mechanism uses the Call-Info header, and the second mechanism defines
   a new value for the 'purpose' parameter in the 'service-uris' element
   in the SIP conferencing event package.


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

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   http://www.ietf.org/shadow.html



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Copyright and License 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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   described in the Simplified BSD License.





































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Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  4
   2  Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1 Call-Info  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2 Service URI purpose  . . . . . . . . . . . . . . . . . . . .  6
   3. Overall Process . . . . . . . . . . . . . . . . . . . . . . . .  6
   4  Security Considerations . . . . . . . . . . . . . . . . . . . .  7
   5  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  7
     5.1 Call-Info Purpose Registration . . . . . . . . . . . . . . .  7
     5.2 URI Purpose Registration . . . . . . . . . . . . . . . . . .  7
   6  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .  8
   7  References  . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1  Normative References  . . . . . . . . . . . . . . . . . . .  9
   Appendix A. Other Approaches Considered  . . . . . . . . . . . . . 11
     A.1 Feature Tag  . . . . . . . . . . . . . . . . . . . . . . . . 11
     A.2 Conference URI purpose . . . . . . . . . . . . . . . . . . . 11
   Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
































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1  Introduction

   RFC 5239 [RFC5239] defines a framework for Centralized Conferencing
   (XCON), which allows participants to exchange media in a centralized
   unicast conference. The framework also outlines a set of conferencing
   protocols for building advanced conferencing applications.

   The CCMP protocol RFC 6503 [RFC6503] allows authenticated and
   authorized users to create, manipulate and delete conference objects.
   Operations on conferences include adding and removing participants,
   changing their roles, as well as adding and removing media streams
   and associated end points.

   The CCMP defines a way for an XCON-aware client to discover whether a
   conference control server supports CCMP. However, it does not define
   a way for a SIP client involved in a conference to determine if the
   conference focus [RFC4353] supports CCMP. Knowing that a focus
   supports CCMP would allow a SIP client (that is also XCON-aware) that
   joins a conference using SIP based conferencing [RFC4579] to also
   register for the XCON conference event package [RFC6502] and take
   advantage of CCMP operations on the conference.

   This document describes two options to address the above limitation,
   depending on the need of the User Agent (UA). The first option uses
   the Call-Info [RFC3261] header, which is suitable for application
   servers that need to discover if a UA supports CCMP. The second
   option defines a new value for the 'purpose' parameter in the
   'service-uris' element in the SIP conferencing event package
   [RFC4575], which is suitable to a UA that would typically subscribe
   to the conference event package.

   Appendix A has a brief description to other options that we
   considered as possible solutions but were not selected because the
   selected options better address the problem we are trying to solve.


1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].










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2  Solutions

   This section defines two mechanisms that can be used by a SIP UA to
   discover whether the conference which a client has joined, per the
   SIP signaling procedures defined in [RFC4579], supports CCMP.
   Specifically, the mechanisms allow the client to know that the URI
   representing the conference focus, as defined in [RFC4579], is an
   XCON-URI as defined in [RFC6501].

2.1 Call-Info

   This approach uses the Call-Info header in various requests and
   responses.

   The Call-Info header consists of two parts: a URI and a parameter.
   The URI provides the XCON-URI of the conference focus, and the
   parameter indicates that the conference focus supports CCMP.

   While the XCON-URI by itself should be enough to indicate that the
   conference focus supports CCMP, the purpose parameter with a value of
   'ccmp' provides an easier way for a UA that does not use the
   conference event package to discover that the conference focus
   supports CCMP, without parsing the URI.

   The Call-Info header, with the XCON-URI and the purpose parameter
   with the 'ccmp' value, can be used with any INVITE request or
   response and with a response to an OPTIONS request.

   This approach would be suitable for a UA, like an application server
   that acts as a B2BUA, that is interested in discovering that a
   conference focus supports CCMP but does not use the XCON conference
   event package [RFC6502]. In this case the application could use the
   OPTIONS request and discover the CCMP support from the response.

   This approach would also be suitable for a conference focus that
   initiates an INVITE request to a SIP UA to add a participant to a
   conference, as it would allow the conference focus to indicate that
   it supports CCMP with the INVITE request sent to the UA.

   The advantage of this approach is the ability to discover that a
   conference focus supports CCMP without subscribing to the XCON event
   package [RFC6502]. The disadvantage is the need, in some cases, for
   an extra request, i.e. OPTIONS request, to discover that a conference
   focus supports CCMP.







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2.2 Service URI purpose

   This approach defines an additional URI 'purpose' of 'ccmp'
   associated with a 'service-uris' element in the SIP conferencing
   event package.  The XCON-URI for the conference is included in the
   'uri' element, per the following example:

      <service-uris>
        <entry>
          <uri>XCON:conf1@example.com</uri>
          <purpose>ccmp</purpose>
        </entry>
      </service-uris>


   The advantage of this approach is that it uses an existing mechanism
   for extending the <purpose> field of the <service-uris> element in
   the conferencing event package [RFC4353]. The disadvantage is that it
   requires the client to subscribe to the conference event package.

   This approach would be suitable for a SIP UA that would typically
   subscribe to the conference event package.  Knowing that a conference
   supports CCMP allows a SIP UA that is XCON-aware to make use of the
   CCMP operations and allows them to subscribe to the XCON event
   package [RFC6502] to get additional information related to the
   conference.

3. Overall Process

   CCMP capability is discovered using the two methods described in
   Section 2.  The order in which the two methods are tried depends on
   whether an implementation subscribes to the conference event package
   by default.

   A UA implementation that subscribes to the conference event package
   can examine the conference description to see if a URI with
   <purpose>ccmp</purpose> is specified (Section 2.2).   An
   implementation that does not subscribe to the conference event
   package can perform an OPTIONS query when connecting to the
   conference server.  UAs MUST NOT attempt both methods with the same
   server.

   Conference servers MUST reflect the same information using both
   discovery channels.  A server MUST indicate CCMP support through the
   conference event package if and only if it indicates support through
   the Call-Info header in OPTIONS responses.  This prevents the need
   for UAs to try both methods.




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4  Security Considerations

   This document defines no new headers or data elements and are reusing
   existing headers and data elements. The CCMP protocol already allows
   a client the ability to discover if a conference server supports
   CCMP, using a DNS mechanism as defined in RFC 6503 [RFC6503] section
   12.4.

   For these reasons, we think that this document does not introduce any
   new security risks.



5  IANA Considerations

5.1 Call-Info Purpose Registration

   This specification adds a new predefined value "ccmp" for the
   "purpose" header field parameter of the Call-Info header field. This
   modifies the registry header field parameters and parameter values by
   adding this RFC as a reference to the line for header field "Call-
   Info" and parameter name "purpose":

   Header Field: Call-Info
   Parameter Name: purpose
   Predefined Values: yes
   Reference: [RFC3261][RFC5367][RFC6910][RFC6993][RFC XXXX]


5.2 URI Purpose Registration

   This specification adds a new predefined value "ccmp" for the "URI
   Purposes" sub-registry, which defines XML elements to be encoded in
   the conference event package RFC 4575 [RFC4575].

   This modifies the registry as follows:

   Value: ccmp
   Description: The URI can be used to indicate that the conference
                focus supports CCMP.
   Reference: [RFC XXXX]

   (Note for RFC Editor: Please fill in XXXX with the RFC number of this
   specification)







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6  Acknowledgments

   The authors would like to thank Alan Johnston, Robert Sparks, Cullen
   Jennings, Glenn Parsons, Ben Campbell, Barry Leiba, Spencer Dawkins,
   Sean Turner, Pete Resnick, and Adrian Farrel for their careful review
   and feedback.

   Special thanks to Adam Roach for his thorough review, comments, and
   suggestions. Special thanks also to Richard Barnes for his review and
   for the text he provided for section 3 of this document.









































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7  References


7.1  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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.

   [RFC5239]  Barnes, M., Boulton, C., and O. Levin, "A Framework for
   Centralized Conferencing", RFC 5239, June 2008.

   [RFC4575]  Rosenberg, J., Schulzrinne, H., and O. Levin, Ed., "A
   Session Initiation Protocol (SIP) Event Package for Conference
   State", RFC 4575, August 2006.

   [RFC5239]  Barnes, M., Boulton, C., and O. Levin, "A Framework for
   Centralized Conferencing", RFC 5239, June 2008.

   [RFC4353]  Rosenberg, J., "A Framework for Conferencing with the
   Session Initiation Protocol (SIP)", RFC 4353, February 2006.

   [RFC4579]  Johnston, A. and O. Levin, "Session Initiation Protocol
   (SIP) Call Control - Conferencing for User Agents", BCP 119,
   RFC 4579, August 2006.

   [RFC5367]  Camarillo, G., Roach, A., and O. Levin, "Subscriptions to
   Request-Contained Resource Lists in the Session Initiation Protocol
   (SIP)", RFC 5367, October 2008.

   [RFC6503]  Barnes M., Boulton, C., Romano S P., and Schulzrinne H.,
   "Centralized Conferencing Manipulation Protocol", RFC6503, March
   2012.

   [RFC6501]  Novo, O., Camarillo, G., Morgan, D., and J. Urpalainen,
   "Conference Information Data Model for Centralized Conferencing
   (XCON)", RFC 6501, March 2012.

   [RFC6502]  Camarillo, G., Srinivasan, S., Even, R., and J.
   Urpalainen, "Conference Event Package Data Format Extension for
   Centralized Conferencing (XCON)", RFC 6502, March 2012.

   [RFC6910] Worley, D., Huelsemann, M., Jesske, R., Alexeitsev, D.,
   "Completion of Calls for the Session Initiation Protocol (SIP)", RFC
   6910, April 2013.



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   [RFC6993] Saint-Andre, P., "Instant Messaging and Presence Purpose
   for the Call-Info Header Field in the Session Initiation Protocol
   (SIP)", RFC 6993, July 2013.



   7.2  Informative References












































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Appendix A. Other Approaches Considered

   The following two options were considered as possible solutions but
   were not selected because the selected options better address the
   problem we are trying to solve.


A.1 Feature Tag

   This approach defines a feature parameter 'ccmp' to express that a
   SIP dialog belongs to a conference that supports CCMP.  The use of
   feature parameters in Contact header fields to describe the
   characteristics and capabilities of a UA is described in the User
   Agent Capabilities document.

   The conference focus behavior regarding the handling of the 'ccmp'
   feature is the same as the handling of the 'isfocus' feature
   parameter. In session establishment, a conference focus MUST include
   the 'ccmp' feature parameter in the Contact header field unless the
   conference focus wishes to hide the fact that it is a conference
   focus.

   The advantages of this approach is a one step discovery of the
   conference focus and its ccmp support, and the fact that it can be
   used in response to an OPTIONS request, and that it enables the
   discovery of the ccmp capability by any network element that does not
   need the conference event package. The disadvantage is the definition
   of a new feature parameter.


A.2 Conference URI purpose

   Define an additional URI 'purpose' of 'ccmp' associated with a
   'confs-uris' element in the SIP conferencing event package.

   ccmp: Indicates that the conference focus represented by this URI
   supports ccmp, which allows a client to use the CCMP protocol to
   manipulate the conference. This URI MUST be an XCON-URI as defined in
   the xcon-data-model.

         <conf-uris>
           <entry>
             <uri>XCON:conf1@example.com</uri>
             <display-text>whatever</display-text>
             <purpose>ccmp</purpose>
           </entry>
         </conf-uris>




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   The advantage of the SIP conference event package options is the use
   of an existing mechanism for extending the <purpose> field of the
   <service-uris> or <conf-uris> elements. The disadvantage is the
   requirement that the client register for the conference event
   package.




Author's Addresses


   Rifaat Shekh-Yusef
   Avaya
   250 Sidney Street
   Belleville, Ontario
   Canada

   Phone: +1-613-967-5267
   Email: rifaat.ietf@gmail.com



   Mary Barnes
   Polycom
   TX
   US

   Email: mary.ietf.barnes@gmail.com






















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