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rfc:rfc6770

Internet Engineering Task Force (IETF) G. Bertrand, Ed. Request for Comments: 6770 E. Stephan Obsoletes: 3570 France Telecom - Orange Category: Informational T. Burbridge ISSN: 2070-1721 P. Eardley

                                                                    BT
                                                                 K. Ma
                                                   Azuki Systems, Inc.
                                                             G. Watson
                                              Alcatel-Lucent (Velocix)
                                                         November 2012
       Use Cases for Content Delivery Network Interconnection

Abstract

 Content Delivery Networks (CDNs) are commonly used for improving the
 End User experience of a content delivery service while keeping cost
 at a reasonable level.  This document focuses on use cases that
 correspond to identified industry needs and that are expected to be
 realized once open interfaces and protocols supporting the
 interconnection of CDNs are specified and implemented.  This document
 can be used to motivate the definition of the requirements to be
 supported by CDN Interconnection (CDNI) interfaces.  It obsoletes RFC
 3570.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6770.

Bertrand, et al. Informational [Page 1] RFC 6770 CDNI Use Cases November 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
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 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
   1.2.  Abbreviations  . . . . . . . . . . . . . . . . . . . . . .  3
   1.3.  Rationale for CDN Interconnection  . . . . . . . . . . . .  4
 2.  Footprint Extension Use Cases  . . . . . . . . . . . . . . . .  6
   2.1.  Geographic Extension . . . . . . . . . . . . . . . . . . .  6
   2.2.  Inter-Affiliates Interconnection . . . . . . . . . . . . .  6
   2.3.  ISP Handling of Third-Party Content  . . . . . . . . . . .  7
   2.4.  Nomadic Users  . . . . . . . . . . . . . . . . . . . . . .  7
 3.  Offload Use Cases  . . . . . . . . . . . . . . . . . . . . . .  8
   3.1.  Overload Handling and Dimensioning . . . . . . . . . . . .  8
   3.2.  Resiliency . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.2.1.  Failure of Content Delivery Resources  . . . . . . . .  9
     3.2.2.  Content Acquisition Resiliency . . . . . . . . . . . . 10
 4.  Capability Use Cases . . . . . . . . . . . . . . . . . . . . . 11
   4.1.  Device and Network Technology Extension  . . . . . . . . . 11
   4.2.  Technology and Vendor Interoperability . . . . . . . . . . 12
   4.3.  QoE and QoS Improvement  . . . . . . . . . . . . . . . . . 12
 5.  Enforcement of Content Delivery Policy . . . . . . . . . . . . 12
 6.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 12
 7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
 8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   8.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
   8.2.  Informative References . . . . . . . . . . . . . . . . . . 13
 Appendix A.  Content Service Providers' Delivery Policies  . . . . 14
   A.1.  Content Delivery Policy Enforcement  . . . . . . . . . . . 14
   A.2.  Secure Access  . . . . . . . . . . . . . . . . . . . . . . 15
   A.3.  Branding . . . . . . . . . . . . . . . . . . . . . . . . . 15

Bertrand, et al. Informational [Page 2] RFC 6770 CDNI Use Cases November 2012

1. Introduction

 Content Delivery Networks (CDNs) are commonly used for improving the
 End User experience of a content delivery service while keeping cost
 at a reasonable level.  This document focuses on use cases that
 correspond to identified industry needs and that are expected to be
 realized once open interfaces and protocols supporting the
 interconnection of CDNs are specified and implemented.  The document
 can be used to motivate the definition of the requirements (as
 documented in [CDNI-REQ]) to be supported by the set of CDN
 Interconnection (CDNI) interfaces defined in [RFC6707].
 [RFC3570] describes slightly different terminologies and models for
 "Content Internetworking (CDI)".  This document obsoletes RFC 3570 to
 avoid confusion.
 This document identifies the main motivations for a CDN Provider to
 interconnect its CDN:
 o  CDN Footprint Extension Use Cases (Section 2)
 o  CDN Offload Use Cases (Section 3)
 o  CDN Capability Use Cases (Section 4)
 Then, the document highlights the need for interoperability in order
 to exchange and enforce content delivery policies (Section 5).

1.1. Terminology

 In this document, the first letter of each CDNI-specific term is
 capitalized.  We adopt the terminology described in [RFC6707].
 We extend this terminology with the following term:
 Access CDN:
 A CDN that includes Surrogates in the same administrative network as
 the End User.  Such a CDN can use accurate information on the End
 User's network context to provide additional Content Delivery
 Services to Content Service Providers.

1.2. Abbreviations

 o  CDN: Content Delivery Network, also known as Content Distribution
    Network
 o  CSP: Content Service Provider

Bertrand, et al. Informational [Page 3] RFC 6770 CDNI Use Cases November 2012

 o  dCDN: downstream CDN
 o  DNS: Domain Name System
 o  EU: End User
 o  ISP: Internet Service Provider
 o  NSP: Network Service Provider
 o  QoE: Quality of Experience
 o  QoS: Quality of Service
 o  uCDN: upstream CDN
 o  URL: Uniform Resource Locator
 o  WiFi: Wireless local area network (WLAN) based on IEEE 802.11

1.3. Rationale for CDN Interconnection

 Content Delivery Networks (CDNs) are used to deliver content because
 they can:
 o  improve the experience for the End User; for instance delivery has
    lower latency (decreased round-trip-time and higher throughput
    between the user and the delivery server) and better robustness
    (ability to use multiple delivery servers),
 o  reduce the network operator's costs; for instance, lower delivery
    cost (reduced bandwidth usage) for cacheable content,
 o  reduce the Content Service Provider's (CSP) internal
    infrastructure costs, such as data center capacity, space, and
    electricity consumption, as popular content is delivered
    externally through the CDN rather than through the CSP's own
    servers.
 Indeed, many Network Service Providers (NSPs) and Enterprise Service
 Providers are deploying or have deployed their own CDNs.  Despite the
 potential benefits of interconnecting CDNs, today each CDN is a
 stand-alone network.  The objective of CDN Interconnection is to
 overcome this restriction; the interconnected CDNs should be able to
 collectively behave as a single delivery infrastructure.
 An example is depicted in Figure 1, where two CDN Providers establish
 a CDN Interconnection.  The Content Service Provider CSP-1 reaches an

Bertrand, et al. Informational [Page 4] RFC 6770 CDNI Use Cases November 2012

 agreement with CDN Provider 'A' for the delivery of its content.
 Independently, CDN Provider 'A' and CDN Provider 'B' agree to
 interconnect their CDNs.
 When a given User Agent requests content from CSP-1, CDN-A may
 consider that delivery by CDN-B is appropriate, for instance, because
 CDN-B is an Access CDN and the user is directly attached to it.
 Through the CDN Interconnection arrangements put in place between
 CDN-A and CDN-B (as a result of the CDN Interconnection agreement
 established between CDN Provider 'A' and CDN Provider 'B'), CDN-A can
 redirect the request to CDN-B and the content is actually delivered
 to the User Agent by CDN-B.
 The End User benefits from this arrangement through a better Quality
 of Experience (QoE, see [RFC6390]), because the content is delivered
 from a nearby Surrogate (e.g., lower latency, bottlenecks avoided).
 CDN Provider 'A' benefits because it does not need to deploy such an
 extensive CDN, while CDN Provider 'B' may receive some compensation
 for the delivery.  CSP-1 benefits because it only needs to make one
 business agreement and one technical arrangement with CDN Provider
 'A', but its End Users get a service quality as though CSP-1 had also
 gone to the trouble of making a business agreement and technical
 arrangement with CDN Provider 'B'.
  +-------+ +-------+
  | CSP-1 | | CSP-2 |
  +-------+ +-------+
      |         |
     ,--,--,--./            ,--,--,--.
  ,-'          `-.       ,-'          `-.
 (CDN Provider 'A')=====(CDN Provider 'B')
  `-.  (CDN-A) ,-'       `-. (CDN-B)  ,-'
     `--'--'--'             `--'--'--'
                                |
                          +----------+
                          | End User |
                          +----------+
  === CDN Interconnection
                               Figure 1
 To extend the example, another Content Service Provider, CSP-2, may
 also reach an agreement with CDN Provider 'A'.  However, CSP-2 may
 not want its content to be distributed by CDN Provider B; for
 example, CSP-2 may not want to distribute its content in the area
 where CDN Provider 'B' operates.  This example illustrates that
 policy considerations are an important part of CDNI.

Bertrand, et al. Informational [Page 5] RFC 6770 CDNI Use Cases November 2012

2. Footprint Extension Use Cases

 Footprint extension is expected to be a major use case for CDN
 Interconnection.

2.1. Geographic Extension

 In this use case, the CDN Provider wants to extend the geographic
 distribution that it can offer to its CSPs:
 o  without compromising the quality of delivery.
 o  without incurring additional transit and other network costs that
    would result from serving content from geographically or
    topologically remote Surrogates.
 o  without incurring the cost of deploying and operating Surrogates
    and the associated CDN infrastructure that may not be justified in
    the corresponding geographic region (e.g., because of relatively
    low delivery volume, or conversely because of the high investments
    that would be needed to satisfy the high volume).
 If there are several CDN Providers that have a geographically limited
 footprint (e.g., restricted to one country), or do not serve all End
 Users in a geographic area, then interconnecting their CDNs enables
 these CDN Providers to provide their services beyond their own
 footprint.
 As an example, suppose a French CSP wants to distribute its TV
 programs to End Users located in France and various countries in
 North Africa.  It asks a French CDN Provider to deliver the content.
 The French CDN Provider's network only covers France, so it makes an
 agreement with another CDN Provider that covers North Africa.
 Overall, from the CSP's perspective, the French CDN Provider provides
 a CDN service for both France and North Africa.
 In addition to video, this use case applies to other types of content
 such as automatic software updates (browser updates, operating system
 patches, virus database update, etc.).

2.2. Inter-Affiliates Interconnection

 The previous section describes the case of geographic extension
 between CDNs operated by different entities.  A large CDN Provider
 may have several subsidiaries that each operate their own CDN (which
 may rely on different CDN technologies, see Section 4.2).  In certain

Bertrand, et al. Informational [Page 6] RFC 6770 CDNI Use Cases November 2012

 circumstances, the CDN Provider needs to make these CDNs interoperate
 to provide consistent service to its customers on the whole
 collective footprint.

2.3. ISP Handling of Third-Party Content

 Consider an ISP carrying to its subscribers a lot of content that
 comes from a third-party CSP and that is injected into the ISP's
 network by an Authoritative CDN Provider.  There are mutual benefits
 to the ISP (acting as an Access CDN), the Authoritative CDN, and the
 CSP that would make a case for establishing a CDNI agreement.  For
 example:
 o  allowing the CSP to offer improved QoE and QoE services to
    subscribers, for example, reduced content startup time or
    increased video quality and resolution of adaptive streaming
    content.
 o  allowing the Authoritative CDN to reduce hardware capacity and
    footprint, by using the ISP caching and delivery capacity.
 o  allowing the ISP to reduce traffic load on some segments of the
    network by caching inside of the ISP network.
 o  allowing the ISP to influence and/or control the traffic ingress
    points.
 o  allowing the ISP to derive some incremental revenue for transport
    of the traffic and to monetize QoE services.

2.4. Nomadic Users

 In this scenario, a CSP wishes to allow End Users who move between
 access networks to continue to access their content.  The motivation
 of this case is to allow nomadic End Users to maintain access to
 content with a consistent QoE across a range of devices and/or
 geographic regions.
 This use case covers situations like:
 o  End Users moving between different access networks, which may be
    located within the same geographic region or different geographic
    regions.
 o  End Users switching between different devices or delivery
    technologies, as discussed in Section 4.

Bertrand, et al. Informational [Page 7] RFC 6770 CDNI Use Cases November 2012

 Consider the following example, illustrated in Figure 2: End User A
 has a subscription to a broadband service from ISP A, her "home ISP".
 ISP A hosts CDN-A.  Ordinarily, when End User A accesses content via
 ISP A (her "home ISP"), the content is delivered from CDN-A, which in
 this example is within ISP A's network.
 However, while End User A is not connected to ISP A's network, for
 example, because it is connected to a WiFi provider or mobile
 network, End User A can also access the same content.  In this case,
 End User A may benefit from accessing the same content delivered by
 an alternate CDN (CDN-B), in this case, hosted in the network of the
 WiFi or mobile provider (ISP B), rather than from CDN-A in ISP A's
 network.
     +-------+
     |Content|
     +-------+
         |
     ,--,--,--.             ,--,--,--.
  ,-'  ISP A   `-.       ,-'  ISP B   `-.
 (    (CDN-A)     )=====(    (CDN-B)     )
  `-.          ,-'       `-.          ,-'
     `--'--'--'             `--'--'--'
          |                     |
    +------------+      +---------------+
    + EU A (home)|      | EU A (nomadic)|
    +------------+      +---------------+
  === CDN Interconnection
                               Figure 2
 Though the content of CSP A is not accessible by typical End Users of
 CDN-B, End User A is able to gain access to her "home" content (i.e.,
 the content of CSP A) through the alternate CDN (CDN-B).
 Depending on the CSP's content delivery policies (see Appendix A.1),
 a user moving to a different geographic region may be subject to geo-
 blocking content delivery restrictions.  In this case, he/she may not
 be allowed to access some pieces of content.

3. Offload Use Cases

3.1. Overload Handling and Dimensioning

 A CDN is likely to be dimensioned to support an expected maximum
 traffic load.  However, unexpected spikes in content popularity
 (flash crowd) may drive load beyond the expected peak.  The prime
 recurrent time peaks of content distribution may differ between two

Bertrand, et al. Informational [Page 8] RFC 6770 CDNI Use Cases November 2012

 CDNs.  Taking advantage of the different traffic peak times, a CDN
 may interconnect with another CDN to increase its effective capacity
 during the peak of traffic.  This brings dimensioning savings to the
 CDNs, as they can use each other's resources during their respective
 peaks of activity.
 Offload also applies to planned situations in which a CDN Provider
 needs CDN capacity in a particular region during a short period of
 time.  For example, a CDN can offload traffic to another CDN for the
 duration of a specific maintenance operation or for the distribution
 of a special event, as in the scenario depicted in Figure 3.  For
 instance, consider a TV channel that is the distributor for a major
 event, such as a celebrity's wedding or a major sport competition,
 and this TV channel has contracted particular CDNs for the delivery.
 The CDNs (CDN-A and CDN-B) that the TV channel uses for delivering
 the content related to this event are likely to experience a flash
 crowd during the event and will need to offload traffic, while other
 CDNs (CDN-C) will support a more typical traffic load and be able to
 handle the offloaded traffic.
 In this use case, the Delivering CDN on which requests are offloaded
 should be able to handle the offloaded requests.  Therefore, the uCDN
 might require information on the dCDNs to be aware of the amount of
 traffic it can offload to each dCDN.
   +------------+
   | TV Channel |
   +------------+
       |         \
    ,-,--,-.      \ ,-,--,-.        ,-,--,-.
  ,'        `.    ,'        `.    ,' CDN-C  `.
 (   CDN-A    )  (   CDN-B    )==(  offload   )
  `.        ,'    `.        ,'    `.        ,'
    `-'--'-'        `-'--'-'        `-'--'-'
  === CDN Interconnection
                               Figure 3

3.2. Resiliency

3.2.1. Failure of Content Delivery Resources

 It is important for CDNs to be able to guarantee service continuity
 during partial failures (e.g., failure of some Surrogates).  In
 partial failure scenarios, a CDN Provider has at least three options:

Bertrand, et al. Informational [Page 9] RFC 6770 CDNI Use Cases November 2012

 1.  if possible, use internal mechanisms to redirect traffic onto
     surviving equipment,
 2.  depending on traffic management policies, forward some requests
     to the CSP's origin servers, and/or
 3.  redirect some requests toward another CDN, which must be able to
     serve the redirected requests.
 The last option is a use case for CDNI.

3.2.2. Content Acquisition Resiliency

 Source content acquisition may be handled in one of two ways:
 o  CSP origin, where a CDN acquires content directly from the CSP's
    origin server, or
 o  CDN origin, where a downstream CDN acquires content from a
    Surrogate within an upstream CDN.
 The ability to support content acquisition resiliency is an important
 use case for interconnected CDNs.  When the content acquisition
 source fails, the CDN might switch to another content acquisition
 source.  Similarly, when several content acquisition sources are
 available, a CDN might balance the load between these multiple
 sources.
 Though other server and/or DNS load-balancing techniques may be
 employed in the network, interconnected CDNs may have a better
 understanding of origin-server availability, and be better equipped
 to both distribute load between origin servers and attempt content
 acquisition from alternate content sources when acquisition failures
 occur.  When normal content acquisition fails, a CDN may need to try
 other content source options, for example:
 o  an upstream CDN may acquire content from an alternate CSP origin
    server,
 o  a downstream CDN may acquire content from an alternate Surrogate
    within an upstream CDN,
 o  a downstream CDN may acquire content from an alternate upstream
    CDN, or
 o  a downstream CDN may acquire content directly from the CSP's
    origin server.

Bertrand, et al. Informational [Page 10] RFC 6770 CDNI Use Cases November 2012

 Though content acquisition protocols are beyond the scope of CDNI,
 the selection of content acquisition sources should be considered and
 facilitated.

4. Capability Use Cases

4.1. Device and Network Technology Extension

 In this use case, the CDN Provider may have the right geographic
 footprint, but may wish to extend the supported range of devices and
 User Agents or the supported range of delivery technologies.  In this
 case, a CDN Provider may interconnect with a CDN that offers services
 that:
 o  the CDN Provider is not willing to provide, or
 o  its own CDN is not able to support.
 The following examples illustrate this use case:
 1.  CDN-A cannot support a specific delivery protocol.  For instance,
     CDN-A may interconnect with CDN-B to serve a proportion of its
     traffic that requires HTTPS [RFC2818].  CDN-A may use CDN-B's
     footprint (which may overlap with its own) to deliver HTTPS
     without needing to deploy its own infrastructure.  This case
     could also be true of other formats, delivery protocols (e.g.,
     the Real Time Messaging Protocol (RTMP), the Real Time Streaming
     Protocol (RTSP), etc.), and features (specific forms of
     authorization such as tokens, per session encryption, etc.).
 2.  CDN-A has a footprint covering traditional fixed-line broadband
     and wants to extend coverage to mobile devices.  In this case,
     CDN-A may contract and interconnect with CDN-B, who has both:
  • a physical footprint inside the mobile network,
  • the ability to deliver content over a protocol that is

required by specific mobile devices.

 3.  CDN-A only supports IPv4 within its infrastructure but wants to
     deliver content over IPv6.  CDN-B supports both IPv4 and IPv6
     within its infrastructure.  CDN-A interconnects with CDN-B to
     serve out its content over native IPv6 connections.
 These cases can apply to many CDN features that a given CDN Provider
 may not be able to support or not be willing to invest in, and thus,
 that the CDN Provider would delegate to another CDN.

Bertrand, et al. Informational [Page 11] RFC 6770 CDNI Use Cases November 2012

4.2. Technology and Vendor Interoperability

 A CDN Provider may deploy a new CDN to run alongside its existing CDN
 as a simple way of migrating its CDN service to a new technology.  In
 addition, a CDN Provider may have a multi-vendor strategy for its CDN
 deployment.  Finally, a CDN Provider may want to deploy a separate
 CDN for a particular CSP or a specific network.  In all these
 circumstances, CDNI benefits the CDN Provider, as it simplifies or
 automates some inter-CDN operations (e.g., migrating the request
 routing function progressively).

4.3. QoE and QoS Improvement

 Some CSPs are willing to pay a premium for enhanced delivery of
 content to their End Users.  In some cases, even if the CDN Provider
 could deliver the content to the End Users, it would not meet the
 CSP's service-level requirements.  As a result, the CDN Provider may
 establish a CDN Interconnection agreement with another CDN Provider
 that can provide the expected QoE to the End User, e.g., via an
 Access CDN that is able to deliver content from Surrogates located
 closer to the End User and with the required service level.

5. Enforcement of Content Delivery Policy

 An important aspect common to all the above use cases is that CSPs
 typically want to enforce content delivery policies.  A CSP may want
 to define content delivery policies that specify when, how, and/or to
 whom the CDN delivers content.  These policies apply to all
 interconnected CDNs (uCDNs and dCDNs) in the same or similar way that
 a CSP can define content delivery policies for content delivered by a
 single, non-interconnected CDN.  Appendix A provides examples of CSP-
 defined policies.

6. Acknowledgments

 The authors would like to thank Kent Leung, Francois Le Faucheur, Ben
 Niven-Jenkins, and Scott Wainner for lively discussions, as well as
 for their reviews and comments on the mailing list.
 They also thank the contributors of the EU FP7 OCEAN and ETICS
 projects for valuable inputs.
 Finally, the authors acknowledge the work of the former CDI working
 group.  This document obsoletes [RFC3570] to avoid confusion.

Bertrand, et al. Informational [Page 12] RFC 6770 CDNI Use Cases November 2012

7. Security Considerations

 This document focuses on the motivational use cases for CDN
 Interconnection and does not analyze the associated threats.  Those
 threats are discussed in [RFC6707].  Appendix A.2 of this document
 provides example security policies that CSPs might impose on CDNs to
 mitigate the threats.

8. References

8.1. Normative References

 [RFC6707]   Niven-Jenkins, B., Le Faucheur, F., and N. Bitar,
             "Content Distribution Network Interconnection (CDNI)
             Problem Statement", RFC 6707, September 2012.

8.2. Informative References

 [CDNI-REQ]  Leung, K. and Y. Lee, "Content Distribution Network
             Interconnection (CDNI) Requirements", Work in Progress,
             June 2012.
 [RFC2818]   Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
 [RFC3570]   Rzewski, P., Day, M., and D. Gilletti, "Content
             Internetworking (CDI) Scenarios", RFC 3570, July 2003.
 [RFC6390]   Clark, A. and B. Claise, "Guidelines for Considering New
             Performance Metric Development", BCP 170, RFC 6390,
             October 2011.

Bertrand, et al. Informational [Page 13] RFC 6770 CDNI Use Cases November 2012

Appendix A. Content Service Providers' Delivery Policies

 CSPs commonly apply different delivery policies to given sets of
 content assets delivered through CDNs.  Interconnected CDNs need to
 support these policies.  This appendix presents examples of CSPs'
 delivery policies and their consequences on CDNI operations.

A.1. Content Delivery Policy Enforcement

 The content distribution policies that a CSP attaches to a content
 asset may depend on many criteria.  For instance, distribution
 policies for audiovisual content often combine constraints of varying
 levels of complexity and sophistication, for example:
 o  temporal constraints (e.g., available for 24 hours, available 28
    days after DVD release, etc.),
 o  user agent platform constraints (e.g., mobile device platforms,
    desktop computer platforms, set-top-box platforms, etc.),
 o  resolution-based constraints (e.g., high definition vs. standard
    definition encodings),
 o  user agent identification or authorization,
 o  access network constraints (e.g., per NSP), and
 o  IP geo-blocking constraints (e.g., for a given coverage area).
 CSPs may use sophisticated policies in accordance with their business
 model.  However, the enforcement of those policies does not
 necessarily require that the delivery network understand the policy
 rationales or how policies apply to specific content assets.  Content
 delivery policies may be distilled into simple rules that can be
 commonly enforced across all dCDNs.  These rules may influence dCDN
 delegation and Surrogate selection decisions, for instance, to ensure
 that the specific rules (e.g., time-window, geo-blocking, pre-
 authorization validation) can indeed be enforced by the Delivering
 CDN.  In turn, this can guarantee to the CSP that content delivery
 policies are properly applied.

Bertrand, et al. Informational [Page 14] RFC 6770 CDNI Use Cases November 2012

 +-----+
 | CSP |  Policies driven by business (e.g., available only
 +-----+  in the UK and only from July 1st to September 1st)
    \
     \ Translate policies into
      \simple rules (e.g., provide an authorization token)
       \
        V
      +-----+
      | CDN | Apply simple rules (e.g., check an
      +-----+ authorization token and enforce geo-blocking)
          \
           \ Distribute simple rules
            V
          +-----+
          | CDN | Apply simple rules
          +-----+
                               Figure 4

A.2. Secure Access

 Many protocols exist for delivering content to End Users.  CSPs may
 dictate a specific protocol or set of protocols that are acceptable
 for delivery of their content, especially in the case where a secured
 content transmission is required (e.g., must use HTTPS).  CSPs may
 also perform a per-request authentication/authorization decision and
 then have the CDNs enforce that decision (e.g., must validate URL
 signing, etc.).

A.3. Branding

 Preserving the branding of the CSP throughout delivery is often
 important to the CSP.  CSPs may desire to offer content services
 under their own name, even when the associated CDN service involves
 other CDN Providers.  For instance, a CSP may desire to ensure that
 content is delivered with URIs appearing to the End Users under the
 CSP's own domain name, even when the content delivery involves
 separate CDN Providers.  The CSP may wish to prevent the delivery of
 its content by specific dCDNs that lack support for such branding
 preservation features.
 Analogous cases exist when the uCDN wants to offer CDN services under
 its own branding even if dCDNs are involved, and so it restricts the
 delivery delegation to a chain that preserves its brand visibility.

Bertrand, et al. Informational [Page 15] RFC 6770 CDNI Use Cases November 2012

Authors' Addresses

 Gilles Bertrand (editor)
 France Telecom - Orange
 38-40 rue du General Leclerc
 Issy les Moulineaux,   92130
 FR
 Phone: +33 1 45 29 89 46
 EMail: gilles.bertrand@orange.com
 Stephan Emile
 France Telecom - Orange
 2 avenue Pierre Marzin
 Lannion  F-22307
 FR
 EMail: emile.stephan@orange.com
 Trevor Burbridge
 BT
 B54 Room 70, Adastral Park, Martlesham
 Ipswich,   IP5 3RE
 UK
 EMail: trevor.burbridge@bt.com
 Philip Eardley
 BT
 B54 Room 77, Adastral Park, Martlesham
 Ipswich,   IP5 3RE
 UK
 EMail: philip.eardley@bt.com
 Kevin J. Ma
 Azuki Systems, Inc.
 43 Nagog Park
 Acton, MA  01720
 USA
 Phone: +1 978-844-5100
 EMail: kevin.ma@azukisystems.com
 Grant Watson
 Alcatel-Lucent (Velocix)
 3 Ely Road
 Milton, Cambridge  CB24 6AA
 UK
 EMail: gwatson@velocix.com

Bertrand, et al. Informational [Page 16]

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