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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
Intended status: Standards Track                           J. Urpalainen
Expires: December 31, 2009                                         Nokia
                                                           June 29, 2009


  An Extensible Markup Language (XML) Document Format for Indicating A
      Change in XML Configuration Access Protocol (XCAP) Resources
                     draft-ietf-simple-xcap-diff-13

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may contain material
   from IETF Documents or IETF Contributions published or made publicly
   available before November 10, 2008.  The person(s) controlling the
   copyright in some of this material may not have granted the IETF
   Trust the right to allow modifications of such material outside the
   IETF Standards Process.  Without obtaining an adequate license from
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   document may not be modified outside the IETF Standards Process, and
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 31, 2009.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

Abstract

   This specification defines a document format that can be used to
   indicate that a change has occurred in a document managed by the
   Extensible Markup Language (XML) Configuration Access Protocol
   (XCAP).  This format indicates the document that has changed and its
   former and new entity tags.  It also can indicate the specific change
   that was made in the document, using an XML patch format.  This
   format allows also indications of element and attribute content of an
   XML document.  XCAP diff documents can be delivered to clients using
   a number of means, including a Session Initiation Protocol (SIP)
   event package.

































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Structure of an XCAP Diff Document . . . . . . . . . . . . . .  5
   4.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Example Document . . . . . . . . . . . . . . . . . . . . . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  application/xcap-diff+xml MIME Type  . . . . . . . . . . . 12
     7.2.  URN Sub-Namespace Registration for
           urn:ietf:params:xml:ns:xcap-diff . . . . . . . . . . . . . 13
     7.3.  Schema Registration  . . . . . . . . . . . . . . . . . . . 14
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

































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1.  Introduction

   The Extensible Markup Language (XML) Configuration Access Protocol
   (XCAP) [RFC4825] 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 [RFC4662] 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 a Session Initiation
   Protocol (SIP) [RFC3261] event package [RFC3265] to subscribe to
   change events in XCAP documents.  This notification needs to indicate
   the specific resource that changed, and how it changed.  One solution
   for the format of such a change notification would be a content
   indirection object [RFC4483].  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.  Furthermore, content indirections don't indicate how a
   document changed; they would only be able to indicate that it did
   change.

   To resolve these problems, this document defines a data format which
   can convey the fact that an XML document managed by XCAP has changed.
   This data format is an XML document format, called an XCAP diff
   document.  This format can indicate that a document has changed, and
   provide its previous and new entity tags.  It can also optionally
   include a set of patch operations [RFC5261], which indicate how to
   transform the document from the version prior to the change, to the
   version after it.  XML element and attribute content of XCAP
   documents can also be delivered with this format.



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   XML documents that are equivalent for the purposes of many
   applications may differ in their physical representation.  Similar to
   XCAP, the canonical form with comments [W3C.REC-xml-c14n-20010315] of
   an XML document determines the logical equivalence when this format
   is used to patch XML documents.


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 RFC 2119 [RFC2119] 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), the client
      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 [W3C.REC-xml-20060816] 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 [RFC2141], using the namespace identifier
   'ietf' defined by [RFC2648] and extended by [RFC3688].  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



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   only represent changes in documents within the same XCAP root.  The
   content of the <xcap-diff> element is a sequence of <document>,
   <element> and <attribute> elements followed by any number of elements
   from other namespaces for the purposes of extensibility.  Wherever
   the XML schema (see Section 4) allows extension elements or
   attributes, any such unknown content MUST be ignored by the client.

   Each <document> element specifies changes in a specific document
   within the XCAP root.  If several <document> elements pinpoint to the
   same specific document, i.e. for example, the full ETag change
   history is indicated, the corresponding patches MUST be appliable in
   the given document order.

   The <document> element has one mandatory attribute, "sel", and a two
   optional attributes, "new-etag" and "previous-etag".  The "sel"
   attribute of the <document> element 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 entity tag
   (ETag) for the document after the application of the changes,
   assuming the document exists after those changes.  The "previous-
   etag" attribute provides an identifier for the document instance
   prior to the change.  If the change being reported is the removal of
   a document, the "previous-etag" MUST only be included and the "new-
   etag" attribute will not be present.  The "new-etag" attribute MUST
   only exist alone when the document either exists or it was just
   created (no patch included).  Both attributes are present when a
   patch (or series of XCAP operations) has been applied to the
   resource.  Also both attributes MAY be used to indicate an ETag
   change without any document modifications (patches).

   The "previous-etag" and "new-etag" need not have been sequentially
   assigned ETags at the server.  An XCAP diff document can indicate
   changes that have occurred over a series of XCAP operations.  The
   only requirement then is that, 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".  Also the
   series of operations do not have to be the same exact series of
   operations that occurred at the server.

   Each <document> element contains either a sequence of patching
   instructions or an indication that the body hasn't semantically
   changed.  The latter means that the document has been assigned a new
   ETag but its content is unchanged and it is indicated by the <body-
   not-changed> element.  Patching instructions are described by the
   <add>, <replace> and <remove> elements.  These elements use the
   corresponding add, replace and remove types defined in [RFC5261], and
   define a set of patch operations that can be applied to transform the



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   document.  See [RFC5261] for instructions on how this transformation
   is effected.  The <document> element can also contain elements from
   other namespaces for the purposes of extensibility.  The <add>,
   <replace> and <remove> elements allow extension attributes from any
   namespace.

   Figure 1 shows <document> element content and how corresponding
   resource or metadata changes.  An external document retrieval means
   in practice HTTP GET requests for target resources.


   +-----------+----------+-----------+----------+-------------------+
   | previous- | new-     | <add>     | <body-   | XCAP resource/    |
   | etag      | etag     | <replace> | not-     | metadata change   |
   |           |          | <remove>  | changed> |                   |
   +-----------+----------+-----------+----------+-------------------+
   | xxx       | yyy      | *         | -        | resource patched, |
   |           |          |           |          | patch included    |
   +-----------+----------+-----------+----------+-------------------+
   | xxx       | yyy      | -         | -        | resource patched, |
   |           |          |           |          | external document |
   |           |          |           |          | retrieval         |
   +-----------+----------+-----------+----------+-------------------+
   | xxx       | yyy      | -         | *        | only ETag changed |
   +-----------+----------+-----------+----------+-------------------+
   | -         | yyy      | -         | -        | resource created  |
   |           |          |           |          | or exists,        |
   |           |          |           |          | external document |
   |           |          |           |          | retrieval         |
   +-----------+----------+-----------+----------+-------------------+
   | xxx       | -        | -         | -        | resource removed  |
   +-----------+----------+-----------+----------+-------------------+


   Figure 1: <document> element content / corresponding resource changes

   Each <element> element indicates the existing element content of an
   XCAP document.  It has one mandatory attribute, "sel", and one
   optional attribute, "exists".  The "sel" attribute of the <element>
   element identifies an XML element of an XCAP document.  It is a
   percent endoced relative URI following XCAP conventions when
   selecting elements.  The XCAP Node Selector MUST always locate a
   unique node, the "exists" attribute thus shows whether an element
   exists or not in the XCAP document.  When the "exists" attribute is
   absent from the <element> element, the indicated element still exists
   in the XCAP document.  The located result element exists as a child
   element of the <element> element.  It should be noted, that only the
   full content of an element is shown if it exists, there are no



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   conventions for patching these elements.  In a corner case where the
   content of this element cannot be presented for some reason, although
   it exists in the XCAP document, the <element> element MUST NOT have
   any child nodes.

   As the result XML element is typically namespace qualified, all
   needed namespace declarations MUST exist within the <xml-diff>
   document.  The possible local namespace declarations within the
   result element exist unmodified as in the source document, similar to
   XCAP conventions.  Other namespace references MUST be resolved from
   the context of the <element> or its parent elements.  The prefixes of
   qualified names (QName) [W3C.REC-xml-names-20060816] of XML nodes
   also remain as they exist originally in the source XCAP document.

   Each <attribute> element indicates the existing attribute content of
   an XCAP document.  It has one mandatory attribute, "sel", and one
   optional attribute, "exists".  The "sel" attribute of the <attribute>
   element identifies an XML attribute of an XCAP document.  It is a
   percent endoced relative URI following XCAP conventions when
   selecting attributes.  The "exists" attribute indicates whether an
   attribute exists or not in the XCAP document.  When the "exists"
   attribute is absent from the <attribute> element, the indicated
   attribute still exists in the XCAP document.  The child text node of
   the <attribute> element indicates the value of the located attribute.
   Note that if the attribute is namespace qualified, the query
   parameter of the XCAP URI indicates the attached namespace URI and
   the prefix in the XCAP source document.

   Namespaces of the "sel" attribute of the <attribute> and <element>
   elements MUST also be resolved properly.  The Section 6.4. of
   [RFC4825] describes the rules when using namespace prefixes in XCAP
   Node Selectors.  Without a namespace prefix in an element selector,
   an XCAP Default Document Namespace MUST be applied.  The namespace
   resolving rules of Patch operation elements: <add>, <replace> and
   <remove> are described in Section 4.2.1 of [RFC5261].


4.  XML Schema

   The XML Schema for the XCAP diff format.

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




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    <!-- include patch-ops -->
    <xs:include
     schemaLocation="urn:ietf:params:xml:schema:patch-ops"/>

    <!-- document root -->
    <xs:element name="xcap-diff">
     <xs:complexType>
      <xs:sequence minOccurs="0">
       <xs:sequence minOccurs="0" maxOccurs="unbounded">
        <xs:choice>
         <xs:element name="document" type="documentType"/>
         <xs:element name="element" type="elementType"/>
         <xs:element name="attribute" type="attributeType"/>
        </xs:choice>
       </xs:sequence>
       <xs:any namespace="##other" processContents="lax"
               minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="xcap-root" type="xs:anyURI" use="required"/>
      <xs:anyAttribute processContents="lax"/>
     </xs:complexType>
    </xs:element>

    <!-- xcap document type -->
    <xs:complexType name="documentType">
     <xs:choice minOccurs="0">
      <xs:element name="body-not-changed" type="emptyType"/>
      <xs:sequence minOccurs="0" maxOccurs="unbounded">
       <xs:choice>
        <xs:element name="add">
         <xs:complexType mixed="true">
          <xs:complexContent>
           <xs:extension base="add">
            <xs:anyAttribute processContents="lax"/>
           </xs:extension>
          </xs:complexContent>
         </xs:complexType>
        </xs:element>
        <xs:element name="remove">
         <xs:complexType>
          <xs:complexContent>
           <xs:extension base="remove">
            <xs:anyAttribute processContents="lax"/>
           </xs:extension>
          </xs:complexContent>
         </xs:complexType>
        </xs:element>
        <xs:element name="replace">



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         <xs:complexType mixed="true">
          <xs:complexContent>
           <xs:extension base="replace">
            <xs:anyAttribute processContents="lax"/>
           </xs:extension>
          </xs:complexContent>
         </xs:complexType>
        </xs:element>
        <xs:any namespace="##other" processContents="lax"/>
       </xs:choice>
      </xs:sequence>
     </xs:choice>
     <xs:attribute name="sel" type="xs:anyURI" use="required"/>
     <xs:attribute name="new-etag" type="xs:string"/>
     <xs:attribute name="previous-etag" type="xs:string"/>
     <xs:anyAttribute processContents="lax"/>
    </xs:complexType>

    <!-- xcap element type -->
    <xs:complexType name="elementType">
     <xs:complexContent mixed="true">
      <xs:restriction base="xs:anyType">
       <xs:sequence>
        <xs:any processContents="lax" namespace="##any"
                minOccurs="0" maxOccurs="1"/>
       </xs:sequence>
       <xs:attribute name="sel" type="xs:string"
                     use="required"/>
       <xs:attribute name="exists" type="xs:boolean"/>
      </xs:restriction>
     </xs:complexContent>
    </xs:complexType>

    <!-- xcap attribute type -->
    <xs:complexType name="attributeType">
     <xs:simpleContent>
      <xs:extension base="xs:string">
       <xs:attribute name="sel" type="xs:string"
                     use="required"/>
       <xs:attribute name="exists" type="xs:boolean"/>
      </xs:extension>
     </xs:simpleContent>
    </xs:complexType>

    <!-- empty type -->
    <xs:complexType name="emptyType"/>

   </xs:schema>



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5.  Example Document

   The following is an example of a document compliant to the schema.

   <?xml version="1.0" encoding="UTF-8"?>
   <d:xcap-diff xmlns:d="urn:ietf:params:xml:ns:xcap-diff"
                xmlns="urn:ietf:params:xml:ns:rls-services"
                xcap-root="http://xcap.example.com/root/">

    <d:document new-etag="7ahggs"
              sel="resource-lists/users/sip:joe@example.com/coworkers"
              previous-etag="8a77f8d"/>

    <d:element sel="rls-services/users/sip:joe@example.com/index/~~
   /*/service%5b@uri='sip:marketing@example.com'%5d"
             xmlns:rl="urn:ietf:params:xml:ns:resource-lists"
       ><service uri="sip:marketing@example.com">
         <list name="marketing">
           <rl:entry uri="sip:joe@example.com"/>
           <rl:entry uri="sip:sudhir@example.com"/>
         </list>
         <packages>
           <package>presence</package>
         </packages>
       </service></d:element>

    <d:attribute
    sel="rls-services/users/sip:joe@example.com/index/~~/*/service/@uri"
         >sip:marketing@example.com</d:attribute>

   </d:xcap-diff>


   This indicates that the document with URI "http://xcap.example.com/
   root/resource-lists/users/sip:joe@example.com/coworkers" has changed.
   Its previous entity tag is "8a77f8d" and its new one is "7ahggs" but
   actual changes are not shown.  The <service> element exists in the
   rls-services "index" document and its full content is shown.  Note
   that the <service> element is attached with a default namespace
   declaration within the original document.  Similarly, a "uri"
   attribute content is shown from the same "index" document as an
   illustrative example.


6.  Security Considerations

   XCAP diff documents can include changes from one document to another.
   As a consequence, if the document itself is sensitive and requires



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   confidentiality, integrity or authentication, then the same applies
   to the XCAP diff format.  Therefore, protocols which transport XCAP
   diff documents must provide sufficient security capabilities for
   transporting the document itself.

   The SIP event package framework specified in RFC 3265 [RFC3265] is
   the most typical use-case for this format.  Then in general its
   security considerations apply, but event packages MAY also have other
   specific threats which MUST be considered on an application-by-
   application basis.


7.  IANA Considerations

   There are several IANA considerations associated with this
   specification.

7.1.  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 [RFC3023].

      Encoding considerations: Same as encoding considerations of
      application/xml as specified in RFC 3023 [RFC3023].

      Security considerations: See Section 10 of RFC 3023 [RFC3023] and
      Section 6 of RFCXXXX [[NOTE TO RFC-EDITOR/IANA: Please replace
      XXXX with the RFC number of this specification.]].

      Interoperability considerations: none.

      Published specification: This document.

      Applications which use this media type: This document type has
      been used to support manipulation of resource lists [RFC4826]
      using XCAP.

      Additional Information:







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         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.

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

   This section registers a new XML namespace, as per the guidelines in
   [RFC3688]

      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:


              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




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7.3.  Schema Registration

   This section registers a new XML schema per the procedures in
   [RFC3688].

      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.


8.  Acknowledgments

   The authors would like to thank Pavel Dostal, Jeroen van Bemmel,
   Martin Hynar, Anders Lindgren, Mary Barnes and Ben Campbell for their
   valuable comments.


9.  References

9.1.  Normative References

   [W3C.REC-xml-20060816]
              Maler, E., Paoli, J., Bray, T., Yergeau, F., and C.
              Sperberg-McQueen, "Extensible Markup Language (XML) 1.0
              (Fourth Edition)", World Wide Web Consortium
              Recommendation REC-xml-20060816, August 2006,
              <http://www.w3.org/TR/2006/REC-xml-20060816>.

   [W3C.REC-xml-c14n-20010315]
              Boyer, J., "Canonical XML Version 1.0", World Wide Web
              Consortium Recommendation REC-xml-c14n-20010315,
              March 2001,
              <http://www.w3.org/TR/2001/REC-xml-c14n-20010315>.

   [W3C.REC-xml-names-20060816]
              Hollander, D., Bray, T., Layman, A., and R. Tobin,
              "Namespaces in XML 1.0 (Second Edition)", World Wide Web
              Consortium Recommendation REC-xml-names-20060816,
              August 2006,
              <http://www.w3.org/TR/2006/REC-xml-names-20060816>.

   [RFC2141]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media



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              Types", RFC 3023, January 2001.

   [RFC2648]  Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
              August 1999.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4825]  Rosenberg, J., "The Extensible Markup Language (XML)
              Configuration Access Protocol (XCAP)", RFC 4825, May 2007.

   [RFC5261]  Urpalainen, J., "An Extensible Markup Language (XML) Patch
              Operations Framework Utilizing XML Path Language (XPath)
              Selectors", RFC 5261, September 2008.

9.2.  Informative References

   [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.

   [RFC3265]  Roach, A., "Session Initiation Protocol (SIP)-Specific
              Event Notification", RFC 3265, June 2002.

   [RFC4662]  Roach, A., Campbell, B., and J. Rosenberg, "A Session
              Initiation Protocol (SIP) Event Notification Extension for
              Resource Lists", RFC 4662, August 2006.

   [RFC4826]  Rosenberg, J., "Extensible Markup Language (XML) Formats
              for Representing Resource Lists", RFC 4826, May 2007.

   [RFC4483]  Burger, E., "A Mechanism for Content Indirection in
              Session Initiation Protocol (SIP) Messages", RFC 4483,
              May 2006.













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Authors' Addresses

   Jonathan Rosenberg
   Cisco
   Edison, NJ
   US

   Email: jdrosen@cisco.com
   URI:   http://www.jdrosen.net


   Jari Urpalainen
   Nokia
   Itamerenkatu 11-13
   Helsinki  00180
   Finland

   Phone: +358 7180 37686
   Email: jari.urpalainen@nokia.com
































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