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Versions: (draft-ietf-sipping-multiple-refer) 00 01 02 03 RFC 5368

SIP Working Group                                           G. Camarillo
Internet-Draft                                                  Ericsson
Intended status: Standards Track                                A. Niemi
Expires: July 12, 2007                                        M. Isomaki
                                                        M. Garcia-Martin
                                                                   Nokia
                                                            H. Khartabil
                                            Khartabil Internet Telephony
                                                              Consulting
                                                         January 8, 2007


Referring to Multiple Resources in the Session Initiation Protocol (SIP)
                  draft-ietf-sip-multiple-refer-01.txt

Status of this Memo

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   This Internet-Draft will expire on July 12, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document defines extensions to the SIP REFER method so that this
   method can be used to refer servers to multiple resources.  These



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   extensions include the use of pointers to Uniform Resource Identifier
   (URI)-lists in the Refer-To header field and the "multiple-refer" SIP
   option-tag.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview of operation  . . . . . . . . . . . . . . . . . . . .  3
   4.  The multiple-refer SIP Option-Tag  . . . . . . . . . . . . . .  4
   5.  Suppressing REFER's Implicit Subscription  . . . . . . . . . .  4
   6.  URI-List Format  . . . . . . . . . . . . . . . . . . . . . . .  5
   7.  Behavior of SIP REFER-Issuers  . . . . . . . . . . . . . . . .  7
   8.  Behavior of REFER-Recipients . . . . . . . . . . . . . . . . .  7
   9.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     12.1.  Normative References  . . . . . . . . . . . . . . . . . . 11
     12.2.  Informative References  . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
   Intellectual Property and Copyright Statements . . . . . . . . . . 15




























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1.  Introduction

   RFC 3261 (SIP) [5] is extended by RFC 3515 [7] with a REFER method
   that allows a user agent to request a server to send a request to a
   third party.  Still, a number of applications need to request a
   server to initiate transactions towards a set of destinations.  In
   one example, the moderator of a conference may want the conference
   server to send BYE requests to a group of participants.  In another
   example, the same moderator may want the conference server to INVITE
   a set of new participants.

   We define an extension to the REFER method so that REFER request can
   be used to refer servers to multiple destinations.  In addition, this
   mechanism uses the suppression of the REFER method implicit
   subscription specified in RFC 4488 [8] to suppress REFER's implicit
   subscription.


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 BCP 14, RFC 2119 [1]
   and indicate requirement levels for compliant implementations.

   We define the following three new terms:

   REFER-Issuer:  the user agent issuing the REFER request.

   REFER-Recipient:  the user agent receiving the REFER request.

   REFER-Target:  the intended final recipient of the request to be
      generated by the REFER-Recipient.


3.  Overview of operation

   This document defines an extension to the SIP REFER method specified
   in RFC 3515 [7] that allows a SIP User Agent Client (UAC) to include
   a URI-list as specified in the XML Format for Representing Resource
   Lists [9] of REFER-Targets in a REFER request and send it to a
   server.  The server will create a new request for each entry in the
   list of REFER-Target URIs.

   The URI-list of REFER-Targets is used in conjunction with the XML
   Format Extension for Representing Copy Control Attributes in Resource
   Lists [11] to allow the sender indicate the role (e.g., 'to', 'cc',
   or anonymous) in which the REFER-Target is involved in the



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   signalling.

   We represent the multiple REFER-Targets of a REFER using a URI-list
   as specified in the XML Format for Representing Resource Lists [9].
   A UAC (User Agent Client) that wants to refer a server to a set of
   destinations creates a SIP REFER request.  The Refer-To header
   contains a pointer to a URI-list, which is included in a body part,
   and an option-tag in the Require header field: "multiple-refer".
   This option-tag indicates the requirement to support the
   functionality described in this specification.

   When the server receives such request it creates a new request per
   destination and sends them.

   This document does not provide any mechanism for UACs to find out
   about the results of a REFER with multiple REFER-Targets.
   Furthermore, it does not provide support for the implicit
   subscription mechanism that is part of the SIP REFER method.  The way
   UACs are kept informed about the results of a REFER is service
   specific.  For example, a UAC sending a REFER to INVITE a set of
   participants to a conference can discover which participants were
   successfully brought into the conference by subscribing to the
   conference state event (RFC 4575) [12].


4.  The multiple-refer SIP Option-Tag

   We define a new SIP option-tag for the Require and Supported header
   fields: "multiple-refer".

   A user agent including the "multiple-refer" option-tag in a Supported
   header field indicates compliance with this specification.

   A user agent generating a REFER with a pointer to a URI-list in its
   Refer-To header field MUST include the "multiple-refer" option-tag in
   the Require header field of the REFER.


5.  Suppressing REFER's Implicit Subscription

   REFER requests with a single REFER-Target establish implicitly a
   subscription to the refer event.  The REFER-Issuer is informed about
   the result of the transaction towards the REFER-Target through this
   implicit subscription.  As described in RFC 3515 [7], NOTIFY requests
   sent as a result of an implicit subscription created by a REFER
   request contain a body of type "message/sipfrag", RFC 3420 [6], that
   describes the status of the transaction initiated by the REFER-
   Recipient.



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   In the case of a REFER-Issuer that generates a REFER with multiple
   REFER-targets, the REFER-Issuer is typically already subscribed to
   other event package that can provide the information about the result
   of the transactions towards the REFER-Targets.  For example, a
   moderator instructing a conference server to send a BYE request to a
   set of participants is usually subscribed to the conference state
   event package for the conference.  Notifications to this event
   package will keep the moderator and the rest of the subscribers
   informed of the current list of conference participants.

   Most of the applications using multiple REFER do not need its
   implicit subscription.  Consequently, a SIP REFER-Issuer generating a
   REFER request with multiple REFER-Targets SHOULD include the
   "norefersub" option-tag in a Require header field and SHOULD include
   a Refer-Sub header field set to "false" to indicate that no
   notifications about the requests should be sent to the REFER-Issuer.
   The REFER-Recipient SHOULD honor the suggestion and also include a
   Refer-Sub header field set to "false" in the 200 (OK) response.  The
   "norefersub" SIP option-tag and the Refer-Sub header field are
   specified in RFC 4488 [8].

      RFC 4488 [8] indicates that a condition for the REFER-Issuer to
      include a Refer-Sub header is that the REFER-Issuer is sure that
      the REFER request will not fork.

   At the time of writing, there is no extension that allows to report
   the status of several transactions over the implicit subscription
   associated with a REFER dialog.  That is the motivation for this
   document to recommend the usage of the "norefersub" option-tag.  If
   in the future such an extension is defined, REFER-Issuers using it
   could refrain from using the "norefersub" option-tag and use the new
   extension instead.


6.  URI-List Format

   As described in the Framework and Security Considerations for SIP
   URI-List Services [10], specifications of individual URI-list
   services, 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 Formats for Representing
   Resource Lists [9] extended with the XML Format Extension for
   Representing Copy Control Attributes in Resource Lists [11].  REFER-
   Recipients handling 'recipient-list' bodies MUST support both of
   these formats and MAY support other formats.




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   As described in the XML Format Extension for Representing Copy
   Control Attributes in Resource Lists [11], 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 referred SIP
   request.  However, depending on the target SIP method, a
   'copyControl' attribute lacks sense.  For example, while a
   'copyControl' attribute can be applied to INVITE requests, it does
   not make sense with mid-dialog requests such as BYE requests.

   In addition to the 'copyControl' attribute, URIs can be tagged with
   the 'anonymize' attribute, also specified in the XML Format Extension
   for Representing Copy Control Attributes in Resource Lists [11] to
   prevent that the server discloses the target URI in a URI-list.

   Additionally, the XML Format Extension for Representing Copy Control
   Attributes in Resource Lists [11] 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 Formats for Representing Resource Lists [9] extended with the XML
   Format Extension for Representing Copy Control Attributes in Resource
   Lists [11].  Conferencing servers supporting this specification MUST
   support both of these formats; UASes MAY support these formats.  Both
   conferencing servers and UASes MAY support other formats.

   Nevertheless, the XML Format for Representing Resource Lists [9]
   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 multiple REFER service defined in
   this document.

   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"
              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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7.  Behavior of SIP REFER-Issuers

   As indicated in Section 4 and Section 5 a SIP REFER-Issuer that
   creates a REFER request with multiple REFER-Targets includes a
   "multiple-refer" and "norefersub" option-tags in the Require header
   field and, if appropriate, a Refer-Sub header field set to "false".
   The REFER-Issuer includes the set of REFER-Targets in a recipient-
   list body whose disposition type is 'recipient-list', as defined in
   the Framework and Security Considerations for SIP URI-List Services
   [10].  The URI-list body is further described in Section 6.

   The Refer-To header field of a REFER request with multiple REFER-
   Targets MUST contain a pointer (i.e., a Content-ID Uniform Resource
   Locator (URL) as per RFC 2392 [3]) that points to the body part that
   carries the URI-list.  The REFER-Issuer SHOULD NOT include any
   particular URI more than once in the URI-list.

   The XML Format for Representing Resource Lists [9] document provides
   features, such as hierarchical lists and the ability to include
   entries by reference relative to the XCAP root URI.  However, these
   features are not needed by the multiple REFER service defined in this
   document.  Therefore, when using the default resource list document,
   SIP REFER-Issuers generating REFER requests with multiple REFER-
   Targets SHOULD use flat lists (i.e., no hierarchical lists) and
   SHOULD NOT use <entry-ref> elements.


8.  Behavior of REFER-Recipients

   The REFER-Recipient follows the rules in Section 2.4.2 of RFC 3515
   [7] to determine the status code of the response to the REFER.

   The REFER-Recipient SHOULD not create an implicit subscription, and
   SHOULD add a Refer-Sub header field set to "false" in the 200 OK
   response.

   If the URI-list of the REFER request contains a repeated URI, the
   REFER-Recipient MUST behave as if that URI appeared in the URI-list
   only once.  The REFER-Recipient uses the comparison rules specific to
   the URI scheme of each of the URIs in the URI-list to determine if
   there is any URI which appears more than once.

   The incoming REFER request typically contains a URI-list document or
   reference 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", and if appropriate for the service, e.g., if
   it is non-mid dialog request, the URI-list server SHOULD include a
   URI-list in each of the outgoing requests.  This list SHOULD be



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   formatted according to the XML Format for Representing Resource Lists
   [9] and the XML Format Extension for Representing Copy Control
   Attributes in Resource Lists [11].  The URI-list server MUST follow
   the procedures specified in XML Format for Representing Resource
   Lists [9] with respect handling of the 'anonymize', 'count' and
   'copyControl' attributes.

   If the server includes a URI-list in an outgoing request, it MUST
   include a Content-Disposition header field, specified in RFC 2183
   [2], with the value set to 'recipient-list-history' and a 'handling'
   parameter, specified in RFC 3204 [4], set to "optional".

   Since the multiple REFER service does not use hierarchical lists nor
   lists that include entries by reference to the XCAP root URI, a
   REFER-Recipient receiving a URI-list with more information than what
   has been described in Section 6 MAY discard all the extra
   information.

   The REFER-Recipient follows the rules in RFC 3515 [7] to generate the
   necessary requests towards the REFER-Targets, acting as if it had
   received a regular (no URI-list) REFER per each URI in the URI-list.


9.  Example

   Figure 2 shows an example flow where a REFER-Issuer sends a multiple-
   REFER request to the focus of a conference, which acts as the REFER-
   Recipient.  The REFER-Recipient generates a BYE request per REFER-
   Target.  Details for using REFER request to remove participants from
   a conference are specified in RFC 4579 [13].





















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   +--------+         +---------+    +--------+  +--------+  +--------+
   | REFER  |         |  REFER  |    | REFER  |  | REFER  |  | REFER  |
   | issuer |         |recipient|    |target 1|  |target 2|  |target 3|
   +--------+         +---------+    +--------+  +--------+  +--------+
        | 1. REFER         |             |           |           |
        | ---------------->|             |           |           |
        | 2. 202 Accepted  |             |           |           |
        |<---------------- |   3. BYE    |           |           |
        |                  | ----------->|           |           |
        |                  |   4. BYE    |           |           |
        |                  | ----------------------->|           |
        |                  |   5. BYE    |           |           |
        |                  | ----------------------------------->|
        |                  |   6. 200 OK |           |           |
        |                  |<----------- |           |           |
        |                  |   7. 200 OK |           |           |
        |                  |<----------------------- |           |
        |                  |   8. 200K OK|           |           |
        |                  |<----------------------------------- |
        |                  |             |           |           |
        |                  |             |           |           |
        |                  |             |           |           |

    Figure 2: Example flow or a REFER request containin multiple REFER-
                                  Targets

   The REFER request (1) contains a Refer-To header field that includes
   a pointer to the message body, which carries a list with the URIs of
   the REFER-Targets.  In this example, the URI-list does not contain
   the copyControl attribute extension.  The REFER's Require header
   field carries the "multiple-refer" and "norefersub" option-tags.  The
   Request-URI is set to a Globally Routable User Agent URIs (GRUU) [14]
   (as a guarantee that the REFER request will not fork).  The Refer-Sub
   header field is set to "false" to request the suppression of the
   implicit subscription.  Figure 3 shows an example of this REFER
   request.  The resource list document contains the list of REFER-
   Target URIs along with the method of the SIP request that the REFER-
   Recipient generates.













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   REFER sip:conf-123@example.com;gruu;opaque=hha9s8d-999a  SIP/2.0
   Via: SIP/2.0/TCP client.chicago.example.com
           ;branch=z9hG4bKhjhs8ass83
   Max-Forwards: 70
   To: "Conference 123" <sip:conf-123@example.com>
   From: Carol <sip:carol@chicago.example.com>;tag=32331
   Call-ID: d432fa84b4c76e66710
   CSeq: 2 REFER
   Contact: <sip:carol@client.chicago.example.com>
   Refer-To: <cid:cn35t8jf02@example.com>
   Refer-Sub: false
   Require: multiple-refer, norefersub
   Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
   Allow-Events: dialog
   Accept: application/sdp, message/sipfrag
   Content-Type: application/resource-lists+xml
   Content-Disposition: recipient-list
   Content-Length: 362
   Content-ID: <cn35t8jf02@example.com>

   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns="urn:ietf:params:xml:ns:resource-lists"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
     <list>
       <entry uri="sip:bill@example.com?method=BYE" />
       <entry uri="sip:joe@example.org?method=BYE" />
       <entry uri="sip:ted@example.net?method=BYE" />
     </list>
   </resource-lists>

            Figure 3: REFER request with multiple REFER-Targets

   Figure 4 shows an example of the BYE request (3) that the REFER-
   Recipient sends to the first REFER-Target.

   BYE sip:bill@example.com SIP/2.0
   Via: SIP/2.0/TCP conference.example.com
           ;branch=z9hG4bKhjhs8assmm
   Max-Forwards: 70
   From: "Conference 123" <sip:conf-123@example.com>;tag=88734
   To: <sip:bill@example.com>;tag=29872
   Call-ID: d432fa84b4c34098s812
   CSeq: 34 BYE
   Content-Length: 0

                           Figure 4: BYE request





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10.  Security Considerations

   The Framework and Security Considerations for SIP URI-List Services
   [10] discusses issues related to SIP URI-list services.  Given that a
   REFER-Recipient accepting REFER requests with multiple REFER-targets
   acts as an URI-list service, implementations of this type of server
   MUST follow the security-related rules in the Framework and Security
   Considerations for SIP URI-List Services [10].  These rules include
   mandatory authentication and authorization of clients, and opt-in
   lists.

   Additionally, REFER-Recipients SHOULD only accept REFER requests
   within the context of an application the server understands (e.g., a
   conferencing application).  This implies that servers MUST NOT accept
   REFER requests for methods they do not understand.  The idea behind
   these two rules is that servers are not used as dumb servers whose
   only function is to fan-out random messages they do not understand.


11.  IANA Considerations

   This document defines a new SIP option-tag: "multiple-refer".  This
   option-tag should be registered in the SIP Parameters registry.

   The following row shall be added to the "Option Tags" section of the
   SIP Parameter Registry:

   +-----------------+-------------------------------------+-----------+
   | Name            | Description                         | Reference |
   +-----------------+-------------------------------------+-----------+
   | multiple-refer  | This option tag indicates support   | [RFCXXXX] |
   |                 | for REFER requests that contain a   |           |
   |                 | resource list document describing   |           |
   |                 | multiple REFER targets.             |           |
   +-----------------+-------------------------------------+-----------+

      Table 1: Registration of the 'multiple-refer' Option-Tag in SIP

   Note to the RFC Editor: Please replace [RFCXXXX] with the RFC number
   of this specification.


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.



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

   [3]   Levinson, E., "Content-ID and Message-ID Uniform Resource
         Locators", RFC 2392, August 1998.

   [4]   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.

   [5]   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.

   [6]   Sparks, R., "Internet Media Type message/sipfrag", RFC 3420,
         November 2002.

   [7]   Sparks, R., "The Session Initiation Protocol (SIP) Refer
         Method", RFC 3515, April 2003.

   [8]   Levin, O., "Suppression of Session Initiation Protocol (SIP)
         REFER Method Implicit Subscription", RFC 4488, May 2006.

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

   [10]  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.

   [11]  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 (work in progress),
         December 2006.

12.2.  Informative References

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

   [13]  Johnston, A. and O. Levin, "Session Initiation Protocol (SIP)



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         Call Control - Conferencing for User Agents", BCP 119,
         RFC 4579, August 2006.

   [14]  Rosenberg, J., "Obtaining and Using Globally Routable User
         Agent (UA) URIs (GRUU) in the  Session Initiation Protocol
         (SIP)", draft-ietf-sip-gruu-11 (work in progress),
         October 2006.


Authors' Addresses

   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Gonzalo.Camarillo@ericsson.com


   Aki Niemi
   Nokia
   P.O. Box 321
   NOKIA GROUP, FIN 00045
   Finland

   Email: Aki.Niemi@nokia.com


   Markus Isomaki
   Nokia
   Itamerenkatu 11-13
   Helsinki  00180
   Finland

   Email: Markus.Isomaki@nokia.com


   Miguel A. Garcia-Martin
   Nokia
   P.O.Box 407
   NOKIA GROUP, FIN  00045
   Finland

   Email: miguel.an.garcia@nokia.com






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   Hisham Khartabil
   Khartabil Internet Telephony Consulting

   Phone: +61 416 108 890
   Email: hisham.khartabil@gmail.com














































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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   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, et al.         Expires July 12, 2007                [Page 15]


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