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CDNi Content De-duplication Optimization
draft-jin-cdni-content-deduplication-optimization-00

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors WeiYi Jin , Wei Wang , ZhenWu Hao , Yu Meng
Last updated 2012-02-01
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draft-jin-cdni-content-deduplication-optimization-00
CDNI                                                              W. Jin
Internet-Draft                                                   W. Wang
Intended status: Informational                                    Z. Hao
Expires: August 5, 2012                                          Y. Meng
                                                         ZTE Corporation
                                                        February 2, 2012

                CDNi Content De-duplication Optimization
          draft-jin-cdni-content-deduplication-optimization-00

Abstract

   Some CDNi deployments are likely to lead to content repetition in the
   same dCDN.  This document gives the cases and then discusses the
   optimization approach to de-duplicate of the repeated content in CDNi
   network.  To implement the optimization, the enhancement to CDNi
   metadata model and interface is required.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 5, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Scenarios 1  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Scenarios 2  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.3.  Scenarios 3  . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Content Naming for CDNi  . . . . . . . . . . . . . . . . . . .  6
     3.1.  Uniqueness . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2.  Ownership  . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  CDNi Content De-duplication Optimization Implementation  . . .  7
     4.1.  Constant URL . . . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  Content Naming Mechanism . . . . . . . . . . . . . . . . .  8
     4.3.  Details for Content De-duplication . . . . . . . . . . . .  9
       4.3.1.  Pre-Positioned Content Acquisition . . . . . . . . . .  9
       4.3.2.  Dynamic Content Acquisition  . . . . . . . . . . . . . 11
       4.3.3.  Content Removal  . . . . . . . . . . . . . . . . . . . 13
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 15
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Appendix A.  Additional Stuff  . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

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1.  Introduction

   In some CDNi deployments, the dCDN may be required to cache the same
   content copy from the same Content Service Provider (CSP).  For
   example, the CSP has the agreement with two Authoritative CDNs, and
   both are the upstream CDN of the same dCDN.  Another example appears
   in the cascaded mode.  The top-layer uCDN establishes connection with
   two intermediate-layer uCDNs, and both connect to the same bottom-
   layer dCDN.  In such scenarios, the dCDN may be requested to download
   the content from one uCDN, then be requested to deliver the same
   content from another uCDN.  Content repetition wastes the dCDN's the
   memory or storage resource, and wastes bandwidth to deliver the
   repeated content.  So it is necessary to avoid delivering the
   repeated content from separated uCDNs to dCDN.  In this draft, we
   list scenarios where content repetition may happen.  And a solution
   named content de-duplication is discussed.

   To address the content repetition problem, several issues may need to
   be considered.

   * How to detect content repetition by dCDN, and a content naming
   mechanism is required for CDNi network.

   * How to avoid content repetition, when one or more uCDNs selects one
   dCDN to deliver the same content to multiple User Agents.

   This document provides detailed analysis for the issues of content
   de-duplication.

1.1.  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].

   This document reuses the terminology defined in [I-D.jenkins-cdni-
   problem-statement].

   Resource Id: a metadata object (e.g.  URL) which identifies the
   resource on a specific CDNi interface associated with a particular
   Authoritative CDN.

   Content Id: a metadata object (e.g.  URN) which uniquely identifies
   the content in the scope of CDNi.

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2.  Deployment Scenarios

   This section shows several CDNi deployments that typically lead to
   content repetition.

2.1.  Scenarios 1

   As depicted in Figure 1, two interconnected CDN-A(uCDN) and CDN-
   B(dCDN) both have contracts with CSP.  CDN-B play two roles at the
   same time: down streaming CDN of CDN-A and Authoritative CDN of CSP.
   When an end-user of CDN-A initiate content acquisition from the CSP,
   CDN-A decides CDN-B as the serving CDN.  Then CDN-A redirects the
   request to CDN-B, and indicate CDN-B to retrieve the content from it.
   Normally CDN-B as Authoritative CDN is very likely to have cached the
   content from original server.  If CDN-B cannot identify the said
   contents are the same content, the same content will be repeatedly
   cached.

   As the location of the content in a CDN is normally planned by CDN
   itself, the URLs of the same content are likely different between
   CDNs.  So it is not enough to decide whether the content to be cached
   is the same only by URL.

                                 +-------+
                                 |  CSP  |
                                 +-------+
                                /         \
                     ,--,--,--./           \,--,--,--.
                  ,-'          `-.       ,-'          `-.
                 ( CDN Provider A )=====( CDN Provider B )
                  `-.  (CDN-A) ,-'       `-. (CDN-B)  ,-'
                     `--'--'--'             `--'--'--'
                                               |
                                       +------------+
                                       | User Agent |
                                       +------------+
                 === CDN Interconnect

                                                  Figure 1

2.2.  Scenarios 2

   As depicted in Figure 2, both CDN-A and CDN-B establish
   interconnections with CDN-C which acts as a dCDN.  Thus, CDN-C will
   cache the content for CDN-A and CDN-B.  When both CDN provider A and
   CDN provider B have agreements with the same CSP for content delivery
   at the same time, CDN-C may be required by CDN-A and CDN-B separately

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   to cache the same content of CSP.  Similar to Scenario 1, CDN-C is
   also likely to suffer from content repetition troubles.

                                 +-------+
                                 |  CSP  |
                                 +-------+
                                /         \
                     ,--,--,--./           \,--,--,--.
                  ,-'          `-.       ,-'          `-.
                 ( CDN Provider A )     ( CDN Provider B )
                  `-.  (CDN-A) ,-'       `-. (CDN-B)  ,-'
                     `--'--'--'             `--'--'--'
                              \\            //
                               \\,--,--,--.//
                              ,-'          `-.
                             ( CDN Provider C )
                              `-. (CDN-C)  ,-'
                                 `--'--'--'
                                      |
                               +------------+
                               | User Agent |
                               +------------+
                 === CDN Interconnect

                                   Figure 2

2.3.  Scenarios 3

   Now we consider the case of cascaded CDNs, as depicted in Figure 3,
   wherein the top-layer Upstream CDN-A directly relate to CSP and
   interconnects with two middle-layer CDNs (CDN-B and CDN-C) which have
   the same bottom-layer Downstream CDN-D interconnected.  So there are
   two possible delivery paths for CDN-D to cache the contents of CSP,
   CDN-A -> CDN-B -> CDN-D or CDN-A -> CDN-C -> CDN-D.  CDN-D may be
   required to cache the same content by upstream CDNs(CDN-B and CDN-C)
   on different paths.  If the URL of the content is changed by CDN-B or
   CDN-C, CDN-D cannot be aware of the contents to be cached and
   therefore this likely leads to content repetition.

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                                ,--,--,--.
                             ,-'          `-.     +-------+
                            ( CDN Provider A )----|  CSP  |
                             `-. (CDN-A)  ,-'     +-------+
                               //-'--'-\\
                    ,--,--,--.//         \\,--,--,--.
                 ,-'          `-.       ,-'          `-.
                ( CDN Provider B )     ( CDN Provider C )
                 `-.  (CDN-B) ,-'       `-. (CDN-C)  ,-'
                    `--'--'--'             `--'--'--'
                             \\            //
                              \\,--,--,--.//
                             ,-'          `-.
                            ( CDN Provider D )
                             `-. (CDN-D)  ,-'
                                `--'--'--'
                                     |
                              +------------+
                              | User Agent |
                              +------------+
                === CDN Interconnect

                                  Figure 3

3.  Content Naming for CDNi

   It is well known that CDNs have their own content naming mechanisms
   most of which are independent and separated from each other due to
   the use of different algorithms such as Hash algorithms.  It implies
   that for the same content distributed by two CDNs, the corresponding
   content identifiers are likely to be quite different.
   [I-D.lefaucheur-cdni-requirements] treats the information regarding
   CDN content naming as intra-CDN information and the CDNI solution
   MUST not require intra-CDN information to be exposed to other CDNs
   for effective and efficient delivery of the content.  Therefore,
   establishing a uniform content naming mechanism is urgently needed
   for CDNi network.  This mechanism which can be implemented by CDNI
   Metadata Distribution Protocol may possess the following properties
   below.

3.1.  Uniqueness

   CDNi content naming mechanism must guarantee the uniqueness of
   content identification.  URL is widely used for identifying network
   resource, but it is not quite suitable for content identification in
   CDNi network where content de-duplication is needed.  Although the
   method of URL match is usually used by many cache systems to detect

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   the repetitive files with same name in order to avoid content
   repetition, it is probably failed for CDNi due to different
   forwarding mechanisms that is the user-originated requests are always
   snooped by devices like DPI before transmitted to the original
   server, whereas the requests received by dCDN are always redirected
   by one or more uCDNs.  Since there is no guarantee of unchanged URLs
   through the redirected process, some other object need to be defined
   to represent the uniqueness of content identification.

   For the CSP's content distributed into different interconnected CDNs,
   the related metadata objects may be somewhat different in many cases.
   Taking the example in Figure 2, when both CDN-A and CDN-B delegate
   the delivery of the same CSP's content, the content metadata such as
   content description, access policy and security policy may be not
   quite similar to each other.  Obviously, such metadata information is
   not suitable for content identification.  Thus, we need to define
   some other metadata object that uniquely identifies the same content.

3.2.  Ownership

   CDNi content naming mechanism should embody the ownership of content
   identification.  Typically, a CDN provider has contracts with many
   CSPs for delivering their content, as well as operates its own
   content.  However, lots of contents published by these CSPs are
   usually highly resembled, and part of them are even exactly the same.
   So the problem is whether these identical copies originated from the
   same CSP or how the interconnected CDNs know they are identical.
   (Note: Such copies are pointed by the same content identification
   only if they are from the same content source.)  For a traditional
   (non-interconnected) CDN, there is no problem to distinguish them via
   its intra content naming mechanism.  While a CDN interconnects with
   other CDNs, the condition becomes more complicated due to the lack of
   awareness of CSP's content when the CDN acts as a dCDN.

4.  CDNi Content De-duplication Optimization Implementation

4.1.  Constant URL

   Of course, URL can be used to implement content de-duplication in
   CDNi network.  As refered in section 2, the URL is different from
   uCDN to uCDN and is likely changed in the redirection process.  There
   is an usage of agreement of configuration URL between a pair of
   interconnected CDN in [I-D.davie-cdni-framework], however it is
   difficult to expand to the complex CDNi network.  So a feasible
   proposal is a mechanism for CDNi network to guarantee CSP's contents
   cached in different uCDNs are identified by the same URL and the URL
   is unchanged or at least the path part is remained unchanged in the

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   redirection process.  The main problem of this mechanism is lack of
   resilience and we prefer an alternative mechanism to be introduced in
   section 4.2.

4.2.  Content Naming Mechanism

   This section provides detailed implementation of CDNi content naming
   mechanism using CDNi Metadata Protocol.

   CSP's content as well as its copies cached in interconnected CDNs are
   delivered to numerous End-Users.  [I-D.davie-cdni-framework] assigns
   each copy identifiers in terms of URLs embedded with "CDN-Domain"
   used to distinguish a download request from an end-user or an uCDN.
   We use the term Resource Identifier to represent the URLs pointing to
   the content copies in interconnected CDNs.  However, unlike to the
   usage in [I-D.davie-cdni-framework], in this document CDNi content
   naming mechanism makes Resource Identifiers are only related to
   contents in uCDNs and cannot be changed during the forwarding
   process.  Taking the example in section 2.3, we use Resource
   Identifier A point to content originated through uCDN A. When two
   users acquire the same content from uCDN D, with two different
   request forwarding paths, CDN A->CDN B->CDN D and CDN A->CDNC->CDN
   D,respectively, uCDN D is able to find out that the visited content
   and the related metadata are originally distributed from uCDN A using
   the Resource Identifier A.

   Although the Resource Identifier is able to indentify content,
   uniqueness of content identification can't be guaranteed, as CSP may
   have contracts with different uCDNs.  In order to resolve it, we
   introduce the term Content Identifier which is assigned to associate
   with Resource Identifier to uniquely identifies the content and is
   similar to the URN usage.  (Note: The Content Identifier MUST be
   globally unique.)  A metadata model depicted in Figure 4 shows the
   relationship between the two kinds of Identifier.  Depending upon
   this model, dCDN is able to be aware of such requests towards the
   same targeted content.

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                        +----------------------+
                        |  Content Identifier  |
                        +----------------------+
                        /          |          \
                       /           |           \
          +--------------+  +--------------+     +--------------+
          | Resouce      |  | Resouce      |     | Resouce      |
          | Indentifier 1|  | Indentifier 2| ... | Indentifier n|
          +--------------+  +--------------+     +--------------+

                                                  Figure 4

   Note: Who is responsible for creating and maintaining the Content
   Identifier needs to further study.

4.3.  Details for Content De-duplication

   This section details the solution making use of CDNi Content Naming
   mechanism for content de-duplication.

   Using the content identification model included in content metadata,
   an interconnected CDN is able to detect content repetition.  The
   content status must be synchronously updated by the interconnected
   CDN.  According to content status, the interconnected CDN can judge
   the resource copy is cached or not.

   We present several procedures below to illustrate how to implement
   optimization for CDNi content de-duplication.

4.3.1.  Pre-Positioned Content Acquisition

   The following flow illustrates how the two uCDNs successively pre-
   position the same content in the dCDN.  In this flow, the content to
   be re-positioned in the dCDN is identified by different Resource
   Identifiers corresponding to the uCDN A and uCDN B.

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       +--------+                 +--------+                 +--------+
       |  dCDN  |                 | uCDN A |                 | uCDN B |
       +--------+                 +--------+                 +--------+
           |   Pre-position Request   |                           |
           |<-------------------------|                           |
    +--------------+                  |                           |
    | Detection of |                  |                           |
    | content rep- |                  |                           |(1)
    | etition      |                  |                           |
    +--------------+                  |                           |
           |          OK              |                           |
           |------------------------->|                           |
           |                          |                           |
           |   Acquisition Request    |                           |
           |------------------------->|                           |
           |                          |                           |
           |     Content Data         |                           |(2)
           |<-------------------------|                           |
    +--------------+                  |                           |
    | Update cont- |                  |                           |
    | ent status   |                  |                           |
    +--------------+                  |                           |
           |                Pre-position Request                  |
           |<-----------------------------------------------------|
    +--------------+                  |                           |
    | Detection of |                  |                           |
    | content rep- |                  |                           |(3)
    | etition      |                  |                           |
    +--------------+                  |                           |
           |                         OK                           |
           |----------------------------------------------------->|
           |                          |                           |

                                      Figure 5

   The steps illustrated in the figure are as follows:

   1.  The uCDN A requests that the dCDN pre-positions a particular
   content item identified by its Resource Identifier and Content
   Identifier.  Receiving the message, the dCDN uses the Content
   Identifier to look up target metadata to see whether the same content
   item is cached.  With the result that the metadata does not exist,
   the dCDN then replies to uCDN A with a OK message to notify that no
   such copy has been cached and content pre-position is required.

   2.  The dCDN acquires the item of content from uCDN A. Once the
   content is pre-positioned, dCDN updates the content status and

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   maintains the content identification metadata.

   3.  The uCDN B requests that dCDN pre-positions the same content item
   identified by its Resource Identifier and Content Identifier.
   Receiving the message, the dCDN uses the Content Identifier to look
   up target metadata.  Because such metadata exists, dCDN determines
   that the content is already cached.  Then, dCDN replies to uCDN A
   with a OK message to notify that the same copy has been cached and
   pre-position should be canceled.

4.3.2.  Dynamic Content Acquisition

   The following flows illustrate how the dCDN performs content de-
   duplication in cases of a cache miss and a cache hit without content
   pre-positioning.

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     +----------+                 +------+                     +------+
     | end-user |                 | dCDN |                     | uCDN |
     +----------+                 +------+                     +------+
        |      Content Request      |                            |
        |------------------------------------------------------->|
        |      Content Redirection  |                            |
        |<-------------------------------------------------------|(1)
        |      Content Request      |                            |
        |-------------------------->|                            |
        |                           |    Content id Acquisition  |
        |                           |<-------------------------->|
        |                    +--------------+                    |
        |                    | Detection of |                    |
        |                    | content rep- |                    |(2)
        |                    | etition      |                    |
        |                    +--------------+                    |
        |                           |    Acquisition Request     |
        |                           |--------------------------->|
        |                           |    Content Data            |
        |                           |<---------------------------|
        |                    +--------------+                    |(3)
        |                    | Update cont- |                    |
        |                    | ent status   |                    |
        |                    +--------------+                    |
        |       Content Data        |                            |
        |<--------------------------|                            |
        |                           |                            |

                                         Figure 6

   The steps illustrated in the figure are as follows:

   1.  A content request originated by a end-user arrives at uCDN.  The
   uCDN processes the request and recognizes that the end-user is best
   served by dCDN.  So uCDN redirects the request to dCDN by sending
   redirection response to the end-user who then requests the content
   from dCDN.

   2.  Receiving the request, the dCDN uses the Resource Identifier
   pointing to the requested resource to fetch the corresponding Content
   Identifier from the uCDN.  The dCDN then uses the Content Identifier
   to look up target metadata indicates whether the content item is
   cached.  With the result that such metadata does not exist, the case
   of a cache miss is decided by the dCDN so that the content needs to
   be downloaded from the uCDN before delivered to the end-user.

   3.  The dCDN acquires the requested content from uCDN A. Once the

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   content cached, dCDN updates the content status and maintains the
   content identification metadata.  The dCDN then delivers content data
   to the end-user.

     +----------+                 +------+                    +------+
     | end-user |                 | dCDN |                    | uCDN |
     +----------+                 +------+                    +------+
        |      Content Request      |                            |
        |------------------------------------------------------->|
        |      Content Redirection  |                            |
        |<-------------------------------------------------------|(1)
        |      Content Request      |                            |
        |-------------------------->|                            |
        |                           |    Content id Acquisition  |
        |                           |<-------------------------->|
        |                    +--------------+                    |
        |                    | Detection of |                    |
        |                    | content rep- |                    |(2)
        |                    | etition      |                    |
        |                    +--------------+                    |
        |       Content Data        |                            |
        |<--------------------------|                            |
        |                           |                            |

                                         Figure 7

   The steps illustrated in the figure are as follows:

   Steps 1 and 2 are exactly the same as steps 1 and 2 of Figure 5, only
   in this time dCDN deciding the case of a cache hit according to the
   existence of such a content identification metadata.

   This flow differs from the one in Figure 5 only without triggering
   dynamic content acquisition (step 3), since the content has been
   cached by dCDN.

4.3.3.  Content Removal

   The following flow illustrates how the dCDN removes the content
   resource under the control of the uCDN.

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     +----------+                 +------+                     +------+
     | end-user |                 | dCDN |                     | uCDN |
     +----------+                 +------+                     +------+
        |                           |       Content Removal      |
        |                           |<---------------------------|
        |                    +--------------+                    |
        |                    |  Removal of  |                    |
        |                    |    content   |                    |(1)
        |                    +--------------+                    |
        |                           |                            |
        |                    +--------------+                    |
        |                    |  Removal of  |                    |
        |                    | conjunction  |                    |
        |                    |   metadata   |                    |(2)
        |                    +--------------+                    |
        |                           |           OK               |
        |                           |--------------------------->|
        |                           |                            |

                                         Figure 8

   A premise is that the content resource to be removed is cached in the
   dCDN from the uCDN.  The steps illustrated in the figure are as
   follows:

   1.  The uCDN requests that the dCDN removes some content resource
   identified by the Content Identifier due to the deployment policy or
   expiration of life-time.  The dCDN then removes the resource.

   2.  Once removal of the content resource, the dCDN updates the
   content status as well as removes the content identification
   metadata, and then replies a OK response to the uCDN.

5.  Security Considerations

   TBD

6.  IANA Considerations

   This document has no IANA Considerations.

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7.  Acknowledgments

   TBD

8.  References

8.1.  Normative References

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

8.2.  Informative References

   [I-D.davie-cdni-framework]
              Davie, B. and L. Peterson, "Framework for CDN
              Interconnection", July 2011.

   [I-D.jenkins-cdni-problem-statement]
               Niven-Jenkins, B., Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement", March 2011.

   [I-D.lefaucheur-cdni-requirements]
              Leung, K., Lee, F., Faucheur, F., Viveganandhan, M., and
              G. Watson, "Content Distribution Network Interconnection
              (CDNI) Requirements", July 2011.

   [I-D.narten-iana-considerations-rfc2434bis]
              Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs",
              draft-narten-iana-considerations-rfc2434bis-09 (work in
              progress), March 2008.

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

Appendix A.  Additional Stuff

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Internet-Draft  CDNi Content De-duplication Optimization   February 2012

Authors' Addresses

   WeiYi Jin
   ZTE Corporation
   Nanjing,   210012
   China

   Phone: +86 025-52871364
   Email: jin.weiyi@zte.com.cn

   Wei Wang
   ZTE Corporation
   Nanjing,   210012
   China

   Phone: +86 025-88014631
   Email: wang.wei108@zte.com.cn

   ZhenWu Hao
   ZTE Corporation
   Nanjing,   210012
   China

   Phone: +86 025-52871304
   Email: hao.zhenwu@zte.com.cn

   Yu Meng
   ZTE Corporation
   Nanjing,   210012
   China

   Phone: +86 025-88014632
   Email: meng.yu@zte.com.cn

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