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rfc:rfc5366

Network Working Group G. Camarillo Request for Comments: 5366 Ericsson Category: Standards Track A. Johnston

                                                                 Avaya
                                                          October 2008
      Conference Establishment Using Request-Contained Lists
              in the Session Initiation Protocol (SIP)

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

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.

Table of Contents

 1. Introduction ....................................................2
 2. Terminology .....................................................2
 3. User Agent Client Procedures ....................................2
    3.1. Response Handling ..........................................2
    3.2. Re-INVITE Request Generation ...............................3
 4. URI-List Document Format ........................................3
 5. Conference Server Procedures ....................................5
    5.1. Re-INVITE Request Handling .................................6
 6. Example .........................................................6
 7. Security Considerations ........................................10
 8. IANA Considerations ............................................10
 9. Acknowledgments ................................................11
 10. References ....................................................11
    10.1. Normative References .....................................11
    10.2. Informative References ...................................12

Camarillo & Johnston Standards Track [Page 1] RFC 5366 INVITE-Contained Lists October 2008

1. Introduction

 Section 5.4 of [RFC4579] describes how to create a conference using
 ad hoc SIP [RFC3261] 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 [RFC4579].
 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 [RFC5363].

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 [RFC2119].

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 [RFC5363],
 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.
 The INVITE transaction is also part of an offer/answer exchange that
 will establish a session between the UAC and the conference server,
 as specified in [RFC4579].  Therefore, the INVITE request may need to
 carry a multipart body: a session description and a URI list.

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

Camarillo & Johnston Standards Track [Page 2] RFC 5366 INVITE-Contained Lists October 2008

 the conference, and that the server understood the URI list.  If the
 UAC wishes to obtain information about the status of other users in
 the conference, it SHOULD use general conference mechanisms, such as
 the conference package, which is defined in [RFC4575].

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 'recipient-
 list' bodies in re-INVITE requests (although future extensions may
 define them).  Therefore, UACs SHOULD NOT include 'recipient-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 [RFC5363], 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
 [RFC4826]) extended with the "Extensible Markup Language (XML) Format
 Extension for Representing Copy Control Attributes in Resource Lists"
 [RFC5364].  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 "Extensible Markup Language (XML) Format Extension
 for Representing Copy Control Attributes in Resource Lists"
 [RFC5364], each URI can be tagged with a 'copyControl' attribute set

Camarillo & Johnston Standards Track [Page 3] RFC 5366 INVITE-Contained Lists October 2008

 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 the conference
 server from disclosing the target URI in a URI list.
 In addition, "Extensible Markup Language (XML) Format Extension for
 Representing Copy Control Attributes in Resource Lists" [RFC5364]
 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 [RFC4826] extended with "Extensible Markup Language
 (XML) Format Extension for Representing Copy Control Attributes in
 Resource Lists" [RFC5364].  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 [RFC4826]
 provides features, such as hierarchical lists and the ability to
 include entries by reference relative to the XML Configuration Access
 Protocol (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 [RFC4826]) extended with
 "Extensible Markup Language (XML) Format Extension for Representing
 Copy Control Attributes in Resource Lists" [RFC5364].
 <?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

Camarillo & Johnston Standards Track [Page 4] RFC 5366 INVITE-Contained Lists October 2008

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 [RFC4579] 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
 [RFC4579].
 The INVITE transaction is also part of an offer/answer exchange that
 will establish a session between the UAC and the conference server,
 as specified in [RFC4579].  Therefore, the INVITE request may carry a
 multipart body: a session description and a URI list.
 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 [RFC4579].
 The incoming INVITE request will contain a URI-list body or reference
 (as specified in [RFC5363]) 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 [RFC4826]) and the
 copyControl extension specified in [RFC5364].
 The URI-list service MUST follow the procedures specified in
 [RFC5364] 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 [RFC2183]) with the value set to 'recipient-list-
 history' and a 'handling' parameter (as specified in [RFC3204]) set
 to "optional".

Camarillo & Johnston Standards Track [Page 5] RFC 5366 INVITE-Contained Lists October 2008

5.1. Re-INVITE Request Handling

 At this point, there are no semantics associated with 'recipient-
 list' bodies in re-INVITE requests (although future extensions may
 define them).  Therefore, a conference server receiving a re-INVITE
 request with a 'recipient-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.
    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) identified 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.

Camarillo & Johnston Standards Track [Page 6] RFC 5366 INVITE-Contained Lists October 2008

 +--------+        +---------+      +--------+ +--------+ +--------+
 |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.
 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

Camarillo & Johnston Standards Track [Page 7] RFC 5366 INVITE-Contained Lists October 2008

  1. -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
  1. -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>
 </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 that 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.

Camarillo & Johnston Standards Track [Page 8] RFC 5366 INVITE-Contained Lists October 2008

 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
 Content-Type: multipart/mixed;boundary="boundary1"
 Content-Length: 690
  1. -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
  1. -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

Camarillo & Johnston Standards Track [Page 9] RFC 5366 INVITE-Contained Lists October 2008

7. Security Considerations

 This document discusses setup of SIP conferences using a request-
 contained URI list.  Both conferencing and URI-list services have
 specific security requirements, which are 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 -- [RFC4245] and [RFC4353].
 For conference creation using a list, there are some additional
 security considerations.  "Framework and Security Considerations for
 Session Initiation Protocol (SIP) URI-List Services" [RFC5363]
 discusses issues related to SIP URI-list services.  Given that a
 conference server sending INVITE requests to a set of users acts as a
 URI-list service, implementations of conference servers that handle
 lists MUST follow the security-related rules in [RFC5363].  These
 rules include opt-in lists and mandatory authentication and
 authorization of clients.

8. IANA Considerations

 This document defines the 'recipient-list-invite' SIP option-tag.  It
 has been registered in the Option Tags subregistry under the SIP
 parameter registry.  The following is the description used in the
 registration:
 +------------------------+------------------------------+-----------+
 | Name                   | Description                  | Reference |
 +------------------------+------------------------------+-----------+
 | recipient-list-invite  | The body contains a list of  | [RFC5366] |
 |                        | URIs that indicates the      |           |
 |                        | recipients of the SIP INVITE |           |
 |                        | request                      |           |
 +------------------------+------------------------------+-----------+
   Table 1: Registration of the 'recipient-list-invite' option-tag
                                in SIP

Camarillo & Johnston Standards Track [Page 10] RFC 5366 INVITE-Contained Lists October 2008

9. Acknowledgments

 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

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2183]  Troost, R., Dorner, S., and K. Moore, Ed., "Communicating
            Presentation Information in Internet Messages: The
            Content-Disposition Header Field", RFC 2183, August 1997.
 [RFC3204]  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.
 [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.
 [RFC4579]  Johnston, A. and O. Levin, "Session Initiation Protocol
            (SIP) Call Control - Conferencing for User Agents", BCP
            119, RFC 4579, August 2006.
 [RFC4826]  Rosenberg, J., "Extensible Markup Language (XML) Formats
            for Representing Resource Lists", RFC 4826, May 2007.
 [RFC5363]  Camarillo, G. and A.B. Roach, "Framework and Security
            Considerations for Session Initiation Protocol (SIP) URI-
            List Services", RFC 5363, October 2008.
 [RFC5364]  Garcia-Martin, M. and G. Camarillo, "Extensible Markup
            Language (XML) Format Extension for Representing Copy
            Control Attributes in Resource Lists", RFC 5364, October
            2008.

Camarillo & Johnston Standards Track [Page 11] RFC 5366 INVITE-Contained Lists October 2008

10.2. Informative References

 [RFC4245]  Levin, O. and R. Even, "High-Level Requirements for
            Tightly Coupled SIP Conferencing", RFC 4245, November
            2005.
 [RFC4353]  Rosenberg, J., "A Framework for Conferencing with the
            Session Initiation Protocol (SIP)", RFC 4353, February
            2006.
 [RFC4575]  Rosenberg, J., Schulzrinne, H., and O. Levin, Ed., "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

Camarillo & Johnston Standards Track [Page 12] RFC 5366 INVITE-Contained Lists October 2008

Full Copyright Statement

 Copyright (C) The IETF Trust (2008).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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Camarillo & Johnston Standards Track [Page 13]

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