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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: November 23, 2012                                F. Le Faucheur
                                                                K. Leung
                                                           Cisco Systems
                                                            May 22, 2012


        Models for adaptive-streaming-aware CDN Interconnection
                     draft-brandenburg-cdni-has-01

Abstract

   This documents presents thoughts 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 could, and should, deal with content
   delivered using adaptive streaming technologies and to facilitate
   working group decisions.

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 November 23, 2012.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  HTTP Adaptive Streaming aspects relevant to CDNI . . . . . . .  5
     2.1.  Segmentation versus Fragmentation  . . . . . . . . . . . .  5
     2.2.  Addressing chunks  . . . . . . . . . . . . . . . . . . . .  6
       2.2.1.  Relative URLs  . . . . . . . . . . . . . . . . . . . .  7
       2.2.2.  Absolute URLs with Redirection . . . . . . . . . . . .  8
       2.2.3.  Absolute URL without Redirection . . . . . . . . . . .  9
   3.  Possible HAS Optimizations . . . . . . . . . . . . . . . . . . 10
     3.1.  File Management and Content Collections  . . . . . . . . . 10
       3.1.1.  Option 1.1: No HAS awareness . . . . . . . . . . . . . 11
       3.1.2.  Option 1.2: Allow single file storage of
               fragmented content . . . . . . . . . . . . . . . . . . 11
     3.2.  Content Acquisition of Content Collections . . . . . . . . 12
       3.2.1.  Option 2.1: No HAS awareness . . . . . . . . . . . . . 12
       3.2.2.  Option 2.2: Allow single file acquisition of
               fragmented content . . . . . . . . . . . . . . . . . . 13
     3.3.  Request Routing of HAS content . . . . . . . . . . . . . . 13
       3.3.1.  Option 3.1: No HAS awareness . . . . . . . . . . . . . 14
       3.3.2.  Option 3.2: Manifest File rewriting by uCDN  . . . . . 16
       3.3.3.  Option 3.3: Two-step Manifest File rewriting . . . . . 17
     3.4.  Logging  . . . . . . . . . . . . . . . . . . . . . . . . . 18
       3.4.1.  HAS Considerations for CDNI Logging  . . . . . . . . . 18
       3.4.2.  Candidate Approaches . . . . . . . . . . . . . . . . . 19
         3.4.2.1.  Option 4.1: "Do-Nothing" Approach  . . . . . . . . 19
         3.4.2.2.  Option 4.2: "CDNI Metadata Content Collection
                   ID" Approach . . . . . . . . . . . . . . . . . . . 20
         3.4.2.3.  Option 4.3: "CDNI Metadata Content Collection
                   ID With dCDN Summarization" Approach . . . . . . . 21
         3.4.2.4.  Option 4.4: "CDNI Logging Interface
                   Compression" Approach  . . . . . . . . . . . . . . 22
         3.4.2.5.  Option 4.5: "Full HAS awareness" Approach  . . . . 23
     3.5.  URL Signing  . . . . . . . . . . . . . . . . . . . . . . . 24
       3.5.1.  URL Signing in CDNI  . . . . . . . . . . . . . . . . . 25
       3.5.2.  Option 5.1: No HAS awareness . . . . . . . . . . . . . 26
       3.5.3.  Option 5.2: HAS-awareness with Authorization Token . . 27
       3.5.4.  Option 5.3: HAS-awareness with Session Based
               Encryption . . . . . . . . . . . . . . . . . . . . . . 28
     3.6.  Content Purge  . . . . . . . . . . . . . . . . . . . . . . 28
       3.6.1.  Option 6.1: No HAS awareness . . . . . . . . . . . . . 29



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       3.6.2.  Option 6.2: Purge Identifiers  . . . . . . . . . . . . 29
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 30
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 30
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 30
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 31
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31












































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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
   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 pull-based 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 and what HAS-specific optimizations may be
   required or may be desirable.  The scope of this document in its
   current form is explicitly not to propose any specific solution, but
   merely to present the available options so that the WG can make an
   informed decision on which way to go.

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 addressable 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.

   Chunk: a fixed length element that is the result of a segmentation or
   fragmentation operation and that is independently addressable.

   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.

   Original Content: Not-chunked content that is the basis for a
   segmentation of fragmentation operation.  Based on Original Content,
   multiple alternative representations (using different encoding
   methods, supporting different resolutions and/or targeting different
   bitrates) may be derived, each of which may be fragmented or
   segmented.



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   Chunk Collection: The set of all chunks that are the result of a
   single segmentation or fragmentation operation being performed on a
   single representation 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 corresponding to a single
   representation 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 (possibly for multiple encodings) 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 (HSS) and
   Adobe's HTTP Dynamic Streaming (HDS), and various standardized
   solutions such as 3GPP Adaptive HTTP Streaming (AHS) and MPEG Dynamic
   Adaptive Streaming over HTTP (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 common characteristics and some
   of the differences between these technologies and how those 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 duration 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 at chunk boundaries.  Before requesting a
   particular chunk, a client can choose between multiple alternative
   encodings of the same chunk, irrespective of the encoding of the
   chunks it has requested earlier.

   While every HAS implementation uses some form of chunking, not all
   implementations store the resulting chunks in the same way.  In



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   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 Apple's 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 separate 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 addressable 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 easier to cache.  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); i.e. 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,
   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.



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   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 representations (e.g., in different qualities, encoding
   methods, resolutions and/or bitrates).  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
   separate 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.  Relative URLs

   One method for specifying chunk locations in a Manifest File is
   through the use of relative URLs.  A relative URL is a URL that does
   not include the HOST part of a URL but only includes (part of) the
   PATH part of a URL.  In practice, a relative URL is used by the
   client as being relative to the location where the Manifest File has
   been acquired from.  In these cases a relative URL 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 relative URLs is used, all chunks will be
   delivered by the same surrogate that delivered the Manifest File.  A
   relative URL will therefore not include a hostname.

   For example, in the case a Manifest File has been requested (and
   received) from:



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      http://surrogate.server.cdn.example.com/content_1/manifest.xml

   , a relative URL 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 URL.  In this case, the segment would
   then be requested from http://surrogate.server.cdn.example.com/
   content_1/segments/segment1_1.ts

   The downside of using relative URLs is that it forces a CDN to
   deliver all segments belonging to a given content item with the same
   surrogate that delivered the Manifest File for that content item.
   The advantage of relative URLs is that it is very easy to transfer
   content between different surrogates and even CDNs.

2.2.2.  Absolute URLs with Redirection

   Another method for specifying locations of chunks (or other manifest
   files) in a Manifest File is through the use of an absolute URL.  An
   absolute URL contains a fully formed URL (i.e. the client does not
   have to calculate the URL as in the case of the relative URL but can
   use the URL from the manifest directly).

   In the context of Manifest Files, there are two types of absolute
   URLs imaginable: Absolute URLs with Redirection and Absolute URLs
   without Redirection.  The two methods differ in whether the URL
   points to a request routing node which will redirect the client to a
   surrogate (Absolute URL with Redirection) or point directly to a
   surrogate hosting the requested content (Absolute URL without
   Redirection).

   In the case of Absolute URLs with Redirection, a request for a chunk
   is handled by the request routing system of a CDN just as if it were
   a standalone (non-HAS) content request, which might include looking
   up the surrogate (and/or CDN) 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 surrogate (and/or CDN), or a DNS response pointing to the
   specific surrogate.

   An example of an Absolute URL with Redirection might look as follows:







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      http://requestrouting.cdn.example.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.

   The advantage of using Absolute URLs with Redirection is that it
   allows for maximum flexibility (since chunks can be distributed
   across surrogates and CDN in any imaginable way) without having to
   modify the Manifest File every time one or more chunks are moved (as
   is the case when Absolute URLs without Redirection are used).  The
   downside of this method is that it can adds significant load to a CDN
   request routing system, since it has to perform a redirect every time
   a client requests a new chunk.

2.2.3.  Absolute URL without Redirection

   In the case of the Absolute URL without Redirection, the URL points
   directly to the specific chunk on the actual surrogate that will
   deliver the requested chunk to the client.  In other words, there
   will be no HTTP redirection operation taking place between the client
   requesting the chunk and the chunk being delivered to the client by
   the surrogate.

   An example of an Absolute URLs without Redirection is the following:

      http://surrogate.cdn.example.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 surrogate.cdn.example.com).  With this, the client has enough
   information to directly request the specific segment from the
   specified surrogate.

   The advantage of using Absolute URLs without Redirection is that it
   allows more flexibility compared to using Relative URLs (since
   segments do not necessarily have to be delivered by the same server)
   while not requiring per-segment redirection (which would add
   significant load to the node doing the redirection).  The drawback of
   Absolute URLs without Redirection is that it requires a modification
   of the Manifest File every time content is moved to a different
   location (either within a CDN or across CDNs).







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3.  Possible HAS Optimizations

   In the previous chapter, some of the unique properties of HAS have
   been discussed.  Furthermore, some of the CDN-specific design
   decisions with regards to addressing chunks have been detailed.  In
   this chapter, the impact of supporting HAS in CDN Interconnection
   scenarios will be discussed.

   There are a number of topics, or problem areas, that are of
   particular interest when considering the combination of HAS and CDNI.
   For each of these problem areas it holds that there are a number of
   different ways in which the CDNI Interfaces can deal with them.  In
   general it can be said that each problem area can either be solved in
   a way that minimizes the amount of HAS-specific changes to the CDNI
   Interfaces or in way that maximizes the flexibility and efficiency
   with which the CDNI Interfaces can deliver HAS content.  The goal for
   the CDNI WG should probably be to try to find the middle ground
   between these two extremes and try to come up with solutions that
   optimize the balance between efficiency and additional complexity.

   In order to allow the WG to make this decision, this chapter will
   briefly describe each of the following problem areas together with a
   number of different options for dealing with them.  Section 3.1 will
   discuss the problem of how to deal with file management of groups of
   files, or Content Collections.  Section 3.2 will deal with a related
   topic: how to do content acquisition of Content Collections between
   the uCDN and dCDN.  After that, Section 3.3 describes the various
   options for the request routing of HAS content, particularly related
   to Manifest Files.  Section 3.4 talks about a number of possible
   optimizations for the logging of HAS content, while Section 3.5
   discusses the options regarding URL signing.  Section 3.6 finally,
   describes different scenarios for dealing with the removal of HAS
   content from CDNs.

3.1.  File Management and Content Collections

   One of the unique properties of HAS content is that it does not
   consist of a single file or stream but of multiple interrelated files
   (segment, fragments and/or Manifest Files).  In this document this
   group of files is also referred to as a Content Collection.  Another
   important aspect is the difference between segments and fragments
   (see Section 2.1).

   Irrespective of whether segments or fragments are used, different
   CDNs might handle Content Collections differently from a file
   management perspective.  For example, some CDNs might handle all
   files belonging to a Content Collection as individual files, which
   are stored independently from each other.  An advantage of this



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   approach is that makes it easy to cache individual chunks.  Other
   CDNs might store all fragments belonging to a Content Collection in a
   bundle, as if they were a single file (e.g. by using a fragmented MP4
   container).  The advantage of this approach is that it reduces file
   management overhead.

   This section will look at the various ways with which the CDNI
   interfaces might deal with these differences in handling Content
   Collections from a file management perspective.  The different
   options can be distinguished based on the level of HAS-awareness they
   require on the part of the different CDNs and the CDNI interfaces.

3.1.1.  Option 1.1: No HAS awareness

   This first option assumes no HAS awareness in both the involved CDNs
   and the CDNI Interfaces.  This means that the uCDN uses individual
   files and the dCDN is not explicitely made aware of the relationship
   between chunks and it doesn't know which files are part of the same
   Content Collection.  In practice this scenario would mean that the
   file management method used by the uCDN is simply imposed on the dCDN
   as well.

   This scenario also means that it is not possible for the dCDN to use
   any form of file bundling, such as the single-file mechanism which
   can be to store fragmented content as a single file (see
   Section 2.1).  The one exception to this rule is the situation where
   the content is fragmented and the Manifest Files on the uCDN contains
   byte range requests, in which case the dCDN might be able to acquire
   fragmented content as a single file (see Section 3.2.2).

   Effect on CDN Interfaces:

   o  None

   Advantages/Drawbacks:

   +  No HAS awareness necessary in CDNs, no changes to CDNI Interfaces
      necessary

   -  The dCDN is forced to store chunks as individual files.

3.1.2.  Option 1.2: Allow single file storage of fragmented content

   In some cases, the dCDN might prefer to store fragmented content as a
   single file on its surrogates to reduce file management overhead.  In
   order to do so, it needs to be able to either acquire the content as
   a single file (see Section 3.2.2), or merge the different chunks
   together and place them in the same container (e.g. fragmented MP4).



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   The downside of this is that in order to do so, the dCDN needs to be
   fully HAS aware.

   Effect on CDN Interfaces:

   o  CDNI Metadata Interface: Add fields for indicating the particular
      type of HAS (e.g.  MPEG DASH or HLS) that is used and whether
      segments or fragments are used

   o  CDNI Metadata Interface: Add field for indicating the name and
      type of the manifest file(s)

   Advantages/Drawbacks:

   +  Allows dCDN to store fragmented content as a single file, reducing
      file management overhead

   -  Complex operation, requiring dCDN to be fully HAS aware

3.2.  Content Acquisition of Content Collections

   In the previous section the relationship between file management and
   HAS in a CDNI scenario has been discussed.  This section will discuss
   a related topic, which is content acquisition between two CDNs.

3.2.1.  Option 2.1: No HAS awareness

   This first option assumes no HAS awareness in both the involved CDNs
   and the CDNI Interfaces.  Just as with Option 1.1 discussed in the
   previous section with regards to file management, having no HAS
   awareness means that the dCDN is not aware of the relationship
   between chunks.  In the case of content acquisition, this means that
   each and every file belonging to a Content Collection will have to be
   individually acquired from the uCDN by the dCDN.  The exception to
   the rule is in cases with fragmented content where the uCDN uses
   Manifest Files which contain byte range requests.  In this case the
   dCDN can simply omit the byte range identifier and acquire the
   complete file.

   The advantage of this approach is that it is highly flexible.  If a
   client only requests a small portion of the chunks belonging to a
   particular Content Collection, the dCDN only has to acquire those
   chunks from the uCDN, saving both bandwidth and storage capacity.

   The downside of acquiring content on a per-chunk basis is that it
   creates more transaction overhead between the dCDN and uCDN compared
   to a method in which entire Content Collections can be acquired as
   part of one transaction.



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   Effect on CDN Interfaces:

   o  None

   Advantages/Drawbacks:

   +  Per-chunk content acquisition allows for high level of flexibility
      between dCDN and uCDN

   -  Per-chunk content acquisition creates more transaction overhead
      between dCDN and uCDN

3.2.2.  Option 2.2: Allow single file acquisition of fragmented content

   As discussed in Section 3.2.1, there is one (fairly rare) in cases
   where fragmented content can be acquired as a single file without any
   HAS awareness and that is when fragmented content is used and where a
   Manifest File includes byte range request.  This section discusses
   how to perform single file acquisition in the other (very common)
   cases.  To do so, the dCDN would have to have full-HAS awareness (at
   least to the extent of being able to map between single file and
   individual chunks to serve).

   Effect on CDN Interfaces:

   o  CDNI Metadata Interface: Add fields for indicating the particular
      type of HAS (e.g.  MPEG DASH or HLS) that is used and whether
      segments or fragments are used

   o  CDNI Metadata Interface: Add field for indicating the name and
      type of the manifest file(s)

   Advantages/Drawbacks:

   +  Allows for more efficient content acquisition in all HAS-specific
      supported forms

   -  Requires full HAS awareness on part of dCDN

   -  Requires significant CDNI Metadata Interface extensions

3.3.  Request Routing of HAS content

   In this section the effect HAS content has on request routing will be
   identified.  Of particular interest in this case are the different
   types of Manifest Files that might be used.  In Section 2.2, three
   different methods for identifying and addressing chunks from within a
   Manifest File were described: Relative URLs, Absolute URLs without



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   Redirection and Absolute URLs with Redirection.  Of course not every
   current CDN will use and/or support all three methods.  Some CDNs may
   only use one of the three methods, while others may support two or
   all three.

   An important factor in deciding which chunk addressing method is used
   is the Content Provider.  Some Content Providers may have a strong
   preference for a particular method and deliver the Manifest Files to
   the CDN in a particular way.  Depending on the CDN and the agreement
   it has with the Content Provider, a CDN may either host the Manifest
   Files as they were created by the Content Provider, or modify the
   Manifest File to adapt it to its particular architecture (e.g. by
   changing relative URLs to Absolute URLs which point to the CDN
   Request Routing function).

3.3.1.  Option 3.1: No HAS awareness

   This first option assumes no HAS awareness in both the involved CDNs
   and the CDNI Interfaces.  This scenario also assumes that neither the
   dCDN nor the uCDN have the ability to actively manipulate Manifest
   Files.  As was also discussed with regards to file management and
   content acquisition, having no HAS awareness means that each file
   constituting a Content Collections is handled on an individual basis,
   with the dCDN unaware of any relationship between files.

   The only chunk addressing method that works without question in this
   case is Absolute URLs with Redirection.  In other words, the Content
   Provider that ingested the content into the uCDN created a Manifest
   File with each chunk location pointing to the Request Routing
   function of the uCDN.  Alternatively, the Content Provider may have
   ingested the Manifest File containing relative URLs and the uCDN
   ingestion function has translated these to Absolute URLs pointing to
   the Request Routing function.

   In this Absolute URL with Redirection case, the uCDN can simply have
   the Manifest File be delivered by the dCDN as if it were a regular
   file.  Once the client parses the Manifest File, it will request any
   subsequent chunks from the uCDN Request Routing function.  That
   function can then decide to outsource the delivery of that chunk to
   the dCDN.  In that case it will probably redirect the client to the
   Request Routing function of the dCDN (assuming it does not have the
   necessary information to redirect the client directly to a surrogate
   in the dCDN).  The drawback of this method is that it creates a large
   amount of request routing overhead for both the uCDN and dCDN.  For
   each chunk the full inter-CDN Request Routing process is invoked
   (which can result in two redirections in the case of iterative
   redirection, or result in one redirection plus one CDNI Request
   Routing/Redirection Interface request/response).



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   With no HAS awareness, Relative URLs might or might not work
   depending on the HAS client implementation that is used.  When a uCDN
   delegates the delivery of a Manifest File containing Relative URLs to
   a dCDN, the client goes directly to the dCDN surrogate from which it
   has received the Manifest File for every subsequent chunk.  The
   question here is whether the HAS client uses the IP address or the
   hostname in its chunk request to the dCDN surrogate.  In case it uses
   the exact same hostname with which it requested the manifest file
   (and which is the result of a request routing operation) than
   everything works properly (because the dCDN can easily associate the
   CDNI metadata for the corresponding chuck and therefor serve the
   corresponding request).  However, in situations where the client uses
   the IP address of the surrogate or does a reverse DNS look-up, the
   dCDN surrogate may not be able to associate CDNI metadata with the
   chucnk request and therefore may not be able to serve it.  One
   exception to this is in the scenario where the PATH or QUERY part of
   the chunk request URL is enough to uniquely identify the particular
   chunk, in which case the dCDN Surrigate can associate CDNI metadata
   and serve the request

   Since using Absolute URLs without Redirection inherently require a
   HAS aware CDN, they also cannot be used in this case.  The reason for
   this is that with Absolute URLs without Redirection, the URLs in the
   Manifest File will point directly to a surrogate in the uCDN.  Since
   this scenario assumes no HAS awareness on the part of the dCDN or
   uCDN, it is impossible for either of these CDNs to rewrite the
   Manifest File and thus allow the client to either go to a surrogate
   in the dCDN or to a request routing function.

   Effect on CDN Interfaces:

   o  None

   Advantages/Drawbacks:

   +  Supports Absolute URLs with Redirection

   +  Does not require HAS awareness and/or changes to the CDNI
      Interfaces

   -  Not possible to use Absolute URLs without Redirection

   -  Support for Relative URLs suffers from some brittleness.  Makes
      assumptions on client-side implementation of the HAS client or on
      structure of PATH or QUERY






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   -  Creates significant signaling overhead in case Absolute URLs with
      Redirection are used (inter-CDN request redirection for each
      chunk)

3.3.2.  Option 3.2: Manifest File rewriting by uCDN

   While Option 3.1 does allow for Absolute URLs with Redirection to be
   used, it does so in a way that creates a high-level of request
   routing overhead for both the dCDN and the uCDN.  This option
   presents a solution to significantly reduce this overhead.

   In this scenario, the uCDN is able to modify the Manifest File to be
   able to remove itself from the request routing chain for chunks being
   referenced in the Manifest File.  As described in Section 3.3.1, in
   the case of no HAS awareness the client will go to the uCDN request
   routing function for each chunk request.  This request routing
   function can then redirect the client to the dCDN request routing
   function.  By rewriting the Manifest File, the uCDN is able to remove
   this first step, and have the Manifest File point directly to the
   dCDN request routing function.

   In order for the uCDN to be able to do this, it needs the location of
   the dCDN request routing function (or even better: the location of
   the dCDN surrogate).  The simplest way to obtain this information is
   to use the CDNI Request Routing Interface in one of two ways.  The
   first way would be to have the uCDN ask the dCDN for the location of
   its request routing node (through the CDNI Request Routing/
   Redirection Interface) every time a request for a Manifest File comes
   in at the uCDN request routing node.  The uCDN would then modify the
   manifest file and deliver the manifest file to the client.  A second
   way to do it would be for the modification of the manifest file to
   only happen once, when the first client for that particular Content
   Collection (and redirected to that particular dCDN) sends a Manifest
   File request.  The advantage of the first method is that it maximizes
   effiency and flexibility by allowing the dCDN to respond with the
   locations of its surrogates instead of the location of its request
   routing function (and effectively turning the URLs into Absolute URLs
   without Redirection).  The advantage of the second method is that the
   uCDN only has to modify the Manifest File once.

   Effect on CDN Interfaces:

   o  CDNI Request Routing Interface: Allow uCDN to query dCDN for the
      location of its request routing function (is this covered by the
      existing RR interface?)

   o  uCDN: Allow for modification of manifest file




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   Advantages/Drawbacks:

   +  Possible to significantly decrease signalling overhead when using
      Absolute URLs.

   +  (Optional) Possible to have uCDN modify manifest with locations of
      surrogates in dCDN (turning Absolute URLs with Redirection in
      Absolute URLs without Redirection)

   +  Minimal changes to CDNI Interfaces (no HAS awareness)

   +  Does not require HAS awareness in dCDN

   -  Requires high level of HAS awareness in uCDN (for modifying
      manifest files)

3.3.3.  Option 3.3: Two-step Manifest File rewriting

   One of the possibilities with Option 3.3 is allowing the dCDN to
   provide the locations of a specific surrogate to the uCDN, so that
   the uCDN can fit the Manifest File with Absolute URLs without
   Redirection and the client can request chunks directly from a dCDN
   surrogate.  However, some dCDNs might not be willing to provide this
   sensitive information to the uCDN.  In that case they can only
   provide the uCDN with the location of their request routing function
   and thereby not be able to use Absolute URLs without Redirection.

   One method for solving this limitation is allowing two-step Manifest
   File manipulation.  In the first step the uCDN would perform its own
   modification, and place the locations of the dCDN request routing
   function in the Manifest File.  Then, once a request for the Manifest
   File comes in at the dCDN request routing function, it would perform
   a second modification in which it replaces the URLs in the Manifest
   Files with the URLs of its surrogates.  This way the dCDN can still
   profit from having minimal request routing traffic, while not having
   to share sensitive surrogate information with the uCDN.

   The downside of this approach is that it not only assumes HAS
   awareness in the dCDN but that it also requires some HAS-specific
   additions to the CDNI Metadata Interface.  In order for the dCDN to
   be able to change the Manifest File, it has to have some information
   about the structure of the content.  Specifically, it needs to have
   information about which chunks make up the Content Collection.

   Effect on CDN Interfaces (apart from those listed under Option 3.3):






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   o  CDNI Metadata Interface: Add necessary fields for conveying HAS
      specific information (e.g. the files that make up the Content
      Collection) to the dCDN.

   o  dCDN: Allow for modification of manifest file

   Advantages/Drawbacks (apart from those listed under Option 3.3):

   +  Allows dCDN to use Absolute URLs without Redirection without
      having to convey sensitive information to the uCDN

   -  Requires high level of HAS awareness in dCDN (for modifying
      manifest files)

   -  Requires adding HAS-specific information to the CDNI Metadata
      Interface

3.4.  Logging

3.4.1.  HAS Considerations for CDNI Logging

   As stated in [I-D.ietf-cdni-problem-statement], "the CDNI Logging
   interface enables details of logs or events to be exchanged between
   interconnected CDNs".

   As discussed in [I-D.draft-bertrand-cdni-logging], the CDNI logging
   information can be used fort multiple purposes including maintenance/
   debugging by uCDN, accounting (e.g. in view of billing or
   settlement), reporting and management of end-user experience (e.g. to
   the CSP), analytics (e.g. by the CSP) and control of content
   distribution policy enforcement (e.g. by the CSP).

   The key consideration for HAS with respect to logging is the
   potential increase of the number of Log records by two to three
   orders of magnitude, as compared to regular HTTP delivery of a video,
   since log records would typically be generated on a per-chunk-
   delivery basis instead of per-content-item-delivery basis.  This
   impacts the scale of every processing step in the Logging Process
   (see Section 8 of [I-D.draft-bertrand-cdni-logging]), including:

   a.  Logging Generation and Storing of logs on CDN elements
       (Surrogate, Request Routers,..)

   b.  Logging Aggregation within a CDN

   c.  Logging Manipulation (including Logging Protection, Logging
       Filtering , Logging Update and Rectification)




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   d.  (Where needed) Logging CDNI Reformatting (e.g. reformatting from
       CDN-specific format to the CDNI Logging Interface format for
       export by dCDN to uCDN)

   e.  Logging exchange via CDNI Logging Interface

   f.  (Where needed) Logging Re-Reformatting (e.g. reformatting from
       CDNI Logging Interface format into log-consuming specific
       application)

   g.  Logging consumption/processing (e.g. feed logs into uCDN
       accounting application, feed logs into uCDN reporting system to
       provide per CSP views, feed logs into debugging tool to debug)

   Note that there may be multiple instances of step [f] and [g] running
   in parallel.

   While the CDNI Logging Interface is only used to perform step [e], we
   note that its format directly affects step [d] and [f] and that its
   format also indirectly affects the other steps (for example if the
   CDNI Logging Interface requires per-chunk log records, step [a], [b]
   and [d] cannot operate on a per-HAS-session basis and also need to
   operate on a per-chunk basis).

3.4.2.  Candidate Approaches

   The following sub-sections discusses the main candidate approaches
   identified so far for CDNI in terms of dealing with HAS with respect
   to Logging.

3.4.2.1.  Option 4.1: "Do-Nothing" Approach

   In this approach, each HAS-chunk delivery is considered, for CDNI
   Logging, as a standalone content delivery.  In particular, a separate
   log record for each HAS-chunk delivery is included in the CDNI
   Logging Interface in step [e].  This approach requires that step [a],
   [b] , [c], [d] and [e] be performed on per-chunk basis.  This
   approach allows [g] to be performed either on a per-chunk basis
   (assuming step [e] maintains per-chunk records) or on a more
   "summarized" manner such as per-HAS-Session basis assuming step [e]
   summarizes per-chunk records into per-HAS-session records).

   Effect on CDN Interfaces:

   o  None

   Effect on uCDN and dCDN:




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   o  None

   Advantages/Drawbacks:

   +  No information loss (i.e. all details of each individual chunk
      delivery are preserved).  While this full level of detail may not
      be needed for some Log consuming applications (e.g. billing), this
      full level of detail is likely valuable (possibly required) for
      some Log consuming applications (e.g. debugging)

   +  Easier integration (at least in the short term) into existing
      Logging tools since those are all capable of handling per-chunk
      records

   +  No extension needed on CDNI interfaces

   -  High volume of logging information to be handled (storing &
      processing) at every step of the Logging process from [a] to [g]
      (while summarization in step [f] is conceivable, it may be
      difficult to achieve in practice without any hints for correlation
      in the log records).  While the high volume of logging information
      is a potential concern, we are seeking expert input on whether it
      is a real practical issue, and if yes, then in what timeframe/
      assumptions.

3.4.2.2.  Option 4.2: "CDNI Metadata Content Collection ID" Approach

   In this approach, a "Content Collection ID" (CCID) field is
   distributed through the CDNI Metadata Interface and the same CCID
   value is associated with every chunk of the same Content Collection.
   The objective of this field is to facilitate summarization of per-
   chunk records at step [f] into something along the lines of per-HAS-
   session logs, at least for the Log Consuming application that do not
   require per-chunk detailed information (for example billing).

   [Editor's Note: would there be value in adding a little more info in
   the metadata such as which HAS-scheme is used?]

   Effect on CDN Interfaces:

   o  One additional metadata field (CCID) in CDNI Metadata Interface

   Effect on uCDN and dCDN:

   o  None

   Advantages/Drawbacks:




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   +  No information loss (i.e. all details of each individual chunk
      delivery are preserved).  While this full level of detail may not
      be needed for some Log consuming applications (e.g. billing), this
      full level of detail is likely valuable (possibly required) for
      some Log consuming applications (e.g. debugging)

   +  Easier integration (at least in the short term) into existing
      Logging tools since those are all capable of handling per-chunk
      records

   +  Very minor extension to CDNI interfaces needed

   +  Facilitated summarization of records related to a HAS session in
      step [f] and therefore ability to operate on lower volume of
      logging information in step [g] by log consuming applications that
      do not need per-chunk record details (e.g. billing)

   -  High volume of logging information to be handled (storing &
      processing) at every step of the Logging process from [a] to [f].
      While the high volume of logging information is a potential
      concern, we are seeking input on whether it is a real practical
      issue, and if yes in what timeframe/assumptions

3.4.2.3.  Option 4.3: "CDNI Metadata Content Collection ID With dCDN
          Summarization" Approach

   In this approach, a "Content Collection ID" (CCID) field is
   distributed through the CDNI Metadata Interface and the same CCID
   value is associated with every chunk of the same Content Collection.
   In this approach, a summarization of per-chunk records is performed
   at step [d] (or in earlier steps) taking advantage of the CCID, so
   that a reduced volume of logging information is to be handled in
   steps [e] to [g] of the logging process (and is optionally also
   possible in steps [a] to [c]).  The objective of this approach is to
   reduce the volume of logging information early in the Logging process

   Regarding the summarization performed at step [d] (or in earlier
   steps), there is a continuum in terms of trade-off between level of
   summarization of per-chunk records and information loss.  For
   example, it appears possible to perform a summarization that results
   is significant gains with limited information loss, perhaps using
   summarized logs along the lines of the Event-Based Logging format
   discussed in section 3.2.2 of
   [I-D.draft-lefaucheur-cdni-logging-delivery].  Alternatively, it may
   be possible to perform a summarization that results in very
   significant gains with significant information loss, perhaps using
   summarized logs along the lines of the Summary-Based Logging format
   discussed in section 3.2.3 of



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   [I-D.draft-lefaucheur-cdni-logging-delivery].

   Effect on CDN Interfaces:

   o  One additional metadata field (CCID) in CDNI Metadata Interface

   o  Summarized logging information in CDNI Logging Information

   Effect on uCDN and dCDN:

   o  None

   Advantages/Drawbacks:

   +  Lower volume of logging information to be handled (storing &
      processing) at every step of the Logging process from [e] to [g],
      and optionally from [a] to [d] also

   +  Small extensions to CDNI interfaces needed

   -  Some information loss (i.e. all details of each individual chunk
      delivery are not preserved).  The actual information loss depends
      on the summarization approach selected (typically the lower the
      information loss, the lower the summarization gain) so the right
      sweet-spot would had ego be selected.  While full level of detail
      may not be needed for some Log consuming applications (e.g.
      billing), the full level of detail is likely valuable (possibly
      required) for some Log consuming applications (e.g. debugging)

   -  Less easy integration (at least in the short term) into existing
      Logging tools since those are all capable of handling per-chunk
      records and may not be capable of handling CDNI summarized records

3.4.2.4.  Option 4.4: "CDNI Logging Interface Compression" Approach

   In this approach, a loss-less compression technique is applied to the
   sets of Logging records (e.g.  Logging files) for transfer on the
   IETF CDNI Logging Interface.  The objective of this approach is to
   reduce the volume of information to be stored and transferred in step
   [e].

   Effect on CDN Interfaces:

   o  One additional compression mechanism to be included in the CDNI
      Logging Interface

   Effect on uCDN and dCDN:




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   o  None

   Advantages/Drawbacks:

   +  No information loss (i.e. all details of each individual chunk
      delivery are preserved).  While this full level of detail may not
      be needed for some Log consuming applications (e.g. billing), this
      full level of detail is likely valuable (possibly required) for
      some Log consuming applications (e.g. debugging)

   +  Easier integration (at least in the short term) into existing
      Logging tools since those are all capable of handling per-chunk
      records

   +  Small extension to CDNI interfaces needed

   +  Reduced volume of logging information in step [e]

   -  High volume of logging information to be handled (storing &
      processing) at every step of the Logging process from [a] to [g],
      except [e].  While the high volume of logging information is a
      potential concern, we are seeking expert input on whether it is a
      real practical issue, and if yes, then in what timeframe/
      assumptions

   Input is sought on expected compression gains achievable in practice
   over sets of logs containing per-chunk records.

3.4.2.5.  Option 4.5: "Full HAS awareness" Approach

   In this approach, HAS-awareness is assumed across the CDNs
   interconnected via CDNI and the necessary information to describe the
   HAS relationship across all chunks of the same Content Collection is
   distributed through the CDNI Metadata Interface.  In this approach,
   the dCDN Surrogates leverage the HAS information distributed through
   the CDNI metadata and their HAS-awareness to generate summarized
   logging information in the very first place.  The objective of that
   approach is to operate on lower volume of logging information right
   from the very first step of the Logging process.

   The summarized HAS logs generated by the Surrogates in this approach
   are similar to those discussed in the section " "CDNI Metadata
   Content Collection ID With dCDN Summarization" Approach" and the same
   trade-offs between information loss and summarization gain apply.

   Effect on CDN Interfaces:





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   o  One significant extension of the CDNI Metadata Interface to convey
      HAS relationship across chunks of a Content Collection.  Note that
      this extension requires specific support for every HAS-protocol to
      be supported over the CDNI mesh

   Effect on uCDN and dCDN:

   o  Full HAS-awareness by dCDN Surrogates

   Advantages/Drawbacks:

   +  Lower volume of logging information to be handled (storing &
      processing) at every step of the Logging process from [a] to [g]

   +  Accurate generation of summarized logs because of HAS awareness on
      Surrogate

   -  Very significant extensions to CDNI interfaces needed including
      per HAS-protocol specific support

   -  Very significant additional requirement for HAS awareness on dCDN

   -  Some information loss (i.e. all details of each individual chunk
      delivery are not preserved).  The actual information loss depends
      on the summarization approach selected (typically the lower the
      information loss, the lower the summarization gain) so the right
      sweet-spot would had ego be selected.  While full level of detail
      may not be needed for some Log consuming applications (e.g.
      billing), the full level of detail is likely valuable (possibly
      required) for some Log consuming applications (e.g. debugging)

   -  Less easy integration (at least in the short term) into existing
      Logging tools since those are all capable of handling per-chunk
      records and may not be capable of handling CDNI summarized records

   Input is sought on expected compression gains achievable in practice
   over sets of logs containing per-chunk records.

3.5.  URL Signing

   URL Signing is an authorization method for content delivery.  This is
   based on embedding the HTTP URL with information that can be
   validated to ensure the request has legitimate access to the content.
   There are two parts: 1) parameters that convey authorization
   restrictions (e.g. source IP address and time period) and/or
   protected URL portion, and 2) authenticator value that confirms the
   integrity of the URL and authenticates the URL creator.  The
   authorization parameters can be anything agreed upon between the



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   entity that creates the URL and the entity that validates the URL.  A
   key is used to generate the authenticator (i.e. sign the URL) and
   validate the authenticator.  This may or may not be the same key.

   There are two types of keys: asymmetric keys and symmetric key.
   Asymmetric keys always have a key pair made up of a public key and
   private key.  The private key and public key are used for signing and
   validating the URL, respectively.  A symmetric key is the same key
   that is used for both functions.  Regardless of the type of key, the
   entity that validates the URL has obtain the key.  Distribution for
   the symmetric key requires security to prevent others from taking it.
   Public key can be distributed freely while private key is kept by the
   URL signer.

   URL Signing operates in the following way.  A signed URL is provided
   by the content owner (i.e.  URL signer) to the user during website
   navigation.  When the user selects the URL, the HTTP request is sent
   to the delivery node which validates that the URL before delivering
   the content.

3.5.1.  URL Signing in CDNI

   For CDNI, URL Signing is based on the Upstream CDN and Downstream CDN
   as entities that sign and validate the URL, respectively.  HTTP-based
   request routing changes the URL.  Thus, each redirection requires the
   URL to be re-signed.  The alternative is protection of only the
   invariant portion of the URL to avoid re-signing by the transit CDN.
   DNS-based request routing maintains the same URL.  In essence, there
   are three cases: 1) The URL is validated, rewritten, and re-signed at
   each request routing hop, 2) The URL is changed but only the
   invariant portion of URL is validated, and 3) The URL remains the
   same and validated by the delivery CDN surrogate.

   The Downstream CDN needs to obtain the key for validating the URL.
   When asymmetric keys are used, the public key can be retrieved from
   the authorization parameters embedded in the URL.  The Downstream CDN
   can validate the URL with the public key, regardless of the
   relationship with the URL signer (i.e.  Downstream CDN has or does
   not have a direct relationship with the Upstream CDN that signed the
   URL).  When symmetric key is used, the Downstream CDN needs to obtain
   the key in a secure method that is out of scope.  For cascaded CDNs,
   a common key is distributed for validation of unaltered URL to
   support DNS-based request routing.  Alternatively, a shared key is
   distributed between adjacent CDNs to support rewritten URL that is
   used in HTTP-based request routing.

   URL Signing requires support in most of the CDNI Interfaces.  The
   CDNI Metadata interface should specify the content that is subject to



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   URL signing and provide information to perform the function.  The
   Downstream CDN should inform the Upstream CDN that it supports URL
   Signing in the asynchronous capabilities information advertisement as
   part of the Request Routing interface.  This allows the CDN selection
   function in request routing to choose the Downstream CDN with URL
   signing capability when the CDNI metadata of the content requires
   this authorization method.  The Logging interface provides
   information on the authorization method (e.g.  URL Signing) and
   related authorization parameters used for content delivery.  URL
   Signing has no impact on the Control interface.

3.5.2.  Option 5.1: No HAS awareness

   For HTTP Adaptive Streaming, the Manifest File contains the Relative
   Locator, Absolute Locator without Redirection, or Absolute Locator
   with Redirection for specifying the chunk location.  The
   Authoritative CDN performs URL signing for the Manifest File and
   chunks.  The delivery CDN surrogate has to obtain the key to validate
   the URL.  Although the Manifest file and chunk are treated the same
   by the CDN that is not HAS aware, there are some implications for URL
   Signing based on the method used to reference the chunk location in
   the Manifest file.

   For Absolute URL without Redirection, the Authoritative CDN signs the
   chunk URL which is associated with the delivery CDN surrogate.  Since
   the entire URL is set and does not change during request routing
   (i.e.  DNS-based redirection only and no HTTP-based redirection),
   there are no issues for signing and validating the URL.

   For Relative URL, the Authoritative CDN does not know the URL that
   will be ultimately used by a Downstream CDN to deliver the chunk.
   This uncertainty makes it impossible to accurately sign the URL in
   the Manifest File.  URL Basically, URL Signing using this reference
   method, "as is" for entire URL protection, is not supported.
   However, instead of signing the entire URL, the Authoritative CDN
   signs the Relative URL (i.e. invariant portion of the URL) and
   conveys the protected portion in the authorization parameters
   embedded in the chunk URL.  This approach works the same way as
   Absolute URL, except the HOST part and (part of) the PATH part of the
   URL are not signed and validated.  The tradeoff is flexibility vs
   security.  The advantage is that the content can be authorized to be
   delivered from any host with arbitrary directory path.  The drawback
   is lack of protection for the entire URL.  One aspect may outweigh
   the other depending on the needs of the Authoritative CDN.

   For Absolute URL with Redirection, the Authoritative CDN signs the
   chunk URL with the intent that the targeted Request Routing function
   will validate and redirect the URL with a new URL signature.  This



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   method is same as the Absolute URL without Redirection from URL
   Signing perspective because the signed URL is the same URL that is
   validated.  Only difference is that the request routing function
   needs to redirect the request with a new URL which may be signed or
   not.

   Effect on CDN Interfaces:

   o  oURL Signing is enabled on the CDNI Request Routing (i.e.
      Capabilities advertisement), Metadata, and Logging interfaces

   Advantages/Drawbacks:

   +  No HAS awareness necessary in CDNs, no changes to CDNI interface
      necessary

   -  URL Signing for every chunk may be considered as processing
      overhead

3.5.3.  Option 5.2: HAS-awareness with Authorization Token

   Up to this point, the Manifest File and chunks are treated as normal
   file in the HTTP delivery.  There are no specific changes needed for
   the CDN to support HAS.  However, if CDN is aware of HAS, then the
   Manifest File and chunk can be treated differently and appropriately.

   URL Signing is fundamentally about authorizing access to a Content
   Item or its specific Content Collections (representations) for a
   specific user during a time period with possibly some other criteria.
   A chunk is an instance of the sets of chunks referenced by the
   Manifest File for the Content Item or its specific Content
   Collections.  This relationship means that once the Downstream CDN
   has authorized the Manifest File, it can assume that the associated
   chunks are implicitly authorized.  The new function for the CDN is to
   link the Manifest File with the chunks for the HTTP session.  This
   can be accomplished by using authorization token or session based
   encryption.  This section covers the former and next section covers
   the latter.

   After validating the URL and detecting that the requested content is
   a Manifest File, the delivery CDN surrogate creates a state and sets
   a HTTP cookie with authorization token for the HTTP session.  When a
   request for a chunk arrives, the surrogate confirms that the HTTP
   cookie value contains the correct authorization token.  If so, the
   chunk is delivered due to transitive authorization property.

   Effect on CDN Interfaces:




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   o  URL Signing is enabled on the CDNI Request Routing (i.e.
      Capabilities advertisement), Metadata, and Logging interfaces

   Advantages/Drawbacks:

   +  Not necessary to validate every chunk URL

   +  Less exposure to attacks on the URL Signing keys

   -  Surrogate needs to maintain state for the authorization token

3.5.4.  Option 5.3: HAS-awareness with Session Based Encryption

   After validating the URL and detecting that the requested content is
   a Manifest File, the delivery CDN surrogate manipulates the Manifest
   File by adding a reference to the key server for protection of
   specific chunks before it delivers the content.  Also, the surrogate
   sets a HTTP cookie for the HTTP session.  When a request for a chunk
   arrives, the surrogate identifies that the HTTP cookie value is for
   the same session.  If so, the chunk is encrypted with the symmetric
   key obtained from the key server and then is delivered to the user.

   Effect on CDN Interfaces:

   o  URL Signing is enabled on the CDNI Request Routing (i.e.
      Capabilities advertisement), Metadata, and Logging interfaces

   Advantages/Drawbacks:

   +  Not necessary to validate every chunk URL

   +  Less exposure to attacks on the URL Signing keys

   +  Confidentiality for the chunk

   -  Surrogate needs to change the Manifest File

   -  Surrogate needs to maintain state for the HTTP session

   -  Key server is required to distribute key to surrogate and user

   -  Encryption and decryption processing

3.6.  Content Purge

   At some point in time, a uCDN might want to remove content from a
   dCDN.  With regular content, this process can be relatively
   straightforward; a uCDN will typically send the request for content



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   removal to the dCDN including a reference to the content which it
   wants to remove (e.g. in the form of a URL).  Due to the fact that
   HAS content consists of large groups of files however, things might
   be more complex.  Section 3.1 describes a number of different
   scenarios for doing file management on these groups of files, while
   Section 3.2 list the options for performing Content Acquisition on
   these Content Collections.  This section will present the options for
   requesting a Content Purge for the removal of a Content Collection
   from a dCDN.

3.6.1.  Option 6.1: No HAS awareness

   The most straightforward way to signal content purge requests is to
   just send a single purge request for every file that makes up the
   Content Collection.  While this method is very simple and does not
   require HAS awareness, it obviously creates a large signalling
   overhead between the uCDN and dCDN.

   Effect on CDN Interfaces:

   o  None

   Advantages/Drawbacks (apart from those listed under Option 3.3):

   +  Does not require changes to the CDNI Interfaces or HAS awareness

   -  Requires individual purge request for every file making up a
      Content Collection which creates large signalling overhead

3.6.2.  Option 6.2: Purge Identifiers

   There exists a potentially more efficient method for performing
   content removal of large numbers of files simultaneously.  By
   including purge identifiers in the metadata of a particular file, it
   is possible to virtually group together different files making up a
   Content Collection.  A purge identifier can take the form of a random
   number which is communicated as part of the CDNI Metadata Interface
   and which is the same for all files making up a particular Content
   Item.  If a uCDN wants to request the dCDN to remove a Content
   Collection, it can send a purge request containing this purge
   identifier.  The dCDN can then remove all files that contain the
   shared identifier.

   The advantage of this method is that it is relatively simple to use
   by both the dCDN and uCDN and requiring only limited additions to the
   CDNI Metadata Interface and CDNI Control Interface.

   [Editor's Note: Could the Purge Identifier introduced in this section



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   be related to the Content Collection Identifier introduced in
   Section 3.4.2.2?  Chould they be the same identifier?]

   Effect on CDN Interfaces:

   o  CDNI Metadata Interface: Add metadata field for indicating Purge
      Identifier

   o  CDNI Control Interface: Add functionality to be able to send
      content purge requests containing Purge Identifiers

   Advantages/Drawbacks:

   +  Allows for efficient purging of content from a dCDN

   +  Does not require HAS awareness on part of dCDN


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.

   [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.





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6.2.  Informative References

   [I-D.draft-bertrand-cdni-logging]
              Bertrand, G., Ed. and E. Stephan, "CDNI Logging
              Interface".

   [I-D.draft-lefaucheur-cdni-logging-delivery]
              Le Faucheur, F., Viveganandhan, M., and K. Leung, "CDNI
              Logging Formats for HTTP and HTTP Adaptive Streaming
              Deliveries".


Authors' Addresses

   Ray van Brandenburg
   TNO
   Brassersplein 2
   Delft  2612CT
   the Netherlands

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


   Oskar van Deventer
   TNO
   Brassersplein 2
   Delft  2612CT
   the Netherlands

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


   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









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   Kent Leung
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Phone: +1 408-526-5030
   Email: kleung@cisco.com











































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