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rfc:rfc6707

Internet Engineering Task Force (IETF) B. Niven-Jenkins Request for Comments: 6707 Velocix (Alcatel-Lucent) Category: Informational F. Le Faucheur ISSN: 2070-1721 Cisco

                                                              N. Bitar
                                                               Verizon
                                                        September 2012

Content Distribution Network Interconnection (CDNI) Problem Statement

Abstract

 Content Delivery Networks (CDNs) provide numerous benefits for
 cacheable content: reduced delivery cost, improved quality of
 experience for End Users, and increased robustness of delivery.  For
 these reasons, they are frequently used for large-scale content
 delivery.  As a result, existing CDN Providers are scaling up their
 infrastructure, and many Network Service Providers (NSPs) are
 deploying their own CDNs.  It is generally desirable that a given
 content item can be delivered to an End User regardless of that End
 User's location or attachment network.  This is the motivation for
 interconnecting standalone CDNs so they can interoperate as an open
 content delivery infrastructure for the end-to-end delivery of
 content from Content Service Providers (CSPs) to End Users.  However,
 no standards or open specifications currently exist to facilitate
 such CDN Interconnection.
 The goal of this document is to outline the problem area of CDN
 Interconnection for the IETF CDNI (CDN Interconnection) working
 group.

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/rfc6707.

Niven-Jenkins, et al. Informational [Page 1] RFC 6707 CDN Interconnection Problem Statement September 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 ................................................4
    1.2. CDN Background .............................................9
 2. CDN Interconnection Use Cases ...................................9
 3. CDN Interconnection Model and Problem Area for IETF ............11
 4. Scoping the CDNI Problem .......................................15
    4.1. CDNI Control Interface ....................................16
    4.2. CDNI Request Routing Interface ............................16
    4.3. CDNI Metadata Interface ...................................17
    4.4. CDNI Logging Interface ....................................17
 5. Security Considerations ........................................17
    5.1. Security of the CDNI Control Interface ....................18
    5.2. Security of the CDNI Request Routing Interface ............18
    5.3. Security of the CDNI Metadata Interface ...................19
    5.4. Security of the CDNI Logging Interface ....................19
 6. Acknowledgements ...............................................19
 7. Informative References .........................................20
 Appendix A. Design Considerations for Realizing the CDNI
             Interfaces ............................................22
   A.1. CDNI Control Interface .....................................22
   A.2. CDNI Request Routing Interface .............................23
   A.3. CDNI Metadata Interface ....................................25
   A.4. CDNI Logging Interface .....................................26
 Appendix B. Additional Material ...................................27
   B.1. Non-Goals for IETF .........................................27
   B.2. Relationship to Relevant IETF Working Groups and IRTF
        Research Groups ............................................29
     B.2.1. ALTO WG ................................................29
     B.2.2. DECADE WG ..............................................29
     B.2.3. PPSP WG ................................................31
     B.2.4. IRTF P2P Research Group ................................31

Niven-Jenkins, et al. Informational [Page 2] RFC 6707 CDN Interconnection Problem Statement September 2012

1. Introduction

 The volume of video and multimedia content delivered over the
 Internet is rapidly increasing and expected to continue doing so in
 the future.  In the face of this growth, Content Delivery Networks
 (CDNs) provide numerous benefits for cacheable content: reduced
 delivery cost, improved quality of experience for End Users (EUs),
 and increased robustness of delivery.  For these reasons, CDNs are
 frequently used for large-scale content delivery.  As a result,
 existing CDN Providers are scaling up their infrastructure, and many
 Network Service Providers (NSPs) are deploying their own CDNs.
 It is generally desirable that a given content item can be delivered
 to an EU regardless of that EU's location or the network they are
 attached to.  However, a given CDN in charge of delivering a given
 content may not have a footprint that expands close enough to the
 EU's current location or attachment network, or may not have the
 necessary resources, to realize the user experience and cost benefit
 that a more distributed CDN infrastructure would allow.  This is the
 motivation for interconnecting standalone CDNs so that their
 collective CDN footprint and resources can be leveraged for the
 end-to-end delivery of content from Content Service Providers (CSPs)
 to EUs.  As an example, a CSP could contract with an "authoritative"
 CDN Provider for the delivery of content, and that Authoritative CDN
 Provider could contract with one or more downstream CDN Providers to
 distribute and deliver some or all of the content on behalf of the
 Authoritative CDN Provider.
 A typical end-to-end content delivery scenario would then involve the
 following business arrangements:
 o  A business arrangement between the EU and his CSP, authorizing
    access by the EU to content items controlled by the CSP.
 o  A business arrangement between the CSP and an "authoritative" CDN
    Provider where the CSP mandates that the CDN Provider perform the
    content delivery on behalf of the CSP.
 o  A business arrangement between the Authoritative CDN Provider and
    another (or other) CDN(s) where the Authoritative CDN may delegate
    the actual serving of some of the content delivery requests to the
    other CDN(s).  A particular case is where this other CDN Provider
    happens to also be the Network Service Provider providing network
    access to the EU, in which case there is also a separate and
    independent business relationship between the EU and the NSP for
    the corresponding network access.

Niven-Jenkins, et al. Informational [Page 3] RFC 6707 CDN Interconnection Problem Statement September 2012

 The formation and details of any business relationships between a CSP
 and a CDN Provider as well as between one CDN Provider and another
 CDN Provider are out of scope of this document.  However, this
 document concerns itself with the fact that no standards or open
 specifications currently exist to facilitate such CDN Interconnection
 from a technical perspective.
 One possible flow for performing an end-to-end content delivery
 across a CDN Interconnection is described below:
 o  The initial content request from an EU's User Agent is first
    received by the authoritative (upstream) CDN, which is the CDN
    with a business arrangement with the CSP.
 o  The authoritative (upstream) CDN may serve the request itself, or
    it may elect to use CDN Interconnection to redirect the request to
    a Downstream CDN that is in a better position to do so (e.g., a
    Downstream CDN that is "closer" to the EU).
 o  The EU's User Agent will "follow" the redirect returned by the
    Authoritative CDN and request the content from the Downstream CDN.
    If required, the Downstream CDN will acquire the requested content
    from the authoritative (upstream) CDN, and if necessary the
    Authoritative CDN will acquire the requested content from the
    Content Service Provider.
 The goal of this document is to outline the problem area of CDN
 Interconnection.  Section 2 discusses the use cases for CDN
 Interconnection.  Section 3 presents the CDNI model and problem area
 being considered by the IETF.  Section 4 describes each CDNI
 interface individually and highlights example candidate protocols
 that could be considered for reuse or leveraging to implement the
 CDNI interfaces.  Appendix B.2 describes the relationships between
 the CDNI problem space and other relevant IETF working groups and
 IRTF research groups.

1.1. Terminology

 This document uses the following terms:
 Authoritative CDN: A CDN that has a direct relationship with a CSP
 for the distribution and delivery of that CSP's content by the
 Authoritative CDN or by Downstream CDNs of the Authoritative CDN.
 CDN Interconnection (CDNI): A relationship between a pair of CDNs
 that enables one CDN to provide content delivery services on behalf
 of another CDN.  A CDN Interconnection may be wholly or partially
 realized through a set of interfaces over which a pair of CDNs

Niven-Jenkins, et al. Informational [Page 4] RFC 6707 CDN Interconnection Problem Statement September 2012

 communicate with each other in order to achieve the delivery of
 content to User Agents by Surrogates in one CDN (the Downstream CDN)
 on behalf of another CDN (the Upstream CDN).
 CDN Provider: The service provider who operates a CDN and offers a
 service of content delivery, typically used by a Content Service
 Provider or another CDN Provider.  Note that a given entity may
 operate in more than one role.  For example, a company may
 simultaneously operate as a Content Service Provider, a Network
 Service Provider, and a CDN Provider.
 CDNI Metadata: The subset of Content Distribution Metadata that
 has an inter-CDN scope.  For example, CDNI Metadata may include
 geo-blocking information (i.e., information defining geographical
 areas where the content is to be made available or blocked),
 availability windows (i.e., information defining time windows during
 which the content is to be made available or blocked) and access
 control mechanisms to be enforced (e.g., URI signature validation).
 CDNI Metadata may also include information about desired distribution
 policy (e.g., pre-positioned vs dynamic acquisition) and about where/
 how a CDN can acquire the content.
 Content: Any form of digital data.  One important form of Content
 with additional constraints on distribution and delivery is
 continuous media (i.e., where there is a timing relationship between
 source and sink).
 Content Distribution Metadata: The subset of Content Metadata that is
 relevant to the distribution of the content.  This is the metadata
 required by a CDN in order to enable and control content distribution
 and delivery by the CDN.  In a CDN Interconnection environment, some
 of the Content Distribution Metadata may have an intra-CDN scope (and
 therefore need not be communicated between CDNs), while some of the
 Content Distribution Metadata may have an inter-CDN scope (and
 therefore needs to be communicated between CDNs).
 Content Distribution Network (CDN) / Content Delivery Network (CDN):
 Network infrastructure in which the network elements cooperate at
 Layers 4 through 7 for more effective delivery of Content to User
 Agents.  Typically, a CDN consists of a Request Routing system, a
 Distribution system (that includes a set of Surrogates), a Logging
 system, and a CDN Control system.

Niven-Jenkins, et al. Informational [Page 5] RFC 6707 CDN Interconnection Problem Statement September 2012

 Content Metadata: This is metadata about Content.  Content Metadata
 comprises:
 1.  Metadata that is relevant to the distribution of the content (and
     therefore relevant to a CDN involved in the delivery of that
     content).  We refer to this type of metadata as "Content
     Distribution Metadata".  See also the definition of Content
     Distribution Metadata.
 2.  Metadata that is associated with the actual Content or content
     representation, and not directly relevant to the distribution of
     that Content.  For example, such metadata may include information
     pertaining to the Content's genre, cast, rating, etc. as well as
     information pertaining to the Content representation's
     resolution, aspect ratio, etc.
 Content Service: The service offered by a Content Service Provider.
 The Content Service encompasses the complete service, which may be
 wider than just providing access to items of Content; e.g., the
 Content Service also includes any middleware, key distribution,
 program guide, etc. that may not require any direct interaction with
 the CDN, or CDNs, involved in the distribution and delivery of the
 content.
 Content Service Provider (CSP): Provides a Content Service to End
 Users (which they access via a User Agent).  A CSP may own the
 Content made available as part of the Content Service, or may license
 content rights from another party.
 Control system: The function within a CDN responsible for
 bootstrapping and controlling the other components of the CDN as well
 as for handling interactions with external systems (e.g., handling
 delivery service creation/update/removal requests, or specific
 service provisioning requests).
 Delivery: The function within CDN Surrogates responsible for
 delivering a piece of content to the User Agent.  For example,
 delivery may be based on HTTP progressive download or HTTP adaptive
 streaming.
 Distribution system: The function within a CDN responsible for
 distributing Content Distribution Metadata as well as the Content
 itself inside the CDN (e.g., down to the Surrogates).
 Downstream CDN: For a given End User request, the CDN (within a pair
 of directly interconnected CDNs) to which the request is redirected
 by the other CDN (the Upstream CDN).  Note that in the case of
 successive redirections (e.g., CDN1-->CDN2-->CDN3), a given CDN

Niven-Jenkins, et al. Informational [Page 6] RFC 6707 CDN Interconnection Problem Statement September 2012

 (e.g., CDN2) may act as the Downstream CDN for a redirection (e.g.,
 CDN1-->CDN2) and as the Upstream CDN for the subsequent redirection
 of the same request (e.g., CDN2-->CDN3).
 Dynamic CDNI Metadata acquisition: In the context of CDN
 Interconnection, dynamic CDNI Metadata acquisition means that a
 Downstream CDN acquires CDNI Metadata for content from the Upstream
 CDN at some point in time after a request for that content is
 delegated to the Downstream CDN by an Upstream CDN (and that specific
 CDNI Metadata is not yet available in the Downstream CDN).  See also
 the definitions for Downstream CDN and Upstream CDN.
 Dynamic content acquisition: Dynamic content acquisition is where a
 CDN acquires content from the content source in response to an End
 User requesting that content from the CDN.  In the context of CDN
 Interconnection, dynamic acquisition means that a Downstream CDN
 acquires the content from content sources (including Upstream CDNs)
 at some point in time after a request for that content is delegated
 to the Downstream CDN by an Upstream CDN (and that specific content
 is not yet available in the Downstream CDN).
 End User (EU): The 'real' user of the system, typically a human but
 maybe some combination of hardware and/or software emulating a human
 (e.g., for automated quality monitoring etc.).
 Logging system: The function within a CDN responsible for collecting
 the measurement and recording of distribution and delivery
 activities.  The information recorded by the Logging system may be
 used for various purposes, including charging (e.g., of the CSP),
 analytics, and monitoring.
 Metadata: Metadata in general is data about data.
 Network Service Provider (NSP): Provides network-based connectivity/
 services to End Users.
 Over-the-top (OTT): A service, e.g., content delivery using a CDN,
 operated by a different operator than the NSP to which the users of
 that service are attached.
 Pre-positioned CDNI Metadata acquisition: In the context of CDN
 Interconnection, CDNI Metadata pre-positioning is where the
 Downstream CDN acquires CDNI Metadata for content prior to, or
 independently of, any End User requesting that content from the
 Downstream CDN.

Niven-Jenkins, et al. Informational [Page 7] RFC 6707 CDN Interconnection Problem Statement September 2012

 Pre-positioned content acquisition: Content pre-positioning is where
 a CDN acquires content from the content source prior to, or
 independently of, any End User requesting that content from the CDN.
 In the context of CDN Interconnection, the Upstream CDN instructs the
 Downstream CDN to acquire the content from content sources (including
 Upstream CDNs) in advance of, or independently of, any End User
 requesting it.
 Quality of Experience (QoE): As defined in Section 2.4 of [RFC6390].
 Request Routing system: The function within a CDN responsible for
 receiving a Content Request from a User Agent, obtaining and
 maintaining necessary information about a set of candidate Surrogates
 or candidate CDNs, and for selecting and redirecting the user to the
 appropriate Surrogate or CDN.  To enable CDN Interconnection, the
 Request Routing system must also be capable of handling User Agent
 Content Requests passed to it by another CDN.
 Surrogate: A device/function (often called a cache) that interacts
 with other elements of the CDN for the control and distribution of
 Content within the CDN and interacts with User Agents for the
 delivery of the Content.  Typically, Surrogates will cache requested
 content so that they can directly deliver the same content in
 response to requests from multiple User Agents (and their End Users),
 avoiding the need for the content to transit multiple times through
 the network core (i.e., from the content origin to the Surrogate).
 Upstream CDN: For a given End User request, the CDN (within a pair of
 directly interconnected CDNs) that redirects the request to the
 other CDN.
 User Agent (UA): Software (or a combination of hardware and software)
 through which the End User interacts with a Content Service.  The
 User Agent will communicate with a Content Service for the selection
 of content and one or more CDNs for the delivery of the Content.
 Such communication is not restricted to HTTP and may be via a variety
 of protocols.  Examples of User Agents (non-exhaustive) are browsers,
 Set Top Boxes (STBs), dedicated content applications (e.g., media
 players), etc.

Niven-Jenkins, et al. Informational [Page 8] RFC 6707 CDN Interconnection Problem Statement September 2012

1.2. CDN Background

 Readers are assumed to be familiar with the architecture, features,
 and operation of CDNs.  For readers less familiar with the operation
 of CDNs, the following resources may be useful:
 o  RFC 3040 [RFC3040] describes many of the component technologies
    that are used in the construction of a CDN.
 o  Taxonomy [TAXONOMY] compares the architecture of a number of CDNs.
 o  RFC 3466 [RFC3466] and RFC 3570 [RFC3570] are the output of the
    IETF Content Distribution Internetworking (CDI) working group,
    which was closed in 2003.
 Note: Some of the terms used in this document are similar to terms
 used in the above referenced documents.  When reading this document,
 terms should be interpreted as having the definitions provided in
 Section 1.1.

2. CDN Interconnection Use Cases

 An increasing number of NSPs are deploying CDNs in order to deal
 cost-effectively with the growing usage of on-demand video services
 and other content delivery applications.
 CDNs allow caching of content closer to the edge of a network so that
 a given item of content can be delivered by a CDN Surrogate (i.e., a
 cache) to multiple User Agents (and their End Users) without
 transiting multiple times through the network core (i.e., from the
 content origin to the Surrogate).  This contributes to bandwidth cost
 reductions for the NSP and to improved quality of experience for the
 End Users.  CDNs also enable replication of popular content across
 many Surrogates, which enables content to be served to large numbers
 of User Agents concurrently.  This also helps in dealing with
 situations such as flash crowds and denial-of-service attacks.
 The CDNs deployed by NSPs are not just restricted to the delivery of
 content to support the Network Service Provider's own 'walled garden'
 services, such as IP delivery of television services to Set Top
 Boxes, but are also used for delivery of content to other devices,
 including PCs, tablets, mobile phones, etc.
 Some service providers operate over multiple geographies and federate
 multiple affiliate NSPs.  These NSPs typically operate independent
 CDNs.  As they evolve their services (e.g., for seamless support of
 content services to nomadic users across affiliate NSPs), there is a

Niven-Jenkins, et al. Informational [Page 9] RFC 6707 CDN Interconnection Problem Statement September 2012

 need for interconnection of these CDNs; this represents a first use
 case for CDNI.  However, there are no open specifications, nor common
 best practices, defining how to achieve such CDN Interconnection.
 CSPs have a desire to be able to get (some of) their content to very
 large numbers of End Users, who are often distributed across a number
 of geographies, while maintaining a high quality of experience, all
 without having to maintain direct business relationships with many
 different CDN Providers (or having to extend their own CDN to a large
 number of locations).  Some NSPs are considering interconnecting
 their respective CDNs (as well as possibly over-the-top CDNs) so that
 this collective infrastructure can address the requirements of CSPs
 in a cost-effective manner.  This represents a second use case for
 CDNI.  In particular, this would enable the CSPs to benefit from
 on-net delivery (i.e., within the Network Service Provider's own
 network/CDN footprint) whenever possible and off-net delivery
 otherwise, without requiring the CSPs to maintain direct business
 relationships with all the CDNs involved in the delivery.  Again, CDN
 Providers (NSPs or over-the-top CDN operators) are faced with a lack
 of open specifications and best practices.
 NSPs have often deployed CDNs as specialized cost-reduction projects
 within the context of a particular service or environment.  Some NSPs
 operate separate CDNs for separate services.  For example, there may
 be a CDN for managed IPTV service delivery, a CDN for web-TV
 delivery, and a CDN for video delivery to mobile terminals.  As NSPs
 integrate their service portfolio, there is a need for
 interconnecting these CDNs, representing a third use case for CDNI.
 Again, NSPs face the problem of lack of open interfaces for CDN
 Interconnection.
 For operational reasons (e.g., disaster, flash crowd) or commercial
 reasons, an over-the-top CDN may elect to make use of another CDN
 (e.g., an NSP CDN with on-net Surrogates for a given footprint) for
 serving a subset of the user requests (e.g., requests from users
 attached to that NSP), which results in a fourth use case for CDNI
 because CDN Providers (over-the-top CDN Providers or NSPs) are faced
 with a lack of open specifications and best practices.
 Use cases for CDN Interconnection are further discussed in
 [CDNI-USE-CASES].

Niven-Jenkins, et al. Informational [Page 10] RFC 6707 CDN Interconnection Problem Statement September 2012

3. CDN Interconnection Model and Problem Area for IETF

 This section discusses the problem area for the IETF work on CDN
 Interconnection.
 Interconnecting CDNs involves interactions among multiple different
 functions and components that form each CDN.  Only some of those
 require additional specification by the IETF.
 Some NSPs have started to perform experiments to explore whether
 their CDN use cases can already be addressed with existing CDN
 implementations.  One set of such experiments is documented in
 [CDNI-EXPERIMENTS].  The conclusions of those experiments are that
 while some basic limited CDN Interconnection functionality can be
 achieved with existing CDN technology, the current lack of any
 standardized CDNI interfaces with the necessary level of
 functionality such as those discussed in this document is preventing
 the deployment of CDN Interconnection.
 Listed below are the four interfaces required to interconnect a pair
 of CDNs and that constitute the problem space of CDN Interconnection
 along with the required functionality of each interface for which
 standards do not currently exist.  As part of the development of the
 CDNI interfaces, it will also be necessary to agree on common
 mechanisms for how to identify and name the data objects that are to
 be interchanged between interconnected CDNs.
 The use of the term "interface" is meant to encompass the protocol
 over which CDNI data representations (e.g., CDNI Metadata objects)
 are exchanged as well as the specification of the data
 representations themselves (i.e., what properties/fields each object
 contains, its structure, etc.).
 o  CDNI Control interface: This interface allows the "CDNI Control"
    system in interconnected CDNs to communicate.  This interface may
    support the following:
  • Allow bootstrapping of the other CDNI interfaces (e.g.,

interface address/URL discovery and establishment of security

       associations).
  • Allow configuration of the other CDNI interfaces (e.g.,

Upstream CDN specifies information to be reported through the

       CDNI Logging interface).
  • Allow the Downstream CDN to communicate static (or fairly

static) information about its delivery capabilities and

       policies.

Niven-Jenkins, et al. Informational [Page 11] RFC 6707 CDN Interconnection Problem Statement September 2012

  • Allow bootstrapping of the interface between CDNs for content

acquisition (even if that interface itself is outside the scope

       of the CDNI work).
  • Allow an Upstream CDN to initiate or request specific actions

to be undertaken in the Downstream CDN. For example, to allow

       an Upstream CDN to initiate content or CDNI Metadata
       acquisition (pre-positioning) or to request the invalidation
       or purging of content files and/or CDNI Metadata in a
       Downstream CDN.
 o  CDNI Request Routing interface: This interface allows the Request
    Routing systems in interconnected CDNs to communicate to ensure
    that an End User request can be (re)directed from an Upstream CDN
    to a Surrogate in the Downstream CDN, in particular where
    selection responsibilities may be split across CDNs (for example,
    the Upstream CDN may be responsible for selecting the Downstream
    CDN, while the Downstream CDN may be responsible for selecting the
    actual Surrogate within that Downstream CDN).  In particular, the
    functions of the CDN Request Routing interface may be divided as
    follows:
  • A CDNI Request Routing Redirection interface, which allows the

Upstream CDN to query the Downstream CDN at request routing

       time before redirecting the request to the Downstream CDN.
  • A CDNI Footprint & Capabilities advertisement interface, which

allows the Downstream CDN to provide to the Upstream CDN

       (static or dynamic) information (e.g., resources, footprint,
       load) to facilitate selection of the Downstream CDN by the
       Upstream CDN Request Routing system when processing subsequent
       Content Requests from User Agents.
 o  CDNI Metadata interface: This interface allows the Distribution
    system in interconnected CDNs to communicate to ensure that CDNI
    Metadata can be exchanged across CDNs.  See Section 1.1 for the
    definition and examples of CDNI Metadata.
 o  CDNI Logging interface: This interface allows the Logging system
    in interconnected CDNs to communicate the relevant activity logs
    in order to allow log-consuming applications to operate in a
    multi-CDN environment.  For example, an Upstream CDN may collect
    delivery logs from a Downstream CDN in order to perform
    consolidated charging of the CSP or for settlement purposes across
    CDNs.  Similarly, an Upstream CDN may collect delivery logs from a
    Downstream CDN in order to provide consolidated reporting and
    monitoring to the CSP.

Niven-Jenkins, et al. Informational [Page 12] RFC 6707 CDN Interconnection Problem Statement September 2012

 Note that the actual grouping of functionalities under these four
 interfaces is considered tentative at this stage and may be changed
 after further study (e.g., some subset of functionality may be moved
 from one interface into another).
 The above list covers a significant potential problem space, in part
 because in order to interconnect two CDNs there are several 'touch
 points' that require standardization.  However, it is expected that
 the CDNI interfaces need not be defined from scratch and instead can
 reuse or leverage existing protocols to a very significant extent;
 this is discussed further in Section 4.
 The interfaces that form the CDNI problem area are illustrated in
 Figure 1.

Niven-Jenkins, et al. Informational [Page 13] RFC 6707 CDN Interconnection Problem Statement September 2012

  1. ——-

/ \

  |   CSP  |
  \        /
   --------
       *
       *
       *                         /\
       *                        /  \
   ----------------------      |CDNI|        ----------------------
  /     Upstream CDN     \     |    |       /    Downstream CDN    \
  |      +-------------+ | Control Interface| +-------------+      |
  |*******   Control   |<======|====|========>|   Control   *******|
  |*     +------*----*-+ |     |    |       | +-*----*------+     *|
  |*            *    *   |     |    |       |   *    *            *|
  |*     +------*------+ | Logging Interface| +------*------+     *|
  |* *****   Logging   |<======|====|========>|   Logging   ***** *|
  |* *   +-*-----------+ |     |    |       | +-----------*-+   * *|
  |* *     *         *   | Request Routing  |   *         *     * *|
.....*...+-*---------*-+ |    Interface     | +-*---------*-+...*.*...
. |* * *** Req-Routing |<======|====|========>| Req-Routing *** * *| .
. |* * * +-------------+.|     |    |       | +-------------+ * * *| .
. |* * *                 .  CDNI Metadata   |                 * * *| .
. |* * * +-------------+ |.   Interface     | +-------------+ * * *| .
. |* * * | Distribution|<==.===|====|========>| Distribution| * * *| .
. |* * * |             | |  .   \  /        | |             | * * *| .
. |* * * |+---------+  | |   .   \/         | |  +---------+| * * *| .
. |* * ***| +---------+| |    ....Request......+---------+ |*** * *| .
. |* *****+-|Surrogate|************************|Surrogate|-+***** *| .
. |*******  +---------+| |   Acquisition    | |+----------+ *******| .
. |      +-------------+ |                  | +-------*-----+      | .
. \                      /                  \         *            / .
.  ----------------------                    ---------*------------  .
.                                                     *              .
.                                                     * Delivery     .
.                                                     *              .
.                                                  +--*---+          .
...............Request.............................| User |..Request..
                                                   | Agent|
                                                   +------+
<==>  interfaces inside the scope of CDNI
****  interfaces outside the scope of CDNI
....  interfaces outside the scope of CDNI
              Figure 1: A Model for the CDNI Problem Area

Niven-Jenkins, et al. Informational [Page 14] RFC 6707 CDN Interconnection Problem Statement September 2012

 As illustrated in Figure 1, the acquisition of content between
 interconnected CDNs is out of scope for CDNI; this deserves some
 additional explanation.  The consequence of such a decision is that
 the CDNI problem space described in this document is focused on only
 defining the control plane for CDNI, and the CDNI data plane (i.e.,
 the acquisition and distribution of the actual content objects) is
 out of scope.  The rationale for such a decision is that CDNs today
 typically already use standardized protocols such as HTTP, FTP,
 rsync, etc. to acquire content from their CSP customers, and it is
 expected that the same protocols could be used for acquisition
 between interconnected CDNs.  Therefore, the problem of content
 acquisition is considered already solved, and all that is required
 with respect to content acquisition from specifications developed by
 the CDNI working group is to describe within the CDNI Metadata the
 parameters to use to retrieve the content -- for example, the IP
 address/hostname to connect to, what protocol to use to retrieve the
 content, etc.

4. Scoping the CDNI Problem

 This section outlines how the scope of work addressing the CDNI
 problem space can be constrained through reuse or leveraging of
 existing protocols to implement the CDNI interfaces.  This discussion
 is not intended to preempt any working group decision as to the most
 appropriate protocols, technologies, and solutions to select to
 realize the CDNI interfaces but is intended as an illustration of the
 fact that the CDNI interfaces need not be created in a vacuum and
 that reuse or leverage of existing protocols is likely possible.
 The four CDNI interfaces (CDNI Control interface, CDNI Request
 Routing interface, CDNI Metadata interface, and CDNI Logging
 interface) described in Section 3 within the CDNI problem area are
 all control plane interfaces operating at the application layer
 (Layer 7 in the OSI network model).  Firstly, since it is not
 expected that these interfaces would exhibit unique session,
 transport, or network requirements as compared to the many other
 existing applications in the Internet, it is expected that the CDNI
 interfaces will be defined on top of existing session, transport, and
 network protocols.
 Secondly, although a new application protocol could be designed
 specifically for CDNI, our analysis below shows that this is
 unnecessary, and it is recommended that existing application
 protocols be reused or leveraged (HTTP [RFC2616], the Atom Publishing
 Protocol [RFC5023], the Extensible Messaging and Presence Protocol
 (XMPP) [RFC6120], for example) to realize the CDNI interfaces.

Niven-Jenkins, et al. Informational [Page 15] RFC 6707 CDN Interconnection Problem Statement September 2012

4.1. CDNI Control Interface

 The CDNI Control interface allows the Control system in
 interconnected CDNs to communicate.  The exact inter-CDN control
 functionality required to be supported by the CDNI Control interface
 is less well defined than the other three CDNI interfaces at this
 time.
 It is expected that for the Control interface, as for the other CDNI
 interfaces, existing protocols can be reused or leveraged.

4.2. CDNI Request Routing Interface

 The CDNI Request Routing interface enables a Request Routing function
 in an Upstream CDN to query a Request Routing function in a
 Downstream CDN to determine if the Downstream CDN is able (and
 willing) to accept the delegated Content Request.  It also allows the
 Downstream CDN to control what should be returned to the User Agent
 in the redirection message by the upstream Request Routing function.
 The CDNI Request Routing interface is therefore a fairly
 straightforward request/response interface and could be implemented
 over any number of request/response protocols.  For example, it may
 be implemented as a WebService using one of the common WebServices
 methodologies (Extensible Markup Language-Remote Procedure Calling
 (XML-RPC), HTTP query to a known URI, etc.).  This removes the need
 for the CDNI working group to define a new protocol for the request/
 response element of the CDNI Request Routing interface.
 Additionally, as discussed in Section 3, the CDNI Request Routing
 interface is also expected to enable a Downstream CDN to provide to
 the Upstream CDN (static or dynamic) information (e.g., resources,
 footprint, load) to facilitate selection of the Downstream CDN by the
 Upstream CDN Request Routing system when processing subsequent
 Content Requests from User Agents.  It is expected that such
 functionality of the CDNI request routing could be specified by the
 CDNI working group with significant leveraging of existing IETF
 protocols supporting the dynamic distribution of reachability
 information (for example, by leveraging existing routing protocols)
 or supporting application-level queries for topological information
 (for example, by leveraging Application-Layer Traffic Optimization
 (ALTO) [RFC5693]).

Niven-Jenkins, et al. Informational [Page 16] RFC 6707 CDN Interconnection Problem Statement September 2012

4.3. CDNI Metadata Interface

 The CDNI Metadata interface enables the Distribution system in a
 Downstream CDN to request CDNI Metadata from an Upstream CDN so that
 the Downstream CDN can properly process and respond to redirection
 requests received over the CDNI Request Routing interface and Content
 Requests received directly from User Agents.
 The CDNI Metadata interface is therefore similar to the CDNI Request
 Routing interface because it is a request/response interface with the
 potential addition that CDNI Metadata search may have more complex
 semantics than a straightforward Request Routing redirection request.
 Therefore, like the CDNI Request Routing interface, the CDNI Metadata
 interface may be implemented as a WebService using one of the common
 WebServices methodologies (XML-RPC, HTTP query to a known URI, etc.)
 or possibly using other existing protocols such as XMPP [RFC6120].
 This removes the need for the CDNI working group to define a new
 protocol for the request/response element of the CDNI Metadata
 interface.

4.4. CDNI Logging Interface

 The CDNI Logging interface enables details of content distribution
 and delivery activities to be exchanged between interconnected CDNs
 -- for example, the exchange of log records related to the delivery
 of content, similar to the log records recorded in a web server's
 access log.
 Several protocols already exist that could potentially be used to
 exchange CDNI logs between interconnected CDNs, including the Simple
 Network Management Protocol (SNMP), syslog, FTP (and secure
 variants), HTTP POST, etc.

5. Security Considerations

 Distribution of content by a CDN comes with a range of security
 considerations, such as how to enforce control of access to the
 content by End Users in line with the CSP policy, or how to trust the
 logging information generated by the CDN for the purposes of charging
 the CSP.  These security aspects are already dealt with by CDN
 Providers and CSPs today in the context of standalone CDNs.  However,
 interconnection of CDNs introduces a new set of security
 considerations by extending the trust model to a chain of trust
 (i.e., the CSP "trusts" a CDN that "trusts" another CDN).  The
 mechanisms used to mitigate these risks in multi-CDN environments may
 be similar to those used in the single-CDN case, but their
 suitability in this more complex environment must be validated.

Niven-Jenkins, et al. Informational [Page 17] RFC 6707 CDN Interconnection Problem Statement September 2012

 The interconnection of CDNs may also introduce additional privacy
 considerations on top of those that apply to the single-CDN case.  In
 a multi-CDN environment, the different CDNs may reside in different
 legal regimes that require differing privacy requirements to be
 enforced.  Such privacy requirements may impact the granularity of
 information that can be exchanged across the CDNI interfaces.  For
 example, the Logging system in a Downstream CDN may need to apply
 some degree of anonymization, obfuscation, or even the complete
 removal of some fields before exchanging log records containing
 details of End User deliveries with an Upstream CDN.
 Maintaining the security of the content itself, its associated
 metadata (including delivery policies), and the CDNs distributing and
 delivering it, are critical requirements for both CDN Providers and
 CSPs, and the CDN Interconnection interfaces must provide sufficient
 mechanisms to maintain the security of the overall system of
 interconnected CDNs as well as the information (content, metadata,
 logs, etc.) distributed and delivered through any set of
 interconnected CDNs.

5.1. Security of the CDNI Control Interface

 Information exchanged between interconnected CDNs over this interface
 is of a sensitive nature.  A pair of CDNs use this interface to allow
 bootstrapping of all the other CDNI interfaces, possibly including
 establishment of the mechanisms for securing these interfaces.
 Therefore, corruption of that interface may result in corruption of
 all other interfaces.  Using this interface, an Upstream CDN may
 pre-position or delete content or metadata in a Downstream CDN, a
 Downstream CDN may provide administrative information to an Upstream
 CDN, etc.  All of these operations require that the peer CDNs are
 appropriately authenticated and that the confidentiality and
 integrity of information flowing between them can be ensured.

5.2. Security of the CDNI Request Routing Interface

 Appropriate levels of authentication and confidentiality must be used
 in this interface because it allows an Upstream CDN to query the
 Downstream CDN in order to redirect requests, and conversely, allows
 the Downstream CDN to influence the Upstream CDN's Request Routing
 function.
 In the absence of appropriate security on this interface, a rogue
 Upstream CDN could inundate Downstream CDNs with bogus requests or
 have the Downstream CDN send the rogue Upstream CDN private
 information.  Also, a rogue Downstream CDN could influence the

Niven-Jenkins, et al. Informational [Page 18] RFC 6707 CDN Interconnection Problem Statement September 2012

 Upstream CDN so the Upstream CDN redirects requests to the rogue
 Downstream CDN or another Downstream CDN in order to, for example,
 attract additional delivery revenue.

5.3. Security of the CDNI Metadata Interface

 This interface allows a Downstream CDN to request CDNI Metadata from
 an Upstream CDN, and therefore the Upstream CDN must ensure that the
 former is appropriately authenticated before sending the data.
 Conversely, a Downstream CDN must authenticate an Upstream CDN before
 requesting metadata to insulate itself from poisoning by rogue
 Upstream CDNs.  The confidentiality and integrity of the information
 exchanged between the peers must be protected.

5.4. Security of the CDNI Logging Interface

 Logging data consists of potentially sensitive information (which End
 User accessed which media resource, IP addresses of End Users,
 potential names and subscriber account information, etc.).
 Confidentiality of this information must be protected as log records
 are moved between CDNs.  This information may also be sensitive from
 the viewpoint that it can be the basis for charging across CDNs.
 Therefore, appropriate levels of protection are needed against
 corruption, duplication, and loss of this information.

6. Acknowledgements

 The authors would like to thank Andre Beck, Gilles Bertrand, Mark
 Carlson, Bruce Davie, David Ferguson, Yiu Lee, Kent Leung, Will Li,
 Kevin Ma, Julien Maisonneuve, Guy Meador, Larry Peterson, Emile
 Stephan, Oskar van Deventer, Mahesh Viveganandhan, and Richard Woundy
 for their review comments and contributions to the text.

Niven-Jenkins, et al. Informational [Page 19] RFC 6707 CDN Interconnection Problem Statement September 2012

7. Informative References

 [ALTO-CDN-USE-CASES]
            Niven-Jenkins, B., Ed., Watson, G., Bitar, N., Medved, J.,
            and S. Previdi, "Use Cases for ALTO within CDNs", Work
            in Progress, June 2012.
 [ALTO-Charter]
            "IETF ALTO WG Charter",
            <http://datatracker.ietf.org/wg/alto/charter/>.
 [CDNI-EXPERIMENTS]
            Bertrand, G., Ed., Le Faucheur, F., and L. Peterson,
            "Content Distribution Network Interconnection (CDNI)
            Experiments", Work in Progress, February 2012.
 [CDNI-USE-CASES]
            Bertrand, G., Ed., Emile, S., Burbridge, T., Eardley, P.,
            Ma, K., and G. Watson, "Use Cases for Content Delivery
            Network Interconnection", Work in Progress, August 2012.
 [DECADE-Charter]
            "IETF DECADE WG Charter",
            <http://datatracker.ietf.org/wg/decade/charter/>.
 [P2PRG-CDNI]
            Davie, B. and F. Le Faucheur, "Interconnecting CDNs aka
            'Peering Peer-to-Peer'", March 2010,
            <http://www.ietf.org/proceedings/77/slides/P2PRG-2.pdf>.
 [PPSP-Charter]
            "IETF PPSP WG Charter",
            <http://datatracker.ietf.org/wg/ppsp/charter/>.
 [RFC2616]  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.
 [RFC3040]  Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
            Replication and Caching Taxonomy", RFC 3040, January 2001.
 [RFC3466]  Day, M., Cain, B., Tomlinson, G., and P. Rzewski, "A Model
            for Content Internetworking (CDI)", RFC 3466,
            February 2003.
 [RFC3570]  Rzewski, P., Day, M., and D. Gilletti, "Content
            Internetworking (CDI) Scenarios", RFC 3570, July 2003.

Niven-Jenkins, et al. Informational [Page 20] RFC 6707 CDN Interconnection Problem Statement September 2012

 [RFC5023]  Gregorio, J., Ed., and B. de hOra, Ed., "The Atom
            Publishing Protocol", RFC 5023, October 2007.
 [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
            Optimization (ALTO) Problem Statement", RFC 5693,
            October 2009.
 [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
            Protocol (XMPP): Core", RFC 6120, March 2011.
 [RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New
            Performance Metric Development", BCP 170, RFC 6390,
            October 2011.
 [TAXONOMY] Pathan, A. and R. Buyya, "A Taxonomy and Survey of Content
            Delivery Networks", 2007,
            <http://www.cloudbus.org/reports/CDN-Taxonomy.pdf>.

Niven-Jenkins, et al. Informational [Page 21] RFC 6707 CDN Interconnection Problem Statement September 2012

Appendix A. Design Considerations for Realizing the CDNI Interfaces

 This section expands on how CDNI interfaces can reuse and leverage
 existing protocols before describing each CDNI interface individually
 and highlighting example candidate protocols that could be considered
 for reuse or leveraging to implement the CDNI interfaces.  However,
 the options discussed here are purely examples and do not present any
 consensus on protocols to be used later on.

A.1. CDNI Control Interface

 The CDNI Control interface allows the Control system in
 interconnected CDNs to communicate.  The exact inter-CDN control
 functionality required to be supported by the CDNI Control interface
 is less well defined than the other three CDNI interfaces at this
 time.
 However, as discussed in Section 3, the CDNI Control interface may be
 required to support functionality similar to the following:
 o  Allow an Upstream CDN and Downstream CDN to establish, update, or
    terminate their CDNI interconnection.
 o  Allow bootstrapping of the other CDNI interfaces (e.g., protocol
    address discovery and establishment of security associations).
 o  Allow configuration of the other CDNI interfaces (e.g., Upstream
    CDN specifies information to be reported through the CDNI Logging
    interface).
 o  Allow the Downstream CDN to communicate static information about
    its delivery capabilities, resources, and policies.
 o  Allow bootstrapping of the interface between CDNs for content
    acquisition (even if that interface itself is outside the scope of
    the CDNI work).
 It is expected that for the Control interface, as for the other CDNI
 interfaces, existing protocols can be reused or leveraged.  Those
 will be considered once the requirements for the Control interface
 have been refined.

Niven-Jenkins, et al. Informational [Page 22] RFC 6707 CDN Interconnection Problem Statement September 2012

A.2. CDNI Request Routing Interface

 The CDNI Request Routing interface enables a Request Routing function
 in an Upstream CDN to query a Request Routing function in a
 Downstream CDN to determine if the Downstream CDN is able (and
 willing) to accept the delegated Content Request and to allow the
 Downstream CDN to control what the upstream Request Routing function
 should return to the User Agent in the redirection message.
 Therefore, the CDNI Request Routing interface needs to offer a
 mechanism for an Upstream CDN to issue a "Redirection Request" to a
 Downstream CDN.  The Request Routing interface needs to be able to
 support scenarios where the initial User Agent request to the
 Upstream CDN is received over DNS as well as over a content-specific
 application protocol (e.g., HTTP, the Real Time Streaming Protocol
 (RTSP), the Real Time Messaging Protocol (RTMP), etc.).
 Therefore, a Redirection Request is expected to contain information
 such as:
 o  The protocol (e.g., DNS, HTTP) over which the Upstream CDN
    received the initial User Agent request.
 o  Additional details of the User Agent request that are required to
    perform effective Request Routing by the Downstream CDN.  For DNS,
    this would typically be the IP address of the DNS resolver making
    the request on behalf of the User Agent.  For requests received
    over content-specific application protocols, the Redirection
    Request could contain significantly more information related to
    the original User Agent request but at a minimum is expected to
    include the User Agent's IP address, the equivalent of the HTTP
    Host header, and the equivalent of the HTTP abs_path as defined in
    [RFC2616].
 It should be noted that the CDNI architecture needs to consider that
 a Downstream CDN may receive requests from User Agents without first
 receiving a Redirection Request from an Upstream CDN for the
 corresponding User Agent request because, for example:
 o  User Agents (or DNS resolvers) may cache DNS or application
    responses from Request Routers.
 o  Responses to Redirection Requests over the Request Routing
    interface may be cacheable.

Niven-Jenkins, et al. Informational [Page 23] RFC 6707 CDN Interconnection Problem Statement September 2012

 o  Some CDNs may rely on simple coarse policies, e.g., CDN B agrees
    to always serve CDN A's delegated redirection requests, in which
    case the necessary redirection details are exchanged out of band
    (of the CDNI interfaces), e.g., configured.
 On receiving a Redirection Request, the Downstream CDN will use the
 information provided in the request to determine if it is able (and
 willing) to accept the delegated Content Request and needs to return
 the result of its decision to the Upstream CDN.
 Thus, a Redirection Response from the Downstream CDN is expected to
 contain information such as:
 o  Status code indicating acceptance or rejection (possibly with
    accompanying reasons).
 o  Information to allow redirection by the Upstream CDN.  In the case
    of DNS-based request routing, this is expected to include the
    equivalent of a DNS record(s) (e.g., a CNAME) that the Upstream
    CDN should return to the requesting DNS resolver.  In the case of
    application-based request routing, this is expected to include the
    information necessary to construct the application-specific
    redirection response(s) to return to the requesting User Agent.
    For HTTP requests from User Agents, this could include a URI that
    the Upstream CDN could return in an HTTP 3xx response.
 The CDNI Request Routing interface is therefore a fairly
 straightforward request/response interface and could be implemented
 over any number of request/response protocols.  For example, it may
 be implemented as a WebService using one of the common WebServices
 methodologies (XML-RPC, HTTP query to a known URI, etc.).  This
 removes the need for the CDNI working group to define a new protocol
 for the request/response element of the CDNI Request Routing
 interface.  Thus, the CDNI working group would be left only with the
 task of specifying:
 o  The recommended request/response protocol to use along with any
    additional semantics and procedures that are specific to the CDNI
    Request Routing interface (e.g., handling of malformed requests/
    responses).
 o  The syntax (i.e., representation/encoding) of the redirection
    requests and responses.
 o  The semantics (i.e., meaning and expected contents) of the
    redirection requests and responses.

Niven-Jenkins, et al. Informational [Page 24] RFC 6707 CDN Interconnection Problem Statement September 2012

 Additionally, as discussed in Section 3, the CDNI Request Routing
 interface is also expected to enable a Downstream CDN to provide to
 the Upstream CDN (static or dynamic) information (e.g., resources,
 footprint, load) to facilitate selection of the Downstream CDN by the
 Upstream CDN Request Routing system when processing subsequent
 Content Requests from User Agents.  It is expected that such
 functionality of the CDNI request routing could be specified by the
 CDNI working group with significant leveraging of existing IETF
 protocols supporting the dynamic distribution of reachability
 information (for example, by leveraging existing routing protocols)
 or supporting application-level queries for topological information
 (for example, by leveraging ALTO).

A.3. CDNI Metadata Interface

 The CDNI Metadata interface enables the Distribution system in a
 Downstream CDN to obtain CDNI Metadata from an Upstream CDN so that
 the Downstream CDN can properly process and respond to:
 o  Redirection Requests received over the CDNI Request Routing
    interface.
 o  Content Requests received directly from User Agents.
 The CDNI Metadata interface needs to offer a mechanism for an
 Upstream CDN to:
 o  Distribute/update/remove CDNI Metadata to a Downstream CDN.
 and/or to allow a Downstream CDN to:
 o  Make direct requests for CDNI Metadata objects.
 o  Make recursive requests for CDNI Metadata -- for example, to
    enable a Downstream CDN to walk down a tree of objects with
    inter-object relationships.
 The CDNI Metadata interface is therefore similar to the CDNI Request
 Routing interface because it is a request/response interface with the
 potential addition that CDNI Metadata search may have more complex
 semantics than a straightforward Request Routing redirection request.
 Therefore, like the CDNI Request Routing interface, the CDNI Metadata
 interface may be implemented as a WebService using one of the common
 WebServices methodologies (XML-RPC, HTTP query to a known URI, etc.)
 or possibly using other existing protocols such as XMPP [RFC6120].
 This removes the need for the CDNI working group to define a new
 protocol for the request/response element of the CDNI Metadata
 interface.

Niven-Jenkins, et al. Informational [Page 25] RFC 6707 CDN Interconnection Problem Statement September 2012

 Thus, the CDNI working group would be left only with the task of
 specifying:
 o  The recommended request/response protocol to use along with any
    additional semantics that are specific to the CDNI Metadata
    interface (e.g., handling of malformed requests/responses).
 o  The syntax (i.e., representation/encoding) of the CDNI Metadata
    objects that will be exchanged over the interface.
 o  The semantics (i.e., meaning and expected contents) of the
    individual properties of a Metadata object.
 o  How the relationships between different CDNI Metadata objects are
    represented.

A.4. CDNI Logging Interface

 The CDNI Logging interface enables details of content distribution
 and delivery activities to be exchanged between interconnected CDNs,
 such as log records related to the delivery of content (similar to
 the log records recorded in a web server's access log).
 Within CDNs today, log records are used for a variety of purposes.
 Specifically, CDNs use logs to generate Call Data Records (CDRs) for
 passing to billing and payment systems and to real-time (and near
 real-time) analytics systems.  Such applications place requirements
 on the CDNI Logging interface to support guaranteed and timely
 delivery of log messages between interconnected CDNs.  It may also be
 necessary to be able to prove the integrity of received log messages.
 Several protocols already exist that could potentially be used to
 exchange CDNI logs between interconnected CDNs, including SNMP traps,
 syslog, FTP, HTTP POST, etc., although it is likely that some of the
 candidate protocols may not be well suited to meet all the
 requirements of CDNI.  For example, SNMP traps pose scalability
 concerns, and SNMP does not support guaranteed delivery of traps and
 therefore could result in log records being lost and the consequent
 CDRs and billing records for that content delivery not being
 produced, as well as that content delivery being invisible to any
 analytics platforms.

Niven-Jenkins, et al. Informational [Page 26] RFC 6707 CDN Interconnection Problem Statement September 2012

 Although it is not necessary to define a new protocol for exchanging
 logs across the CDNI Logging interface, the CDNI working group would
 still need to specify:
 o  The recommended protocol to use.
 o  A default set of log fields and of their syntax and semantics.
    Today there is no standard set of common log fields across
    different content delivery protocols, and in some cases there is
    not even a standard set of log field names and values for
    different implementations of the same delivery protocol.
 o  A default set of conditions that trigger log records to be
    generated.

Appendix B. Additional Material

 This section records related information that was produced as part of
 defining the CDNI problem statement.

B.1. Non-Goals for IETF

 Listed below are aspects of content delivery that the authors propose
 be kept outside of the scope of the CDNI working group:
 o  The interface between the Content Service Provider and the
    Authoritative CDN (i.e., the Upstream CDN contracted by the CSP
    for delivery by this CDN or by its Downstream CDNs).
 o  The delivery interface between the delivering CDN Surrogate and
    the User Agent, such as streaming protocols.
 o  The request interface between the User Agent and the Request
    Routing system of a given CDN.  Existing IETF protocols (e.g.,
    HTTP, RTSP, DNS) are commonly used by User Agents to request
    content from a CDN and by CDN Request Routing systems to redirect
    the User Agent requests.  The CDNI working group need not define
    new protocols for this purpose.  Note, however, that the CDNI
    control plane interface may indirectly affect some of the
    information exchanged through the request interface (e.g., URI).
 o  The content acquisition interface between CDNs (i.e., the data
    plane interface for actual delivery of a piece of content from one
    CDN to the other).  This is expected to use existing protocols
    such as HTTP or protocols defined in other forums for content
    acquisition between an origin server and a CDN (e.g., HTTP-based
    C2 reference point of the Alliance for Telecommunications Industry
    Solutions IPTV Interoperability Forum Content on Demand service

Niven-Jenkins, et al. Informational [Page 27] RFC 6707 CDN Interconnection Problem Statement September 2012

    (ATIS IIF CoD)).  The CDN Interconnection problem space described
    in this document may therefore only concern itself with the
    agreement/negotiation aspects of which content acquisition
    protocol is to be used between two interconnected CDNs in view of
    facilitating interoperability.
 o  End User/User Agent Authentication.  End User/User Agent
    authentication and authorization are the responsibility of the
    Content Service Provider.
 o  Content preparation, including encoding and transcoding.  The CDNI
    architecture aims at allowing distribution across interconnected
    CDNs of content treated as opaque objects.  Interpretation and
    processing of the objects, as well as optimized delivery of these
    objects by the Surrogate to the End User, are outside the scope of
    CDNI.
 o  Digital Rights Management (DRM).  DRM is an end-to-end issue
    between a content protection system and the User Agent.
 o  Applications consuming CDNI logs (e.g., charging, analytics,
    reporting, ...).
 o  Internal CDN interfaces and protocols (i.e., interfaces and
    protocols within one CDN).
 o  Scalability of individual CDNs.  While scalability of the CDNI
    interfaces/approach is in scope, how an individual CDN scales is
    out of scope.
 o  Actual algorithms for selection of CDNs or Surrogates by Request
    Routing systems (however, some specific parameters required as
    input to these algorithms may be in scope when they need to be
    communicated across CDNs).
 o  Surrogate algorithms.  For example, caching algorithms and content
    acquisition methods are outside the scope of the CDNI work.
    Content management (e.g., Content Deletion) as it relates to CDNI
    content management policies is in scope, but the internal
    algorithms used by a cache to determine when to no longer cache an
    item of Content (in the absence of any specific metadata to the
    contrary) is out of scope.
 o  Element management interfaces.
 o  Commercial, business, and legal aspects related to the
    interconnections of CDNs.

Niven-Jenkins, et al. Informational [Page 28] RFC 6707 CDN Interconnection Problem Statement September 2012

B.2. Relationship to Relevant IETF Working Groups and IRTF Research

    Groups

B.2.1. ALTO WG

 As stated in the ALTO working group charter [ALTO-Charter]:
    The Working Group will design and specify an Application-Layer
    Traffic Optimization (ALTO) service that will provide applications
    with information to perform better-than-random initial peer
    selection.  ALTO services may take different approaches at
    balancing factors such as maximum bandwidth, minimum cross-domain
    traffic, lowest cost to the user, etc.  The working group will
    consider the needs of BitTorrent, tracker-less P2P, and other
    applications, such as content delivery networks (CDN) and mirror
    selection.
 In particular, the ALTO service can be used by a CDN Request Routing
 system to improve its selection of a CDN Surrogate to serve a
 particular User Agent request (or to serve a request from another
 Surrogate).  [ALTO-CDN-USE-CASES] describes a number of use cases for
 a CDN to be able to obtain network topology and cost information from
 an ALTO server(s) and discusses how CDN Request Routing could be used
 as an integration point of ALTO into CDNs.  It is possible that the
 ALTO service could be used in the same manner in a multi-CDN
 environment based on CDN Interconnection.  For example, an Upstream
 CDN may take advantage of the ALTO service in its decision for
 selecting a Downstream CDN to which a user request should be
 delegated.
 However, the current work of ALTO is complementary to and does not
 overlap with the work described in this document because the
 integration between ALTO and a CDN is an internal decision for a
 specific CDN and is therefore out of scope for the CDNI working
 group.  One area for further study is whether additional information
 should be provided by an ALTO service to facilitate CDNI CDN
 selection.

B.2.2. DECADE WG

 The DECADE working group [DECADE-Charter] is addressing the problem
 of reducing traffic on the last-mile uplink, as well as backbone and
 transit links caused by peer-to-peer (P2P) streaming and file-sharing
 applications.  It addresses the problem by enabling an application
 endpoint to make content available from an in-network storage service
 and by enabling other application endpoints to retrieve the content
 from there.

Niven-Jenkins, et al. Informational [Page 29] RFC 6707 CDN Interconnection Problem Statement September 2012

 Exchanging data through the in-network storage service in this
 manner, instead of through direct communication, provides significant
 gain where:
 o  The network capacity/bandwidth from the in-network storage service
    to the application endpoint significantly exceeds the capacity/
    bandwidth from application endpoint to application endpoint (e.g.,
    because of an end-user uplink bottleneck); and
 o  The content is to be accessed by multiple instances of application
    endpoints (e.g., as is typically the case for P2P applications).
 While, as is the case for any other data distribution application,
 the DECADE architecture and mechanisms could potentially be used for
 exchange of CDNI control plane information via an in-network storage
 service (as opposed to directly between the entities terminating the
 CDNI interfaces in the neighbor CDNs), we observe that:
 o  CDNI would operate as a "Content Distribution Application" from
    the DECADE viewpoint (i.e., would operate on top of DECADE).
 o  There do not seem to be obvious benefits in integrating the DECADE
    control plane responsible for signaling information relating to
    control of the in-network storage service itself, and the CDNI
    control plane responsible for application-specific CDNI
    interactions (such as exchange of CDNI Metadata, CDNI request
    redirection, and transfer of CDNI logging information).
 o  There would typically be limited benefits in making use of a
    DECADE in-network storage service because the CDNI interfaces are
    expected to be terminated by a very small number of CDNI clients
    (if not one) in each CDN, and the CDNI clients are expected to
    benefit from high bandwidth/capacity when communicating directly
    to each other (at least as high as if they were communicating via
    an in-network storage server).
 The DECADE in-network storage architecture and mechanisms may
 theoretically be used for the acquisition of the content objects
 themselves between interconnected CDNs.  It is not expected that this
 would have obvious benefits in typical situations where a content
 object is acquired only once from an Upstream CDN to a Downstream CDN
 (and then distributed as needed inside the Downstream CDN).  But it
 might have benefits in some particular situations.  Since the
 acquisition protocol between CDNs is outside the scope of the CDNI
 work, this question is left for further study.

Niven-Jenkins, et al. Informational [Page 30] RFC 6707 CDN Interconnection Problem Statement September 2012

 The DECADE in-network storage architecture and mechanisms may
 potentially also be used within a given CDN for the distribution of
 the content objects themselves among Surrogates of that CDN.  Since
 the CDNI work does not concern itself with operation within a CDN,
 this question is left for further study.
 Therefore, the work of DECADE may be complementary to, but does not
 overlap with, the CDNI work described in this document.

B.2.3. PPSP WG

 As stated in the PPSP working group charter [PPSP-Charter]:
    The Peer-to-Peer Streaming Protocol (PPSP) working group develops
    two signaling and control protocols for a peer-to-peer (P2P)
    streaming system for transmitting live and time-shifted media
    content with near real-time delivery requirements...
    ...  The PPSP working group designs a protocol for signaling and
    control between trackers and peers (the PPSP "tracker protocol")
    and a signaling and control protocol for communication among the
    peers (the PPSP "peer protocol").  The two protocols enable peers
    to receive streaming data within the time constraints required by
    specific content items.
 Therefore, PPSP is concerned with the distribution of the streamed
 content itself along with the necessary signaling and control
 required to distribute the content.  As such, it could potentially be
 used for the acquisition of streamed content across interconnected
 CDNs.  But since the acquisition protocol is outside the scope of the
 work proposed for CDNI, we leave this for further study.  Also,
 because of its streaming nature, PPSP is not seen as applicable to
 the distribution and control of the CDNI control plane and CDNI data
 representations.
 Therefore, the work of PPSP may be complementary to, but does not
 overlap with, the work described in this document for CDNI.

B.2.4. IRTF P2P Research Group

 Some information on CDN Interconnection motivations and technical
 issues were presented in the P2P research group at IETF 77.  The
 presentation can be found in [P2PRG-CDNI].

Niven-Jenkins, et al. Informational [Page 31] RFC 6707 CDN Interconnection Problem Statement September 2012

Authors' Addresses

 Ben Niven-Jenkins
 Velocix (Alcatel-Lucent)
 326 Cambridge Science Park
 Milton Road, Cambridge  CB4 0WG
 UK
 EMail: ben@velocix.com
 Francois Le Faucheur
 Cisco Systems
 Greenside, 400 Avenue de Roumanille
 Sophia Antipolis  06410
 France
 Phone: +33 4 97 23 26 19
 EMail: flefauch@cisco.com
 Nabil Bitar
 Verizon
 60 Sylvan Road
 Waltham, MA  02145
 USA
 EMail: nabil.n.bitar@verizon.com

Niven-Jenkins, et al. Informational [Page 32]

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