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Versions: 00 01 02 RFC 5366

SIPPING Working Group                                       G. Camarillo
Internet-Draft                                                  Ericsson
Expires: March 22, 2007                                      A. Johnston
                                                                   Avaya
                                                      September 18, 2006


 Conference Establishment Using Request-Contained Lists in the Session
                       Initiation Protocol (SIP)
              draft-ietf-sip-uri-list-conferencing-00.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes how to create a conference using SIP URI-list
   services.  In particular, it describes a mechanism that allows a
   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.  Providing a Conference Server with a URI-List  . . . . . . . .  3
   4.  URI-List Document  . . . . . . . . . . . . . . . . . . . . . .  3
   5.  Conference Server Behavior . . . . . . . . . . . . . . . . . .  5
   6.  Re-INVITEs . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   7.  Option-tag . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   8.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   11. Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 12
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     12.1.  Normative References  . . . . . . . . . . . . . . . . . . 12
     12.2.  Informative References  . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 15

































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1.  Introduction

   Section 5.4 of [5] describes how to create a conference using ad-hoc
   SIP [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).

   Once the client obtains the conference URI, it can add participants
   to the newly created conference in several ways, which are described
   in [5].

   Some environments have tough requirements regarding conference
   establishment time.  They require the client to be able to request
   the creation of an ad-hoc conference and to provide the 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 [6].


2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
   RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
   described in BCP 14, RFC 2119 [1] and indicate requirement levels for
   compliant implementations.


3.  Providing a Conference Server with a URI-List

   A client that wants to include the set of initial participants in its
   initial INVITE to create an ad-hoc conference, adds a body whose
   disposition type is 'recipient-list', as defined in [6], with a URI-
   list that contains the participants that the client wants the server
   to INVITE.  The client sends this INVITE to the conference factory
   URI.


4.  URI-List Document

   As described in [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) and servers is the XML resource list format [7]



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   extended with the XML Format Extension for Representing Copy Control
   Attributes in Resource Lists [8].  So, conferencing UACs and servers
   handling '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 [8], each URI can be tagged with
   a 'copyControl' attribute set to either "to", "cc", or "bcc",
   indicating the role in which the 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.

   Additionally, the XML Format Extension for Representing Copy Control
   Attributes in Resource Lists [8] defines a 'recipient-list-history'
   body that contains the list of recipients.  The default format for
   'recipient-list-history' bodies for conference services is also the
   XML resource list document format [7] extended with the XML Format
   Extension for Representing Copy Control Attributes in Resource Lists
   [8].  Conferencing servers MUST support both of these formats; UASes
   MAY support these formats.  Both conferencing servers and UASes MAY
   support other formats.

   Nevertheless, the XML resource list document [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 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 [7] extended with the XML Format Extension for
   Representing Copy Control Attributes in Resource Lists [8].












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   <?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


5.  Conference Server Behavior

   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 [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
   [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 [5].

   Note that the status code in the response to the INVITE 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) means that the conference was created
   successfully, that the client that generated the INVITE is in the
   conference, and that the server understood the URI-list.  If the
   client wishes to obtain information about the status of other users
   in the conference it SHOULD use general conference mechanisms, such
   as the conference package [9].

   The incoming INVITE request typically contains a URI-list body or
   reference [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
   [7] and the copyControl extension specified in [8].  The URI-list
   service MUST follow the procedures specified in XML format for
   representing resource lists [8] with respect to the handling of the
   'anonymize', 'count' and 'copyControl' attributes.



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


6.  Re-INVITEs

   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 client and the conference server has
   been established, the client may need to send subsequent INVITE
   requests (typically referred to as re-INVITEs) 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-INVITEs (although future extensions may define them).
   Therefore, clients SHOULD NOT include resource-list bodies in re-
   INVITEs sent to a conference server.

   A conference server receiving a re-INVITE with a resource-list body,
   following standard SIP procedures, rejects it with a 415 (Unsupported
   Media Type) response.

      Note that a difference between an initial INVITE request and a re-
      INVITE is that while the initial INVITE is sent to the conference
      factory URI, the re-INVITE is sent to the URI provided by the
      server in a Contact header field when the dialog was established.
      Therefore, from the client'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.


7.  Option-tag

   This document defines the 'recipient-list-invite' option-tag for use
   in the Require and Supported SIP header fields.

      This option-tag is used to ensure that a server can process the
      'recipient-list' body used in an INVITE request.  It also provides
      a mechanism to discover the capability of the server in responses
      to OPTIONS requests.

   User agent clients generating an INVITE request containing a
   'recipient-list' body, as described in previous sections, MUST
   include this option-tag in a Require header field.  User agents that
   are able to receive and process INVITEs with a 'recipient-list' body,



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   as described in previous sections, SHOULD include this option-tag in
   a Supported header field when responding to OPTIONS requests.

      Note that according to Section 6, requests and responses coming
      from the URI of an ongoing conference would not carry this option-
      tag in a Supported header field.  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 this option-tag in, for example,
      responses to OPTIONS requests.


8.  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 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




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   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.

   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" />



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       <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>
   </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
   Conten-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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9.  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 may or may
   not join a conference, what type of media may or may not 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 [6] discusses issues related to SIP URI-
   list services.  Given that a conference server sending INVITEs 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 [6].  These rules include mandatory authentication and
   authorization of clients, and opt-in lists.


10.  IANA Considerations

   This document defines the 'recipient-list-invite' SIP option-tag in
   Section 7.  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
   number of this specification.



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11.  Acknowledges

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


12.  References

12.1.  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-05 (work in progress),
        January 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 Capacity  Attributes in
        Resource Lists", draft-ietf-sipping-capacity-attribute-01 (work
        in progress), September 2006.






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12.2.  Informative References

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














































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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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