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Versions: 00 01 02 RFC 5366

SIPPING Working Group                                       G. Camarillo
Internet-Draft                                                  Ericsson
Expires: July 30, 2007                                       A. Johnston
                                                                   Avaya
                                                        January 26, 2007


 Conference Establishment Using Request-Contained Lists in the Session
                       Initiation Protocol (SIP)
              draft-ietf-sip-uri-list-conferencing-01.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document describes how to create a conference using SIP URI-list
   services.  In particular, it describes a mechanism that allows a user
   agent client to provide a conference server with the initial list of
   participants using an INVITE-contained URI-list.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  User Agent Client Procedures . . . . . . . . . . . . . . . . .  3
     3.1.  Response Handling  . . . . . . . . . . . . . . . . . . . .  3
     3.2.  Re-INVITE Request Generation . . . . . . . . . . . . . . .  4
   4.  URI-List Document Format . . . . . . . . . . . . . . . . . . .  4
   5.  Conference Server Procedures . . . . . . . . . . . . . . . . .  6
     5.1.  Re-INVITE Request Handling . . . . . . . . . . . . . . . .  6
   6.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   9.  Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 12
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 12
     10.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
   Intellectual Property and Copyright Statements . . . . . . . . . . 14
































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1.  Introduction

   Section 5.4 of RFC 4579 [5] describes how to create a conference
   using ad-hoc SIP (which is specified in RFC 3261 [4]) methods.  The
   client sends an INVITE request to a conference factory URI and
   receives the actual conference URI, which contains the "isfocus"
   feature tag, in the Contact header field of a response - typically a
   200 (OK) response.

   Once the UAC (User Agent Client) obtains the conference URI, it can
   add participants to the newly created conference in several ways,
   which are described in RFC 4579 [5].

   Some environments have tough requirements regarding conference
   establishment time.  They require the UAC to be able to request the
   creation of an ad-hoc conference and to provide the conference server
   with the initial set of participants in a single operation.  This
   document describes how to meet this requirement using the mechanism
   to transport URI-lists in SIP messages described in RFC xxxx [6].


2.  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 [1].


3.  User Agent Client Procedures

   A UAC that wants to include the set of initial participants in its
   initial INVITE request to create an ad-hoc conference, adds a body
   whose disposition type is 'recipient-list', as defined in RFC xxxx
   [6], with a URI-list that contains the participants that the UAC
   wants the conference server to invite.  Additionally, the UAC MUST
   include the 'recipient-list-invite' option-tag, which is registered
   with the IANA in Section 8 in a Require header field.  The UAC sends
   this INVITE request to the conference factory URI.

3.1.  Response Handling

   The status code in the response to the INVITE request does not
   provide any information about whether or not the conference server
   was able to bring the users in the URI-list into the conference.
   That is, a 200 (OK) response means that the conference was created
   successfully, that the UAC that generated the INVITE request is in
   the conference, and that the server understood the URI-list.  If the
   UAC wishes to obtain information about the status of other users in



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   the conference it SHOULD use general conference mechanisms, such as
   the conference package, which is defined in RFC 4575 [9].

3.2.  Re-INVITE Request Generation

   The previous sections have specified how to include a URI-list in an
   initial INVITE request to a conference server.  Once the INVITE-
   initiated dialog between the UAC and the conference server has been
   established, the UAC can send subsequent INVITE requests (typically
   referred to as re-INVITE requests) to the conference server to, for
   example, modify the characteristics of the media exchanged with the
   server.

   At this point, there are no semantics associated with resource-list
   bodies in re-INVITE requests (although future extensions may define
   them).  Therefore, UACs SHOULD NOT include resource-list bodies in
   re-INVITE requests sent to a conference server.

      Note that a difference between an initial INVITE request and a re-
      INVITE request is that while the initial INVITE request is sent to
      the conference factory URI, the re-INVITE request is sent to the
      URI provided by the server in a Contact header field when the
      dialog was established.  Therefore, from the UAC's point of view,
      the resource identified by the former URI supports 'recipient-
      list' bodies while the resource identified by the latter does not
      support them.


4.  URI-List Document Format

   As described in RFC xxxx [6], specifications of individual URI-list
   services, like the conferencing service described here, need to
   specify a default format for 'recipient-list' bodies used within the
   particular service.

   The default format for 'recipient-list' bodies for conferencing UAs
   (User Agents) is the XML resource list format (which is specified in
   RFC xxxx [7]) extended with the XML Format Extension for Representing
   Copy Control Attributes in Resource Lists (which is specified in RFC
   xxxx [8]).  Consequently, conferencing UACs generating 'recipient-
   list' bodies MUST support both of these formats and MAY support other
   formats.  Conferencing servers able to handle 'recipient-list' bodies
   MUST support both of these formats and MAY support other formats.

   As described in the XML Format Extension for Representing Copy
   Control Attributes in Resource Lists (which is specified in RFC xxxx
   [8]), each URI can be tagged with a 'copyControl' attribute set to
   either "to", "cc", or "bcc", indicating the role in which the



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   recipient will get the INVITE request.  Additionally, URIs can be
   tagged with the 'anonymize' attribute to prevent that the conference
   server discloses the target URI in a URI-list.

   In addition, the XML Format Extension for Representing Copy Control
   Attributes in Resource Lists (which is specified in RFC xxxx [8])
   defines a 'recipient-list-history' body that contains the list of
   recipients.  The default format for 'recipient-list-history' bodies
   for conferencing UAs is also the XML resource list document format
   specified in RFC xxxx [7] extended with the XML Format Extension for
   Representing Copy Control Attributes in Resource Lists specified in
   [8].  Consequently, conferencing UACs able to generate 'recipient-
   list-history' bodies MUST support these formats and MAY support
   others.  Conferencing UAs able to understand 'recipient-list-history'
   MUST support these formats and MAY support others.  Conferencing
   servers able to handle 'recipient-list-history' bodies MUST support
   these formats and MAY support others.

   Nevertheless, the XML resource list document specified in RFC xxxx
   [7] provides features, such as hierarchical lists and the ability to
   include entries by reference relative to the XCAP root URI, that are
   not needed by the conferencing service defined in this document,
   which only needs to transfer a flat list of URIs between a UA (User
   Agent) and the conference server.  Therefore, when using the default
   resource list document, conferencing UAs SHOULD use flat lists (i.e.,
   no hierarchical lists) and SHOULD NOT use <entry-ref> elements.  A
   conference factory application receiving a URI-list with more
   information than what has just been described MAY discard all the
   extra information.

   Figure 1 shows an example of a flat list that follows the XML
   resource list document (specified in RFC xxxx [7]) extended with the
   XML Format Extension for Representing Copy Control Attributes in
   Resource Lists (specified in RFC xxxx [8]).


   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
             xmlns:cp="urn:ietf:params:xml:ns:copycontrol">
     <list>
       <entry uri="sip:bill@example.com" cp:copyControl="to"  />
       <entry uri="sip:joe@example.org" cp:copyControl="cc" />
       <entry uri="sip:ted@example.net" cp:copyControl="bcc" />
     </list>
   </resource-lists>

                            Figure 1: URI-List




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5.  Conference Server Procedures

   Conference servers that are able to receive and process INVITE
   requests with a 'recipient-list' body SHOULD include a 'recipient-
   list-invite' option-tag in a Supported header field when responding
   to OPTIONS requests.

   On reception of an INVITE request containing a 'recipient-list' body
   as described in Section 3, a conference server MUST follow the rules
   described in RFC 4579 [5] to create ad-hoc conferences.  Once the ad-
   hoc conference is created, the conference server SHOULD attempt to
   add the participants in the URI-list to the conference as if their
   addition had been requested using any of the methods described in RFC
   4579 [5].

   Once the conference server has created the ad-hoc conference and has
   attempted to add the initial set of participants, the conference
   server behaves as a regular conference server and MUST follow the
   rules in RFC 4579 [5].

   The incoming INVITE request will contain a URI-list body or reference
   (as specified in RFC xxxx [6]) with the actual list of recipients.
   If this URI-list includes resources tagged with the 'copyControl'
   attribute set to a value of "to" or "cc", the conference server
   SHOULD include a URI-list in each of the outgoing INVITE requests.
   This list SHOULD be formatted according to the XML format for
   representing resource lists (specified in RFC xxxx [7]) and the
   copyControl extension specified in RFC xxxx [8].  The URI-list
   service MUST follow the procedures specified in RFC xxxx [8] with
   respect to the handling of the 'anonymize', 'count' and 'copyControl'
   attributes.

   If the conference server includes a URI-list in an outgoing INVITE
   request, it MUST include a Content-Disposition header field (which is
   specified in RFC 2183 [2]) with the value set to 'recipient-list-
   history' and a 'handling' parameter (as specified in RFC 3204 [3])
   set to "optional".

5.1.  Re-INVITE Request Handling

   At this point, there are no semantics associated with resource-list
   bodies in re-INVITE requests (although future extensions may define
   them).  Therefore, a conference server receiving a re-INVITE request
   with a resource-list body and, consequently, a 'recipient-list-
   invite' option-tag, following standard SIP procedures, rejects it
   with a 420 (Bad Extension), which carries an Unsupported header field
   listing the 'recipient-list-invite' option-tag.




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      This is because the resource identified by the conference URI does
      not actually support this extension.  On the other hand, the
      resource identified by the conference factory URI does support
      this extension and, consequently, would include the 'recipient-
      list-invite' option-tag in, for example, responses to OPTIONS
      requests.


6.  Example

   Figure 2 shows an example of operation.  A UAC sends an INVITE
   request (F1) that contains an SDP body and a URI-list to the
   conference server.  The conference server answers with a 200 (OK)
   response and generates an INVITE request to each of the UASs (USer
   Agent Servers) identifies by the URIs included in the URI-list.  The
   conference server includes SDP and a manipulated URI-list in each of
   the outgoing INVITE requests.

   +--------+        +---------+      +--------+ +--------+ +--------+
   |SIP UAC |        | confer. |      |SIP UAS | |SIP UAS | |SIP UAS |
   |        |        | server  |      |   1    | |   2    | |   n    |
   +--------+        +---------+      +--------+ +--------+ +--------+
       |                  |               |          |          |
       | F1. INVITE       |               |          |          |
       | ---------------->|               |          |          |
       | F2. 200 OK       |               |          |          |
       |<---------------- |  F3. INVITE   |          |          |
       |                  | ------------->|          |          |
       |                  |  F4. INVITE   |          |          |
       |                  | ------------------------>|          |
       |                  |  F5. INVITE   |          |          |
       |                  | ----------------------------------->|
       |                  |  F6. 200 OK   |          |          |
       |                  |<------------- |          |          |
       |                  |  F7. 200 OK   |          |          |
       |                  |<------------------------ |          |
       |                  |  F8. 200 OK   |          |          |
       |                  |<----------------------------------- |
       |                  |               |          |          |
       |                  |               |          |          |
       |                  |               |          |          |

                      Figure 2: Example of operation

   Figure 3 shows an example of the INVITE request F1, which carries a
   multipart/mixed body composed of two other bodies: an application/sdp
   body that describes the session and an application/resource-lists+xml
   body that contains the list of target URIs.



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   INVITE sip:conf-fact@example.com SIP/2.0
   Via: SIP/2.0/TCP atlanta.example.com
       ;branch=z9hG4bKhjhs8ass83
   Max-Forwards: 70
   To: "Conf Factory" <sip:conf-fact@example.com>
   From: Alice <sip:alice@example.com>;tag=32331
   Call-ID: d432fa84b4c76e66710
   CSeq: 1 INVITE
   Contact: <sip:alice@atlanta.example.com>
   Allow: INVITE, ACK, CANCEL, BYE, REFER
   Allow-Events: dialog
   Accept: application/sdp, message/sipfrag
   Require: recipient-list-invite
   Content-Type: multipart/mixed;boundary="boundary1"
   Content-Length: 690

   --boundary1
   Content-Type: application/sdp

   v=0
   o=alice 2890844526 2890842807 IN IP4 atlanta.example.com
   s=-
   c=IN IP4 192.0.2.1
   t=0 0
   m=audio 20000 RTP/AVP 0
   a=rtpmap:0 PCMU/8000
   m=video 20002 RTP/AVP 31
   a=rtpmap:31 H261/90000

   --boundary1
   Content-Type: application/resource-lists+xml
   Content-Disposition: recipient-list

   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
             xmlns:cp="urn:ietf:params:xml:ns:copyControl">
     <list>
       <entry uri="sip:bill@example.com" cp:copyControl="to" />
       <entry uri="sip:randy@example.net" cp:copyControl="to"
                                          cp:anonymize="true"/>
       <entry uri="sip:eddy@example.com" cp:copyControl="to"
                                         cp:anonymize="true"/>
       <entry uri="sip:joe@example.org" cp:copyControl="cc" />
       <entry uri="sip:carol@example.net" cp:copyControl="cc"
                                          cp:anonymize="true"/>
       <entry uri="sip:ted@example.net" cp:copyControl="bcc" />
       <entry uri="sip:andy@example.com" cp:copyControl="bcc" />
     </list>



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   </resource-lists>
   --boundary1--

        Figure 3: INVITE request received at the conference server

   The INVITE requests F3, F4, and F5 are similar in nature.  All those
   INVITE requests contain a multipart/mixed body which is composed of
   two other bodies: an application/sdp body describing the session and
   an application/resource-lists+xml containing the list of recipients.
   The application/resource-lists+xml bodies are not equal to the
   application/resource-lists+xml included in the received INVITE
   request F1, because the conference server has anonymized those URIs
   tagged with the 'anonymize' attribute and has removed those URIs
   tagged with a "bcc" 'copyControl' attribute.  Figure 4 shows an
   example of the message F3.




































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   INVITE sip:bill@example.com SIP/2.0
   Via: SIP/2.0/TCP conference.example.com
       ;branch=z9hG4bKhjhs8as454
   Max-Forwards: 70
   To: <sip:bill@example.com>
   From: Conference Server <sip:conf34@example.com>;tag=234332
   Call-ID: 389sn189dasdf
   CSeq: 1 INVITE
   Contact: <sip:conf34@conference.example.com>;isfocus
   Allow: INVITE, ACK, CANCEL, BYE, REFER
   Allow-Events: dialog, conference
   Accept: application/sdp, message/sipfrag
   Require: recipient-list-invite
   Content-Type: multipart/mixed;boundary="boundary1"
   Content-Length: 690

   --boundary1
   Content-Type: application/sdp

   v=0
   o=conf 2890844343 2890844343 IN IP4 conference.example.com
   s=-
   c=IN IP4 192.0.2.5
   t=0 0
   m=audio 40000 RTP/AVP 0
   a=rtpmap:0 PCMU/8000
   m=video 40002 RTP/AVP 31
   a=rtpmap:31 H261/90000

   --boundary1
   Content-Type: application/resource-lists+xml
   Content-Disposition: recipient-list-history; handling=optional

   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
             xmlns:cp="urn:ietf:params:xml:ns:copycontrol">
     <list>
       <entry uri="sip:bill@example.com" cp:copyControl="to" />
       <entry uri="sip:anonymous@anonymous.invalid" cp:copyControl="to"
                                                    cp:count="2"/>
       <entry uri="sip:joe@example.org" cp:copyControl="cc" />
       <entry uri="sip:anonymous@anonymous.invalid" cp:copyControl="cc"
                                                    cp:count="1"/>
     </list>
   </resource-lists>
   --boundary1--

          Figure 4: INVITE request sent by the conference server



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7.  Security Considerations

   This document discusses setup of SIP conferences using a request-
   contained URI-list.  Both conferencing and URI-lists services have
   specific security requirements which will be summarized here.
   Conferences generally have authorization rules about who can or
   cannot join a conference, what type of media can or cannot be used,
   etc.  This information is used by the focus to admit or deny
   participation in a conference.  It is RECOMMENDED that these types of
   authorization rules be used to provide security for a SIP conference.

   For this authorization information to be used, the focus needs to be
   able to authenticate potential participants.  Normal SIP mechanisms
   including Digest authentication and certificates can be used.  These
   conference specific security requirements are discussed further in
   the requirements and framework documents.

   For conference creation using a list, there are some additional
   security considerations.  The Framework and Security Considerations
   for SIP URI-List Services (which is documented in RFC xxxx [6])
   discusses issues related to SIP URI-list services.  Given that a
   conference server sending INVITE requests to a set of users acts as
   an URI-list service, implementations of conference servers that
   handle lists MUST follow the security-related rules in RFC xxxx [6].
   These rules include mandatory authentication and authorization of
   clients, and opt-in lists.


8.  IANA Considerations

   This document defines the 'recipient-list-invite' SIP option-tag.  It
   should be registered in the Option Tags subregistry under the SIP
   parameter registry.  The following is the description to be used in
   the registration.

   +------------------------+------------------------------+-----------+
   | Name                   | Description                  | Reference |
   +------------------------+------------------------------+-----------+
   | recipient-list-invite  | The body contains a list of  | [RFCXXXX] |
   |                        | URIs that indicates the      |           |
   |                        | recipients of the SIP INVITE |           |
   |                        | request                      |           |
   +------------------------+------------------------------+-----------+

    Table 1: Registration of the 'recipient-list-invite' Option-Tag in
                                    SIP

   Note to IANA and the RFC editor: replace RFCXXXX above with the RFC



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   number of this specification.


9.  Acknowledges

   Cullen Jennings, Hisham Khartabil, Jonathan Rosenberg, and Keith
   Drage provided useful comments on this document.  Miguel Garcia-
   Martin assembled the dependencies to the 'copyControl' attribute
   extension.


10.  References

10.1.  Normative References

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

   [2]  Troost, R., Dorner, S., and K. Moore, "Communicating
        Presentation Information in Internet Messages: The Content-
        Disposition Header Field", RFC 2183, August 1997.

   [3]  Zimmerer, E., Peterson, J., Vemuri, A., Ong, L., Audet, F.,
        Watson, M., and M. Zonoun, "MIME media types for ISUP and QSIG
        Objects", RFC 3204, December 2001.

   [4]  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.

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

   [6]  Camarillo, G. and A. Roach, "Framework and Security
        Considerations for Session Initiation Protocol (SIP)  Uniform
        Resource Identifier (URI)-List Services",
        draft-ietf-sipping-uri-services-06 (work in progress),
        September 2006.

   [7]  Rosenberg, J., "Extensible Markup Language (XML) Formats for
        Representing Resource Lists",
        draft-ietf-simple-xcap-list-usage-05 (work in progress),
        February 2005.

   [8]  Garcia-Martin, M. and G. Camarillo, "Extensible Markup Language
        (XML) Format Extension for Representing Copy  Control Attributes
        in Resource Lists", draft-ietf-sipping-capacity-attribute-03



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        (work in progress), December 2006.

10.2.  Informative References

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


Authors' Addresses

   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Gonzalo.Camarillo@ericsson.com


   Alan Johnston
   Avaya
   St. Louis, MO  63124
   USA

   Email: alan@sipstation.com

























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Full Copyright Statement

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Acknowledgment

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   Administrative Support Activity (IASA).





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