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Versions: 00 01 02 03 04 05 06 07 RFC 5364

SIPPING Working Group                                   M. Garcia-Martin
Internet-Draft                                                     Nokia
Intended status: Standards Track                            G. Camarillo
Expires: September 28, 2007                                     Ericsson
                                                          March 27, 2007


Extensible Markup Language (XML) Format Extension for Representing Copy
                  Control Attributes in Resource Lists
              draft-ietf-sipping-capacity-attribute-04.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   In certain types of multimedia communications, a Session Initiation
   Protocol (SIP) request is distributed to a group of SIP User Agents
   (UAs).  The sender sends a single SIP request to a server which
   further distributes the request to the group.  This SIP request
   contains a list of Uniform Resource Identifiers (URIs), which
   identify the recipients of the SIP request.  This URI-list is



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   expressed as a resource list XML document.  This specification
   defines an XML extension to the XML resource list format that allows
   the sender of the request to qualify a recipient with a copy control
   level similar to the copy control level of existing e-mail systems.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview of operation  . . . . . . . . . . . . . . . . . . . .  4
   4.  Extension to the resource lists data format  . . . . . . . . .  6
   5.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  Carrying URI-lists in SIP  . . . . . . . . . . . . . . . . . . 11
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     9.1.  Disposition Type Registration  . . . . . . . . . . . . . . 13
     9.2.  XML Namespace Registration . . . . . . . . . . . . . . . . 13
     9.3.  XML Schema Registration  . . . . . . . . . . . . . . . . . 14
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     11.2. Informational References . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
   Intellectual Property and Copyright Statements . . . . . . . . . . 17

























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1.  Introduction

   The Framework and Security Considerations for Session Initiation
   Protocol (SIP) URI-List Services [9] describes a generic framework
   for carrying Uniform Resource Identifier (URI)-lists in SIP [4]
   messages.  Specifically, the document provides a common framework for
   specific implementations of URI-list services, such as conferences
   initiated with INVITE requests [10] or Multiple-recipient MESSAGE
   requests [11].

   Common to all URI-list services is the presence of a SIP request that
   contains a collection of resources, typically expressed as an XML
   resource list [7].  SIP requests carrying resource lists can appear
   either in requests received by the URI-list server, indicating the
   list of intended recipients, or in each of the requests that the URI-
   list server sends to recipients, indicating the list of recipients of
   the same SIP request.

   Although the XML resource list [7] provides a powerful mechanism for
   describing a list of resources, there is a need for a copy control
   attribute to determine whether a resource is receiving a SIP request
   as a primary recipient, a carbon copy, or a blind carbon copy.  This
   is similar to common e-mail systems, where the sender can categorize
   each recipient as To, Cc, or Bcc recipient.

   This document addresses this problem by providing an extension to the
   XML resource list [7] that enables the sender to supply a copy
   control attribute that labels each recipient as a "to", "cc", or
   "bcc" recipient.  This attribute indicates whether the recipient is
   receiving a primary copy of the SIP request, a carbon copy, or a
   blind carbon copy.  Additionally, we provide the sender with the
   capability of indicating in the URI-list that one or more resources
   should be anonymized, so that some recipients' URIs are not disclosed
   to the other recipients.  Instead, these URIs are replaced with
   anonymous URIs.

   The remainder of this document is organized as follows: Section 2
   introduces the terminology used throughout this specification.
   Section 3 gives an overview of operation.  Section 4 formally defines
   an extension to URI-lists.  The XML schema definition is provided in
   Section 5.  Section 6 shows examples of the URI-lists with the
   extensions defined in this document.  Section 7 discusses the
   implications of carrying URI-lists in SIP messages.


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",



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   "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.

   URI-list service:  SIP application service that receives a SIP
      request containing a URI-list and sends a similar SIP request to
      each URI in the list.

   Intended recipient:  The intended final recipient of the request to
      be generated by URI-list service.

   Copy control:   An attribute assigned by the sender to a URI in a XML
      resource list.  Its purpose is to indicate to the recipient
      whether he is getting a primary, carbon, or blind carbon copy of
      the SIP request.

   Recipient list or recipient XML resource list:   An XML resource list
      containing the list of intended recipients.  The sender sets this
      list in the SIP request he sends to the URI-list server.

   Recipient-history list or recipient-history XML resource list:   An
      XML resource list containing the visible list of recipients (i.e.,
      those non-anonymous non-bcc).  The URI-list server creates this
      list, based on the recipient list, and includes it in each of the
      SIP requests it sends to each recipient.



3.  Overview of operation

   Figure 1 depicts a general overview of the operation of a URI-list
   server.  A SIP User Agent Client (UAC) issuer sends a SIP request
   (F1) to a URI-list server containing a recipient list.  The URI-list
   server generates a SIP request to each recipient, according to the
   specific SIP method.  Each of these SIP requests contains a
   recipient-history list that indicates the visible list of recipients
   of the SIP request.














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   +--------+        +---------+        +--------+ +--------+ +--------+
   |SIP UAC |        | URI-list|        |intended| |intended| |intended|
   | issuer |        |  server |        | recip. | | recip. | | recip. |
   |        |        |         |        |   1    | |   2    | |   3    |
   +--------+        +---------+        +--------+ +--------+ +--------+
       |                  |                 |          |          |
       | F1. SIP request  |                 |          |          |
       |  (recipt. list)  |                 |          |          |
       | ---------------->|                 |          |          |
       | F2. 2xx response |                 |          |          |
       |<---------------- | F3. SIP request |          |          |
       |                  | (recp-hist.list)|          |          |
       |                  | --------------->|          |          |
       |                  | F4. SIP request |          |          |
       |                  | (recp-hist.list)|          |          |
       |                  | -------------------------->|          |
       |                  | F5. SIP request |          |          |
       |                  | (recp-hist.list)|          |          |
       |                  | ------------------------------------->|
       |                  |  F6. 200 OK     |          |          |
       |                  |<--------------- |          |          |
       |                  |  F7. 200 OK     |          |          |
       |                  |<-------------------------- |          |
       |                  |  F8. 200 OK     |          |          |
       |                  |<------------------------------------- |
       |                  |                 |          |          |
       |                  |                 |          |          |
       |                  |                 |          |          |

                      Figure 1: Example of operation

   The URI-list mechanism allows a sender to specify multiple targets
   for a SIP request by including a recipient XML resource list [7] in
   the body of the SIP request.  This recipient list includes the target
   URIs of the SIP request (the actual procedures are method specific
   and outside the scope of this document).  Each target URI may also be
   marked with a copy control attribute to indicate the copy level in
   which the recipient is receiving the SIP request.  This is achieved
   by the sender qualifying each URI in the URI-list with a
   'copyControl' attribute.  The available values of the 'copyControl'
   attribute include "to", "cc", and "bcc" (analogous to e-mail).  This
   is discussed in greater detailed in Section 4.  When the URI-list
   server expands the request to each recipient, the URI-list server
   includes a recipient-history XML resource list built upon the
   recipient list received from the sender.  The recipient-history XML
   resource list replaces the recipient list in the SIP requests
   generated by the URI-list server towards each recipient.  The URI-
   list server copies from the recipient list those targets which are



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   marked with the "to" and "cc" copy control level, and pastes them in
   the recipient-history list.  The URI-list server explicitly excludes
   from the copy those URIs marked with a "bcc" copy control.  When a
   recipient receives the SIP request containing the recipient-history
   XML resource list, he is able to determine which other visible
   recipients are getting the same SIP requests, and whether they are
   marked with the "to" or "cc" copy control level.  Later, if needed,
   the recipient can generate a reply to those visible recipients.

   In addition to the 'copyControl' attribute for a URI in an XML
   resource list, we define a second boolean attribute called
   'anonymize'.  The sender of a SIP request can mark a URI in a
   recipient XML resource list with the 'anonymize' attribute to
   indicate the URI-list server that the URI marked with that attribute
   is to be replaced with an anonymous URI in the recipient-history XML
   resource list.  This provides a knowledge to recipients of a SIP
   request of a number of additional recipients whose URIs have not been
   disclosed.

   There are cases when the sender marks several URIs with the
   'anonymize' attribute.  The URI-list server can group the anonymized
   URIs in a single anonymized URI within its copy control level, and
   provide a count of the number of anonymized URIs.  To support this
   scenario, we define a new 'count' attribute to a URI in the
   recipient-history XML resource list.  It is expected that the 'count'
   attribute is only used with anonymous URIs, although syntactically it
   is possible to add a 'count' attribute to any URI in any XML resource
   list.

   Initially, it may be thought that the 'anonymize' attribute overlaps
   with the "bcc" value of the 'copyControl' attribute.  However, there
   are differences between them.  If the sender qualifies a URI with a
   'copyControl' attribute of "bcc" in the recipient XML resource list,
   the URI-list server will completely remove that URI from the
   recipient-history XML resource list.  Recipients of the SIP request
   will not notice that one or more extra URIs also received the
   request.  However, if the sender qualifies a URI with the 'anonymize'
   attribute in the recipient XML resource list, the URI-list server
   will replace the URI with an anonymous one in the recipient-history
   list.  Recipients of the SIP request will notice that there have been
   one or more additional recipients of the same request, but their URIs
   have not been disclosed.


4.  Extension to the resource lists data format

   This document defines an extension to the XML resource list data
   format [7] that allows the sender to indicate a copy control



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   attribute that qualifies a recipient with a copy control level.  We
   define a new 'copyControl' attribute to the <entry> element of the
   resource list document format [7].  The 'copyControl' attribute has
   similar semantics to the type of destination address in e-mail
   systems.  It can take the values "to", "cc", and "bcc".  A "to" value
   of the 'copyControl' attribute indicates that the resource is
   considered a primary recipient of the SIP request.  A "cc" value
   indicates that the resource receives a carbon copy of the SIP
   request.  A "bcc" value indicates that the resource receives a blind
   carbon copy of the SIP request (i.e., this URI is not disclosed in
   the recipient-history list).  The default 'copyControl' value is
   "bcc".  That is, the absence of a 'copyControl' attribute MUST be
   treated as if the 'copyControl' was set to "bcc".  URI-list servers
   use URIs marked with the "bcc" 'copyControl' attribute to route SIP
   requests, but MUST NOT include them in recipient-history lists.

   A new 'anonymize' attribute can be included in a <entry> element of
   the resource list document format [7].  If set to a "true" value, it
   provides an indication to the URI-list server for not disclosing the
   URI itself in a URI-list sent to the recipient, but instead, to
   anonymize the URI (i.e., making it bogus in the recipient-history XML
   resource list).  URI-list servers can use URIs tagged with the
   'anonymize' attribute for routing SIP requests, but MUST convert them
   to an anonymized URI (such as sip:anonymous@anonymous.invalid) in
   recipient-history lists.  The default value of the 'anonymize'
   attribute is "false".

   There are occasions where the URI-list server encounters the same URI
   entry duplicated in a resource list, where duplicated URI entries are
   tagged with the same or different values of the 'copyControl'
   attribute.  There are no reasonable usages that justify duplicated
   URIs in resource lists, thus, this is considered an error.  URI-list
   servers MUST NOT send duplicated copies of the same SIP request to
   the same intended recipient.  In case the URI-list server encounters
   the same URI entry in a resource list, it MUST send at most a single
   copy of the request to that intended recipient.  The URI-list server
   MUST select the highest precedence value of the 'copyControl'
   attribute of the duplicated entries for the same intended recipient.
   The order of precedence of the values of the 'copyControl' attribute
   is: "to", "cc", and "bcc".  Once the URI-list server has selected a
   value for the 'copyControl' attribute of an intended recipient, the
   URI-list can continue processing the request.

   Processing of URIs tagged with a 'copyControl' attribute set to a
   "bcc" value has higher precedence over the 'anonymize' attribute.
   Thus, if the 'copyControl' of a URI is set to "bcc", the URI-list
   server MUST remove that URI from the recipient-history list, and the
   'anonymize' attribute will be ignored.  Therefore, the 'anonymize'



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   attribute is only useful for those URIs tagged with a 'copyControl'
   of "to" or "cc".

   A new 'count' attribute can be also included in a <entry> element of
   the resource list document format [7].  It provides the number of
   equal URIs.  Typically, recipient lists created by UACs will not have
   equal (or duplicate) URI entries, thus, it is not expected to contain
   URIs tagged with 'count' attributes.  However, recipient-history
   lists can contain duplicated anonymized URIs, therefore, it is
   expected that recipient-history lists will contain 'count'
   attributes.  The default value of the 'count' attribute is "1".

   The 'copyControl', 'anonymize', and 'count' attributes SHOULD be
   included as modifiers of any of the child elements included in the
   <list> element of a resource list (e.g., attribute of the <entry> or
   <external> elements).

   Section 5 describes the format of the 'copyControl', 'anonymize', and
   'count' attributes.  Implementations according to this specification
   MUST support this XML Schema.































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5.  XML Schema

  <?xml version="1.0" encoding="UTF-8"?>
  <xs:schema targetNamespace="urn:ietf:params:xml:ns:copycontrol"
      xmlns="urn:ietf:params:xml:ns:copycontrol"
      xmlns:rls="urn:ietf:params:xml:ns:resource-lists"
      xmlns:xs="http://www.w3.org/2001/XMLSchema"
      elementFormDefault="qualified"
      attributeFormDefault="unqualified">

      <xs:annotation>
        <xs:documentation xml:lang="en">
           Adds the copyControl, anonymize, and count attributes
           to URIs included in a resource list.
        </xs:documentation>
      </xs:annotation>

     <xs:import namespace="urn:ietf:params:xml:ns:resource-lists"
            schemaLocation="urn:ietf:params:xml:schema:resource-lists"/>

      <xs:attribute name="copyControl">
         <xs:simpleType>
            <xs:restriction base="xs:string">
               <xs:enumeration value="to"/>
               <xs:enumeration value="cc"/>
               <xs:enumeration value="bcc"/>
            </xs:restriction>
         </xs:simpleType>
      </xs:attribute>

     <xs:attribute name="anonymize" type="xs:boolean" default="false"/>
     <xs:attribute name="count" type="xs:nonNegativeInteger"
                                default="1"/>

  </xs:schema>

     Figure 2: XML Schema of the extension to the resource list format


6.  Examples

   This section shows two examples of URI-lists that can be included in
   SIP requests.  The first example in Figure 3 shows a recipient list
   that the UAC sends to the URI-list server.  This corresponds to a
   list that will be included in the flow F2 in Figure 1.  The recipient
   list contains a flat list according to the resource list data format
   [7].  Each resource indicates the copy control of a resource with a
   'copyControl' attribute.  Some of the resources are also marked with



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   the 'anonymize' attribute.  This provides an indication to the URI-
   list service for not disclosing their URIs in a recipient-history
   list.  The last two <entry> elements are marked with a 'copyControl'
   attribute of "bcc".  This provides an indication to the URI-list
   server for removing these URIs in the recipient-history 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>

     Figure 3: Recipient list sent from the UAC to the URI-list server

   Upon receipt of the SIP request containing the recipient list of
   Figure 3 the URI-list server creates a SIP request to each of the
   URIs listed in the recipient list (so, in our example, it creates 7
   SIP requests).  The URI-list server processes the recipient list and
   creates a recipient-history list that is included in each of the
   outgoing SIP requests.  The process is as follows: the URI-list
   server creates a new recipient-history list, based on the recipient
   list, but with changes.  First it copies all the URIs (<entry>
   elements) marked with the "to" or "cc" 'copyControl' attributes,
   which do not contain an 'anonymize' attribute (or when the
   'anonymize' attribute is set to "false").  Then all the URIs marked
   with a 'copyControl' attribute set to "to" and 'anonymize' attribute
   set to "true" are replaced with an anonymous URI, such as
   "sip:anonymous@anonymous.invalid".  In this entry the URI-list server
   also adds the original value of the 'copyControl' attribute ("to" in
   our example), and it adds a 'count' attribute containing the number
   of anonymous entries in this group ("2" in our example).  Then the
   URI-list server does the same operation to the URIs tagged with the
   'copyControl' attribute set to "cc" and 'anonymize' attribute set to
   "true", adding also the 'count' attribute containing the number of
   anonymous attributes in this group ("1" in the example).  Last, the
   URI-list server completely removes URIs marked with the "bcc"
   'copyControl' attribute.  The resulting recipient-history list is



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   shown in Figure 4.

   <?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>

     Figure 4: Recipient-history list sent from the URI-list server to
                              each recipient


7.  Carrying URI-lists in SIP

   A SIP UAC (User Agent Client) that composes a SIP request can include
   a URI-list with the extensions specified in this document to indicate
   the list of intended recipients.  On doing so, as specified in the
   Framework and Security Considerations for SIP URI-List Services [9],
   the UAC adds a Content-Disposition [2] header field set to the value
   'recipient-list'.  Typically UACs send these 'recipient-list' bodies
   to URI-list services (this corresponds to flow F1 in Figure 1).  A
   body whose Content-Disposition type is 'recipient-list' contains a
   URI-list that includes the intended recipients of the SIP request,
   something known throughout this document as a recipient list.  The
   <entry> element in the URI-list MAY also include a 'copyControl' and
   'anonymize' attributes, as specified in Section 4.

   To be able to inform intended recipients of who else is receiving a
   copy of the SIP request, we define a new mail disposition type to be
   included in a Content-Disposition [2] header field of a SIP request.
   The value of this new disposition type is 'recipient-list-history'
   and its purpose is to indicate a list of recipients that a SIP
   request was sent to, something known throughout this document as a
   recipient-history list.  A body whose Content-Disposition type is
   'recipient-list-history' contains a URI-list with the visible
   (including anonymized) recipients of the SIP request.  The <entry>
   element in the URI-list MAY also include a 'copyControl' and 'count'
   attributes, as specified in Section 4.

   On sending a SIP request that contains a recipient-history list, if
   the intended recipient does not support this specification, the SIP



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   request should not fail.  In order to ensure successful receipt of
   the SIP requests that include 'recipient-list-history' bodies, User
   Agents (such as URI-list servers) that build SIP requests with the
   Content-Disposition header field set to 'recipient-list-history'
   SHOULD add a 'handling' parameter [3] set to "optional".  Otherwise,
   the SIP request could fail and never be received by the intended
   recipient.


8.  Security Considerations

   The Framework and Security Considerations for SIP URI-List Services
   [9] discusses issues related to SIP URI-list services.
   Implementations of this specification MUST follow the security-
   related rules in the Framework and Security Considerations for SIP
   URI-List Services [9].  These rules include mandatory authentication
   and authorization of clients, and opt-in lists.

   User Agent Clients SHOULD NOT hand SIP requests containing URI-list
   services to unauthenticated and untrusted parties.  This is to avoid
   man-in-the-middle attacks or acquiring URI-lists for performing SPAM
   attacks.

   URI-lists may contain private information, such as SIP URIs.  It is
   therefore not desirable that these URI-lists are known by third
   parties.  Eavesdroppers are able to watch URI-lists contained in SIP
   requests unless the SIP message is sent over a secured channel, by
   using any of the available SIP mechanisms, such as Transport Layer
   Security (TLS) [6], or unless the URI-list body itself is encrypted
   with, e.g., S/MIME [8].  Therefore, it is RECOMMENDED that URI-list
   bodies are encrypted with S/MIME [8] or that the SIP request is
   encrypted with TLS [6] or any other suitable encryption mechanism.

   Note that this URI-list does not indicate the actual participants in
   the session.  It indicates only the URIs invited and that might
   accept the request.  It does not assert that these parties actually
   exist, that they are reachable at the given URI, or that they have
   accepted the invitation.  No inferences about billing should be made
   from this information.  It is subject to spoofing by loading the list
   with falsified content.


9.  IANA Considerations

   The following sections instruct the IANA to register: a new
   disposition type, a new XML namespace, and a new XML schema.





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9.1.  Disposition Type Registration

   Section 7 defines a new 'recipient-list-history' value of the Mail
   Content Disposition Values registry.  This value should be registered
   in the IANA registry of Mail Content Disposition Values with the
   following registration data:

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

    Table 1: Registration of the 'recipient-list-history' Mail Content
                             Disposition Value

   Note to IANA and the RFC editor: replace RFCXXXX above with the RFC
   number of this specification.

9.2.  XML Namespace Registration

   This section registers a new XML namespace in the IANA XML registry,
   as per the guidelines in RFC 3688 [5].

   URI: The URI for this namespace is urn:ietf:params:xml:ns:copycontrol

   Registrant Contact: IETF, SIPPING working group, (sipping@ietf.org),
   Miguel Garcia-Martin (miguel.an.garcia@nokia.com).

   XML:


















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         BEGIN
         <?xml version="1.0"?>
         <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
           "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
         <html xmlns="http://www.w3.org/1999/xhtml">
         <head>
           <meta http-equiv="content-type"
              content="text/html;charset=iso-8859-1"/>
           <title>Copy Control Namespace</title>
         </head>
         <body>
           <h1>Namespace for the Copy Control Attribute Extension
           in Resource Lists</h1>
           <h2>urn:ietf:params:xml:ns:copycontrol</h2>
           <p>See <a href="[URL of published RFC]">RFCXXXX
           [NOTE TO IANA/RFC-EDITOR: Please replace XXXX with
           the RFC number of this specification.]</a>.</p>
         </body>
         </html>
         END


9.3.  XML Schema Registration

   This section registers a new XML schema in the IANA XML registry per
   the procedures in RFC 3688 [5].

   URI: urn:ietf:params:xml:schema:copycontrol

   Registrant Contact: IETF, SIPPING working group, (sipping@ietf.org),
   Miguel Garcia-Martin (miguel.an.garcia@nokia.com).

   The XML for this schema can be found as the sole content of
   Section 5.


10.  Acknowledgements

   Thanks to Dean Willis, Jari Urpalainen, Pekka Kuure, Atsushi Sato,
   Brian Rosen, Mary Barnes, and James Polk for reviewing this document
   and providing helpful comments.


11.  References







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11.1.  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]   Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
         January 2004.

   [6]   Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
         Protocol Version 1.1", RFC 4346, April 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]   Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
         (S/MIME) Version 3.1 Message Specification", RFC 3851,
         July 2004.

   [9]   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.

11.2.  Informational References

   [10]  Camarillo, G. and A. Johnston, "Conference Establishment Using
         Request-Contained Lists in the Session  Initiation Protocol
         (SIP)", draft-ietf-sip-uri-list-conferencing-01 (work in
         progress), January 2007.

   [11]  Garcia-Martin, M. and G. Camarillo, "Multiple-Recipient MESSAGE
         Requests in the Session Initiation Protocol  (SIP)",
         draft-ietf-sip-uri-list-message-01 (work in progress),



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         January 2007.


Authors' Addresses

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

   Email: miguel.an.garcia@nokia.com


   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: Gonzalo.Camarillo@ericsson.com






























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Full Copyright Statement

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