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rfc:rfc5005

Network Working Group M. Nottingham Request for Comments: 5005 September 2007 Category: Standards Track

                     Feed Paging and Archiving

Status of This Memo

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

Abstract

 This specification defines three types of syndicated Web feeds that
 enable publication of entries across one or more feed documents.
 This includes "paged" feeds for piecemeal access, "archived" feeds
 that allow reconstruction of the feed's contents, and feeds that are
 explicitly "complete".

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   1.1.  Notational Conventions . . . . . . . . . . . . . . . . . .  2
   1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
 2.  Complete Feeds . . . . . . . . . . . . . . . . . . . . . . . .  3
 3.  Paged Feeds  . . . . . . . . . . . . . . . . . . . . . . . . .  4
 4.  Archived Feeds . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.1.  Publishing Archived Feeds  . . . . . . . . . . . . . . . .  8
   4.2.  Consuming Archived Feeds . . . . . . . . . . . . . . . . .  8
 5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
 6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
 7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
   7.2.  Informative References . . . . . . . . . . . . . . . . . . 10
 Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 12
 Appendix B.  Use in RSS 2.0  . . . . . . . . . . . . . . . . . . . 12

Nottingham Standards Track [Page 1] RFC 5005 Feed Paging and Archiving September 2007

1. Introduction

 Syndicated Web feeds (using formats such as Atom [1]) are often split
 into multiple documents to save bandwidth, allow "sliding window"
 access, or for other purposes.
 This specification formalizes two types of feeds that can span one or
 more feed documents; "paged" feeds and "archived" feeds.
 Additionally, it defines "complete" feeds to cover the case when a
 single feed document explicitly represents all of the feed's entries.
 Each has different properties and trade-offs:
 o  Complete feeds contain the entire set of entries in one document,
    and can be useful when it isn't desirable to "remember"
    previously-seen entries.
 o  Paged feeds split the entries among multiple temporary documents.
    This can be useful when entries in the feed are not long-lived or
    stable, and the client needs to access an arbitrary portion of
    them, usually in close succession.
 o  Archived feeds split the entries among multiple permanent
    documents and can be useful when entries are long-lived, and it is
    important for clients to see every one.
 The semantics of a feed that combines these types is undefined by
 this specification.
 Although they refer to Atom normatively, the mechanisms described
 herein can be used with similar syndication formats; see Appendix B
 for one such use.

1.1. Notational Conventions

 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 [2].
 This specification uses XML Namespaces [3] to uniquely identify XML
 element names.  It uses the following namespace prefix for the
 indicated namespace URI;
 "fh": "http://purl.org/syndication/history/1.0"

Nottingham Standards Track [Page 2] RFC 5005 Feed Paging and Archiving September 2007

1.2. Terminology

 In this specification, "feed document" refers to an Atom Feed
 Document or similar syndication instance document.  It may contain
 any number of entries, and may or may not be a complete
 representation of the logical feed.
 A "logical feed" is the complete set of entries associated with a
 feed (as contrasted with a feed document, which may contain a subset
 of entries).
 "Head section" refers to a document's feed-wide metadata container;
 e.g., the child elements of the atom:feed element in an Atom Feed
 Document.
 This specification uses terms from the XML Infoset [4].  However,
 this specification uses a shorthand; the phrase "Information Item" is
 omitted when naming Element Information Items.  Therefore, when this
 specification uses the term "element," it is referring to an Element
 Information Item in Infoset terms.
 This specification also uses Atom link relations to identify
 different types of links; see the Atom specification [1] for
 information about their syntax, and the IANA link relation registry
 for more information about specific values.
 Note that URI references in link relation values may be relative, and
 when they are used they must be absolutised, as described in Section
 5.1 of [5].

2. Complete Feeds

 A complete feed is a feed document that contains all of the entries
 of a logical feed; any entry not actually in the feed document SHOULD
 NOT be considered part of that feed.
 For example, a feed that represents a ranking that varies over time
 (such as "Top Twenty Records" or "Most Popular Items") should not
 have newer entries displayed alongside older ones.  By marking this
 feed as complete, old entries are discarded when it is refreshed.
 The fh:complete element, when present in a feed's head section,
 indicates that the feed document it occurs in is a complete
 representation of the logical feed's entries.  It is an empty
 element; this specification does not define any content for it.

Nottingham Standards Track [Page 3] RFC 5005 Feed Paging and Archiving September 2007

 Example: Atom-formatted Complete Feed
 <?xml version="1.0" encoding="utf-8"?>
 <feed xmlns="http://www.w3.org/2005/Atom"
  xmlns:fh="http://purl.org/syndication/history/1.0">
  <title>NetMovies Queue</title>
  <subtitle>The DVDs you'll receive next.</subtitle>
  <link href="http://example.org/"/>
  <fh:complete/>
  <link rel="self"
   href="http://netmovies.example.org/jdoe/queue/index.atom"/>
  <updated>2003-12-13T18:30:02Z</updated>
  <author>
    <name>John Doe</name>
  </author>
  <id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>
  <entry>
    <title>Casablanca</title>
    <link href="http://netmovies.example.org/movies/Casablanca"/>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <updated>2003-12-13T18:30:02Z</updated>
    <summary>Here's looking at you, kid...</summary>
  </entry>
 </feed>
 This specification does not address duplicate entries in complete
 feeds.

3. Paged Feeds

 A paged feed is a set of linked feed documents that together contain
 the entries of a logical feed, without any guarantees about the
 stability of each document's contents.
 Paged feeds are lossy; that is, it is not possible to guarantee that
 clients will be able to reconstruct the contents of the logical feed
 at a particular time.  Entries may be added or changed as the pages
 of the feed are accessed, without the client becoming aware of them.
 Therefore, clients SHOULD NOT present paged feeds as coherent or
 complete, or make assumptions to that effect.
 Paged feeds can be useful when the number of entries is very large,
 infinite, or indeterminate.  Clients can "page" through the feed,
 only accessing a subset of the feed's entries as necessary.

Nottingham Standards Track [Page 4] RFC 5005 Feed Paging and Archiving September 2007

 For example, a search engine might make query results available as a
 paged feed, so that queries with very large result sets do not
 overwhelm the server, the network, or the client.
 The feed documents in a paged feed are tied together with the
 following link relations:
 o  "first" - A URI that refers to the furthest preceding document in
    a series of documents.
 o  "last" - A URI that refers to the furthest following document in a
    series of documents.
 o  "previous" - A URI that refers to the immediately preceding
    document in a series of documents.
 o  "next" - A URI that refers to the immediately following document
    in a series of documents.
 Paged feed documents MUST have at least one of these link relations
 present, and should contain as many as practical and applicable.
 Example: Atom-formatted Paged Feed
 <?xml version="1.0" encoding="utf-8"?>
 <feed xmlns="http://www.w3.org/2005/Atom">
  <title>Example Feed</title>
  <link href="http://example.org/"/>
  <link rel="self" href="http://example.org/index.atom"/>
  <link rel="next" href="http://example.org/index.atom?page=2"/>
  <updated>2003-12-13T18:30:02Z</updated>
  <author>
    <name>John Doe</name>
  </author>
  <id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>
  <entry>
    <title>Atom-Powered Robots Run Amok</title>
    <link href="http://example.org/2003/12/13/atom03"/>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <updated>2003-12-13T18:30:02Z</updated>
    <summary>Some text.</summary>
  </entry>
 </feed>
 This specification does not address duplicate entries in paged feeds.

Nottingham Standards Track [Page 5] RFC 5005 Feed Paging and Archiving September 2007

4. Archived Feeds

 An archived feed is a set of feed documents that can be combined to
 accurately reconstruct the entries of a logical feed.
 Unlike paged feeds, archived feeds enable clients to do this without
 losing entries.  This is achieved by publishing a single subscription
 document and (potentially) many archive documents.
 A subscription document is a feed document that always contains the
 most recently added or changed entries available in the logical feed.
 Archive documents are feed documents that contain less recent entries
 in the feed.  The set of entries contained in an archive document
 published at a particular URI SHOULD NOT change over time.  Likewise,
 the URI for a particular archive document SHOULD NOT change over
 time.
 The following link relations are used to tie subscription and
 archived feeds together:
 o  "prev-archive" - A URI that refers to the immediately preceding
    archive document.
 o  "next-archive" - A URI that refers to the immediately following
    archive document.
 o  "current" - A URI that, when dereferenced, returns a feed document
    containing the most recent entries in the feed.
 Subscription documents and archive documents MUST have a "prev-
 archive" link relation, unless there are no preceding archives
 available.  Archive documents SHOULD also have a "next-archive" link
 relation, unless there are no following archives available.
 Archive documents SHOULD indicate their associated subscription
 documents using the "current" link relation.
 Archive documents SHOULD also contain an fh:archive element in their
 head sections to indicate that they are archives. fh:archive is an
 empty element; this specification does not define any content for it.

Nottingham Standards Track [Page 6] RFC 5005 Feed Paging and Archiving September 2007

 Example: Atom-formatted Subscription Document
 <?xml version="1.0" encoding="utf-8"?>
 <feed xmlns="http://www.w3.org/2005/Atom">
  <title>Example Feed</title>
  <link href="http://example.org/"/>
  <link rel="self" href="http://example.org/index.atom"/>
  <link rel="prev-archive"
   href="http://example.org/2003/11/index.atom"/>
  <updated>2003-12-13T18:30:02Z</updated>
  <author>
    <name>John Doe</name>
  </author>
  <id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>
  <entry>
    <title>Atom-Powered Robots Run Amok</title>
    <link href="http://example.org/2003/12/13/atom03"/>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <updated>2003-12-13T18:30:02Z</updated>
    <summary>Some text.</summary>
  </entry>
 </feed>
 Example: Atom-formatted Archive Document
 <?xml version="1.0" encoding="utf-8"?>
 <feed xmlns="http://www.w3.org/2005/Atom"
  xmlns:fh="http://purl.org/syndication/history/1.0">
  <title>Example Feed</title>
  <link rel="current" href="http://example.org/index.atom"/>
  <link rel="self" href="http://example.org/2003/11/index.atom"/>
  <fh:archive/>
  <link rel="prev-archive"
   href="http://example.org/2003/10/index.atom"/>
  <updated>2003-11-24T12:00:00Z</updated>
  <author>
    <name>John Doe</name>
  </author>
  <id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>
  <entry>
    <title>Atom-Powered Robots Scheduled To Run Amok</title>
    <link href="http://example.org/2003/11/24/robots_coming"/>
    <id>urn:uuid:cdef5c6d5-gff8-4ebb-assa-80dwe44efkjo</id>
    <updated>2003-11-24T12:00:00Z</updated>
    <summary>Some text from an old, different entry.</summary>
  </entry>
 </feed>

Nottingham Standards Track [Page 7] RFC 5005 Feed Paging and Archiving September 2007

 In this example, the feed archives are split into monthly chunks, and
 the subscription document points to the most recent complete archive
 "http://example.org/2003/11/index.atom" using the "prev-archive"
 relation.  That document, in turn points to the previous archive
 "http://example.org/2003/10/index.atom", and so on.  Note that the
 "2003/11" archive does not have a "next-archive" relation, because it
 is the most recent complete archive; although another archive
 ("2003/12") may be under construction, it would be an error to link
 to it before completion.

4.1. Publishing Archived Feeds

 The requirement that archive documents be stable allows clients to
 safely assume that if they have retrieved one in the past, it will
 not meaningfully change in the future.  As a result, if an archive
 document's contents are changed, some clients may not become aware of
 the changes.
 Therefore, if a publisher requires a change to be visible to all
 users (e.g., correcting factual errors), they should consider
 publishing the revised entry in the subscription document, in
 addition to (or instead of) the appropriate archive document.
 Conversely, unimportant changes (e.g., spelling corrections) might be
 only effected in archive documents.
 Publishers SHOULD construct their feed documents in such a way as to
 make duplicate removal unambiguous (see Section 4.2).
 Publishers are not required to make all archive documents available;
 they may refuse to serve (e.g., with HTTP status code 403 or 410) or
 be unable to serve (e.g., with HTTP status code 404) an archive
 document.

4.2. Consuming Archived Feeds

 Typically, clients will "subscribe" to an archived feed by polling
 the subscription document for recent changes.  If a URI contained in
 the prev-archive link relation has not been processed in the past,
 the client can "catch up" with any missed entries by dereferencing it
 and adding the contained entries to the logical feed.  This process
 should be repeated recursively until the client encounters a prev-
 archive link relation that has been processed (the end of the archive
 is indicated by a missing prev-archive link relation) or an error is
 encountered.
 If duplicate entries are found, clients SHOULD consider only the most
 recently updated entry to be part of the logical feed.  If duplicate
 entries have the same update time-stamp, or no time-stamps are

Nottingham Standards Track [Page 8] RFC 5005 Feed Paging and Archiving September 2007

 available, the entry sourced from the most recently updated feed
 document SHOULD replace all other duplicates of that entry.
 In Atom-formatted archived feeds, two entries are duplicates if they
 have the same atom:id element.  The update time of an entry is
 determined by its atom:updated element, and likewise the update time
 of a feed document is determined by its feed-level atom:updated
 element.
 Clients SHOULD warn users when they are not able to reconstruct the
 entire logical feed (e.g., by alerting the user that an archive
 document is unavailable, or displaying pseudo-entries that inform the
 user that some entries may be missing).

5. IANA Considerations

 This specification defines the following new relations that have been
 added to the Link Relations registry:
    o  Attribute Value: prev-archive
    o  Description: A URI that refers to the immediately
       preceding archive document.
    o  Expected display characteristics: none
    o  Security considerations: See [RFC5005]
    o  Attribute Value: next-archive
    o  Description: A URI that refers to the immediately
       following archive document.
    o  Expected display characteristics: none
    o  Security considerations: See [RFC5005]
 Additionally, the "previous," "next", and "current" link relations
 should be updated to refer to this document.

6. Security Considerations

 Feeds using this mechanism have the same security considerations as
 Atom [1].  Encryption and authentication security services can be
 obtained by encrypting and/or signing the feed, as described in [1],
 and may also be obtained through channel-based mechanisms (e.g., TLS
 [6], HTTP authentication [7]) and/or transport (e.g., IPsec [8]).
 Feeds using these mechanisms could be crafted in such a way as to
 cause a client to initiate excessive (or even an unending sequence
 of) network requests, causing denial of service (either to the
 client, the target server, and/or intervening networks).  Clients can
 mitigate this risk by requiring user intervention after a certain
 number of requests, or by limiting requests either according to a

Nottingham Standards Track [Page 9] RFC 5005 Feed Paging and Archiving September 2007

 hard limit, or with heuristics.  Servers can mitigate this risk by
 denying requests that they consider abusive (e.g., by closing the
 connection or generating an error).
 Clients should be mindful of resource limits when storing feed
 documents.  To reiterate, they are not required to always store or
 reconstruct the feed when conforming to this specification; they only
 need to inform the user when the reconstructed feed is not complete.
 This specification does not define what it means when a logical
 feed's component feed documents have different security mechanisms
 applied.

7. References

7.1. Normative References

 [1]  Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication
      Format", RFC 4287, December 2005.
 [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [3]  Bray, T., Hollander, D., and A. Layman, "Namespaces in XML",
      World Wide Web Consortium First Edition REC-xml-names-19990114,
      January 1999,
      <http://www.w3.org/TR/1999/REC-xml-names-19990114>.
 [4]  Tobin, R. and J. Cowan, "XML Information Set (Second Edition)",
      World Wide Web Consortium Recommendation REC-xml-infoset-
      20040204, February 2004,
      <http://www.w3.org/TR/2004/REC-xml-infoset-20040204>.
 [5]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
      Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
      January 2005.

7.2. Informative References

 [6]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
      Protocol Version 1.1", RFC 4346, April 2006.
 [7]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
      Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication:
      Basic and Digest Access Authentication", RFC 2617, June 1999.

Nottingham Standards Track [Page 10] RFC 5005 Feed Paging and Archiving September 2007

 [8]  Kent, S. and K. Seo, "Security Architecture for the Internet
      Protocol", RFC 4301, December 2005.
 [9]  Winer, D., "RSS 2.0 Specification", 2005,
      <http://www.rssboard.org/rss-specification>.

Nottingham Standards Track [Page 11] RFC 5005 Feed Paging and Archiving September 2007

Appendix A. Acknowledgements

 The author would like to thank the following people for their
 contributions, comments, and help: Danny Ayers, Thomas Broyer, Lisa
 Dusseault, Stefan Eissing, David Hall, Bill de Hora, Vidya Narayanan,
 Aristotle Pagaltzis, John Panzer, Dave Pawson, Garrett Rooney, Robert
 Sayre, James Snell, Henry Story, and Franklin Tse.
 Any errors herein remain the author's, not theirs.

Appendix B. Use in RSS 2.0

 As previously noted, while this specification's extensions are
 described in terms of the Atom feed format, they are also useful in
 similar formats.  This informative appendix demonstrates how they can
 be used in an RSS 2.0-formatted [9] feed.
 In RSS 2.0-formatted feeds, two entries are duplicates if they have
 the same guid element.  The update time of an entry is not defined by
 RSS 2.0, but the feed-level update time can be determined by the
 lastBuildDate element, if present.
 RSS 2.0-formatted Complete Feed
 <?xml version="1.0"?>
 <rss version="2.0"
  xmlns:fh="http://purl.org/syndication/history/1.0">
  <channel>
   <title>NetMovies Queue</title>
   <link>http://netmovies.example.org/</link>
   <description>The DVDs you'll receive next.</description>
   <fh:complete/>
   <item>
    <title>Casablanca</title>
    <link>http://netmovies.example.org/movies/Casablanca</link>
    <description>Here's looking at you, kid...
    </description>
    <pubDate>Tue, 03 Jun 2003 09:39:21 GMT</pubDate>
    <guid isPermaLink="false"
    >urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</guid>
   </item>
  </channel>
 </rss>

Nottingham Standards Track [Page 12] RFC 5005 Feed Paging and Archiving September 2007

 RSS 2.0-formatted Paged Feed
 <?xml version="1.0"?>
 <rss version="2.0"
  xmlns:atom="http://www.w3.org/2005/Atom">
  <channel>
   <title>Liftoff News</title>
   <link>http://liftoff.example.net/</link>
   <description>Liftoff to Space Exploration.</description>
   <atom:link rel="next"
    href="http://liftof.example.net/index.rss?page=2"/>
   <item>
    <title>Star City</title>
    <link>http://liftoff.example.net/2003/06/news-starcity</link>
    <description>How do Americans get ready to work with Russians
    aboard the International Space Station? They take a crash course
    in culture, language and protocol at Russia's Star City.
    </description>
    <pubDate>Tue, 03 Jun 2003 09:39:21 GMT</pubDate>
    <guid>http://liftoff.example.net/2003/06/03/starcity</guid>
   </item>
  </channel>
 </rss>
 RSS 2.0-formatted Subscription Document
 <?xml version="1.0"?>
 <rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
  <channel>
   <title>Liftoff News</title>
   <link>http://liftoff.example.net/</link>
   <description>Liftoff to Space Exploration.</description>
   <atom:link rel="prev-archive"
    href="http://liftoff.example.net/2003/05/index.rss"/>
   <item>
    <title>Star City</title>
    <link>http://liftoff.example.net/2003/06/news-starcity</link>
    <description>How do Americans get ready to work with Russians
    aboard the International Space Station? They take a crash course
    in culture, language and protocol at Russia's Star City.
    </description>
    <pubDate>Tue, 03 Jun 2003 09:39:21 GMT</pubDate>
    <guid>http://liftoff.example.net/2003/06/03/starcity</guid>
   </item>
  </channel>
 </rss>

Nottingham Standards Track [Page 13] RFC 5005 Feed Paging and Archiving September 2007

 RSS 2.0-formatted Archive Document
 <?xml version="1.0"?>
 <rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom"
  xmlns:fh="http://purl.org/syndication/history/1.0">
  <channel>
   <title>Liftoff News</title>
   <link>http://liftoff.example.net/</link>
   <description>Liftoff to Space Exploration.</description>
   <lastBuildDate>Fri, 30 May 2003 11:06:42 GMT</lastBuildDate>
   <fh:archive/>
   <atom:link rel="current"
    href="http://liftoff.example.net/index.rss"/>
   <atom:link rel="prev-archive"
    href="http://liftoff.example.net/2003/04/index.rss"/>
   <item>
    <title>Upcoming Eclipse</title>
    <link>http://liftoff.example.net/2003/05/30/eclipse</link>
    <description>Sky watchers in Europe, Asia, and parts of
    Alaska and Canada will experience a partial eclipse of the Sun
    on Saturday, May 31st.</description>
    <pubDate>Fri, 30 May 2003 11:06:42 GMT</pubDate>
    <guid>http://liftoff.example.net/2003/05/30/eclipse</guid>
   </item>
   <item>
    <title>The Engine That Does More</title>
    <link>http://liftoff.example.net/2003/05/27/vasmir</link>
    <description>Before man travels to Mars, NASA hopes to
    design new engines that will let us fly through the Solar
    System more quickly.  The proposed VASIMR engine would do
    that.</description>
    <pubDate>Tue, 27 May 2003 08:37:32 GMT</pubDate>
    <guid>http://liftoff.example.net/2003/05/27/vasmir</guid>
   </item>
  </channel>
 </rss>

Author's Address

 Mark Nottingham
 EMail: mnot@pobox.com
 URI:   http://www.mnot.net/

Nottingham Standards Track [Page 14] RFC 5005 Feed Paging and Archiving September 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Nottingham Standards Track [Page 15]

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