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Versions: (draft-jenkins-cdni-problem-statement) 00 01 02 03 04 05 06 07 08 RFC 6707

Network Working Group                                   B. Niven-Jenkins
Internet-Draft                                  Velocix (Alcatel-Lucent)
Intended status: Informational                            F. Le Faucheur
Expires: December 27, 2012                                         Cisco
                                                                N. Bitar
                                                                 Verizon
                                                           June 25, 2012


 Content Distribution Network Interconnection (CDNI) Problem Statement
                  draft-ietf-cdni-problem-statement-08

Abstract

   Content Delivery Networks (CDNs) provide numerous benefits: reduced
   delivery cost for cacheable content, 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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."




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   This Internet-Draft will expire on December 27, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
     1.2.  CDN Background . . . . . . . . . . . . . . . . . . . . . . 10
   2.  CDN Interconnection Use Cases  . . . . . . . . . . . . . . . . 11
   3.  CDN Interconnection Model & Problem Area for IETF  . . . . . . 12
   4.  Scoping the CDNI Problem . . . . . . . . . . . . . . . . . . . 16
     4.1.  CDNI Request Routing Interface . . . . . . . . . . . . . . 17
     4.2.  CDNI Metadata Interface  . . . . . . . . . . . . . . . . . 17
     4.3.  CDNI Logging Interface . . . . . . . . . . . . . . . . . . 18
     4.4.  CDNI Control Interface . . . . . . . . . . . . . . . . . . 18
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
     6.1.  Security of the CDNI Control interface . . . . . . . . . . 19
     6.2.  Security of the CDNI Request Routing Interface . . . . . . 19
     6.3.  Security of the CDNI Metadata interface  . . . . . . . . . 20
     6.4.  Security of the CDNI Logging interface . . . . . . . . . . 20
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 20
   Appendix A.  Design considerations for realizing the CDNI
                Interfaces  . . . . . . . . . . . . . . . . . . . . . 23
     A.1.  CDNI Request Routing Interface . . . . . . . . . . . . . . 23
     A.2.  CDNI Metadata Interface  . . . . . . . . . . . . . . . . . 25
     A.3.  CDNI Logging Interface . . . . . . . . . . . . . . . . . . 26
     A.4.  CDNI Control Interface . . . . . . . . . . . . . . . . . . 27
   Appendix B.  Additional Material . . . . . . . . . . . . . . . . . 27
     B.1.  Non-Goals for IETF . . . . . . . . . . . . . . . . . . . . 28
     B.2.  Relationship to relevant IETF Working Groups & IRTF
           Reserach Groups  . . . . . . . . . . . . . . . . . . . . . 29
       B.2.1.  ALTO WG  . . . . . . . . . . . . . . . . . . . . . . . 29
       B.2.2.  DECADE WG  . . . . . . . . . . . . . . . . . . . . . . 30
       B.2.3.  PPSP WG  . . . . . . . . . . . . . . . . . . . . . . . 31
       B.2.4.  IRTF P2P Research Group  . . . . . . . . . . . . . . . 31
   Appendix C.  Additional Material . . . . . . . . . . . . . . . . . 32
     C.1.  Related standardization activites  . . . . . . . . . . . . 32
       C.1.1.  IETF CDI Working Group (Concluded) . . . . . . . . . . 33
       C.1.2.  3GPP . . . . . . . . . . . . . . . . . . . . . . . . . 33
       C.1.3.  ISO MPEG . . . . . . . . . . . . . . . . . . . . . . . 34
       C.1.4.  ATIS IIF . . . . . . . . . . . . . . . . . . . . . . . 35
       C.1.5.  CableLabs  . . . . . . . . . . . . . . . . . . . . . . 35
       C.1.6.  ETSI MCD . . . . . . . . . . . . . . . . . . . . . . . 35
       C.1.7.  ETSI TISPAN  . . . . . . . . . . . . . . . . . . . . . 35
       C.1.8.  ITU-T  . . . . . . . . . . . . . . . . . . . . . . . . 36
       C.1.9.  Open IPTV Forum (OIPF) . . . . . . . . . . . . . . . . 36
       C.1.10. TV-Anytime Forum . . . . . . . . . . . . . . . . . . . 36



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       C.1.11. SNIA . . . . . . . . . . . . . . . . . . . . . . . . . 37
       C.1.12. Summary of existing standardization work . . . . . . . 37
     C.2.  Related Research Projects  . . . . . . . . . . . . . . . . 39
       C.2.1.  OCEAN  . . . . . . . . . . . . . . . . . . . . . . . . 39
       C.2.2.  Eurescom P1955 . . . . . . . . . . . . . . . . . . . . 39
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40













































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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: reduced delivery cost for cacheable
   content, 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 Provider(s)
   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 authorizes the CDN Provider to 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.

   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



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   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 Interconnect is described below:

   o  The initial 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 Interconnect 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 Reserach Groups.

1.1.  Terminology

   This document uses the following terms:

   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).

   Metadata: Metadata in general is data about data.

   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



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       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 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).

   CDNI Metadata: Content Distribution Metadata with 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. prepositioned vs
   dynamic acquisition) and about where/how a CDN can acquire the
   content.  CDNI Metadata may also include content management
   information (e.g. request for deletion of Content from Surrogates)
   across interconnected CDNs.

   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).

   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.




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   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 independent of any End User
   requesting it.

   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
   independent of any End User requesting that content from 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.)

   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.

   Network Service Provider (NSP): Provides network-based connectivity/
   services to End Users.

   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.

   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. which may not require any direct interaction with
   the CDN, or CDNs, involved in the distribution and delivery of the
   content.

   Content Distribution Network (CDN) / Content Delivery Network (CDN):
   Network infrastructure in which the network elements cooperate at
   layers 4 through layer 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



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   System and a CDN control system.

   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.

   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
   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).

   Authoritative CDN: A CDN which has a direct relationship with a CSP
   for the distribution & delivery of that CSP's content by the
   authoritative CDN or by downstream CDNs of the authoritative CDN.

   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.

   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 (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).

   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.

   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 it can deliver the same content to a number of User
   Agents (and their End Users) avoiding the need for those requests to
   transit multiple times through the network core (i.e from the content
   origin to the surrogate).

   Request Routing System: The function within a CDN responsible for
   receiving a content request from a User Agent, obtaining and



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   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.

   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).

   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.

   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.

   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).

   Quality of Experience (QoE): As defined in Section 2.4 of [RFC6390]

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 Delivery Internetworking (CDI) working group which
      was closed in 2003.

   Note: Some of the terms used in this document are similar to terms
   used the above referenced documents.  When reading this document
   terms should be interpreted as having the definitions provided in
   Section 1.1.





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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 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
   need for interconnection of these CDNs, that 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.




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   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
   [I-D.ietf-cdni-use-cases].


3.  CDN Interconnection Model & 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 standardization.

   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
   [I-D.bertrand-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.




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   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.
      *  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.





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   o  CDNI Metadata distribution interface: This interface allows the
      Distribution system in interconnected CDNs to communicate to
      ensure CDNI Metadata can be exchanged across CDNs.  See
      Section 1.1 for 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 environments.  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.

   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 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
   very significantly reuse or leverage existing protocols; this is
   discussed further in Section 4.

   The interfaces that form the CDNI problem area are illustrated in
   Figure 1.























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     --------
    /        \
    |   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

   As illustrated in Figure 1, the acquisition of content between



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   interconnected CDNs is out of scope for CDNI, which deserves some
   additional explanation.  The consequence of such a decision is that
   the CDNI problem space described in this document is focussed on only
   defining the control plane for CDNI; and the CDNI data plane (i.e.
   the acquisition & 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
   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 pre-empt 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, 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], Atom Publishing Protocol
   [RFC5023], XMPP [RFC6120], for example) to realize the CDNI
   interfaces.







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4.1.  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 (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 ALTO [RFC5693]).

4.2.  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



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   protocol for the request/response element of the CDNI Metadata
   interface.

4.3.  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 SNMP,
   syslog, ftp (and secure variants), HTTP POST, etc.

4.4.  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.


5.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.


6.  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



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   more complex environment must be validated.

   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.

6.1.  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 and 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.

6.2.  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



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

6.3.  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.

6.4.  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.


7.  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.


8.  References

8.1.  Normative References

8.2.  Informative References

   [3GP-DASH]
              "Transparent end-to-end Packet-switched Streaming Service
              (PSS); Progressive Download and Dynamic Adaptive Streaming
              over HTTP (3GP-DASH)
              http://www.3gpp.org/ftp/Specs/html-info/26247.htm".

   [ALTO-Charter]



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              "IETF ALTO WG Charter
              (http://datatracker.ietf.org/wg/alto/charter/)".

   [ATIS]     "ATIS (http://www.atis.org/)".

   [ATIS-COD]
              "ATIS IIF: IPTV Content on Demand Service, January 2011 (h
              ttp://www.atis.org/iif/_Com/Docs/Task_Forces/ARCH/
              ATIS-0800042.pdf)".

   [CDI-Charter]
              "IETF CDI WG Charter
              (http://www.ietf.org/wg/concluded/cdi)".

   [CableLabs]
              "CableLabs (http://www.cablelabs.com/about/)".

   [CableLabs-Metadata]
              "CableLabs VoD Metadata Project Primer
              (http://www.cablelabs.com/projects/metadata/primer/)".

   [DECADE-Charter]
              "IETF DECADE WG Charter
              (http://datatracker.ietf.org/wg/decade/charter/)".

   [I-D.bertrand-cdni-experiments]
              Faucheur, F. and L. Peterson, "Content Distribution
              Network Interconnection (CDNI) Experiments",
              draft-bertrand-cdni-experiments-02 (work in progress),
              February 2012.

   [I-D.ietf-cdni-use-cases]
              Bertrand, G., Emile, S., Burbridge, T., Eardley, P., Ma,
              K., and G. Watson, "Use Cases for Content Delivery Network
              Interconnection", draft-ietf-cdni-use-cases-08 (work in
              progress), June 2012.

   [I-D.jenkins-alto-cdn-use-cases]
              Niven-Jenkins, B., Watson, G., Bitar, N., Medved, J., and
              S. Previdi, "Use Cases for ALTO within CDNs",
              draft-jenkins-alto-cdn-use-cases-03 (work in progress),
              June 2012.

   [MPEG-DASH]
              "Information technology - MPEG systems technologies - Part
              6: Dynamic adaptive streaming over HTTP (DASH), (DIS
              version), February 2011
              http://mpeg.chiariglione.org/



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              working_documents.htm#MPEG-B".

   [OIPF-Overview]
              "OIPF Release 2 Specification Volume 1 - Overview",
              September 2010.

   [P2PRG-CDNI]
              Davie, B. and F. Le Faucheur, "Interconnecting CDNs aka
              "Peering Peer-to-Peer"
              (http://www.ietf.org/proceedings/77/slides/P2PRG-2.pdf)",
              March 2010.

   [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.

   [RFC3568]  Barbir, A., Cain, B., Nair, R., and O. Spatscheck, "Known
              Content Network (CN) Request-Routing Mechanisms",
              RFC 3568, July 2003.

   [RFC3570]  Rzewski, P., Day, M., and D. Gilletti, "Content
              Internetworking (CDI) Scenarios", RFC 3570, July 2003.

   [RFC5023]  Gregorio, J. and B. de hOra, "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.




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   [SNIA-CDMI]
              "SNIA CDMI (http://www.snia.org/tech_activities/standards/
              curr_standards/cdmi)".

   [TAXONOMY]
              Pathan, A., "A Taxonomy and Survey of Content Delivery
              Networks
              (http://www.gridbus.org/reports/CDN-Taxonomy.pdf)", 2007.

   [Y.1910]   "ITU-T Recomendation Y.1910 "IPTV functional
              architecture"", September 2008.

   [Y.2019]   "ITU-T Recomendation Y.2019 "Content delivery functional
              architecture in NGN"", September 2010.


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.

A.1.  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, RTSP, 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



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      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 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, for example because:

   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.
   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 a 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



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   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.

   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.2.  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



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   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.

   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.3.  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



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   platforms.

   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 their syntax & 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.

A.4.  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 also, existing
   protocols can be reused or leveraged.  Those will be considered once
   the requirements for the Control interface have been refined.


Appendix B.  Additional Material

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





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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 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 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 & protocols (i.e. interfaces & 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



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      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.

B.2.  Relationship to relevant IETF Working Groups & IRTF Reserach
      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).  [I-D.jenkins-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.



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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 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.

   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 in-network storage service to
      application endpoint significantly exceeds the capacity/bandwidth
      from application endpoint to application endpoint (e.g. because of
      an end-user uplink bottleneck); and
   o  Where 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 does 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, 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



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   (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.

   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." and "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 RG at IETF 77.  The presentation can
   be found in [P2PRG-CDNI].





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Appendix C.  Additional Material

   Note to RFC Editor: This appendix is to be removed on publication as
   an RFC.

C.1.  Related standardization activites

   There are a number of other standards bodies and industry forums that
   are working in areas related to CDNs, and in some cases related to
   CDNI.  This section outlines any potential overlap with the work of
   the CDNI working group and any component that could potentially be
   reused to realize the CDNI interfaces.

   A number of standards bodies have produced specifications related to
   CDNs, for example:

   o  ETSI TISPAN (Telecommunications and Internet converged Services
      and Protocols for Advanced Networking) has a series of
      specifications focusing on CDNs.
   o  The Open IPTV Forum (OIPF) and ATIS IPTV Interoperability Forum
      (IIF) specify the architecture and the protocols of an IPTV
      solution.  Although OIPF and ATIS specifications include the
      interaction with a CDN, the CDN specifications are coupled with
      their IPTV specifications and do not cover interconnection of
      CDNs.
   o  ATIS Cloud Services Forum (CSF) has started investigating
      interconnection of CDNs.  The ATIS CSF focuses on defining use
      cases and requirements for such CDN interconnection, which are
      expected to be considered as input into the work of the CDNI
      working group.  At the time of writing this document, ATIS CSF is
      not specifying the corresponding protocols or interfaces and is
      expected to leverage the work of the IETF CDNI working group for
      those.
   o  CableLabs, SNIA and ITU have developed (or are working on)
      definitions for content related metadata and specifications for
      its distribution.  However, they do not include metadata specific
      to the distribution of content within a CDN or between
      interconnected CDNs.
   o  IETF CDI working group (now concluded) touched on the same problem
      space as the present document.  However, in accordance with its
      initial charter, the CDI working group did not define any
      protocols or interfaces to actually enable CDN Interconnection and
      at that time (2003) there was not enough industry interest and
      real life requirements to justify rechartering the working group
      to conduct the corresponding protocol work.

   Although some of the specifications describe multi-CDN cooperation or
   include reference points for interconnecting CDNs, none of them



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   specify in sufficient detail all the CDNI interfaces and CDNI
   Metadata representations required to enable even a base level of CDN
   Interconnection functionality to be implemented.

C.1.1.  IETF CDI Working Group (Concluded)

   The Content Distribution Internetworking (CDI) Working Group was
   formed in the IETF following a BoF in December 2000 and closed in mid
   2003.

   For convenience, here is an extract from the CDI working group
   charter [CDI-Charter]:

   "

   o  The goal of this working group is to define protocols to allow the
      interoperation of separately-administered content networks.
   o  A content network is an architecture of network elements, arranged
      for efficient delivery of digital content.  Such content includes,
      but is not limited to, web pages and images delivered via HTTP,
      and streaming or continuous media which are controlled by RTSP.
   o  The working group will first define requirements for three modes
      of content internetworking: interoperation of request-routing
      systems, interoperation of distribution systems, and
      interoperation of accounting systems.  These requirements are
      intended to lead to a follow-on effort to define protocols for
      interoperation of these systems.
   o  In its initial form, the working group is not chartered to deliver
      those protocols [...]

   "

   Thus, the CDI working group touched on the same problem space as the
   present document.

   The CDI working group published 3 Informational RFCs:

   o  RFC 3466 [RFC3466] - "A Model for Content Internetworking (CDI)".
   o  RFC 3568 [RFC3568] - "Known Content Network (CN) Request-Routing
      Mechanisms".
   o  RFC 3570 [RFC3570] - "Content Internetworking (CDI) Scenarios".

C.1.2.  3GPP

   3GPP was the first organization that released a specification related
   to adaptive streaming over HTTP. 3GPP Release 9 specification on
   adaptive HTTP streaming was published in March 2010, and there have
   been some bug fixes on this specification since the publication.  In



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   addition, 3GPP has produced an extended version for Release 10, which
   was published in 2011.  This release will include a number of
   clarifications, improvements and new features.

   [3GP-DASH] is defined as a general framework independent of the data
   encapsulation format.  It has support for fast initial startup and
   seeking, adaptive bitrate switching, re-use of HTTP origin and cache
   servers, re-use of existing media playout engines, on-demand, live
   and time-shifted delivery.  It specifies syntax and semantics of
   Media Presentation Description (MPD), format of segments and delivery
   protocol for segments.  It does not specify content provisioning,
   client behavior or transport of MPD.

   The content retrieved by a client using [3GP-DASH] adaptive streaming
   could be obtained from a CDN but this is not discussed or specified
   in the 3GPP specifications as it is transparent to [3GP-DASH]
   operations.  Similarly, it is expected that [3GP-DASH] can be used
   transparently from the CDNs as a delivery protocol (between the
   delivering CDN surrogate and the User Agent) in a CDN Interconnection
   environment. [3GP-DASH] could also be a candidate for content
   acquisition between CDNs in a CDN Interconnection environment.

C.1.3.  ISO MPEG

   Within ISO MPEG, the Dynamic Adaptive Streaming over HTTP (DASH) ad-
   hoc group adopted the 3GPP Release 9 [3GP-DASH] specification as a
   starting point and has made some improvements and extensions.
   Similar to 3GPP SA4, the MPEG DASH ad-hoc group has been working on
   standardizing the manifest file and the delivery format.
   Additionally, the MPEG DASH ad-hoc group has also been working on the
   use of MPEG-2 Transport Streams as a media format, conversion from/to
   existing file formats, common encryption, and so on.  The MPEG DASH
   specification could also be a candidate for delivery to the User
   Agent and for content acquisition between CDNs in a CDN
   Interconnection environment.  The Draft International Standard (DIS)
   version [MPEG-DASH] is currently publicly available since early
   February 2011.

   In the 95th MPEG meeting in January 2011, the DASH ad-hoc group
   decided to start a new evaluation experiment called "CDN-EE".  The
   goals are to understand the requirements for MPEG DASH to better
   support CDN-based delivery, and to provide a guidelines document for
   CDN operators to better support MPEG DASH streaming services.  The
   ongoing work is still very preliminary and does not currently target
   looking into CDN Interconnection use cases.






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C.1.4.  ATIS IIF

   ATIS ([ATIS]) IIF is the IPTV Interoperability Forum (within ATIS)
   that develops requirements, standards, and specifications for IPTV.

   ATIS IIF is developing the "IPTV Content on Demand (CoD) Service"
   specification.  This includes use of a CDN (referred to in ATIS IIF
   CoD as the "Content Distribution and Delivery Functions") for support
   of a Content on Demand (CoD) Service as part of a broader IPTV
   service.  However, this only covers the case of a managed IPTV
   service (in particular where the CDN is administered by the service
   provider) and does not cover the use, or interconnection, of multiple
   CDNs.

C.1.5.  CableLabs

   "Founded in 1988 by cable operating companies, Cable Television
   Laboratories, Inc. (CableLabs) is a non-profit research and
   development consortium that is dedicated to pursuing new cable
   telecommunications technologies and to helping its cable operator
   members integrate those technical advancements into their business
   objectives."  [CableLabs]

   CableLabs has defined specifications for CoD Content Metadata as part
   of its VOD Metadata project.

C.1.6.  ETSI MCD

   ETSI MCD (Media Content Distribution) is the ETSI technical committee
   "in charge of guiding and coordinating standardization work aiming at
   the successful overall development of multimedia systems (television
   and communication) responding to the present and future market
   requests on media content distribution".

   MCD created a specific work item on interconnection of heterogeneous
   CDNs ("CDN Interconnection, use cases and requirements") in March
   2010.  MCD very recently created a working group to progress this
   work item.  However, no protocol level work has yet started in MCD
   for CDN Interconnection.

C.1.7.  ETSI TISPAN

   ETSI TISPAN has published two sets of IPTV specifications, one of
   which is based on IMS.  In addition, TISPAN has published a CDN
   architecture supporting delivery of various content services such as
   time-shifted TV and VoD to TISPAN devices (UEs) or regular PCs.  The
   use cases allow for hierarchically and geographically distributed CDN
   scenarios, along with multi-CDN cooperation.  As a result, the



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   architecture contains reference points to support interconnection of
   other TISPAN CDNs.  The protocol definition phase for the
   corresponding CDN architecture was kicked-off at the end of 2010 as
   is still in progress.  In line with its long history of leveraging
   IETF protocols, ETSI could potentially leverage CDNI interfaces
   developed in the IETF for their related protocol level work on
   interconnections of CDNs.

C.1.8.  ITU-T

   SG13 is developing standards related to the support of IPTV services
   (i.e.. multimedia services such as television/VoD/audio/text/
   graphics/data delivered over IP-based managed networks).

   ITU-T Recommendation Y.1910 [Y.1910] provides the description of the
   IPTV functional architecture.  This architecture includes functions
   and interfaces for the distribution and delivery of content.  This
   architecture is aligned with the ATIS IIF architecture.

   Based upon ITU-T Rec. Y.1910, ITU-T Rec. Y.2019 [Y.2019] describes in
   more detail the content delivery functional architecture.  This
   architecture allows CDN Interconnection: some interfaces (such as D3,
   D4) at the control level allow relationships between different CDNs,
   in the same domain or in different domains.  Generic procedures are
   described, but the choice of the protocols is open.

C.1.9.  Open IPTV Forum (OIPF)

   The Open IPTV Forum has developed an end-to-end solution to allow any
   OIPF terminal to access enriched and personalized IPTV services
   either in a managed or a non-managed network[OIPF-Overview].  Some
   OIPF services (such as Network PVR) may be hosted in a CDN.

   To that end, the Open IPTV Forum specification is made of 5 parts:

   o  Media Formats including HTTP Adaptive Streaming
   o  Content Metadata
   o  Protocols
   o  Terminal (Declarative or Procedural Application Environment)
   o  Authentication, Content Protection and Service Protection

C.1.10.  TV-Anytime Forum

   Version 1 of the TV-Anytime Forum specifications were published as
   ETSI TS 102 822-1 through ETSI TS 102 822-7 "Broadcast and On-line
   Services: Search, select, and rightful use of content on personal
   storage systems ("TV-Anytime")".  It includes the specification of
   content metadata in XML schemas (ETSI TS 102 822-3) which define



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   technical parameters for the description of CoD and Live contents.
   The specification is referenced by DVB and OIPF.

   The TV-anytime Forum was closed in 2005.

C.1.11.  SNIA

   The Storage Networking Industry Association (SNIA) is an association
   of producers and consumers of storage networking products whose goal
   is to further storage networking technology and applications.

   SNIA has published the Cloud Data Management Interface (CDMI)
   standard ([SNIA-CDMI]).

   "The Cloud Data Management Interface defines the functional interface
   that applications will use to create, retrieve, update and delete
   data elements from the Cloud.  As part of this interface the client
   will be able to discover the capabilities of the cloud storage
   offering and use this interface to manage containers and the data
   that is placed in them.  In addition, metadata can be set on
   containers and their contained data elements through this interface."

C.1.12.  Summary of existing standardization work

   The following sections will summarize the existing work of the
   standard bodies listed earlier against the CDNI problem space.
   Appendix C.1.12.1 summarizes existing interfaces that could be
   leveraged for content acquisition between CDNs and Appendix C.1.12.2
   summarizes existing metadata specifications that may be applicable to
   CDNI.  To date we are not aware of any standardization activities in
   the areas of the remaining CDNI interfaces (CDNI Request Routing,
   CDNI Control and CDNI Logging).

C.1.12.1.  Content Acquisition across CDNs and Delivery to End User
           (Data plane)

   A number of standards bodies have completed work in the areas of
   content acquisition interface between a CSP and a CDN, as well as as
   on the delivery interface between the surrogate and the User Agent.
   Some of this work is summarized below.

   TISPAN, OIPF and ATIS have specified IPTV and/or Content on Demand
   (CoD) services, including the data plane aspects (typically different
   flavors of RTP/RTCP and HTTP) to obtain content and deliver it to
   User Agents.  For example, :
   o  The OIPF data plane includes both RTP and HTTP flavors (HTTP
      progressive download, HTTP Adaptive streaming [3GP-DASH]).




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   o  The ATIS IIF specification "IPTV Content on Demand (CoD) Service"
      [ATIS-COD] defines a reference point (C2) and the corresponding
      HTTP-based data plane protocol for content acquisition between an
      authoritative origin server and the CDN.
   While these protocols have not been explicitly specified for content
   acquisition across CDNs, they are suitable (in addition to others
   such as standard HTTP) for content acquisition between CDNs in a CDN
   Interconnection environment.  Therefore for the purpose of the CDNI
   working group there are already multiple existing data plane
   protocols that can be used for content acquisition across CDNs.

   Similarly, there are multiple existing standards (e.g. the OIPF data
   plane mentioned above, HTTP adaptive streaming [3GP-DASH]) or public
   specifications (e.g. vendor specific HTTP Adaptive streaming
   specifications) so that content delivery can be considered already
   solved (or at least sufficiently addressed in other forums).

   Thus, specification of the content acquisition interface between CDNs
   and the delivery interface between the surrogate and the User Agent
   are out of scope for the CDNI working group.  The CDNI working group
   may only concern itself with the negotiation/selection aspects of the
   acquisition protocol to be used in a CDN interonnect scenario.

C.1.12.2.  CDNI Metadata

   CableLabs, ITU, OIPF and TV-Anytime have work items dedicated to the
   specification of content metadata:

   o  CableLabs has defined specifications for CoD Content Metadata as
      part of its VOD Metadata project.  "The VOD Metadata project is a
      cable television industry and cross-industry-wide effort to
      specify the metadata and interfaces for distribution of video-on-
      demand (VOD) material from multiple content providers to cable
      operators."  [CableLabs-Metadata].  However, while the CableLabs
      work specifies an interface between a content provider and a
      service provider running a CDN, it does not include an interface
      that could be used between CDNs.
   o  ITU Study Group 16 has started work on a number of draft
      Recommendations (H.IPTV-CPMD, H.IPTV-CPMD, HSTP.IPTV-CMA,
      HSTP.IPTV-UMCI) specifying metadata for content distribution in
      IPTV services.
   o  An Open IPTV Terminal receives the technical description of the
      content distribution from the OIPF IPTV platform before receiving
      any content.  The Content distribution metadata is sent in the
      format of a TV-Anytime XSD including tags to describes the
      location and program type (on demand or Live) as well as
      describing the time availability of the on demand and live
      content.



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   However the specifications outlined above do not include metadata
   specific to the distribution of content within a CDN or between
   interconnected CDNs, for example geo-blocking information,
   availability windows, access control mechanisms to be enforced by the
   surrogate, how to map an incoming content request to a file on the
   origin server or acquire it from the upstream CDN etc.

   The CDMI standard ([SNIA-CDMI]) from SNIA defines metadata that can
   be associated with data that is stored by a cloud storage provider.
   While the metadata currently defined do not match the needs of CDN
   Interconnection, it is worth considering CDMI as one of the existing
   pieces of work that may potentially be leveraged for the CDNI
   Metadata interface (e.g by extending the CDMI metadata to address
   more specific CDNI needs).

C.2.  Related Research Projects

C.2.1.  OCEAN

   OCEAN (http://www.ict-ocean.eu/) is an EU funded research project
   that started in February 2010 for 3 years.  Some of its objectives
   are relevant to CDNI.  It aims, among other things, at designing a
   new architectural framework for audiovisual content delivery over the
   Internet, defining public interfaces between its major building
   blocks in order to foster multi-vendor solutions and interconnection
   between Content Networks (the term "Content Networks" corresponds
   here to the definition introduced in [RFC3466], which encompasses
   CDNs).

   OCEAN has not yet published any open specifications, nor common best
   practices, defining how to achieve such CDN interconnection.

C.2.2.  Eurescom P1955

   Eurescom P1955 was a 2010 research project involving a four European
   Network operators, which studied the interests and feasibility of
   interconnecting CDNs by firstly elaborating the main service models
   around CDN interconnection, as well as analyzing an adequate CDN
   interconnection technical architecture and framework, and finally by
   providing recommendations for telcos to implement CDN
   interconnection.  The Eurescom P1955 project ended in July 2010.

   The authors are not aware of material discussing CDN interconnection
   protocols or interfaces made publicly available as a deliverable of
   this project.






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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
   40 Sylvan Road
   Waltham, MA  02145
   USA

   Email: nabil.bitar@verizon.com























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