SIPPING Working Group                                       G. Camarillo
Internet-Draft                                                  Ericsson
Expires: May 28, 2005                                        A. Johnston
                                                       November 27, 2004

 Conference Establishment Using Request-Contained Lists in the Session
                       Initiation Protocol (SIP)

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Copyright Notice

   Copyright (C) The Internet Society (2004).


   This document describes how to create a conference using SIP URI-list
   services.  In particular, we describe 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 Format  . . . . . . . . . . . . . . . . . . . . . . . 3
   5.   Conference Server Behavior . . . . . . . . . . . . . . . . . . 4
   6.   Re-INVITEs . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.   Example  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   8.   Security Considerations  . . . . . . . . . . . . . . . . . . . 6
   9.   Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . 7
   10.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   10.1   Normative References . . . . . . . . . . . . . . . . . . . . 7
   10.2   Informational References . . . . . . . . . . . . . . . . . . 8
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8
        Intellectual Property and Copyright Statements . . . . . . . . 9

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1.  Introduction

   Section 4.5 of [3] describes how to create a conference using ad-hoc
   SIP [2] 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 [3].

   Some environments have tough requirements regarding conference
   establishment time.  So, 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 [4].

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   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 [4], 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 Format

   As described in [4], 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

   The default format for recipient-list bodies for conferencing UAs
   (User Agents) and servers is the resource list format defined in [5].
   So, conferencing UAs and servers handling recipient-list bodies MUST
   support this format and MAY support other formats.

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   Nevertheless, the Extensible Markup Language (XML) Configuration
   Access Protocol (XCAP) resource list document 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 resource
   list document.

   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
       <entry uri="" />
       <entry uri="" />
       <entry uri="" />

                           Figure 1: URI List

5.  Conference Server Behavior

   On reception of an INVITE with a recipient-list body as described in
   Section 3, a conference server MUST follow the rules described in [3]
   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 [3] (e.g., using CPCP [6]).

   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 [3].

   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.

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   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 [7].

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.  Example

   The following is an example of an INVITE request, which carries a URI
   list in a recipient-list body part, sent by a UA to a conference
   factory application.  Note that since the INVITE carries an SDP
   description as well, it contains a multipart body.

   Via: SIP/2.0/TCP
   Max-Forwards: 70
   To: Conf Factory <>

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   From: Carol <>;tag=32331
   Call-ID: d432fa84b4c76e66710
   CSeq: 1 INVITE
   Contact: <>
   Allow-Events: dialog
   Accept: application/sdp, message/sipfrag
   Conten-Type: multipart/mixed;boundary="boundary1"
   Content-Length: 690

   Content-Type: application/sdp

   o=carol 2890844526 2890842807 IN IP4
   c=IN IP4
   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

   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"
       <entry uri="" />
       <entry uri="" />
       <entry uri="" />

                        Figure 2: INVITE request

8.  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

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   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 [4] 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 [4].  These rules include mandatory authentication and
   authorization of clients, and opt-in lists.

9.  Acknowledges

   Cullen Jennings, Hisham Khartabil, and Jonathan Rosenberg provided
   useful comments on this document.

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]  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.

   [3]  Johnston, A. and O. Levin, "Session Initiation Protocol Call
        Control - Conferencing for User Agents",
        draft-ietf-sipping-cc-conferencing-05 (work in progress),
        October 2004.

   [4]  Camarillo, G., "Requirements and Framework for Session
        Initiation Protocol (SIP)Uniform  Resource Identifier (URI)-List
        Services", draft-ietf-sipping-uri-services-01 (work in
        progress), October 2004.

   [5]  Rosenberg, J., "Extensible Markup Language (XML) Formats for
        Representing Resource Lists",

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        draft-ietf-simple-xcap-list-usage-04 (work in progress), October

10.2  Informational References

   [6]  Koskelainen, P. and H. Khartabil, "An Extensible Markup Language
        (XML) Configuration Access Protocol (XCAP)  Usage for Conference
        Policy Manipulation", draft-koskelainen-xcon-xcap-cpcp-usage-02
        (work in progress), February 2004.

   [7]  Rosenberg, J. and H. Schulzrinne, "A Session Initiation Protocol
        (SIP) Event Package for Conference State",
        draft-ietf-sipping-conference-package-06 (work in progress),
        October 2004.

Authors' Addresses

   Gonzalo Camarillo
   Hirsalantie 11
   Jorvas  02420


   Alan Johnston
   100 South 4th Street
   St. Louis, MO  63102


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