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Versions: 00 01 02 03 04 05 RFC 6983

CDNI                                                  R. van Brandenburg
Internet-Draft                                           O. van Deventer
Intended status: Informational                                       TNO
Expires: August 27, 2012                               February 24, 2012


        Models for adaptive-streaming-aware CDN Interconnection
                     draft-brandenburg-cdni-has-00

Abstract

   This documents presents thougths on the potential impact of
   supporting HTTP Adaptive Streaming technologies in CDN
   Interconnection scenarios.  Our intent is to spur discussion on how
   the different CDNI interfaces should deal with content delivered
   using adaptive streaming technologies.

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."

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

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  HTTP Adaptive Streaming aspects relevant to CDNI . . . . . . .  4
     2.1.  Segmentation versus Fragmentation  . . . . . . . . . . . .  4
     2.2.  Addressing chunks  . . . . . . . . . . . . . . . . . . . .  5
       2.2.1.  Full Locator . . . . . . . . . . . . . . . . . . . . .  6
       2.2.2.  Relative Locator . . . . . . . . . . . . . . . . . . .  7
       2.2.3.  Chunk Request Routing  . . . . . . . . . . . . . . . .  7
   3.  Impact of HAS on CDNI  . . . . . . . . . . . . . . . . . . . .  8
     3.1.  General  . . . . . . . . . . . . . . . . . . . . . . . . .  8
       3.1.1.  On the definition of a Content Item in CDNI  . . . . .  8
       3.1.2.  General CDNI-HAS Requirements  . . . . . . . . . . . . 10
     3.2.  Impact on Request Routing Interface  . . . . . . . . . . . 10
       3.2.1.  Dealing with manifest files  . . . . . . . . . . . . . 10
       3.2.2.  HAS Request Routing  . . . . . . . . . . . . . . . . . 11
       3.2.3.  Dividing content over multiple nodes . . . . . . . . . 12
       3.2.4.  HAS Requirements for the CDNI Request Routing
               Interface  . . . . . . . . . . . . . . . . . . . . . . 12
     3.3.  Impact on Metadata Interface . . . . . . . . . . . . . . . 12
       3.3.1.  HAS-specific Metadata  . . . . . . . . . . . . . . . . 12
       3.3.2.  HAS Requirements for the CDNI Metadata Interface . . . 13
     3.4.  Impact on Logging Interface  . . . . . . . . . . . . . . . 13
       3.4.1.  Log processing . . . . . . . . . . . . . . . . . . . . 13
       3.4.2.  HAS Requirements for the CDNI Logging Interface  . . . 14
     3.5.  Impact on Control Interface  . . . . . . . . . . . . . . . 14
       3.5.1.  HAS Requirements for the CDNI Control Interface  . . . 14
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

















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1.  Introduction

   HTTP Adaptive Streaming (HAS) is an umbrella term for various HTTP-
   based streaming technologies that allow a client to adaptively switch
   between multiple bitrates depending on current network conditions.  A
   defining aspect of HAS is that, since it is based on HTTP, it is a
   session-less pull-based mechanism, with a client actively requesting
   content segments, instead of the content being pushed to the client
   by a server.  Due to this session-less nature, media servers
   delivering content using HAS often show different characteristics
   when compared with media servers delivering content using traditional
   streaming methods such as RTP/RTSP, RTMP and MMS.  This document
   presents a discussion on what the impact of these different
   characteristics is to the CDNI interfaces.  The scope of this
   document is explicitely not to define solutions, but merely to
   identify different methods of handling HAS in a CDN and the potential
   problems when using HAS in a CDNI context.  The issues identified in
   this document may be used as input for defining HAS-specific
   requirements for the CDNI interfaces.

1.1.  Terminology

   This document uses the terminology defined in
   [I-D.ietf-cdni-problem-statement].

   In addition, the following terms are used throughout this document:

   Content Item: A uniquely adressable content element in a CDN.  A
   content item is defined by the fact that it has its own Content
   Metadata associated with it.  It is the object of a request routing
   operation in a CDN.  An example of a Content Item is a video file/
   stream, an audio file/stream or an image file.  For a discussion on
   what may constitute a Content Item with regards to HAS, see section
   3.1.1.

   Chunk: A fixed length element that is the result of a segmentation or
   fragmentation operation being performed on a single encoding of the
   Original Content.  A chunk is independently, and uniquely,
   addressable.  Depending on the way a Chunk is stored, it may also be
   referred to as a Segment or Fragment.

   Fragment: A specific form of chunk (see section 2.1).  A fragment is
   stored as part of a larger file that includes all chunks that are
   part of the Chunk Collection.

   Segment: A specific form of chunk (see section 2.1).  A segment is
   stored as a single file from a file system perspective.




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   Original Content: Unchunked content that is the basis for a
   segmentation of fragmentation operation.  Based on Original Content,
   multiple alternative encodings, resolutions or bitrates may be
   derived, each of which may be fragmented or segmented.

   Chunk Collection: The set of all chunks that are the result of a
   single segmentation or fragmentation operation being performed on a
   single encoding of the Original Content.  A Chunk Collection is
   described in a manifest file.

   Content Collection: The set of all Chunk Collections that are derived
   from the same Original Content.  A Content Collection may consist of
   multiple Chunk Collections, each being a single encoding, or variant,
   of the Original Content.  A Content Collection may be described by
   one or more manifest files.

   Manifest File: A manifest file, also referred to as Media
   Presentation Description (MPD) file, is a file that list the way the
   content has been chunked and where the various chunks are located (in
   the case of segments) or how they can be addressed (in the case of
   fragments).


2.  HTTP Adaptive Streaming aspects relevant to CDNI

   In the last couple of years, a wide variety of HAS-like protocols
   have emerged.  Among them are proprietary solutions such as Apple's
   HTTP Live Streaming (HLS), Microsoft's Smooth Streaming (MSS) and
   Adobe's HTTP Dynamic Streaming (HDS), and various standardized
   solutions such as 3GPP AHS (AHS) and MPEG DASH (DASH).  While all of
   these technologies share a common set of features, each has its own
   defining elements.  This chapter will look at some of the differences
   between these technologies and how these differences might be
   relevant to CDNI.  In particular, section 2.1 will describe the
   various methods to store HAS content and section 2.2 will list three
   methods that are used to address HAS content in a CDN.

2.1.  Segmentation versus Fragmentation

   All HAS implementations are based around a concept referred to as
   chunking: the concept of having a server split content up in numerous
   fixed length chunks, which are independently decodable.  By
   sequentially requesting and receiving chunks, a client can recreate
   and play out the content.  An advantage of this mechanism is that it
   allows a client to seamlessly switch between different encodings of
   the same Original Content.  Before requesting a particular chunk, a
   client can choose between mulitple alternatives of the same chunk,
   irrespective of the encoding of the chuncks it has requested earlier.



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   NOTE: The set of all chunks belonging to a single encoding, and thus
   the result of a single chunking operation, will from now on be
   referred to as a Chunk Collection.  The set of all encodings of the
   same Original Content will be referred to as a Content Collection.  A
   Content Collection can therefore consist of multiple Chunk
   Collections.

   While every HAS implementation uses some form of chunking, not all
   implementations store the resulting chunks in the same way.  In
   general, there are two distinct methods of performing chunking and
   storing the results: segmentation and fragmentation.

   -  With segmentation, which is for example mandatory in all versions
      of HLS prior to version 7, the chunks, in this case also referred
      to as segments, are stored completely independent from each other,
      with each segment being stored as a seperate file from a file
      system perspective.  This means that each segment has its own
      unique URL with which it can be retrieved.

   -  With fragmentation (or virtual segmentation), which is for example
      used in Microsoft's Smooth Streaming, all chunks, or fragments,
      belonging to the same Chunk Collection are stored together, as
      part of a single file.  While there are a number of container
      formats which allow for storing this type chunked content,
      Fragmented MP4 is most commonly used.  With fragmentation, a
      specific chunk is adressable by subfixing the common file URL with
      an identifier uniquely identifying the chunk one is interested in,
      either by timestamp, by byterange, or in some other way.

   While one can argue about the merits of each of these two different
   methods of handling chunks, both have their advantages and drawbacks
   in a CDN environment.  For example, fragmentation is often regarded
   as a method that introduces less overhead, both from a storage and
   processing perspective.  Segmentation on the other hand, is regarded
   as being more flexible and efficient with regards to caching.  In
   practice, current HAS implementations increasingly support both
   methods.

2.2.  Addressing chunks

   In order for a client to request chunks, either in the form of
   segments or in the form of fragments, it needs to know how the
   content has been chunked and where to find the chunks.  For this
   purpose, most HAS protocols use a concept that is often referred to
   as a manifest file (also known as Media Presentation Description, or
   MPD): a file that lists the way the content has been chunked and
   where the various chunks are located (in the case of segments) or how
   they can be addressed (in the case of fragments).  A manifest file,



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   or set of manifest files, may also identify the different encodings,
   and thus Chunk Collections, the content is available in.

   In general, a HAS client will first request and receive a manifest
   file, and then, after parsing the information in the manifest file,
   proceed with sequentially requesting the chunks listed in the
   manifest file.  Each HAS implementation has its own manifest file
   format and even within a particular format there are different
   methods available to specify the location of a chunk.

   Of course managing the location of files is a core aspect of every
   CDN, and each CDN will have its own method of doing so.  Some CDNs
   may be purely cache-based, with no higher-level knowledge of where
   each file resides at each instant in time.  Other CDNs may have
   dedicated management nodes which, at each instant in time, do know at
   which servers each file resides.  The CDNI interfaces designed in the
   CDNI WG will probably need to be agnostic to these kinds of CDN-
   internal architecture decisions.  In the case of HAS there is a
   strict relationship between the location of the content in the CDN
   (in this case chunks) and the content itself (the locations specified
   in the manifest file).  It is therefore useful to have an
   understanding of the different methods in use in CDNs today for
   specifying chunk locations in manifest files.  The different methods
   for doing so are described in sections 2.2.1 to 2.2.3.

   Although these sections are especially relevant for segmented
   content, due to its inherent distributed nature, the discussed
   methods are also applicable to fragmented content.  Furthermore, it
   should be noted that the methods detailed below for specifying
   locations of content items in manifest files do not only relate to
   temporally segmented content (e.g. segments and fragments), but are
   also relevant in situations where content is made available in
   multiple qualities, encodings, or variants.  In this case the content
   consists of multiple chunk collections, which may be described by
   either a single manifest file or multiple interrelated manifest
   files.  In the latter case, there may be a high-level manifest file
   describing the various available bitrates, with URLs pointing to
   seperate manifest files describing the details of each specific
   bitrate.  For specifying the locations of the other manifest files,
   the same methods apply that are used for specifying chunk locations.

2.2.1.  Full Locator

   One method for specifying locations of chunks (or other manifest
   files) in a manifest file is through the use of a Full Locator.  A
   Full Locator takes the form of an URL and is defined by the fact that
   it directly points to the specific chunk on the actual the server
   that is expected to deliver the requested chunk to the client.



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   An example of a Full Locator is the following:

      http://deliverynode.server.cdn.com/content_1/segments/
      segment1_1.ts

   As can be seen from this example URL, the URL includes both the
   identifier of the requested segment (in this case segment1_1.ts), as
   well as the server that is expected to deliver the segment (in this
   case deliverynode.server.cdn.com).  With this, the client has enough
   information to directly request the specific segment from the
   specified delivery node.

2.2.2.  Relative Locator

   Another method for specifying chunk locations in a manifest file is
   through the use of Relative Locator.  A Relative Locator is a pointer
   that is relative to the location where the manifest file has been
   acquired from.  In most cases a Relative Locator will take the form
   of a string that has to be appended to the location of the manifest
   file to get the location of a specific chunk.  This means that in the
   case a manifest with a Relative Locator is used, all chunks will be
   delivered by the same delivery node that delivered the manifest file.
   A Relative Locator will therefore not include a hostname.

   For example, in the case a manifest file has been requested (and
   received) from
   http://deliverynode.server.cdn.com/content_1/manifest.xml, a Relative
   Locator pointing to a specific segment referenced in the manifest
   might be:

      segments/segment1_1.ts

   Which means that the client should take the location of the manifest
   file and append the Relative Locator.  In this case, the segment
   would then be requested from
   http://deliverynode.server.cdn.com/content_1/segments/segment1_1.ts

2.2.3.  Chunk Request Routing

   A final method for specifying chunk locations in a manifest file is
   through the use of request routing.  In this case, chunks are handled
   by the request routing system of a CDN just as if they were 'normal'
   content items.  A chunk request comes in at a central request routing
   node and is handled just as if it were a regular content request,
   which might include looking up the delivery node best suited for
   delivering the requested chunk to the particular user and sending an
   HTTP redirect to the user with the URL pointing to the requested
   chunk on the specified delivery node.



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   An example of an URL pointing to a redirection mechanism might look
   as follows:

      http://requestrouting.cdn.com/
      content_request?content=content_1&segment=segment1_1.ts

   As can be seen from this example URL, the URL includes a pointer to a
   general CDN request routing function and includes some arguments
   identifying the requested segment.


3.  Impact of HAS on CDNI

   In the previous chapter, some of the unique properties of HAS have
   been discussed.  Furthermore, some of the CDN-specific design
   decision with regards to addressing chunks have been detailed.  In
   this chapter, the impact of supporting HAS in CDNI will be discussed.
   The scope of this chapter is explicitely not to define solutions, but
   merely to identify potential problems and issues that need to be
   agreed on.  For this purpose, each subsection will pose a number of
   open questions that will need to be answered by the CDNI WG.  At a
   later stage, the answers to these questions may be used to solicit
   HAS-related requirements for the CDNI Interfaces.

   The chapter is divided into three subsections.  The first subsection,
   3.1, will discuss the impact supporting HAS has on the general CDNI
   architecture, use cases and requirements.  The other four
   subsections, 3.2 to 3.5, will discuss the impact of HAS on each of
   the four CDNI Interfaces.

3.1.  General

   This section will discuss the impact supporting HTTP Adaptive
   Streaming has on the general CDNI architecture, use cases and
   requirements.

3.1.1.  On the definition of a Content Item in CDNI

   [I-D.ietf-cdni-problem-statement] defines content as

      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).

   This very broad definition of content is useful for generalizing the
   CDNI interfaces in a way that allows them to be agnostic to the type
   of content that is delivered.  However, what a Content Item in a CDN



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   constitutes may become relevant in the context of HAS if one
   considers a Content Item to be the element with which Content
   Metadata is associated, and the element that is the object of a
   CDN(I) request routing operation.

   An example of a Content Item in the general sense is a video file or
   stream, such as a TV show or movie, or an audio file, such as an MP3.
   In a simple case, a single MP3 is a single Content Item.  In a more
   complex case, a particular piece of content is made available in
   multiple resolutions, languages or qualities.  A video item, for
   example, might be made available in three different resolutions.  In
   these cases, it depends on the datamodel of a particular CDN (or a
   particular Content Provider) how it defines a Content Item.  In some
   CDNs, all three video files might be seen as seperate Content Items,
   each with their own set of Content Metadata.  In other CDNs, the
   three alternative encodings of the same content are seen as a single
   Content Item, with a single set of Content Metadata describing that
   the content consists of three different versions.  The CDNI
   Interfaces defined in the CDNI WG are affected by these kinds
   differences in the ways different CDNs work and might need to be
   agnostic to these kinds of CDN-internal (or even Content Provider-
   related) decisions.

   For content delivered using HAS, there is an even wider variety in
   the way different CDNs might interpret the definition of a Content
   Item.  For example, CDNs using the Relative Locator method (see
   section 2.2.2) in their manifest files, might define all chunks that
   are part of the same Content Collection, and therefore referenced in
   the same (set of) manifest file(s), as a single Content Item for the
   purposes of Content Metadata and request routing.  Other CDNs might
   define all chunks related to a single encoding of a particular video
   item, and thus part of the same Chunk Collection, as a single Content
   Item, thereby having multiple inter-related Content Items which are
   part of the same 'parent' Content Item.  Yet another group of CDNs,
   especially those using the Chunk Request Routing method (see Section
   2.2.3), might define every individual chunk as a seperate Content
   Item, with a seperate set of metadata describing each chunk.

   In order for the CDNI WG to realise a standardized method of dealing
   with metadata, logging and request routing, it will be important to
   first have a common understanding of the term Content Item, and what
   it constitutes, especially with regard to HAS.  One option would be
   to not impose a specific model, but allow the CDNI interfaces to
   support all the different definitions of Content Item (i.e. from
   considering each chunk to be a Content Item to considering all chunks
   originating from the same Original Content, and thus part of the same
   Content Collection, to be a single content item).




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   o  Should the CDNI Interfaces be agnostic to the definition of a
      Content Item in a particular CDN?

   And if this is not the case, then

   o  What constitutes a Content Item for the purposes of associating
      metadata and request routing?

   o  How does the definition of a Content Item relate to Chunks, Chunk
      Collections and Content Collection?

   If the WG decides to not impose a specific definition of what
   constitutes a Content Item, it is for further study whether it is
   required for all parties involved in the delivery of a single video
   item, CSP, uCDN and dCDN, to use the same definition.  For example,
   is it possible for the uCDN to define a complete Content Collection
   as a single Content Item, but for the dCDN which delivers the actual
   content to see each chunk as a seperate Content Item and handle the
   metadata accordingly?

   o  Is it necessary for all CDNs involved in the delivery of a single
      video item to use the same definition of a Content Item (e.g. can
      the uCDN define a Content Collection as a Content Item and the
      dCDN define a chunk as a Content Item)?

3.1.2.  General CDNI-HAS Requirements

   This section is a placeholder for HAS-specific CDNI requirements that
   are not related to a specific CDNI interface.

3.2.  Impact on Request Routing Interface

   This section will discuss the impact supporting HTTP Adaptive
   Streaming has on the CDNI Request Routing Interface.

3.2.1.  Dealing with manifest files

   In section 2.2, three different methods for identifying and
   addressing chunks from within a manifest file were described: Full
   Locators, Relative Locators and Chunk Request Routing.  Of course not
   every current CDN will use and/or support all three methods.  Some
   CDNs may only support one of the three methods, while others may
   support two or all three.

   The question is whether all CDNs involved in the delivery of a single
   video item need to support the same method.  Is it for example
   possible for a dCDN to use Chunck Request Routing while the uCDN uses
   Full Locators?  This question boils down to the more fundamental



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   question of who manages manifest file.  Should a dCDN be allowed to
   change a manifest file?  Or even create a new one?

   o  Should the CDNI Interfaces be agnostic to the way chunks are
      identified in the manifest file and requested by the client?

   o  Should it be possible for a uCDN and dCDN to use two different
      methods of addressing chunks in manifest files?

   And, related to this

   o  Should a dCDN be able to adapt a manifest file (i.e. is a manifest
      file part of the content, and therefore by definition not
      adaptable, or is it part of the delivery method) ?

   If the CDNI WG decides that the anwer to these questions is negative,
   this will probably mean that the only supported method for Chunk
   Adressing is using Relative Locators.  For both Full Locators as well
   as Chunk Request Routing, it is necessary for the delivering CDN to
   change the URLs specified in the manifest file.

3.2.2.  HAS Request Routing

   One of the essential questions relating to HAS and request routing is
   whether CDNI request routing is handled on a per chunk level, a per
   Content Collection level, or somewhere in between.  This question is
   tightly related to the definition of a Content Item, discussed in
   section 3.1.1.  If a Content Item is the object of request routing,
   then it depends on the definition of a Content Item what type of
   content element is being request routed.

   o  Should the CDNI Interfaces specify what element of a HAS stream is
      being request routed (i.e. should the CDNI interfaces support per-
      chunk request routing) ?

   While having a seperate request routing operation for every chunk
   will probably not be very efficient, only allowing for entire Content
   Collections to be request routed is very limiting.  For example, it
   might be efficient for a dCDN targeted at mobile devices to only host
   (and thus be able to deliver) the lower resolution encodings of a
   given video item.  In this case it probably wouldn't make sense to
   force the mobile CDN to host all resolutions (including the very high
   ones with multi-channel audio) that are hosted by the uCDN since
   there will be no clients accessing the high resolution content
   through the mobile CDN.






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   o  Should it be possible for a dCDN to host (and deliver) only a
      subset of all the chunks, or chunk collections, of a given Content
      Collection?

3.2.3.  Dividing content over multiple nodes

   An aspect that is related to the issues discussed in sections 3.2.1
   and 3.2.2, is that of dividing content over multiple delivery nodes.
   In non-cache-based CDNs, where the location of content on delivery
   nodes is managed by a centralized process and where content is often
   pre-positioned, different Chunk Collections belonging to the same
   Content Collection, or even different chunks belonging to the same
   Chunk Collection, may be distributed over different delivery nodes.
   For example, the most popular resolutions of a particular Content
   Collection may be hosted on more delivery nodes than the less popular
   resolutions.  In order to allow for this kind of internal CDN
   optimization it is necessary that the dCDN is able adapt the manifest
   file.

   o  Should it be possible for a dCDN to distribute the chunks, or
      Chunk Collections, constituting a given Content Collection over
      its delivery nodes?

3.2.4.  HAS Requirements for the CDNI Request Routing Interface

   This section is a placeholder for HAS-specific requirements for the
   CDNI Request Routing interface.

3.3.  Impact on Metadata Interface

   This section will discuss the impact supporting HTTP Adaptive
   Streaming has on the CDNI Metadata Interface.

3.3.1.  HAS-specific Metadata

   In section 3.1.1, the impact of HAS on the definition of a Content
   Item, and what constitutes a Content Item was discussed.  More
   specifically, it was discussed how different CDNs might see chunks or
   chunk collections as Content Items or as parts of Content Items.
   This question also has an effect on the way the CDNI Metadata
   Interface.  If one defines a Content Item as the CDN element with
   which Content Metadata is associated, this raises the question how
   Content Metadata is associated with HAS content.  For example, is
   there specific metadata element associated with each chunk, with each
   chunk collection, with each content collection, or is there a
   specific form of metadata for HAS content?





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   o  Is Content Metadata associated with Content Collections, Chunk
      Collections or chunks?

   o  Is it necessary to extend the CDNI Metadata model with HAS-
      specific extensions?

3.3.2.  HAS Requirements for the CDNI Metadata Interface

   This section is a placeholder for HAS-specific requirements for the
   CDNI Metadata interface.

3.4.  Impact on Logging Interface

   This section will discuss the impact supporting HTTP Adaptive
   Streaming has on the CDNI Logging Interface.

3.4.1.  Log processing

   One aspect of using HAS in a CDN context that has been getting a lot
   of attention is logging.  In contrast to other streaming solutions
   which are either session-based (e.g.  RTP) or using a single file
   (e.g.  Progressive Download), the chunked nature of HAS means that
   regular logging methods that simply log each content request will
   generate extremely large log files with a seperate entry for each
   chunk being accessed.  Apart from the large file size of these log
   files, a further problem is that due to the distributed nature of
   these log entries it can be difficult to trace them back to a
   specific number of clients or users, which makes reporting difficult.

   For this reason, some CDNs use dedicated log processing software
   which accumulates, processes and aggregates log files.  This log
   processing software is a further element where different CDNs might
   have different approaches.  For example, some CDNs might do the log
   processing at a low-level, such as real-time in the delivery nodes.
   Other CDNs might process the log files in batches at a centralized
   location, such as once every hour or every day.

   For the CDNI Logging interface, it will be necessary to realise a
   common understanding on what type of logging information is passed
   between the uCDn and the dCDN in the case a HAS-like protocol is used
   for delivery.  Ideally, this interface is agnostic to the CDN-
   internal method of log processing.  However, this might not be
   possible.  For example, it can be argued that for transparency
   reasons, it is necessary for the dCDN to communicate the raw log
   files back to the uCDN.  On the other hand, this creates a very large
   overhead in the inter-CDN communication, with log files for popular
   content possibly exceeding the file size of the content itself.
   Another method would be to require the dCDN to aggregate the log



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   files before reporting back to the uCDN, however this would require
   the dCDN to have specific log processing software.

   o  Should the CDNI Logging Interface define a specific log-file
      format to be used for HAS content?

3.4.2.  HAS Requirements for the CDNI Logging Interface

   This section is a placeholder for HAS-specific requirements for the
   CDNI Logging interface.

3.5.  Impact on Control Interface

   This section will discuss the impact supporting HTTP Adaptive
   Streaming has on the CDNI Control Interface.

   NOTE: At this point the impact of HAS on the CDNI Control Interface
   has not yet been determined.

3.5.1.  HAS Requirements for the CDNI Control Interface

   This section is a placeholder for HAS-specific requirements for the
   CDNI Control interface.


4.  IANA Considerations

   This document makes no request of IANA.

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


5.  Security Considerations

   TBD.


6.  References

6.1.  Normative References

   [I-D.ietf-cdni-problem-statement]
              Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
              Distribution Network Interconnection (CDNI) Problem
              Statement, draft-ietf-cdni-problem-statement-03",
              January 2012.




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   [I-D.ietf-cdni-use-cases]
              Bertrand, G., Ed., Stephan, E., Watson, G., Burbridge, T.,
              Eardley, P., and K. Ma, "Use Cases for Content Delivery
              Network Interconnection, draft-ietf-cdni-use-cases-03",
              January 2012.

6.2.  Informative References

   [Anchor]   "".


Authors' Addresses

   Ray van Brandenburg
   TNO
   Brassersplein 2
   Delft  2612CT
   the Netherlands

   Phone: +31-88-866-7000
   Email: ray.vanbrandenburg@tno.nl


   M. Oskar van Deventer
   TNO
   Brassersplein 2
   Delft  2612CT
   the Netherlands

   Phone: +31-88-866-7000
   Email: oskar.vandeventer@tno.nl




















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