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Versions: (draft-ietf-simple-xcap-package) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 5874

SIMPLE                                                      J. Rosenberg
Internet-Draft                                             Cisco Systems
Expires: January 19, 2006                                  July 18, 2005


   An Extensible Markup Language (XML) Document Format for Indicating
     Changes in XML Configuration Access  Protocol (XCAP) Resources
                     draft-ietf-simple-xcap-diff-01

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on January 19, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This specification defines a document format that can be used to
   describe the differences between versions of resources managed by the
   Extensible Markup Language (XML) Configuration Access Protocol
   (XCAP).  XCAP diff documents can be delivered to clients using a
   number of means, including the Session Initiation Protocol (SIP)
   event package for configuration data.  By subscribing to this event
   package, clients can learn about document changes made by other
   clients.



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Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.   Structure of an XCAP Diff Document . . . . . . . . . . . . .   4
   4.   XML Schema . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.   Example Document . . . . . . . . . . . . . . . . . . . . . .   7
   6.   Usage with the Config Framework  . . . . . . . . . . . . . .   8
   7.   Constructing a Document from the Change Log  . . . . . . . .  10
   8.   Security Considerations  . . . . . . . . . . . . . . . . . .  11
   9.   IANA Considerations  . . . . . . . . . . . . . . . . . . . .  11
     9.1  application/xcap-diff+xml MIME Type  . . . . . . . . . . .  11
     9.2  URN Sub-Namespace Registration for
          urn:ietf:params:xml:ns:xcap-diff . . . . . . . . . . . . .  12
     9.3  Schema Registration  . . . . . . . . . . . . . . . . . . .  13
   10.  References . . . . . . . . . . . . . . . . . . . . . . . . .  13
     10.1   Normative References . . . . . . . . . . . . . . . . . .  13
     10.2   Informative References . . . . . . . . . . . . . . . . .  14
        Author's Address . . . . . . . . . . . . . . . . . . . . . .  15
        Intellectual Property and Copyright Statements . . . . . . .  16































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1.  Introduction

   The Extensible Markup Language (XML) Configuration Access Protocol
   (XCAP) [8] is a protocol that allows clients to manipulate XML
   documents stored on a server.  These XML documents serve as
   configuration information for application protocols.  As an example,
   resource list [12] subscriptions (also known as presence lists) allow
   a client to have a single SIP subscription to a list of users, where
   the list is maintained on a server.  The server will obtain presence
   for those users and report it back to the client.  This application
   requires the server, called a Resource List Server (RLS), to have
   access to the list of presentities.  This list needs to be
   manipulated by clients so they can add and remove their friends as
   they desire.

   Complexities arise when multiple clients attempt to simultaneously
   manipulate a document, such as a presence list.  Frequently, a client
   will keep a copy of the current list in memory, so it can render it
   to users.  However, if another client modifies the document, the
   cached version becomes stale.  This modification event must be made
   known to all clients which have cached copies of the document, so
   that they can fetch the most recent one.

   To deal with this problem, clients can use the Session Initiation
   Protocol (SIP) [10] event package [11] for subscribing to changes in
   configuration and profile information [9], including application data
   that resides on an XCAP server.  With that package, a user gets
   notified that a particular document has changed.  This notification
   can include the full content of the new document, or it can be a
   content indirection [15].  However, in both cases, the transfer of
   the entire document is ultimately required.  This may require a lot
   of bandwidth, particularly for wireless devices with large documents
   (such as a resource list [12] with hundreds of users listed).
   Furthermore, though content indirection can tell a client that a
   document has changed, it provides it with MIME Content-ID indicating
   the new version of the document.  The MIME Content-ID is not the same
   as the entity tag, which is used by XCAP for document versioning.  As
   such, a client cannot easily ascertain whether an indication of a
   change in a document is due to a change it just made, or due to a
   change another client made at around the same time.

   To resolve this problem, this document defines a data format which
   can convey changes in XML documents managed by an XCAP server.  This
   data format is an XML document format, called an XCAP diff document.
   This format can indicate that a document has changed, provide its
   previous and new entity tags, and optionally include the xcap
   operation that was performed which resulted in that change.  This
   specification also explains how this format is used in conjunction



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   with the configuration profile framework.

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [7] and
   indicate requirement levels for compliant implementations.

   This specification also defines the following additional terms:

   Document: When the term document is used without the "XCAP diff" in
      front of it, it refers to the XCAP document resource about whom
      the XCAP diff document is reporting a change.

   XCAP diff document: The XML document defined by this specification
      that reports on a set of changes in an XCAP document resource.

   Server: Typically an XCAP server, this is a protocol entity that
      generates XCAP diff documents based on its knowledge of a set of
      XCAP documents.

   Client: Typically an XCAP client and SIP User Agent (UA) that acts as
      a subscriber to the configuration event package, this is a
      protocol entity that consumes XCAP diff documents in order to
      reconstruct the document stored on the server.


3.  Structure of an XCAP Diff Document

   An XCAP diff document is an XML [2] document that MUST be well-formed
   and SHOULD be valid.  XCAP diff documents MUST be based on XML 1.0
   and MUST be encoded using UTF-8.  This specification makes use of XML
   namespaces for identifying XCAP diff documents and document
   fragments.  The namespace URI for elements defined by this
   specification is a URN [3], using the namespace identifier 'ietf'
   defined by [5] and extended by [6].  This URN is:

      urn:ietf:params:xml:ns:xcap-diff

   An XCAP diff document begins with the root element tag <xcap-diff>.
   This element has a single mandatory attribute, "xcap-root".  The
   value of this attribute is the XCAP root URI for the documents in
   which the changes have taken place.  A single XCAP diff document can
   only represent changes in documents within the same XCAP root.  The
   content of the <xcap-diff> element is a sequence of <document>
   elements.  Each <document> element specifies changes in a specific
   document within the XCAP root.  It has one mandatory attribute, "doc-



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   selector", and a three optional attributes, "new-etag", "previous-
   etag" and "hash".  The "doc-selector" identifies the specific
   document within the XCAP root for which changes are indicated.  Its
   content MUST be a relative path reference, with the base URI being
   equal to the XCAP root URI.  The "new-etag" attribute provides the
   etag for the document after the application of the changes, assuming
   the document exists after those changes.  If the change being
   reported is the deletion of the document, the "new-etag" attribute
   will not be present.  A server MUST include the "new-etag" unless the
   document does not exist subsequent to the changes reported in the
   XCAP diff document.  If The "previous-etag" attribute provides an
   identifier for the document instance prior to the change.  If the
   document did not exist prior to the change (that is, the change was
   the creation of the document), the "previous-etag" is not present.
   If the server is reporting a specific set of document changes via the
   <change-log> element described below, a server MUST include the
   "previous-etag" unless the document did not exist prior to changes
   reported in the XCAP diff document.  If the <change-log> element is
   not present, the "previous-etag" SHOULD be present.  The "previous-
   etag" and "new-etag" need not have been sequentially assigned etags
   at the server.  An XCAP diff document can describe changes that have
   occurred over a series of XCAP operations.

   The optional "hash" attribute provides an HMAC of the document
   instance whose etag is "new-etag", once that document is represented
   in canonical form.  See Section 6 for details on how this value is
   computed.  This attribute is optional, and a server MAY elect not to
   include it.  Even if present, a client MAY elect to ignore it.

   Each <document> element contains zero or one <change-log> element,
   followed by any number of elements from another namespace for the
   purposes of extensibility.  Any such unknown elements MUST be ignored
   by the client.  When present, the <change-log> element tells the
   client the specific set of XCAP operations that can be applied to
   transform the document from the version whose etag was "previous-
   etag" to the version whose etag is "new-etag".  If the "previous-
   etag" is not present, the <change-log> element tells the client the
   specific set of XCAP operations that can be applied to create a
   document from nothing, and result in the document whose etag is "new-
   etag".  The series of operations in the <change-log> do not have to
   be the same exact series of operations that occurred at the server.
   The only requirement is that, if the server includes the <change-log>
   element, the sequence of events, when executed serially, will result
   in the transformation of the document with the etag "previous-etag"
   to the one whose etag is "new-etag".  If the <change-log> element is
   not present, it means that the document has changed in some way, but
   the XCAP server has elected not to provide the set of changes.  In
   that case, a client can retrieve the latest document if its cached



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   etag doesn't match the value of "new-etag".

   It is important to note that a <document> element with no <change-
   log> child is not equivalent to a <document> element with a <change-
   log> child that is itself empty.  The latter means that the document
   has been assigned a new etag but its content is unchanged.  The
   former means that it has been assigned a new etag as a result of a
   change, but the specific changes are not being reported in the XCAP
   diff document.

   Each <change-log> element contains zero or more <put-event> or
   <delete-event> elements.  It can also contain elements from other
   namespaces, which allows for extensibility to other events in the
   future.  A client MUST ignore any such elements it does not
   understand.  Each <delete-event> element reports an HTTP DELETE
   operation, and each <put-event> element reports an HTTP PUT
   operation.  Both <put-event> and <delete-event> have a single
   optional attribute, "node-selector", which contains the node selector
   in the Request URI (after removing any escape coding) of the HTTP PUT
   or DELETE request.  The server MUST include the "node-selector" when
   the PUT or DELETE operation was against an XML element or attribute.
   The "node-selector" attribute MUST NOT be present if the PUT or
   DELETE operation was against the document itself.  The <put-event>
   element also has the mandatory attribute "content-type", which
   indicates the Content-Type of the HTTP PUT request.  The content of
   the <put-event> element is text.  This text contains the body of the
   HTTP PUT request.  If that content was an XML type (including
   application/xcap-el+xml) that contains angle brackets, it MUST be
   represented as CDATA.  If the content did not contain angle brackets
   (as is the case with application/xcap-att+xml), it MAY be represented
   as CDATA.

4.  XML Schema


   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema xmlns="urn:ietf:params:xml:ns:xcap-diff"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    targetNamespace="urn:ietf:params:xml:ns:xcap-diff"
    elementFormDefault="qualified" attributeFormDefault="unqualified">
    <xs:element name="document">
     <xs:complexType>
      <xs:sequence>
       <xs:element ref="change-log" minOccurs="0"/>
       <xs:any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="doc-selector" type="xs:anyURI" use="required"/>
      <xs:attribute name="new-etag" type="xs:string" use="optional"/>



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      <xs:attribute name="previous-etag" type="xs:string" use="optional"/>
      <xs:attribute name="hash" type="xs:string" use="optional"/>
      <xs:anyAttribute namespace="##other" processContents="lax"/>
     </xs:complexType>
    </xs:element>
    <xs:element name="xcap-diff">
     <xs:complexType>
      <xs:sequence>
       <xs:element ref="document"/>
      </xs:sequence>
      <xs:attribute name="xcap-root" type="xs:anyURI" use="required"/>
     </xs:complexType>
    </xs:element>
    <xs:element name="change-log">
     <xs:complexType>
      <xs:sequence minOccurs="0" maxOccurs="unbounded">
       <xs:choice>
        <xs:element ref="delete-event"/>
        <xs:element ref="put-event"/>
        <xs:any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
       </xs:choice>
      </xs:sequence>
     </xs:complexType>
    </xs:element>
    <xs:element name="put-event">
     <xs:complexType>
      <xs:simpleContent>
       <xs:extension base="xs:string">
        <xs:attribute name="node-selector" type="xs:anyURI" use="optional"/>
        <xs:attribute name="content-type" type="xs:string" use="required"/>
       </xs:extension>
      </xs:simpleContent>
     </xs:complexType>
    </xs:element>
    <xs:element name="delete-event">
     <xs:complexType>
      <xs:attribute name="node-selector" type="xs:anyURI" use="optional"/>
     </xs:complexType>
    </xs:element>
   </xs:schema>



5.  Example Document

   The following is an example of a document compliant to the schema.
   Line wrapping is for readability purposes only:




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   <?xml version="1.0" encoding="UTF-8"?>
   <xcap-diff xmlns="urn:ietf:params:xml:ns:xcap-diff"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:ietf:params:xml:ns:xcap-diff xcap-diff.xsd"
    xcap-root="http://xcap.example.com/root">
    <document new-etag="7ahggs"
     doc-selector="resource-lists/users/joe/coworkers"
     previous-etag="8a77f8d">
      <change-log>
        <delete-event
         node-selector="resouce-lists/list[@name="friends"]/ent
   ry[@uri="bill@example.com"]"/>
        <put-event
         node-selector="resouce-lists/list[@name="friends"]/ent
   ry[@uri="jane@example.com"]"
         content-type="application/xml"><![CDATA[<entry uri="sip:jane@exa
   mple.com"><display-name>Jane Doe</display-name></entry>]]>
        </put-event>
      </change-log>
    </document>
   </xcap-diff>


   This example XCAP diff document will transform the example document
   in Section 3.3 of [14] by removing the entry for Bill Smith and
   adding one for Jane Doe.

6.  Usage with the Config Framework

   The framework for user agent profile delivery [9] defines an event
   package which can be used to subscribe to user, device, application
   or local-network data that defines the configuration of a client.
   This data can be present in an XCAP server.  Normally, content
   indirection [15] will be used as the NOTIFY body format, to indicate
   the specific document that has changed, and should be re-fetched.
   However, if the client includes an Accept header field including the
   MIME type "application/xcap-diff+xml", the server has the option of
   returning documents in this format instead.

   When the client performs an initial subscription, the rules in [9]
   are used to select the set of documents which the subscription
   applies to.  Upon initial subscription, the server does not know
   which instances of each document (where each instance is identified
   by an etag) the client currently posessses, if any.  Indeed, upon
   startup, the client will not have any documents.  The initial NOTIFY
   in this case MUST include a <document> element for each document
   associated with the subscription.  The <change-log> for each of those
   <document> elements MUST be absent.  The "previous-etag" attribute



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   MUST be absent, and the "new-etag" attribute MUST be present and
   contain the entity tag for the current version of that document
   resource.  An XCAP diff document structured this way is called a
   "reference" XCAP diff document.  It establishes the baseline etags
   and document URIs for the documents covered by the subscription.

   Upon receipt of this document, the client can determine whether its
   local instance documents, if any, match the etags in the XCAP diff
   document.  If they do not match, the client SHOULD perform a
   conditional GET for each document.  The document URI is constructed
   by appending the XCAP root in the "xcap-root" attribute of the <xcap-
   diff> element to the escape coded "doc-selector" from each <document>
   element.  The request is made conditional by including an If-Match
   header field, with the value of the etag from each <document>
   element.  So long as the documents haven't changed between the NOTIFY
   and the GET, the client will obtain the reference versions that the
   server will use for subsequent notifications.

   If the conditional GET should fail, the client SHOULD generate a
   SUBSCRIBE refresh request to trigger a new NOTIFY.  The server will
   always generate a "reference" XML diff document on receipt of a
   SUBSCRIBE refresh.  This establishes a new set of baseline etags, and
   the client can then attempt to do another fetch.  It is anticipated
   that future extensions to the profile delivery framework will allow a
   client to include, in its SUBSCRIBE request, an indicator of the
   current version of the documents it holds.  That would obviate the
   need for a potentially never-ending stream of SUBSCRIBE/GET sequences
   should the documents be rapidly changing, for some reason.

   Once the client has obtained the versions of the documents identified
   in the reference XML diff, it can process NOTIFY requests on that
   subscription.  To process the NOTIFY requests, it makes sure that its
   current version matches the version in the "previous-etag" attribute
   of the <document> element.  It then follows the procedures of
   Section 7.

   Once the client has finished applying the instructions to the
   document, it should end up with the same document the server has.  To
   verify this, the client MAY apply the mandatory XML canonicalization
   defined in the Canonical XML 1.0 [1] specification, and computes an
   HMAC [13] using SHA1 over this canonical document, with a key whose
   value is 0x2238a.  The resulting string is compared with the "hash"
   attribute of the <document> element.  If they match, the client can
   be sure that it has the most up to date version.  If they don't
   match, the client MUST flush its current version of the document from
   memory.  It can then obtain a new XCAP diff reference by sending a
   SUBSCRIBE refresh request on the dialog.




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   Of course, this mechanism for computing the most current document
   from the hash is optional.  A client can elect to ignore the
   information on what changed and simply fetch the most recent document
   every time it gets a change indication where the new version is not
   the same as the one cached by the client.  Furthermore, the server
   may elect to not send the hash, in which case this check cannot be
   made.

7.  Constructing a Document from the Change Log

   When the XCAP diff document contains a <change-log> element for a
   document, and the client possesses the document instance whose etag
   matches the "previous-etag" for the document, the client can follow
   the procedures defined here to obtain the instance document with the
   etag value of "new-etag".  This procedure is relatively
   straightforward, and is done by having the client emulate XCAP server
   behavior as defined in [8]

   The client starts with the its version of the document whose etag is
   "previous-etag" as the current document.  If there was no "previous-
   etag", the client starts with no document.  The client MUST iterate
   through each child of <change-log>, in order.  For each element, it
   MUST apply processing depending on the name of the element.

   If the element is <delete-event>, the client takes the current
   document.  If the "node-selector" attribute was absent, it deletes
   the entire document.  If the "node-selector" attribute was present,
   it selects the element or attribute using that node selector, as
   described in Section 6.3 of [8].  Note that the node selector present
   in the "node-selector" attribute is not escape coded, and will follow
   the grammar defined in that section.  The selected element or
   attribute is deleted from the document, and the result becomes the
   current document.  There is no need for the client to run the
   validity checks or idempotency checks normally performed by the
   server; a client will always be provided with <delete-event>
   operations that succeeded at the server.

   If the element is <put-event>, the client takes the current document.
   It then computes the Request URI that was seen by the server, by
   concatenating the XCAP root with the "doc-selector" attribute of th
   <document> element, appending the path separator, and then adding the
   "node-selector" attribute of the <put-event> element, if present.
   The client then "acts" as if it were the server, having receive an
   HTTP PUT request with the Request URI equal to this value prior to
   escape coding, with a body of Content-Type equal to the value of the
   "content-type" attribute, and whose body equals the value of the
   <put-event> element.  It follows the logic of Section 8.2 of [8] to
   apply the PUT, ignorning all validity checks, resource



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   interdependency computations, error processing and verification of
   document content.  The resulting document becomes the current
   document.  An actual implementation need not literally act as a
   server; the behavior is defined in these terms to specify what the
   correct output of the processing has to be.

   If the element is unknown to the client, it is skipped.

   When each child element of <change-log> has been processed, the
   current document is equal to the document on the server whose etag
   equals "new-etag".

8.  Security Considerations

   XCAP diff documents contain the same information in the documents
   whose differences they describe.  As such, the security
   considerations associated with those documents apply to XCAP diff
   documents.

9.  IANA Considerations

   There are several IANA considerations associated with this
   specification.

9.1  application/xcap-diff+xml MIME Type

      MIME media type name: application

      MIME subtype name: xcap-diff+xml

      Mandatory parameters: none

      Optional parameters: Same as charset parameter application/xml as
      specified in RFC 3023 [4].

      Encoding considerations: Same as encoding considerations of
      application/xml as specified in RFC 3023 [4].

      Security considerations: See Section 10 of RFC 3023 [4] and
      Section 8 of RFCXXXX [[NOTE TO RFC-EDITOR/IANA: Please replace
      XXXX with the RFC number of this specification.]].

      Interoperability considerations: none.

      Published specification: This document.






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      Applications which use this media type: This document type has
      been used to support manipulation of resource lists [14] using
      XCAP.

      Additional Information:

         Magic Number: None

         File Extension: .xdf

         Macintosh file type code: "TEXT"

         Personal and email address for further information: Jonathan
         Rosenberg, jdrosen@jdrosen.net

         Intended usage: COMMON

         Author/Change controller: The IETF.


9.2  URN Sub-Namespace Registration for urn:ietf:params:xml:ns:xcap-diff

   This section registers a new XML namespace, as per the guidelines in
   [6]

      URI: The URI for this namespace is
      urn:ietf:params:xml:ns:xcap-diff.

      Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
      Jonathan Rosenberg (jdrosen@jdrosen.net).

      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>XCAP Diff Namespace</title>
                </head>
                <body>
                  <h1>Namespace for XCAP Diff</h1>
                  <h2>urn:ietf:params:xml:ns:xcap-diff</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  Schema Registration

   This section registers a new XML schema per the procedures in [6].

      URI: urn:ietf:params:xml:schema:xcap-diff

      Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
      Jonathan Rosenberg (jdrosen@jdrosen.net).

      The XML for this schema can be found as the sole content of
      Section 4.


10.  References

10.1  Normative References

   [1]  Boyer, J., "Canonical XML Version 1.0", W3C REC REC-xml-c14n-
        20010315, March 2001.

   [2]  Bray, T., Paoli, J., Sperberg-McQueen, C., and E. Maler,
        "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
        FirstEdition REC-xml-20001006, October 2000.

   [3]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [4]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",



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        RFC 3023, January 2001.

   [5]  Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
        August 1999.

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

   [7]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [8]  Rosenberg, J., "The Extensible Markup Language (XML)
        Configuration Access Protocol (XCAP)", draft-ietf-simple-xcap-07
        (work in progress), June 2005.

   [9]  Petrie, D., "A Framework for Session Initiation Protocol User
        Agent Profile Delivery", draft-ietf-sipping-config-framework-06
        (work in progress), February 2005.

10.2  Informative References

   [10]  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.

   [11]  Roach, A., "Session Initiation Protocol (SIP)-Specific Event
         Notification", RFC 3265, June 2002.

   [12]  Roach, A., Rosenberg, J., and B. Campbell, "A Session
         Initiation Protocol (SIP) Event Notification Extension for
         Resource Lists", draft-ietf-simple-event-list-07 (work in
         progress), January 2005.

   [13]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
         for Message Authentication", RFC 2104, February 1997.

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

   [15]  Burger, E., "A Mechanism for Content Indirection in Session
         Initiation Protocol (SIP)  Messages",
         draft-ietf-sip-content-indirect-mech-05 (work in progress),
         October 2004.






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Author's Address

   Jonathan Rosenberg
   Cisco Systems
   600 Lanidex Plaza
   Parsippany, NJ  07054
   US

   Phone: +1 973 952-5000
   Email: jdrosen@cisco.com
   URI:   http://www.jdrosen.net








































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