One document matched: draft-day-cdnp-model-02.txt

Differences from draft-day-cdnp-model-01.txt



Network Working Group                                             M. Day
Internet-Draft                                                     Cisco
Expires: March 2, 2001                                           B. Cain
                                                   Mirror Image Internet
                                                            G. Tomlinson
                                                                  Entera
                                                          September 2000


                        A Model for CDN Peering
                      draft-day-cdnp-model-02.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on March 2, 2001.

Copyright Notice

   Copyright (C) The Internet Society (2000). All Rights Reserved.

Abstract

   There is wide interest in the technology for interconnecting content
   distribution networks (CDNs), variously called "content peering" or
   "CDN peering".  A common vocabulary helps the process of discussing
   such interconnection and interoperation. This document introduces
   CDNs and CDN peering, and proposes elements for such a common
   vocabulary.

Notes on Mailing List and Content Alliance



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   This document and related documents are discussed on the cdn mailing
   list. To join the list, send mail to cdn-request@ops.ietf.org. To
   contribute to the discussion, send mail to cdn@ops.ietf.org. The
   archives are at ftp://ops.ietf.org/pub/lists/cdn.*

   This document is an interim product of work initiated by the Content
   Alliance. For more information about the Content Alliance, please
   see http://www.content-peering.org.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  CDNs and Other Content Architectures . . . . . . . . . . . . .  4
   2.1 Problem Description  . . . . . . . . . . . . . . . . . . . . .  4
   2.2 Introduction to CDNs . . . . . . . . . . . . . . . . . . . . .  5
   2.3 Extending Reach & Scale  . . . . . . . . . . . . . . . . . . .  6
   3.  CDN Model  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  CDN Examples and Commentary  . . . . . . . . . . . . . . . . . 10
   4.1 Understanding CDNs . . . . . . . . . . . . . . . . . . . . . . 10
   4.2 Understanding content structure  . . . . . . . . . . . . . . . 10
   5.  Peering Model  . . . . . . . . . . . . . . . . . . . . . . . . 11
   6.  Peering Examples and Commentary  . . . . . . . . . . . . . . . 13
   6.1 Understanding Peering  . . . . . . . . . . . . . . . . . . . . 13
   6.2 Content Signalling . . . . . . . . . . . . . . . . . . . . . . 13
   7.  Operational Considerations . . . . . . . . . . . . . . . . . . 14
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
       References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17
       Full Copyright Statement . . . . . . . . . . . . . . . . . . . 19





















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1. Introduction

   Content distribution networks, or CDNs, are of increasing importance
   to the overall architecture of the Web.  This document presents a
   vocabulary for use in developing technology for interconnecting
   CDNs. By analogy with peering of IP networks, this interconnection
   is sometimes called "content peering," or (somewhat more accurately)
   "peering of CDNs". Section 2 describes content distribution, CDNs,
   and the motivation for peering of CDNs in some more detail.  Section
   3 introduces the terms used for elements of a CDN and explains how
   those terms are used. Section 5 deals with CDN peering, introducing
   the terms and explaining how those terms are used. The remainder of
   the document notes various operational and security considerations
   that are relevant to CDN peering.

   The sections defining terms are organized alphabetically, which is
   appropriate for reference but which makes them difficult to read the
   first time. Rather than reading the document from beginning to end,
   the authors recommend that the first-time reader skip past the
   sections defining terms to the following sections with examples,
   referring back to the definitions as necessary.

   The interested reader is also referred to [3], which enumerates
   scenarios for content-peering-related interactions; [4], which
   describes models for accounting and associated issues; and [5],
   which gives an overall architecture of the elements for CDN peering.

























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2. CDNs and Other Content Architectures

   A CDN (content distribution network or content delivery network) is
   an architecture of Web-based network elements, arranged for
   efficient delivery of digital content. The first important use of
   CDNs was for the distribution of heavily-requested graphic files
   (such as GIF files on the home pages of popular servers). However,
   both in principle and increasingly in practice, a CDN can support
   the delivery of any digital content -- including various forms of
   streaming media.

   A number of CDN services have been built and offered commercially.
   In addition, a number of hardware and software vendors have
   developed products that enable the construction of a CDN with
   "off-the-shelf" parts.  The proliferation of CDNs and CDN
   capabilities gives rise to interest in interconnecting CDNs and
   finding ways for distinct CDNs to cooperate for better overall
   service.

   In this section, we describe the problem of content distribution;
   the use of server farms and proxies to improve the performance of
   content distribution; the contrast between CDNs and those solutions;
   and what makes a CDN valuable.

2.1 Problem Description

   Abstractly, the "content distribution problem" is to arrange a
   rendezvous between a content source at an origin server and a
   content sink at a viewer's client. In the trivial case, the
   rendezvous mechanism is that every client sends every request
   directly to the origin server named in the host part of the URL
   identifying the content.

   As the audience for the content source grows, so do the demands on
   the origin server and its associated infrastructure. There are a
   variety of ways in which the trivial system can be modified for
   better performance.  The single logical server may in fact be a
   large "farm" of server machines behind a switch. Both forward and
   reverse proxy caches can be deployed between the client and server,
   so that requests can be satisfied by some cache instead of by the
   server.

   All of these techniques are useful, but have limits. Server farms
   and reverse proxy caches can improve the scalability of the origin
   server. However, since the multiple servers and reverse proxies are
   typically deployed near the origin server, they do little to improve
   performance problems that are due to congestion.  Forward proxy
   caches can improve performance problems due to congestion (since
   they are situated near the clients) but cache objects based on


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   client demand -- so they may not help the distribution load of a
   given origin server.

   Thus, a content provider with a popular content source can find that
   it has to invest in large server farms, load balancing, and
   high-bandwidth connections to keep up with demand. Even with those
   investments, the user experience for viewers may still be relatively
   poor due to congestion in the network as a whole.

2.2 Introduction to CDNs

   A CDN essentially combines the cache-management approach of reverse
   proxy caches with the network placement of forward proxy caches. A
   CDN has multiple replicas of each content item being hosted. A
   request from a browser for a single content item is routed to a
   "good" replica, where "good" usually means that the item is served
   to the client quickly compared to the time it would take fetch it
   from the origin server. Static information about geographic
   locations and network connectivity is typically not sufficient to do
   a good job of choosing a replica. Instead, a CDN must incorporate
   dynamic information about network conditions and load on the
   replicas, routing requests so as to balance the load. 

   As previously noted, a CDN is effectively a collection of
   widely-dispersed caches.  However, there are two important
   differences. First, the caches are potentially populated by a means
   other than the requests from clients; and second, the caches are
   coordinated by a mechanism that routes client requests to a "good"
   cache.

   Compared to some servers and caches in a single data center, a CDN
   is a relatively complex system encompassing multiple points of
   presence around the world. A content provider wants to focus its
   resources on developing high-value content, not on managing network
   infrastructure; so there is an opportunity for a service provider in
   this situation. A service provider can build a CDN and offer a
   content distribution service to a content provider.

   A CDN enables a service provider to act on behalf of the content
   provider to deliver copies of origin server content from multiple
   diverse locations. The increase in number and diversity of locations
   is intended to speed download times and thus improve the user
   experience.  A CDN has some combination of a direction
   infrastructure, a content-delivery infrastructure, and a
   distribution infrastructure.  The content-delivery infrastructure
   consists of a set of "surrogate" servers [2] that deliver copies of
   content to sets of users. The direction infrastructure consists of
   mechanisms that move a client toward a rendezvous with a content
   server. The distribution infrastructure consists of mechanisms that


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   move content from the origin server to the surrogates.  An effective
   CDN serves frequently-accessed content from a surrogate that is
   "best suited" for a given client.

2.3 Extending Reach & Scale

   There are two fundamental elements that give a CDN value:
   outsourcing infrastructure and improved content delivery. A CDN
   allows multiple surrogates to act on behalf of an orgin server,
   therefore removing the delivery of content from a centralized site
   to multiple and (usually) highly distributed sites. We refer to
   increased aggregate infrastructure size as "scale." In addition, a
   CDN can be constructed with copies of content near to end users,
   overcoming issues of network size, network congestion, and network
   failures.  We refer to increased diversity of content locations as
   "reach."

   In a typical (non-peered) CDN, a single service provider operates
   the request routers, the surrogates, and the content distributors.
   In addition, that service provider establishes (business)
   relationships withe content publishers and acts on behalf of their
   origin sites to provide a distributed delivery system.  The value of
   that CDN to a content provider is a combination of its scale and its
   reach.

   There are limits to how large any one network's scale and reach can
   be.  Increasing either scale or reach is ultimately limited by the
   cost of equipment, the space available for deploying equipment,
   and/or the demand for that scale/reach of infrastructure. Sometimes
   a particular audience is tied to a single service provider or a
   small set of providers by constraints of technology, economics, or
   law. Other times, a network provider may be able to manage
   surrogates and a distribution system, but may have no direct
   relationship with content providers. Such a provider wants to have a
   means of affiliating their delivery and distribution infrastructure
   with other parties who have content to distribute. 

   CDN peering allows different CDNs to share resources so as to
   provide larger scale and/or reach to each participant than they
   could otherwise achieve.











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3. CDN Model

   This section consists of the definitions of a number of terms used
   to refer to roles, participants, and objects involved in CDNs.

   ACCOUNTING 
      Measurement and recording of DISTRIBUTION and DELIVERY
      activities, especially when the information recorded is
      ultimately used as a basis for the subsequent transfer of money,
      goods, or obligations.

   ACCOUNTING SYSTEM 
      A collection of NETWORK ELEMENTS that supports ACCOUNTING for a
      single CDN.

   CDN 
      Content Delivery Network or Content Distribution Network.  A
      collection of NETWORK ELEMENTS arranged for more effective
      delivery of CONTENT to CLIENTS.  Typically a CDN consists of a
      DISTRIBUTION SYSTEM, SURROGATES, a DIRECTION SYSTEM, and an
      ACCOUNTING SYSTEM.

   CLIENT 
      The origin of a REQUEST and the destination of the corresponding
      delivered CONTENT.

   CONTENT 
      Digital data resources. CONTENT ultimately consists of CONTENT
      DATA UNITs whose internal structure is unknown by the CDN.
      However, some CONTENT may be in a format known to the CDN. When
      the format is known to the CDN, the CDN may have some ability to
      parse, analyze, or rearrange the structure of CONTENT DATA UNITs.
      (Note that this does not imply an ability to parse, analyze, or
      rearrange any given CONTENT DATA UNIT. A CONTENT DATA UNIT is
      always opaque to the CDN.)  One important form of CONTENT with
      additional constraints on DISTRIBUTION and DELIVERY is CONTINUOUS
      MEDIA.

   CONTENT DATA UNIT 
      A single collection of CONTENT bits, where any internal structure
      or semantics are unknown to the CDN. Thus, a CDN can succeed or
      fail at transporting a CONTENT DATA UNIT, but it cannot parse,
      analyze, or rearrange it.

   CONTENT SIGNAL 
      A message delivered through a DISTRIBUTION SYSTEM that specifies
      information about an item of CONTENT. For example, a CONTENT
      SIGNAL can indicate that the ORIGIN has a new version of some
      piece of CONTENT.


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   CONTINUOUS MEDIA 
      CONTENT where there is a timing relationship between source and
      sink; that is, the sink must reproduce the timing relationship
      that existed at the source. The most common examples of
      CONTINUOUS MEDIA are audio and motion video. CONTINUOUS MEDIA can
      be real-time (interactive), where there is a "tight" timing
      relationship between source and sink, or streaming (playback),
      where the relationship is less strict. 

   DELIVERY 
      The activity of presenting a PUBLISHER's CONTENT for consumption
      by a CLIENT. Contrast with DISTRIBUTION and DIRECTION.

   DIRECTING CDN 
      A CDN whose DIRECTION SYSTEM participates in the DIRECTION of a
      particular REQUEST.

   DIRECTION 
      The activity of directing a REQUEST from a CLIENT to a suitable
      SURROGATE.

   DIRECTION SYSTEM 
      A collection of NETWORK ELEMENTS that support DIRECTION for a
      single CDN.

   DISTRIBUTION 
      The activity of moving a PUBLISHER's CONTENT from its ORIGIN to
      one or more SURROGATEs. DISTRIBUTION can happen either in
      anticipation of a SURROGATE receiving a REQUEST (pre-positioning)
      or in response to a SURROGATE receiving a REQUEST (fetching on
      demand). Contrast with DELIVERY and DIRECTION.

   DISTRIBUTION SYSTEM 
      A collection of NETWORK ELEMENTS that support DISTRIBUTION for a
      single CDN. The DISTRIBUTION SYSTEM also propagates CONTENT
      SIGNALs.

   NETWORK ELEMENT 
      A device or system that affects the processing of network
      messages.

   ORIGIN 
      The point at which CONTENT enters the DISTRIBUTION SYSTEM of the
      BILLING CDN. The ORIGIN for any item of CONTENT is the server or
      set of servers at the "core" of the distribution, holding the
      "master" or "authoritative" copy of that CONTENT.

   PUBLISHER 
      The party that ultimately controls the content and its


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      distribution. The PUBLISHER is the other party to the NEGOTIATED
      RELATIONSHIP with the BILLING CDN.

   REACHABLE SURROGATES 
      The collection of SURROGATES that can be contacted via a
      particular DISTRIBUTION SYSTEM or DIRECTION SYSTEM.

   REQUEST 
      A message identifying a particular item of CONTENT to be
      delivered. [Editor Note: Brad Cain recommends distinguishing
      DIRECTION REQUEST from CONTENT REQUEST. Does this make the model
      too closely tied to DNS-style direction? To be discussed.]

   SURROGATE 
      A delivery server, other than the ORIGIN. Receives a redirected
      REQUEST and delivers the corresponding CONTENT. Note: This
      definition has a narrower semantic context than the more
      generally used term defined in [2]. 

































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4. CDN Examples and Commentary

   This section uses the terms of the previous to explain concepts of
   CDNs and content. 

4.1 Understanding CDNs

   The first use of the model, before peering CDNs, is simply to
   describe a single CDN at an abstract level.  The model describes
   CLIENTS that issue REQUESTS for CONTENT.  Each item of CONTENT
   starts from some ORIGIN.

   In the absence of a CDN, each REQUEST could simply go to an
   appropriate ORIGIN, which would deliver the corresponding CONTENT to
   the CLIENT.

   With a CDN, the picture is a little more elaborate. The CLIENT's
   REQUEST enters a DIRECTION SYSTEM, and the ORIGIN's CONTENT enters a
   DISTRIBUTION SYSTEM. Both systems converge on SURROGATES, which are
   non-ORIGIN servers of CONTENT.  Effectively, the DISTRIBUTION SYSTEM
   is moving CONTENT out to SURROGATES, and the DIRECTION SYSTEM is
   then taking advantage of that distribution of CONTENT.

   [Editor Note: Could change this description to deal with DIRECTION
   REQUESTS and CONTENT REQUESTS.]

4.2 Understanding content structure

   The model defines CONTENT as well as two subsidiary but orthogonal
   concepts: CONTENT DATA UNIT and CONTINUOUS MEDIA.

   Any identifiable resource of digital data is an item of CONTENT. So
   CONTENT is the most generic description of what is transported and
   served up by a CDN. Although an item of CONTENT may have some
   internal structure that is known to the CDN, there is some unit
   (possibly as small as a bit) that is opaque to the CDN. These opaque
   elements are CONTENT DATA UNITs.

   In many cases, an item of CONTENT can be delivered by a CDN without
   concern about maintaining timing relationships. However, there are
   some forms of CONTENT where it is critical that some timing
   relationships be met. The model refers to those forms of CONTENT as
   CONTINUOUS MEDIA.








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5. Peering Model

   This section consists of the definitions of a number of terms used
   to refer to roles, participants, and objects involved in peering
   CDNs.

   ACCOUNTING ADVERTISEMENT 
      ADVERTISEMENT from a CDN's ACCOUNTING PEERING SYSTEM about the
      collections of CONTENT for which that CDN requires ACCOUNTING
      information.

   ACCOUNTING PEERING 
      Interconnection of two or more ACCOUNTING SYSTEMS so as to enable
      the exchange of information between them. The form of ACCOUNTING
      PEERING required may depend on the nature of the NEGOTIATED
      RELATIONSHIP between the peering parties -- in particular, on the
      value of the economic exchanges anticipated.

   ADVERTISEMENT 
      Information about available resources, exchanged among PEERING
      SYSTEMS. Types of ADVERTISEMENT include DIRECTION ADVERTISEMENTS,
      DISTRIBUTION ADVERTISEMENTS and ACCOUNTING ADVERTISEMENTS.

   AUTHORITATIVE DIRECTION SYSTEM 
      The DIRECTION SYSTEM that is the correct/final authority for a
      particular item of CONTENT. Typically operated by the BILLING
      CDN. 

   BILLING CDN 
      The single CDN that has a NEGOTIATED RELATIONSHIP with the
      PUBLISHER making that CDN responsible for DISTRIBUTION of some
      particular collection of CONTENT. Contrast with DISTRIBUTING CDN.
      Usually a BILLING CDN is owned and operated by a corresponding
      BILLING ORGANIZATION

   BILLING ORGANIZATION 
      An entity that operates an ACCOUNTING SYSTEM to support billing
      within a NEGOTIATED RELATIONSHIP with a PUBLISHER.

   CONTENT PEERING GATEWAY (CPG) 
      A point through which a CDN can be peered with others through one
      or more kinds of peering. A CPG may be the point of contact for
      DISTRIBUTION PEERING, DIRECTION PEERING, and/or ACCOUNTING
      PEERING, and thus may incorporate some or all of the
      corresponding PEERING SYSTEMs for the CDN.

   DIRECTION ADVERTISEMENT 
      An ADVERTISEMENT from a CDN's DIRECTION PEERING SYSTEM describing
      the availability of collections of CONTENT via that CDN's


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      DIRECTION SYSTEM.

   DIRECTION PEERING 
      Interconnection of two or more DIRECTION SYSTEMS so as to
      increase the number of REACHABLE SURROGATES for at least one of
      the interconnected systems.

   DISTRIBUTING CDN 
      A CDN delivering CONTENT that does not have a NEGOTIATED
      RELATIONSHIP with the PUBLISHER. Contrast with BILLING CDN.

   DISTRIBUTION ADVERTISEMENT 
      An ADVERTISEMENT from a CDN's DISTRIBUTION PEERING SYSTEM
      describing the availability of collections of CONTENT via the
      CDN's DISTRIBUTION SYSTEM.

   DISTRIBUTION PEERING 
      Interconnection of two or more DISTRIBUTION SYSTEMS so as to
      propagate CONTENT SIGNALS and copies of CONTENT to groups of
      SURROGATES.

   FIRST-DIRECTION CDN 
      The CDN whose DIRECTION SYSTEM first receives a particular
      REQUEST. The FIRST-DIRECTION CDN is able to decide how that
      REQUEST should be redirected, if at all. Contrast with REMOTE CDN.

   INTER-CDN 
      Related to an activity that involves more than one CDN. Contrast
      with INTRA-CDN.

   INTRA-CDN 
      Related to an activity within a single CDN. Contrast with
      INTER-CDN.

   NEGOTIATED RELATIONSHIP 
      A relationship whose terms and conditions are partially or
      completely established outside the context of CDN peering
      protocols.

   PEERING SYSTEM 
      A collection of NETWORK ELEMENTS supporting some form of
      interconnected operation among two or more CDNs. Examples (not
      separately defined): ACCOUNTING PEERING SYSTEM, DISTRIBUTION
      PEERING SYSTEM, DIRECTION PEERING SYSTEM.

   REMOTE CDN 
      A CDN able to deliver CONTENT for a particular REQUEST that is
      not the FIRST-DIRECTION CDN for that REQUEST.



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6. Peering Examples and Commentary

   This section uses the terms of the previous to explain concepts of
   CDN peering. 

6.1 Understanding Peering

   The model offers a number of ways in which different CDNs can be
   interconnected.  An arrangement of interconnected DIRECTION SYSTEMS
   is called DIRECTION PEERING. Analogously, interconnected
   DISTRIBUTION SYSTEMS give rise to DISTRIBUTION PEERING, and
   interconnected ACCOUNTING SYSTEMS give rise to ACCOUNTING PEERING.
   The communicating elements on each side are referred to as PEERING
   SYSTEMS. So when two or more DISTRIBUTION SYSTEMS may be
   interconnected by PEERING, it is actually the DISTRIBUTION PEERING
   SYSTEMS that are communicating with each other to accomplish the
   exchange of information required.  A CONTENT PEERING GATEWAY (CPG)
   is a generic term used in the model for one or more PEERING SYSTEMS
   when it is not important to distinguish the PEERING SYSTEM or form
   of PEERING involved.

   CPGs exchange ADVERTISEMENTS. There are three main kinds of
   ADVERTISEMENT: DIRECTION ADVERTISEMENTS, DISTRIBUTION
   ADVERTISEMENTS, and ACCOUNTING ADVERTISEMENTS. A DIRECTION
   ADVERTISEMENT describes a collection of URLs whose content can be
   delivered by DIRECTION through the corresponding CDN.  A
   DISTRIBUTION ANNOUNCEMENT describes the service level(s) available
   from a CDN's SURROGATES (as a whole) to some collection of CLIENT
   addresses. An ACCOUNTING ANNOUNCEMENT a collection of CLIENT
   addresses, and the level of service that it can offer for delivering
   content to those CLIENTS.

6.2 Content Signalling

   CDNs operate on behalf of PUBLISHERs and ORIGINs and therefore must
   provide accurate, up-to-date copies of CONTENT. A CDN DISTRIBUTION
   SYSTEM may deliver CONTENT SIGNALS to relevant SURROGATES when
   appropriate. In the presence of peering, CONTENT SIGNALS must be
   propagated to the each SURROGATE with a copy of the relevant
   CONTENT. 











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7. Operational Considerations

   [Editor's Note: Consider problem of incorrect advertisements of
   content or service levels. Need to ensure that there are means
   within the protocol or recommended practices so that CDNs aren't
   encouraged to pull traffic they can't really handle.]













































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8. Security Considerations

   [Editor's Note: Discuss the issues of delegated authority and trust
   between CDNs and Origin Servers.]

   [Editor's Note: Discuss man-in-the-middle and denial-of-service
   attacks on peered CDNs.]












































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9. Acknowledgements

   The definition of CONTINUOUS MEDIA is adapted from RFC 2326. The
   authors acknowledge the contributions and comments of Fred Douglis
   (AT&T), Don Gilletti (Entera), Barbara Liskov (Cisco), John Martin
   (Network Appliance), Raj Nair (Cisco), and Doug Potter (Cisco). 













































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References

   [1]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
        Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
        HTTP/1.1", RFC 2616, June 1999, 
        <URL:http://www.rfc-editor.org/rfc/rfc2616.txt>.

   [2]  Cooper, I., Melve, I. and G. Tomlinson, "Internet Web
        Replication and Caching Taxonomy",
        draft-ietf-wrec-taxonomy-05.txt (work in progress), June 2000, 
        <URL:http://www.ietf.org/internet-drafts/draft-ietf-wrec-taxonom
        y-05.txt>.

   [3]  Day, M. and D. Gilletti, "CDN Peering Scenarios",
        draft-day-cdnp-scenarios-00.txt (work in progress), September
        2000, 
        <URL:http://www.ietf.org/internet-drafts/draft-day-cdnp-scenario
        s-00.txt>.

   [4]  Gilletti, D., Nair, R. and J. Scharber, "Accounting Models for
        CDN Peering", draft-gilletti-cdnp-accounting-models-01.txt
        (work in progress), September 2000, 
        <URL:http://www.ietf.org/internet-drafts/draft-gilletti-cdnp-acc
        ounting-models-01.txt>.

   [5]  Green, M., Cain, B. and G. Tomlinson, "CDN Peering
        Architectural Overview", draft-green-cdnp-gen-arch-00.txt (work
        in progress), September 2000, 
        <URL:http://www.ietf.org/internet-drafts/draft-green-cdnp-gen-ar
        ch-00.txt>.


Authors' Addresses

   Mark S. Day
   Cisco Systems
   135 Beaver Street
   Waltham, MA  02452
   US

   Phone: +1 781 663 8310
   EMail: markday@cisco.com









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   Brad Cain
   Mirror Image Internet
   49 Dragon Court
   Woburn, MA  01801
   US

   Phone: +1 781 276 1904
   EMail: brad.cain@mirror-image.com


   Gary Tomlinson
   Entera, Inc.
   40971 Encyclopedia Circle
   Freemont, CA  94538
   US

   Phone: +1 510 580 3726
   EMail: garyt@entera.com

































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Full Copyright Statement

   Copyright (C) The Internet Society (2000). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS 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.

Acknowledgement

   Funding for the RFC editor function is currently provided by the
   Internet Society.



















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