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RFC 7933 - Adaptive Video Streaming over Information-Centric Net

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Internet Research Task Force (IRTF)                     C. Westphal, Ed.
Request for Comments: 7933                                        Huawei
Category: Informational                                       S. Lederer
ISSN: 2070-1721                                                 D. Posch
                                                             C. Timmerer
                                       Alpen-Adria University Klagenfurt
                                                                A. Azgin
                                                                  W. Liu
                                                              C. Mueller
                                                                A. Detti
                                          University of Rome Tor Vergata
                                                               D. Corujo
                                    Instituto de Telecomunicacoes Aveiro
                                                                 J. Wang
                                            City University of Hong Kong
                                                            M. Montpetit
                                                               N. Murray
                                         Athlone Institute of Technology
                                                             August 2016

   Adaptive Video Streaming over Information-Centric Networking (ICN)


   This document considers the consequences of moving the underlying
   network architecture from the current Internet to an Information-
   Centric Networking (ICN) architecture on video distribution.  As most
   of the traffic in future networks is expected to be video, we
   consider how to modify the existing video streaming mechanisms.
   Several important topics related to video distribution over ICN are
   presented.  The wide range of scenarios covered includes the
   following: evolving Dynamic Adaptive Streaming over HTTP (DASH) to
   work over ICN and leverage the recent ISO/IEC Moving Picture Experts
   Group (MPEG) standard, layering encoding over ICN, introducing
   distinct requirements for video using Peer-to-Peer (P2P) mechanisms,
   adapting the Peer-to-Peer Streaming Protocol (PPSP) for ICN, creating
   more stringent requirements over ICN because of delay constraints
   added by Internet Protocol Television (IPTV), and managing digital
   rights in ICN.  Finally, in addition to considering how existing
   mechanisms would be impacted by ICN, this document lists some
   research issues to design ICN-specific video streaming mechanisms.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Research Task Force
   (IRTF).  The IRTF publishes the results of Internet-related research
   and development activities.  These results might not be suitable for
   deployment.  This RFC represents the consensus of the Information-
   Centric Networking Research Group of the Internet Research Task Force
   (IRTF).  Documents approved for publication by the IRSG are not a
   candidate for any level of Internet Standard; see Section 2 of
   RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   4
   3.  Use Case Scenarios for ICN and Video Streaming  . . . . . . .   5
   4.  Video Download  . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Video Streaming and ICN . . . . . . . . . . . . . . . . . . .   7
     5.1.  Introduction to Client-Driven Streaming and DASH  . . . .   7
     5.2.  Layered Encoding  . . . . . . . . . . . . . . . . . . . .   8
     5.3.  Interactions of Video Streaming with ICN  . . . . . . . .   8
       5.3.1.  Interactions of DASH with ICN . . . . . . . . . . . .   8
       5.3.2.  Interaction of ICN with Layered Encoding  . . . . . .  10
     5.4.  Possible Integration of Video Streaming and ICN
           Architecture  . . . . . . . . . . . . . . . . . . . . . .  11
       5.4.1.  DASH over CCN . . . . . . . . . . . . . . . . . . . .  11
       5.4.2.  Testbed, Open-Source Tools, and Dataset . . . . . . .  13

   6.  P2P Video Distribution and ICN  . . . . . . . . . . . . . . .  14
     6.1.  Introduction to PPSP  . . . . . . . . . . . . . . . . . .  14
     6.2.  PPSP over ICN: Deployment Concepts  . . . . . . . . . . .  16
       6.2.1.  PPSP Short Background . . . . . . . . . . . . . . . .  16
       6.2.2.  From PPSP Messages to ICN Named-Data  . . . . . . . .  16
       6.2.3.  Support of PPSP Interaction through a Pull-Based ICN
               API . . . . . . . . . . . . . . . . . . . . . . . . .  17
       6.2.4.  Abstract Layering for PPSP over ICN . . . . . . . . .  18
       6.2.5.  PPSP Interaction with the ICN Routing Plane . . . . .  19
       6.2.6.  ICN Deployment for PPSP . . . . . . . . . . . . . . .  19
     6.3.  Impact of MPEG-DASH Coding Schemes  . . . . . . . . . . .  20
   7.  IPTV and ICN  . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.1.  IPTV Challenges . . . . . . . . . . . . . . . . . . . . .  21
     7.2.  ICN Benefits for IPTV Delivery  . . . . . . . . . . . . .  22
   8.  Digital Rights Management in ICN  . . . . . . . . . . . . . .  24
     8.1.  Broadcast Encryption for DRM in ICN . . . . . . . . . . .  24
     8.2.  AAA-Based DRM for ICN Networks  . . . . . . . . . . . . .  27
       8.2.1.  Overview  . . . . . . . . . . . . . . . . . . . . . .  27
       8.2.2.  Implementation  . . . . . . . . . . . . . . . . . . .  28
   9.  Future Steps for Video in ICN . . . . . . . . . . . . . . . .  28
     9.1.  Large-Scale Live Events . . . . . . . . . . . . . . . . .  29
     9.2.  Video Conferencing and Real-Time Communications . . . . .  29
     9.3.  Store-and-Forward Optimized  Rate Adaptation  . . . . . .  29
     9.4.  Heterogeneous  Wireless Environment Dynamics  . . . . . .  30
     9.5.  Network Coding for Video Distribution in ICN  . . . . . .  32
     9.6.  Synchronization Issues for Video Distribution in ICN  . .  32
   10. Security  Considerations  . . . . . . . . . . . . . . . . . .  33
   11. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .  33
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     12.2.  Informative References . . . . . . . . . . . . . . . . .  34
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  38
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  39

1.  Introduction

   The unprecedented growth of video traffic has triggered a rethinking
   of how content is distributed, both in terms of the underlying
   Internet architecture and in terms of the streaming mechanisms to
   deliver video objects.

   In particular, the IRTF ICNRG research group has been chartered to
   study new architectures centered upon information; the main
   contributor to Internet traffic (and information dissemination) is
   video, and this is expected to stay the same in the near future.  If
   ICN is expected to become prominent, it will have to support video
   streaming efficiently.

   As such, it is necessary to discuss going in two separate directions:

      Can the current video streaming mechanisms be leveraged and
      adapted to an ICN architecture?

      Can (and should) new, ICN-specific video streaming mechanisms be
      designed to fully take advantage of the new abstractions exposed
      by the ICN architecture?

   This document focuses on the first question in an attempt to define
   the use cases for video streaming and some requirements.  It also
   focuses on a few scenarios (namely, Netflix-like video streaming, P2P
   video sharing, and IPTV) and identifies how the existing protocols
   can be adapted to an ICN architecture.  In doing so, it also
   identifies the main issues with these protocols in this ICN context.

   In addition to this document, other works have considered specific
   aspects of dynamic adaptive streaming in ICN [Lederer13b]
   [Lederer13a] [Grandl13] [Detti12].  This document is informed by
   these works, as well as others.

   In this document, we give a brief overview of the existing solutions
   for the selected scenarios.  We then examine the interactions of such
   existing mechanisms with the ICN architecture and list some of the
   interactions any video streaming mechanism will have to consider.
   Finally, we identify some areas for future research.

2.  Conventions Used in This Document

   In examples, "C:" and "S:" indicate lines sent by the client and
   server, respectively.

3.  Use Case Scenarios for ICN and Video Streaming

   For ICN-specific descriptions, we refer to the other research group
   documents [RFC7476].  For our purpose, we assume here that "ICN"
   refers to an architecture where content is retrieved by name and with
   no binding of content to a specific network location.

   Both live and on-demand consumption of multimedia content come with
   timing requirements for the delivery of the content.  Additionally,
   real-time use cases (such as audio-video conferencing [Jacobson09a],
   game streaming, etc.) come with stricter timing requirements.  Long
   startup delays, buffering periods, poor video quality, etc., should
   be avoided to achieve a better Quality of Experience (QoE) for the
   consumer of the content.  For a definition of QoE in the context of
   video distribution, please refer to [LeCallet13].  The working
   definition is as follows:

      Quality of Experience (QoE) is the degree of delight or annoyance
      of the user of an application or service.  It results from the
      fulfillment of his or her expectations with respect to the utility
      and/or enjoyment of the application or service in the light of the
      user's personality and current state.

   Of course, these requirements are heavily influenced by routing
   decisions and caching, which are central parts of ICN and that have
   to be considered when streaming video in such infrastructures.

   Due to this range of requirements, we find it useful to narrow the
   focus to four scenarios (more can be included later):

   o  a video download architecture similar to that of Apple iTunes,
      where the whole file is being downloaded to the client and can be
      replayed there multiple times;

   o  a video streaming architecture for playing back movies, which is
      relevant for the naming and caching aspects of ICN as well as the
      interaction with the rate adaptation mechanism necessary to
      deliver the best QoE to the end user;

   o  a P2P architecture for sharing videos, which introduces more
      stringent routing requirements in terms of locating copies of the
      content as the location of the peers evolves and peers join and
      leave the swarm they use to exchange video chunks (for P2P
      definitions and taxonomy, please refer to RFC 5694; and

   o  IPTV, which introduces requirements for multicasting and adds
      stronger delay constraints.

   Other scenarios, such as video conferencing and real-time video
   communications, are not explicitly discussed in this document even
   though they are in scope.  Also, events of mass-media distribution,
   such as a large crowd at a live event, add new requirements to be
   included in later versions.

   The current state-of-the-art protocols in an IP context can be
   modified for the ICN architecture.  The remainder of this document is
   organized as follows: Section 4 discusses video download; Section 5
   briefly describes DASH [ISO-DASH] and Layered Encoding (Modification
   Detection Code (MDC), Scalable Video Coding (SVC)); Section 6 focuses
   on P2P and PPSP; Section 7 highlights the requirements of IPTV;
   Section 8 describes the issues of DRM; and Section 9 lists some
   research issues to be solved for ICN-specific video delivery

   Video-conferencing and real-time-video communications will be
   described in further detail in future works.  Mass distribution of
   content at live, large-scale events (stadiums, concert halls, etc.)
   for which there is no clearly adopted existing protocol is another
   topic for further research.

4.  Video Download

   Video download, namely the fetching of a video file from a server or
   a cache down to the user's local storage, is a natural application of
   ICN.  It should be supported natively without requiring any specific

   This is supported now by a host of protocols (say, Secure Copy (SCP),
   FTP, or over HTTP), which would need to be replaced by new ICN-
   specific protocols to retrieve content in ICNs.

   However, current mechanisms are built atop existing transport
   protocols.  Some ICN proposals (Context-Centric Network (CCN) or
   Named Data Networking (NDN), for instance) attempt to leverage the
   work done upon these transport protocols.  One proposal is to use the
   TCP congestion window (and the associated Adaptive Increase,
   Multiplicative Decrease (AIMD)) to decide how many object requests
   ("Interests" in CCN/NDN terminology) should be in flight at any point
   in time.

   It should be noted that ICN intrinsically supports different
   transport mechanisms, which could achieve better performance than
   TCP, as they subsume TCP into a special case.  For instance, one
   could imagine a link-by-link transport coupled with caching.  This is
   enabled by the ICN architecture and would facilitate the point-to-
   point download of video files.

5.  Video Streaming and ICN

5.1.  Introduction to Client-Driven Streaming and DASH

   Media streaming over HTTP and, in a further consequence, streaming
   over the TCP, has become omnipresent in today's Internet.  Content
   providers such as Netflix, Hulu, and Vudu do not deploy their own
   streaming equipment: they use the existing Internet infrastructure as
   it is and simply deploy their own services Over The Top (OTT).  This
   streaming approach works surprisingly well without any particular
   support from the underlying network due to the use of efficient video
   compression, Content Delivery Networks (CDNs), and adaptive video
   players.  Earlier video streaming research mostly recommended use of
   the User Datagram Protocol (UDP) combined with the Real-time
   Transport Protocol (RTP).  It assumed it would not be possible to
   transfer multimedia data smoothly with TCP, because of its throughput
   variations and large retransmission delays.  This point of view has
   significantly evolved today.  HTTP streaming, and especially its most
   simple form known as progressive download, has become very popular
   over the past few years because it has some major benefits compared
   to RTP streaming.  As a consequence of the consistent use of HTTP for
   this streaming method, the existing Internet infrastructure
   consisting of proxies, caches, and CDNs could be used.  Originally,
   this architecture was designed to support best-effort delivery of
   files and not real-time transport of multimedia data.  Nevertheless,
   real-time streaming based on HTTP could also take advantage of this
   architecture, in comparison to RTP, which could not leverage any of
   the aforementioned components.  Another benefit that results from the
   use of HTTP is that the media stream could easily pass firewalls or
   Network Address Translation (NAT) gateways, which was definitely a
   key for the success of HTTP streaming.  However, HTTP streaming is
   not the holy grail of streaming as it also introduces some drawbacks
   compared to RTP.  Nevertheless, in an ICN-based video streaming
   architecture these aspects also have to be considered.

   The basic concept of DASH [ISO-DASH] is to use segments of media
   content, which can be encoded at different resolutions, bit rates,
   etc., as so-called representations.  These segments are served by
   conventional HTTP web servers and can be addressed via HTTP GET
   requests from the client.  As a consequence, the streaming system is
   pull-based and the entire streaming logic is located on the client,
   which makes it scalable and allows for adaptation of the media stream
   to the client's capabilities.

   In addition to this, the content can be distributed using
   conventional CDNs and their HTTP infrastructure, which also scales
   very well.  In order to specify the relationship between the
   contents' media segments and the associated bit rate, resolution, and

   timeline, the Media Presentation Description (MPD) is used, which is
   an XML document.  The MPD refers to the available media segments
   using HTTP URLs, which can be used by the client for retrieving them.

5.2.  Layered Encoding

   Another approach for video streaming consists in using layered
   encoding.  Namely, scalable video coding formats the video stream
   into different layers: a base layer that can be decoded to provide
   the lowest bit rate for the specific stream and enhancement layers
   that can be transmitted separately if network conditions allow.  The
   higher layers offer higher resolutions and enhancement of the video
   quality, while the layered approach allows for adaptation to the
   network conditions.  This is used in an MPEG-4 scalable profile or
   H.263+.  H264SVC is available but not much deployed.  JPEG2000 has a
   wavelet transform approach for layered encoding but has not been
   deployed much either.  It is not clear if the layered approach is
   fine-grained enough for rate control.

5.3.  Interactions of Video Streaming with ICN

5.3.1.  Interactions of DASH with ICN

   Video streaming (DASH in particular) has been designed with a goal
   that is aligned with that of most ICN proposals: it is a client-based
   mechanism that requests items (in this case, chunks of a video
   stream) by name.

   ICN and MPEG-DASH [ISO-DASH] have several elements in common:

   o  the client-initiated pull approach;

   o  the content being dealt with in pieces (or chunks);

   o  the support of efficient replication and distribution of content
      pieces within the network;

   o  the scalable, session-free nature of the exchange between the
      client and the server at the streaming layer: the client is free
      to request any chunk from any location; and

   o  the support for potentially multiple source locations.

   For the last point, DASH may list multiple source URLs in a manifest,
   and ICN is agnostic to the location of a copy it is receiving.  We do
   not imply that current video streaming mechanisms attempt to draw the

   content from multiple sources concurrently.  This is a potential
   benefit of ICN but is not considered in the current approaches
   mentioned in this document.

   As ICN is a promising candidate for the Future Internet (FI)
   architecture, it is useful to investigate its suitability in
   combination with multimedia streaming standards like MPEG-DASH.  In
   this context, the purpose of this section is to present the usage of
   ICN instead of HTTP in MPEG-DASH.

   However, there are some issues that arise from using a dynamic rate
   adaptation mechanism in an ICN architecture (note that some of the
   issues are related to caching and are not necessarily unique to ICN):

   o  Naming of the data in DASH does not necessarily follow the ICN
      convention of any of the ICN proposals.  Several chunks of the
      same video stream might currently go by different names that, for
      instance, do not share a common prefix.  There is a need to
      harmonize the naming of the chunks in DASH with the naming
      conventions of the ICN.  The naming convention of using a
      filename/time/encoding format could, for instance, be made
      compatible with the convention of CCN.

   o  While chunks can be retrieved from any server, the rate adaptation
      mechanism attempts to estimate the available network bandwidth so
      as to select the proper playback rate and keep its playback buffer
      at the proper level.  Therefore, there is a need to either include
      some location semantics in the data chunks so as to properly
      assess the throughput to a specific location or to design a
      different mechanism to evaluate the available network bandwidth.

   o  The typical issue of access control and accounting happens in this
      context, where chunks can be cached in the network outside of the
      administrative control of the content publisher.  It might be a
      requirement from the owner of the video stream that access to
      these data chunks needs to be accounted/billed/monitored.

   o  Dynamic streaming multiplies the representations of a given video
      stream, therefore diminishing the effectiveness of caching:
      namely, to get a hit for a chunk in the cache, it has to be for
      the same format and encoding values.  Alternatively, to get the
      same hit rate as a stream using a single encoding, the cache size
      must be scaled up to include all the possible representations.

   o  Caching introduces oscillatory dynamics as it may modify the
      estimation of the available bandwidth between the end user and the
      repository from which it is getting the chunks.  For instance, if
      an edge cache holds a low resolution representation near the user,

      the user getting these low resolution chunks will observe a good
      performance and will then request higher resolution chunks.  If
      those are hosted on a server with poor performance, then the
      client would have to switch back to the low representation.  This
      oscillation may be detrimental to the perceived QoE of the user.

   o  The ICN transport mechanism needs to be compatible to some extent
      with DASH.  To take a CCN example, the rate at which interests are
      issued should be such that the chunks received in return arrive
      fast enough and with the proper encoding to keep the playback
      buffer above some threshold.

   o  The usage of multiple network interfaces is possible in ICN,
      enabling a seamless handover between them.  For the combination
      with DASH, an intelligent strategy that should focus on traffic
      load-balancing between the available links may be necessary.  This
      would increase the effective media throughput of DASH by
      leveraging the combined available bandwidth of all links; however,
      it could potentially lead to high variations of the media

   o  DASH does not define how the MPD is retrieved; hence, this is
      compatible with CCN.  However, the current profiles defined within
      MPEG-DASH require the MPD to contain HTTP URLs (including HTTP and
      HTTPS URI schemes) to identify segments.  To enable a more
      integrated approach as described in this document, an additional
      profile for DASH over CCN has to be defined, enabling ICN/CCN-
      based URIs to identify and request the media segments.

   We describe in Section 5.4 a potential implementation of a dynamic
   adaptive video stream over ICN, based upon DASH and CCN

5.3.2.  Interaction of ICN with Layered Encoding

   Issues of interest to an ICN architecture in the context of layered
   video streaming include:

   o  Caching of the multiple layers.  The caching priority should go to
      the base layer and to defining caching policy in order to decide
      when to cache enhancement layers;

   o  Synchronization of multiple content streams, as the multiple
      layers may come from different sources in the network (for
      instance, the base layer might be cached locally while the
      enhancement layers may be stored in the origin server).  Video and
      audio-video streams must be synchronized, and this includes both
      intra-layer synchronization (for the layers of the same video or

      audio stream) and inter-stream synchronization (see Section 9 for
      other synchronization aspects to be included in the "Future Steps
      for Video in ICN"); and

   o  Naming of the different layers: when the client requests an
      object, the request can be satisfied with the base layer alone,
      aggregated with enhancement layers.  Should one request be
      sufficient to provide different streams?  In a CCN architecture,
      for instance, this would violate a "one Interest, one Data packet"
      principle and the client would need to specify each layer it would
      like to receive.  In a Pub/Sub architecture, the Rendezvous Point
      would have to make a decision as to which layers (or which pointer
      to which layer's location) to return.

5.4.  Possible Integration of Video Streaming and ICN Architecture

5.4.1.  DASH over CCN

   DASH is intended to enable adaptive streaming, i.e., each content
   piece can be provided in different qualities, formats, languages,
   etc., to cope with the diversity of today's networks and devices.  As
   this is an important requirement for Future Internet proposals like
   CCN, the combination of those two technologies seems to be obvious.
   Since those two proposals are located at different protocol layers --
   DASH at the application and CCN at the network layer -- they can be
   combined very efficiently to leverage the advantages of both and
   potentially eliminate existing disadvantages.  As CCN is not based on
   classical host-to-host connections, it is possible to consume content
   from different origin nodes as well as over different network links
   in parallel, which can be seen as an intrinsic error resilience
   feature with respect to the network.  This is a useful feature of CCN
   for adaptive multimedia streaming within mobile environments since
   most mobile devices are equipped with multiple network links like 3G
   and Wi-Fi.  CCN offers this functionality out of the box, which is
   beneficial when used for DASH-based services.  In particular, it is
   possible to enable adaptive video streaming handling both bandwidth
   and network link changes.  That is, CCN handles the network link
   decision and DASH is implemented on top of CCN to adapt the video
   stream to the available bandwidth.

   In principle, there are two options to integrate DASH and CCN: a
   proxy service acting as a broker between HTTP and CCN as proposed in
   [Detti12], and the DASH client implementing a native CCN interface.
   The former transforms an HTTP request to a corresponding Interest
   packet as well as a Data packet back to an HTTP response, including
   reliable transport as offered by TCP.  This may be a good compromise
   to implement CCN in a managed network and to support legacy devices.
   Since such a proxy is already described in [Detti12], this document

   focuses on a more integrated approach, aiming at fully exploiting the
   potential of a CCN DASH client.  That is, we describe a native CCN
   interface within the DASH client, which adopts a CCN naming scheme
   (CCN URIs) to denote segments in the MPD.  In this architecture, only
   the network access component on the client has to be modified and the
   segment URIs within MPD have to be updated according to the CCN
   naming scheme.

   Initially, the DASH client retrieves the MPD containing the CCN URIs
   of the content representations including the media segments.  The
   naming scheme of the segments may reflect intrinsic features of CCN
   like versioning and segmentation support.  Such segmentation support
   is already compulsory for multimedia streaming in CCN; thus, it can
   also be leveraged for DASH-based streaming over CCN.  The CCN
   versioning can be adopted in a further step to signal different
   representations of the DASH-based content, which enables an implicit
   adaptation of the requested content to the clients' bandwidth
   conditions.  That is, the Interest packet already provides the
   desired characteristics of a segment (such as bit rate, resolution,
   etc.) within the content name (or potentially within parameters
   defined as extra types in the packet formats).  Additionally, if
   bandwidth conditions of the corresponding interfaces or routing paths
   allow so, DASH media segments could be aggregated automatically by
   the CCN nodes, which reduces the amount of Interest packets needed to
   request the content.  However, such approaches need further research,
   specifically in terms of additional intelligence and processing power
   needed at the CCN nodes.

   After requesting the MPD, the DASH client will start to request
   particular segments.  Therefore, CCN Interest packets are generated
   by the CCN access component and forwarded to the available
   interfaces.  Within the CCN, these Interest packets leverage the
   efficient interest aggregation for, e.g., popular content, as well as
   the implicit multicast support.  Finally, the Interest packets are
   satisfied by the corresponding Data packets containing the video
   segment data, which are stored on the origin server or any CCN node,
   respectively.  With an increasing popularity of the content, it will
   be distributed across the network resulting in lower transmission
   delays and reduced bandwidth requirements for origin servers and
   content providers, respectively.

   With the extensive usage of in-network caching, new drawbacks are
   introduced since the streaming logic is located at the client, i.e.,
   clients are not aware of each other and the network infrastructure
   and cache states.  Furthermore, negative effects are introduced when
   multiple clients compete in a bottleneck and when caching influences
   this bandwidth competition.  As mentioned above, the clients request
   individual portions of the content based on available bandwidth,

   which is calculated using throughput estimations.  This uncontrolled
   distribution of the content influences the adaptation process of
   adaptive streaming clients.  The impact of this falsified throughput
   estimation could be tremendous and leads to a wrong adaptation
   decision that may impact the QoE at the client, as shown in
   [Mueller12].  In ICN, the client does not have the knowledge from
   which source the requested content is actually served or how many
   origin servers of the content are available, as this is transparent
   and depends on the name-based routing.  This introduces the challenge
   that the adaptation logic of the adaptive streaming client is not
   aware of the event when the ICN routing decides to switch to a
   different origin server or content is coming through a different
   link/interface.  As most algorithms implementing the adaption logic
   use bandwidth measurements and related heuristics, the adaptation
   decisions are no longer valid when changing origin servers (or
   links), and these decisions potentially cause playback interruptions
   and, consequently, stalling.  Additionally, ICN supports the usage of
   multiple interfaces.  A seamless handover between these interfaces
   (and different sources for the content) comes together with changes
   in performance, e.g., due to switching between fixed and wireless,
   3G/4G and Wi-Fi networks, different types of servers (say with/
   without Shared Secret Data (SSD) or hardware acceleration), etc.

   Considering these characteristics of ICN, adaptation algorithms
   merely based on bandwidth measurements are not appropriate anymore,
   as potentially each segment can be transferred from another ICN node
   or interface, all with different bandwidth conditions.  Thus,
   adaptation algorithms taking into account these intrinsic
   characteristics of ICN are preferred over algorithms based on mere
   bandwidth measurements.

5.4.2.  Testbed, Open-Source Tools, and Dataset

   For the evaluations of DASH over CCN, a testbed with open-source
   tools and datasets is provided in [ITEC-DASH].  In particular, it
   provides two client-player implementations, (i) a libdash extension
   for DASH over CCN and (ii) a VLC plugin implementing DASH over CCN.
   For both implementations, the CCNx implementation has been used as a

   The general architecture of libdash is organized in modules so that
   the library implements a MPD parser and an extensible connection
   manager.  The library provides object-oriented interfaces for these
   modules to access the MPD and the downloadable segments.  These
   components are extended to support DASH over CCN and are located in a
   separate development branch of the GitHub project available at
   <http://www.github.com/bitmovin/libdash>. libdash comes together with
   a fully featured DASH player with a QT-based front end, demonstrating

   the usage of libdash and providing a scientific evaluation platform.
   As an alternative, patches for the DASH plugin of the VLC player are
   provided.  These patches can be applied to the latest source code
   checkout of VLC resulting in a DASH-over-CCN-enabled VLC player.

   Finally, a DASH-over-CCN dataset is provided in the form of a CCNx
   repository.  It includes 15 different quality representation of the
   well-known Big Buck Bunny Movie, ranging from 100 kbps to 4500 kbps.
   The content is split into segments of two seconds and is described by
   an associated MPD using the presented naming scheme in Section 5.1.
   This repository can be downloaded from [ITEC-DASH] and is also
   provided by a publicly accessible CCNx node.  Associated routing
   commands for the CCNx namespaces of the content are provided via
   scripts coming together with the dataset and can be used as a public

6.  P2P Video Distribution and ICN

   Peer-to-Peer distribution is another form of distributing content --
   and video in particular -- that ICNs need to support.  We see now how
   an existing protocol such as PPSP can be modified to work in an ICN

6.1.  Introduction to PPSP

   P2P Video Streaming (P2PVS) is a popular approach to redistribute
   live media over the Internet.  The proposed P2PVS solutions can be
   roughly classified in two classes:

   o  Push/Tree-based

   o  Pull/Mesh-based

   The Push/Tree-based solution creates an overlay network among Peers
   that has a tree shape [Castro03].  Using a progressive encoding
   (e.g., Multiple Description Coding or H.264 Scalable Video Coding),
   multiple trees could be set up to support video rate adaptation.  On
   each tree, an enhancement stream is sent.  The higher the number of
   received streams, the higher the video quality.  A peer controls the
   video rate by either fetching or not fetching the streams delivered
   over the distribution trees.

   The Pull/Mesh-based solution is inspired by the BitTorrent file
   sharing mechanism.  A tracker collects information about the state of
   the swarm (i.e., the set of participating peers).  A peer forms a
   mesh overlay network with a subset of peers and exchanges data with
   them.  A peer announces what data items it disposes and requests
   missing data items that are announced by connected peers.  In case of

   live streaming, the involved data set includes only a recent window
   of data items published by the source.  Also, in this case, the use
   of a progressive encoding can be exploited for video rate adaptation.

   Pull/Mesh-based P2PVS solutions are the more promising candidate for
   the ICN deployment, since most of ICN approach provides a pull-based
   API [Jacobson09b] [Detti11] [Chai11] [NETINF].  In addition,
   Pull/Mesh-based P2PVS are more robust than the Push/Tree-based one
   [Magharei07], and the PPSP working group [IETF-PPSP] is also
   proposing a Pull/Mesh-based solution.

            |                                                |
            |     +--------------------------------+         |
            |     |            Tracker             |         |
            |     +--------------------------------+         |
            |        |     ^                   ^             |
            |Tracker |     | Tracker           |Tracker      |
            |Protocol|     | Protocol          |Protocol     |
            |        |     |                   |             |
            |        V     |                   |             |
            |     +---------+    Peer     +---------+        |
            |     |   Peer  |<----------->|   Peer  |        |
            |     +---------+   Protocol  +---------+        |
            |       | ^                                      |
            |       | |Peer                                  |
            |       | |Protocol                              |
            |       V |                                      |
            |     +---------------+                          |
            |     |      Peer     |                          |
            |     +---------------+                          |
            |                                                |

               Figure 1: PPSP System Architecture [RFC6972]

   Figure 1 reports the PPSP architecture presented in [RFC6972].  PEERs
   announce and share video chunks and a TRACKER maintains a list of
   PEERs participating in a specific audio-video channel or in the
   distribution of a streaming file.  The TRACKER functionality may be
   centralized in a server or distributed over the PEERs.  PPSP
   standardizes the peer and Tracker Protocols, which can run directly
   over UDP or TCP.

   This document discusses some preliminary concepts about the
   deployment of PPSP on top of an ICN that exposes a pull-based API,
   meanwhile considering the impact of MPEG-DASH streaming format.

6.2.  PPSP over ICN: Deployment Concepts

6.2.1.  PPSP Short Background

   The Peer-to-Peer Streaming Peer Protocol (PPSPP) is defined in
   [Bakker15] and the Peer-to-Peer Streaming Tracker Protocol (PPSP-TP)
   is defined in [RFC7846].

   Some of the operations carried out by the Tracker Protocol are the
   following: when a peer wishes to join the streaming session, it
   contacts the tracker (CONNECT message), obtains a PEER_ID and a list
   of PEER_IDs (and IP addresses) of other peers that are participating
   to the SWARM and that the tracker has singled out for the requesting
   peer (this may be a subset of the all peers of the SWARM); in
   addition to this join operation, a peer may contact the tracker to
   request to renew the list of participating peers (FIND message), to
   periodically update its status to the tracker (STAT_REPORT message),
   and so on.

   Some of the operations carried out by the Peer Protocol include the
   following: using the list of peers delivered by the tracker, a peer
   establishes a session with them (HANDSHAKE message); a peer
   periodically announces to neighboring peers which chunks it has
   available for download (HAVE message); using these announcements, a
   peer requests missing chunks from neighboring peers (REQUEST
   messages), which will be sent back to them (DATA message).

6.2.2.  From PPSP Messages to ICN Named-Data

   An ICN provides users with data items exposed by names.  The bundle
   name and data item is usually referred as "named-data", "named-
   content", etc.  To transfer PPSP messages through an ICN, the
   messages should be wrapped as named-data items and receivers should
   request them by name.

   A PPSP entity receives messages from peers and/or a tracker.  Some
   operations require gathering the messages generated by another
   specific host (peer or tracker).  For instance, if Peer A wishes to
   gain information about video chunks available from Peer B, the former
   shall fetch the PPSP HAVE messages specifically generated by the
   latter.  We refer to these kinds of named-data as "located-named-
   data" since they should be gathered from a specific location (e.g.,
   Peer B).

   For other PPSP operations, such as fetching a DATA message (i.e., a
   video chunk), as long as a peer receives the requested content, it
   doesn't matter which endpoint generated the data.  We refer to this
   information with the generic term "named-data".

   The naming scheme differentiates named-data and located-named-data
   items.  In the case of named-data, the naming scheme only includes a
   content identifier (e.g., the name of the video chunk) without any
   prefix identifying who provides the content.  For instance, a DATA
   message containing the video chunk "#1" may be named as
   "ccnx:/swarmID/chunk/chunkID", where swarmID is a unique identifier
   of the streaming session, "chunk" is a keyword, and chunkID is the
   chunk identifier (e.g., an integer number).

   In case of located-named-data, the naming scheme includes a location-
   prefix, which uniquely identifies the host generating the data item.
   This prefix may be the PEER_ID in case the host was a peer or a
   tracker identifier in case the host was the tracker.  For instance, a
   HAVE message generated by a Peer B may be named as
   "ccnx:/swarmID/peer/PEER_ID/HAVE", where "peer" is a keyword,
   PEER_ID_B is the identifier of Peer B, and HAVE is a keyword.

6.2.3.  Support of PPSP Interaction through a Pull-Based ICN API

   The PPSP procedures are based both on pull and push interactions.
   For instance, the distribution of chunks availability can be
   classified as a push-based operation since a peer sends "unsolicited"
   information (HAVE message) to neighboring peers.  Conversely, the
   procedure used to receive video chunks can be classified as pull-
   based since it is supported by a request/response interaction (i.e.,
   REQUEST, DATA messages).

   As we said, we refer to an ICN architecture that provides a pull-
   based API.  Accordingly, the mapping of PPSP pull-based procedure is
   quite simple.  For instance, using the CCN architecture
   [Jacobson09b], a PPSP DATA message may be carried by a CCN DATA
   message and a REQUEST message can be transferred by a CCN Interest.

   Conversely, the support of push-based PPSP operations may be more
   difficult.  We need an adaptation functionality that carries out a
   push-based operation using the underlying pull-based service
   primitives.  For instance, a possible approach is to use the request/
   response (i.e., Interest/Data) four-way handshakes proposed in
   [Jacobson09a].  Another possibility is that receivers periodically
   send out request messages of the named-data that neighbors will push
   and, when available, the sender inserts the pushed data within a
   response message.

6.2.4.  Abstract Layering for PPSP over ICN

                   |            Application            |
                   |           PPSP (TCP/IP)           |
                   |  ICN - PPSP Adaptation Layer (AL) |
                   |         ICN Architecture          |

                        Figure 2: Mediator Approach

   Figure 2 provides a possible abstract layering for PPSP over ICN.
   The Adaptation Layer acts as a mediator (proxy) between legacy PPSP
   entities based on TCP/IP and the ICN architecture.  In fact, the role
   the mediator is to use ICN to transfer PPSP legacy messages.

   This approach makes it possible to merely reuse TCP/IP P2P
   applications whose software includes also PPSP functionality.  This
   "all-in-one" development approach may be rather common since the PPSP
   application interface is not going to be specified.  Moreover, if the
   operating system will provide libraries that expose a PPSP API, these
   will be initially based on an underlying TCP/IP API.  Also, in this
   case, the mediator approach would make it possible to easily reuse
   both the PPSP libraries and the Application on top of an ICN.

                  |            Application            |
                  |             ICN-PPSP              |
                  |          ICN Architecture         |

                      Figure 3: Clean-Slate Approach

   Figure 3 sketches a clean-slate layering approach in which the
   application directly includes or interacts with a PPSP version based
   on ICN.  It's likely such a PPSP_ICN integration could yield a
   simpler development also because it does not require implementing a
   TCP/IP to ICN translation as in the Mediator approach.  However, the
   clean-slate approach requires developing the application (in case of
   embedded PPSP functionality) or the PPSP library from scratch without
   exploiting what might already exist for TCP/IP.

   Overall, the Mediator approach may be considered the first step of a
   migration path towards ICN-native PPSP applications.

6.2.5.  PPSP Interaction with the ICN Routing Plane

   Upon the ICN API, a user (peer) requests content and the ICN sends it
   back.  The content is gathered by the ICN from any source, which
   could be the closest peer that disposes of the named-data item, an
   in-network cache, etc.  Actually, "where" to gather the content is
   controlled by an underlying ICN routing plane, which sets up the ICN
   forwarding tables (e.g., CCN FIB [Jacobson09b]).

   A cross-layer interaction between the ICN routing plane and the PPSP
   may be required to support a PPSP session.  Indeed, ICN shall forward
   request messages (e.g., CCN Interest) towards the proper peer that
   can handle them.  Depending on the layering approach, this cross-
   layer interaction is controlled either by the Adaptation Layer or by
   the ICN-PPSP.  For example, if a Peer A receives a HAVE message
   indicating that Peer B disposes of the video chunk named
   "ccnx:/swarmID/chunk/chunkID", then the former should insert in its
   ICN forwarding table an entry for the prefix "ccnx:/swarmID/chunk/
   chunkID" whose next hop locator (e.g., IP address) is the network
   address of Peer B [Detti13].

6.2.6.  ICN Deployment for PPSP

   The ICN functionality that supports a PPSP session may be "isolated"
   or "integrated" with one from a public ICN.

   In the isolated case, a PPSP session is supported by an instance of
   an ICN (e.g., deployed on top of an IP) whose functionalities operate
   only on the limited set of nodes participating to the swarm, i.e.,
   peers and the tracker.  This approach resembles the one followed by a
   current P2P application, which usually forms an overlay network among
   peers of a P2P application; intermediate public IP routers do not
   carry out P2P functionalities.

   In the integrated case, the nodes of a public ICN may be involved in
   the forwarding and in-network caching procedures.  In doing so, the
   swarm may benefit from the presence of in-network caches, thus
   limiting uplink traffic on peers and inter-domain traffic, too.
   These are distinctive advantages of using PPSP over a public ICN
   rather than over TCP/IP.  In addition, such advantages aren't likely
   manifested in the case of isolated deployment.

   However, the possible interaction between the PPSP and the routing
   layer of a public ICN may be dramatic, both in terms of explosion of
   the forwarding tables and in terms of security.  These issues

   specifically take place for those ICN architectures for which the
   name resolution (i.e., name to next hop) occurs en route, like the
   CCN architecture.

   For instance, using the CCN architecture, to fetch a named-data item
   offered by a Peer A the on-path public ICN entities have to route the
   request messages towards the Peer A.  This implies that the ICN
   forwarding tables of public ICN nodes may contain many entries, e.g.,
   one entry per video chunk, and these entries are difficult to be
   aggregated since peers may have available only sparse parts of a big
   content, whose names have a same prefix (e.g., "ccnx:/swarmID").
   Another possibility is to wrap all PPSP messages into a located-
   named-data.  In this case, the forwarding tables should contain
   "only" the PEER_ID prefixes (e.g., "ccnx:/swarmID/peer/PEER_ID"),
   thus scaling down the number of entries from number of chunks to
   number of peers.  However, in this case, the ICN mechanisms recognize
   the same video chunk offered by different peers as different content,
   thus losing caching and multicasting ICN benefits.  In any case,
   routing entries should be updated either on the basis of the
   availability of named-data items on peers or on the presence of
   peers, and these events in a P2P session are rapidly changing and
   possibly hampering the convergence of the routing plane.  Finally,
   since peers have an impact on the ICN forwarding table of public
   nodes, this may open obvious security issues.

6.3.  Impact of MPEG-DASH Coding Schemes

   The introduction of video rate adaptation may significantly decrease
   the effectiveness of P2P cooperation and of in-network caching,
   depending of the kind of the video coding used by the MPEG-DASH

   In case of an MPEG-DASH streaming with MPEG AVC encoding, the same
   video chunk is independently encoded at different rates and the
   encoding output is a different file for each rate.  For instance, in
   case of a video encoded at three different rates, R1, R2, and R3; for
   each segment S, we have three distinct files: S.R1, S.R2, and S.R3.
   These files are independent of each other.  To fetch a segment coded
   at R2 kbps, a peer shall request the specific file S.R2.  Receiver-
   driven algorithms, implemented by the video client, usually handle
   the estimation of the best coding rate.

   The independence among files associated with different encoding rates
   and the heterogeneity of peer bandwidths may dramatically reduce the
   interaction among peers, the effectiveness of in-network caching (in
   case of integrated deployment), and consequently, the ability of PPSP
   to offload the video server (i.e., a seeder peer).  Indeed, a Peer A
   may select a coding rate (e.g., R1) different from the one selected

   by a Peer B (e.g., R2), and this prevents the former from fetching
   video chunks from the latter since Peer B only has chunks available
   that are coded at a rate different from the ones needed by Peer A.
   To overcome this issue, a common distributed rate selection algorithm
   could force peers to select the same coding rate [Detti13];
   nevertheless, this approach may be not feasible in the case of many

   The use of an SVC encoding (Annex G extension of the H.264/MPEG-4
   Advanced Video Coding (AVC) video compression standard) should make
   rate adaptation possible while neither reducing peer collaborations
   nor the in-network caching effectiveness.  For a single video chunk,
   an SVC encoder produces different files for the different rates
   (roughly "layers"), and these files are progressively related to each
   other.  Starting from a base layer that provides the minimum rate
   encoding, the next rates are encoded as an "enhancement layer" of the
   previous one.  For instance, in case the video is coded with three
   rates, R1 (base layer), R2 (enhancement layer n.1), and R3
   (enhancement layer n.2), then for each DASH segment, we have three
   files: S.R1, S.R2, and S.R3.  The file S.R1 is the segment coded at
   the minimum rate (base layer).  The file S.R2 enhances S.R1, so S.R1
   and S.R2 can be combined to obtain a segment coded at rate R2.  To
   get a segment coded at rate R2, a peer shall fetch both S.R1 and
   S.R2.  This progressive dependence among files that encode the same
   segment at different rates makes peer cooperation possible, also in
   case peers player have autonomously selected different coding rates.
   For instance, if Peer A has selected the rate R1, the downloaded
   files S.R1 are useful also for a Peer B that has selected the rate
   R2, and vice versa.

7.  IPTV and ICN

7.1.  IPTV Challenges

   IPTV refers to the delivery of quality content broadcast over the
   Internet and is typically associated with strict quality
   requirements, i.e., with a perceived latency of less than 500 ms and
   a packet loss rate that is multiple orders lower than the current
   loss rates experienced in the most commonly used access networks (see
   [ATIS-IIF]).  We can summarize the major challenges for the delivery
   of IPTV service as follows.

   Channel change latency represents a major concern for the IPTV
   service.  Perceived latency during channel change should be less than
   500 ms.  To achieve this objective over the IP infrastructure, we
   have multiple choices:

   i     receive fast unicast streams from a dedicated server (most
         effective but not resource efficient);

   ii    connect to other peers in the network (efficiency depends on
         peer support, effective and resource efficient, if also
         supported with a dedicated server); and

   iii   connect to multiple multicast sessions at once (effective but
         not resource efficient and depends on the accuracy of the
         prediction model used to track user activity).

   The second major challenge is the error recovery.  Typical IPTV
   service requirements dictate the mean time between artifacts to be
   approximately 2 hours (see [ATIS-IIF]).  This suggests the perceived
   loss rate to be less than or equal to 10^-7.  Current IP-based
   solutions rely on the following proactive and reactive recovery
   techniques: (i) joining the Forward Error Correction (FEC) multicast
   stream corresponding to the perceived packet loss rate (not
   efficient, as the recovery strength is chosen based on worst-case
   loss scenarios); (ii) making unicast recovery requests to dedicated
   servers (requires active support from the service provider); (iii)
   probing peers to acquire repair packets (finding matching peers and
   enabling their cooperation is another challenge).

7.2.  ICN Benefits for IPTV Delivery

   ICN presents significant advantages for the delivery of IPTV traffic.
   For instance, ICN inherently supports multicast and allows for quick
   recovery from packet losses (with the help of in-network caching).
   Similarly, peer support is also provided in the shape of in-network
   caches that typically act as the middleman between two peers,
   therefore enabling earlier access to IPTV content.

   However, despite these advantages, delivery of IPTV service over ICNs
   brings forth new challenges.  We can list some of these challenges as

   o  Messaging overhead: ICN is a pull-based architecture and relies on
      a unique balance between requests and responses.  A user needs to
      make a request for each Data packet.  In the case of IPTV, with
      rates up to (and likely to be) above 15 Mbps, we observe
      significant traffic upstream to bring those streams.  As the
      number of streams increases (including the same session at

      different quality levels and other formats), so does the burden on
      the routers.  Even if the majority of requests are aggregated at
      the core, routers close to the edge (where we observe the biggest
      divergence in user requests) will experience a significant
      increase in overhead to process these requests.  The same is true
      at the user side, as the uplink usage multiplies in the number of
      sessions a user requests (for instance, to minimize the impact of
      bandwidth fluctuations).

   o  Cache control: As the IPTV content expires at a rapid rate (with a
      likely expiry threshold of 1 s), we need solutions to effectively
      flush out such content to also prevent degradation impact on other
      cached content, with the help of intelligently chosen naming
      conventions.  However, to allow for fast recovery and optimize
      access time to sessions (from current or new users), the timing of
      such expirations needs to be adaptive to network load and user
      demand.  However, we also need to support quick access to earlier
      content, whenever needed; for instance, when the user accesses the
      rewind feature (note that in-network caches will not be of
      significant help in such scenarios due to the overhead required to
      maintain such content).

   o  Access accuracy: To receive the up-to-date session data, users
      need to be aware of such information at the time of their request.
      Unlike IP multicast, since the users join a session indirectly,
      session information is critical to minimize buffering delays and
      reduce the startup latency.  Without such information, and without
      any active cooperation from the intermediate routers, stale data
      can seriously undermine the efficiency of content delivery.
      Furthermore, finding a cache does not necessarily equate to
      joining a session, as the look-ahead latency for the initial
      content access point may have a shorter lifetime than originally
      intended.  For instance, if the user that has initiated the
      indirect multicast leaves the session early, the requests from the
      remaining users need to experience an additional latency of one
      RTT as they travel towards the content source.  If the startup
      latency is chosen depending on the closeness to the intermediate
      router, going to the content source in-session can lead to
      undesired pauses.

   It should be noted that IPTV includes more than just multicast.  Many
   implementations include "trick plays" (fast forward, pause, rewind)
   that often transform a multicast session into multiple unicast
   sessions.  In this context, ICN is beneficial, as the caching offers
   an implicit multicast but without tight synchronization constraints
   in between two different users.  One user may rewind and start
   playing forward again, thus drawing from a nearby cache of the

   content recently viewed by another user (whereas in a strict
   multicast session, the opportunity of one user lagging off behind
   would be more difficult to implement).

8.  Digital Rights Management in ICN

   This section discusses the need for DRM functionalities for
   multimedia streaming over ICN.  It focuses on two possible
   approaches: modifying Authentication, Authorization, and Accounting
   (AAA) to support DRM in ICN and using Broadcast Encryption.

   It is assumed that ICN will be used heavily for digital content
   dissemination.  It is vital to consider DRM for digital content
   distribution.  In today's Internet, there are two predominant classes
   of business models for on-demand video streaming.  The first model is
   based on advertising revenues.  Non-copyright protected (usually
   User-Generated Content (UGC)) content is offered by large
   infrastructure providers like Google (YouTube) at no charge.  The
   infrastructure is financed by spliced advertisements into the
   content.  In this context, DRM considerations may not be required,
   since producers of UGC may only strive for the maximum possible
   dissemination.  Some producers of UGC are mainly interested in
   sharing content with their families, friends, colleges, or others and
   have no intention making a profit.  However, the second class of
   business model requires DRM, because these entities are primarily
   profit oriented.  For example, large on-demand streaming platforms
   (e.g., Netflix) establish business models based on subscriptions.
   Consumers may have to pay a monthly fee in order to get access to
   copyright-protected content like TV series, movies, or music.  This
   model may be ad supported and free to the content consumer, like
   YouTube Channels or Spotify, but the creator of the content expects
   some remuneration for his work.  From the perspective of the service
   providers and the copyright owners, only clients that pay the fee
   (explicitly or implicitly through ad placement) should be able to
   access and consume the content.  Anyway, the challenge is to find an
   efficient and scalable way of access control to digital content,
   which is distributed in ICNs.

8.1.  Broadcast Encryption for DRM in ICN

   This section discusses Broadcast Encryption (BE) as a suitable basis
   for DRM functionalities in conformance to the ICN communication
   paradigm (network-inherent caching, considered the advantage of BE,
   will be highlighted).

   In ICN, Data packets can be cached inherently in the network, and any
   network participant can request a copy of these packets.  This makes
   it very difficult to implement an access control for content that is

   distributed via ICN.  A naive approach is to encrypt the transmitted
   data for each consumer with a distinct key.  This prohibits everyone
   other than the intended consumers from decrypting and consuming the
   data.  However, this approach is not suitable for ICN's communication
   paradigm, since it would reduce the benefits gained from the inherent
   network caching.  Even if multiple consumers request the same
   content, the requested data for each consumer would differ using this
   approach.  A better, but still insufficient, idea is to use a single
   key for all consumers.  This does not destruct the benefits of ICN's
   caching ability.  The drawback is that if one of the consumers
   illegally distributes the key, the system is broken; any entity in
   the network can access the data.  Changing the key after such an
   event is useless since the provider has no possibility to identify
   the illegal distributor.  Therefore, this person cannot be stopped
   from distributing the new key again.  In addition to this issue,
   other challenges have to be considered.  Subscriptions expire after a
   certain time, and then it has to be ensured that these consumers
   cannot access the content anymore.  For a provider that serves
   millions of daily consumers (e.g., Netflix), there could be a
   significant number of expiring subscriptions per day.  Publishing a
   new key every time a subscription expires would require an unsuitable
   amount of computational power just to re-encrypt the collection of
   audio-visual content.

   A possible approach to solve these challenges is BE [Fiat94] as
   proposed in [Posch13].  From this point on, this section will focus
   only on BE as an enabler for DRM functionality in the use case of ICN
   video streaming.  This subsection continues with the explanation of
   how BE works and shows how BE can be used to implement an access
   control scheme in the context of content distribution in ICN.

   BE actually carries a misleading name.  One might expect a concrete
   encryption scheme.  However, it belongs to the family of key
   management schemes.  These schemes are responsible for the
   generation, exchange, storage, and replacement of cryptographic keys.
   The most interesting characteristics of BE schemes are:

   o  BE schemes typically use a global trusted entity called the
      Licensing Agent (LA), which is responsible for spreading a set of
      pre-generated secrets among all participants.  Each participant
      gets a distinct subset of secrets assigned from the LA.

   o  The participants can agree on a common session key, which is
      chosen by the LA.  The LA broadcasts an encrypted message that
      includes the key.  Participants with a valid set of secrets can
      derive the session key from this message.

   o  The number of participants in the system can change dynamically.
      Entities may join or leave the communication group at any time.
      If a new entity joins, the LA passes on a valid set of secrets to
      that entity.  If an entity leaves (or is forced to leave) the LA
      revokes the entity's subset of keys, which means that it cannot
      derive the correct session key anymore when the LA distributes a
      new key.

   o  Traitors (entities that reveal their secrets) can be traced and
      excluded from ongoing communication.  The algorithms and
      preconditions to identify a traitor vary between concrete BE

   This listing already illustrates why BE is suitable to control the
   access to data that is distributed via an ICN.  BE enables the usage
   of a single session key for confidential data transmission between a
   dynamically changing subset or network participants.  ICN caches can
   be utilized since the data is encrypted only with a single key known
   by all legitimate clients.  Furthermore, traitors can be identified
   and removed from the system.  The issue of re-encryption still exists
   because the LA will eventually update the session key when a
   participant should be excluded.  However, this disadvantage can be
   relaxed in some way if the following points are considered:

   o  The updates of the session key can be delayed until a set of
      compromised secrets has been gathered.  Note that secrets may
      become compromised because of two reasons: first, a traitor could
      have illegally revealed the secret; second, the subscription of an
      entity expired.  Delayed revocation temporarily enables some
      illegitimate entities to consume content.  However, this should
      not be a severe problem in home entertainment scenarios.  Updating
      the session key in regular (not too short) intervals is a good
      trade- off.  The longer the interval lasts, the less computational
      resources are required for content re-encryption and the better
      the cache utilization in the ICN will be.  To evict old data from
      ICN caches that have been encrypted with the prior session key,
      the publisher could indicate a lifetime for transmitted packets.

   o  Content should be re-encrypted dynamically at request time.  This
      has the benefit that untapped content is not re-encrypted if the
      content is not requested during two session key update; therefore,
      no resources are wasted.  Furthermore, if the updates are
      triggered in non-peak times, the maximum amount of resources
      needed at one point in time can be lowered effectively since in
      peak times generally more diverse content is requested.

   o  Since the amount of required computational resources may vary
      strongly from time to time, it would be beneficial for any
      streaming provider to use cloud-based services to be able to
      dynamically adapt the required resources to the current needs.  In
      regard to a lack of computation time or bandwidth, the cloud
      service could be used to scale up to overcome shortages.

   Figure 4 shows the potential usage of BE in a multimedia delivery
   framework that builds upon ICN infrastructure and uses the concept of
   dynamic adaptive streaming, e.g., DASH.  BE would be implemented on
   the top to have an efficient and scalable way of access control to
   the multimedia content.

              +--------Multimedia Delivery Framework--------+
              |                                             |
              |     Technologies            Properties      |
              |  +----------------+     +----------------+  |
              |  |   Broadcast    |<--->|   Controlled   |  |
              |  |   Encryption   |     |     Access     |  |
              |  +----------------+     +----------------+  |
              |  |Dynamic Adaptive|<--->|   Multimedia   |  |
              |  |   Streaming    |     |   Adaptation   |  |
              |  +----------------+     +----------------+  |
              |  |       ICN      |<--->|   Cacheable    |  |
              |  | Infrastructure |     |   Data Chunks  |  |
              |  +----------------+     +----------------+  |

            Figure 4: A Potential Multimedia Framework Using BE

8.2.  AAA-Based DRM for ICN Networks

8.2.1.  Overview

   Recently, a novel approach to DRM has emerged to link DRM to usual
   network management operations, hence linking DRM to AAA services.
   ICN provides the abstraction of an architecture where content is
   requested by name and could be served from anywhere.  In DRM, the
   content provider (the origin of the content) allows the destination
   (the end-user account) to use the content.  The content provider and
   content storage/cache are at two different entities in ITU Carrier
   Code (ICC); for traditional DRM, only source and destination count
   and not the intermediate storage.  The proposed solution allows the
   provider of the caching to be involved in the DRM policies using
   well-known AAA mechanisms.  It is important to note that this
   solution is compatible with the proposal of the BE, proposed earlier
   in this document.  The BE proposes a technology, as this solution is
   more operational.

8.2.2.  Implementation

   With the proposed AAA-based DRM, when content is requested by name
   from a specific destination, the request could link back to both the
   content provider and the caching provider via traditional AAA
   mechanisms and trigger the appropriate DRM policy independently from
   where the content is stored.  In this approach, the caching, DRM, and
   AAA remain independent entities but can work together through ICN
   mechanisms.  The proposed solution enables extending the traditional
   DRM done by the content provider to jointly being done by content
   provider and network/caching provider.

   The solution is based on the concept of a "token".  The content
   provider authenticates the end user and issues an encrypted token to
   authenticate the named-content ID or IDs that the user can access.
   The token will be shared with the network provider and used as the
   interface to the AAA protocols.  At this point, all content access is
   under the control of the network provider and the ICN.  The
   controllers and switches can manage the content requests and handle
   mobility.  The content can be accessed from anywhere as long as the
   token remains valid or the content is available in the network.  In
   such a scheme, the content provider does not need to be contacted
   every time a named-content is requested.  This reduces the load of
   the content provider network and creates a DRM mechanism that is much
   more appropriate for the distributed caching and Peer-to-Peer storage
   characteristic of ICN networks.  In particular, the content requested
   by name can be served from anywhere under the only condition that the
   storage/cache can verify that the token is valid for content access.

   The solution is also fully customizable to both content and network
   provider's needs as the tokens can be issued based on user accounts,
   location, and hardware (Media Access Control (MAC) address, for
   example) linking it naturally to legacy authentication mechanisms.
   In addition, since both content and network providers are involved in
   DRM policies, pollution attacks and other illegal requests for the
   content can be more easily detected.  The proposed AAA-based DRM is
   currently under full development.

9.  Future Steps for Video in ICN

   The explosion of online video services, along with their increased
   consumption by mobile wireless terminals, further exacerbates the
   challenges of ICN mechanisms that leverage Video Adaptation.  The
   following sections present a series of research items derived from
   these challenges, further introducing next steps for the subject.

9.1.  Large-Scale Live Events

   Distributing content, and video in particular, using local
   communications in large-scale events such as sporting events in a
   stadium, a concert, or a large demonstration, is an active area of
   investigation and a potential use case where ICN would provide
   significant benefits.

   Such use cases involve locating content that is generated on the fly
   and requires discovery mechanisms in addition to sharing mechanisms.
   The scalability of the distribution becomes important as well.

9.2.  Video Conferencing and Real-Time Communications

   Current protocols for video conferencing have been designed, and this
   document takes input from them to identify the key research issues.
   Real-time communications add timing constraints (both in terms of
   delay and in terms of synchronization) to the scenario discussed

   An Access Router (AR) and a Virtual Router (VR), and immersive
   multimedia experiences in general, are clearly an area of further
   investigation, as they involve combining multiple streams of data
   from multiple users into a coherent whole.  This raises issues of
   multisource, multidestination multimedia streams that ICN may be
   equipped to deal with in a more natural manner than IP, which is
   inherently unicast.

9.3.  Store-and-Forward Optimized Rate Adaptation

   One of the benefits of ICN is to allow the network to insert caching
   in the middle of the data transfer.  This can be used to reduce the
   overall bandwidth demands over the network by caching content for
   future reuse, but it provides more opportunities for optimizing video

   Consider, for instance, the following scenario: a client is connected
   via an ICN network to a server.  Let's say the client is connected
   wirelessly to a node that has a caching capability, which is
   connected through a WAN to the server.  Further, assume that the
   capacity of each of the links (both the wireless and the WAN logical
   links) varies with time.

   If the rate adaptation is provided in an end-to-end manner, as in
   current mechanisms like DASH, then the maximal rate that can be
   supported at the client is that of the minimal bandwidth on each

   If, for instance, during Time Period 1 the wireless capacity is 1 and
   the wired capacity is 2 and during Time Period 2 the wireless
   capacity is 2 (due to some hotspot) and the wired capacity is 1 (due
   to some congestion in the network), then the best end-to-end rate
   that can be achieved is 1 during each period.

   However, if the cache is used during Time Period 1 to pre-fetch 2
   units of data, then during Time Period 2 there is 1 unit of data at
   the cache and another unit of data that can be streamed from the
   server; therefore, the rate that can be achieved is 2 units of data.
   In this case, the average bandwidth rises from 1 to 1.5 over the two

   This straw-man example illustrates a) the benefit of ICN for
   increasing the throughput of the network and b) the need for the
   special rate adaptation mechanisms to be designed to take advantage
   of this gain.  End-to-end rate adaptation cannot take advantage of
   the cache availability.  The authors of [Rainer16] showed that
   buffer-based adaptation mechanisms can be one approach to tackle this
   challenge.  As buffer-based adaptation does not estimate the
   available bandwidth resources (but solely considers the video buffer
   fill state), measured bandwidth fluctuations caused by cache hits are
   not existent.  Therefore, they cannot negatively impact the
   adaptation decisions (e.g., frequent representation switching).

9.4.  Heterogeneous Wireless Environment Dynamics

   With the ever-growing increase in online services being accessed by
   mobile devices, operators have been deploying different overlapping
   wireless access networking technologies.  In this way, in the same
   area, user terminals are within range of different cellular, Wi-Fi,
   or even Worldwide Interoperability for Microwave Access (WiMAX)
   networks.  Moreover, with the advent of the Internet of Things (e.g.,
   surveillance cameras feeding video footage), this list can be further
   complemented with more-specific short-range technologies, such as
   Bluetooth or ZigBee.

   In order to leverage from this plethora of connectivity
   opportunities, user terminals are coming equipped with different
   wireless access interfaces, providing them with extended connectivity
   opportunities.  In this way, such devices become able to select the
   type of access that best suits them according to different criteria,
   such as available bandwidth, battery consumption, access to different
   link conditions according to the user profile, or even access to
   different content.  Ultimately, these aspects contribute to the QoE
   perceived by the end user, which is of utmost importance when it
   comes to video content.

   However, the fact that these users are mobile and using wireless
   technologies also provides a very dynamic setting where the current
   optimal link conditions at a specific moment might not last or be
   maintained while the user moves.  These aspects have been amply
   analyzed in recently finished projects such as FP7 MEDIEVAL
   [MEDIEVAL], where link events reporting on wireless conditions and
   available alternative connection points were combined with video
   requirements and traffic optimization mechanisms towards the
   production of a joint network and mobile terminal mobility management
   decision.  Concretely, in [Fu13], link information about the
   deterioration of the wireless signal was sent towards a mobility
   management controller in the network.  This input was combined with
   information about the user profile, as well as of the current video
   service requirements, and used to trigger the decrease or increase of
   scalable video layers (adjusting the video to the ongoing link
   conditions).  Incrementally, the video could also be adjusted when a
   new, better connectivity opportunity presents itself.

   In this way, regarding Video Adaptation, ICN mechanisms can leverage
   from their intrinsic multiple source support capability and go beyond
   the monitoring of the status of the current link, thus exploiting the
   availability of different connectivity possibilities (e.g., different
   "interfaces").  Moreover, information obtained from the mobile
   terminal's point of view of its network link, as well as information
   from the network itself (i.e., load, policies, and others), can
   generate scenarios where such information is combined in a joint
   optimization procedure allowing the content to be forward to users
   using the best available connectivity option (e.g., exploiting
   management capabilities supported by ICN intrinsic mechanisms as in

   In fact, ICN base mechanisms can further be exploited in enabling new
   deployment scenarios such as preparing the network for mass requests
   from users attending a large multimedia event (i.e., concert,
   sports), allowing video to be adapted according to content, user and
   network requirements, and operation capabilities in a dynamic way.

   Enabling such scenarios requires further research, with the main
   points highlighted as follows:

   o  how to develop a generic video services (and obviously content)
      interface allowing the definition and mapping of their
      requirements (and characteristics) into the current capabilities
      of the network;

   o  how to define a scalable mechanism allowing either the video
      application at the terminal or some kind of network management
      entity, to adapt the video content in a dynamic way;

   o  how to develop the previous research items using intrinsic ICN
      mechanisms (i.e., naming and strategy layers);

   o  how to leverage intelligent pre-caching of content to prevent
      stalls and poor quality phases, which lead to a worse QoE for the
      user: this includes, in particular, the usage in mobile
      environments, which are characterized by severe bandwidth changes
      as well as connection outages, as shown in [Crabtree13]; and

   o  how to take advantage of the multipath opportunities over the
      heterogeneous wireless interfaces.

9.5.  Network Coding for Video Distribution in ICN

   An interesting research area for combining heterogeneous sources is
   to use network coding [Montpetit13b].  Network coding allows for
   asynchronous combining of multiple sources by having each of them
   send information that is not duplicated by the other but that can be
   combined to retrieve the video stream.

   However, this creates issues in ICN in terms of defining the proper
   rate adaptation for the video stream, securing the encoded data,
   caching the encoded data, timeliness of the encoded data, overhead of
   the network coding operations both in network resources and in added
   buffering delay, etc.

   Network coding has shown promise in reducing buffering events in
   unicast, multicast, and P2P settings.  [Medard12] considers
   strategies using network coding to enhance QoE for multimedia
   communications.  Network coding can be applied to multiple streams,
   but also within a single stream as an equivalent of a composable
   erasure code.  Clearly, there is a need for further investigation of
   network coding in ICN, potentially as a topic of activity in the
   research group.

9.6.  Synchronization Issues for Video Distribution in ICN

   ICN decouples the fetching of video chunks from their locations.
   This means an audio chunk may be received from one network element
   (cache/storage/server), a video chunk may be received from another,
   while yet another chunk (say, the next one, or another layer from the
   same video stream) may come from a third element.  This introduces
   disparity in the retrieval times and locations of the different
   elements of a video stream that need to be played at the same (or
   almost same) time.  Synchronization of such delivery and playback may
   require specific synchronization tools for video delivery in ICN.

   Other aspects involve synchronizing:

   o  within a single stream, for instance, the consecutive chunks of a
      single stream or the multiple layers of a layered scheme when
      sources and transport layers may be different.

   o  re-ordering the packets of a stream distributed over multiple
      sources at the video client, or ensuring that multiple chunks
      coming from multiple sources arrive within an acceptable time

   o  multiple streams, such as the audio and video components of a
      video stream, which can be received from independent sources; and

   o  multiple streams from multiple sources to multiple destinations,
      such as mass distribution of live events.  For instance, for live
      video streams or video conferencing, some level of synchronization
      is required so that people watching the stream view the same
      events at the same time.

   Some of these issues were addressed in [Montpetit13a] in the context
   of social video consumption.  Network coding, with traffic
   engineering, is considered as a potential solution for
   synchronization issues.  Other approaches could be considered that
   are specific to ICN as well.

   Traffic engineering in ICN [Su14] [Chanda13] may be required to
   provide proper synchronization of multiple streams.

10.  Security Considerations

   This is informational.  There are no specific security considerations
   outside of those mentioned in the text.

11.  Conclusions

   This document proposes adaptive video streaming for ICN, identified
   potential problems, and presents the combination of CCN with DASH as
   a solution.  As both concepts, DASH and CCN, maintain several
   elements in common, like, e.g., the content in different versions
   being dealt with in segments, combination of both technologies seems
   useful.  Thus, adaptive streaming over CCN can leverage advantages
   such as, e.g., efficient caching and intrinsic multicast support of
   CCN, routing based on named-data URIs, intrinsic multilink and
   multisource support, etc.

   In this context, the usage of CCN with DASH in mobile environments
   comes together with advantages compared to today's solutions,
   especially for devices equipped with multiple network interfaces.
   The retrieval of data over multiple links in parallel is a useful
   feature, specifically for adaptive multimedia streaming since it
   offers the possibility to dynamically switch between the available
   links depending on their bandwidth capabilities, which are
   transparent to the actual DASH client.

12.  References

12.1.  Normative References

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              the Performance of Pull-based Dynamic Adaptive Streaming
              in NDN", IEEE Journal on Selected Areas in Communications
              (J-SAC): Special Issue on Video Distribution over Future
              Internet, Volume 34, Number 8,
              DOI 10.1109/JSAC.2016.2577365, August 2016.

   [RFC6972]  Zhang, Y. and N. Zong, "Problem Statement and Requirements
              of the Peer-to-Peer Streaming Protocol (PPSP)", RFC 6972,
              DOI 10.17487/RFC6972, July 2013,

12.2.  Informative References

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              de Blas, G., Ramon-Salguero, F., Liang, L., Spirou, S.,
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              Based Traffic Engineering in Software Defined Information
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   [Corujo12] Corujo, D., Vidal, I., Garcia-Reinoso, J., and R. Aguiar,
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              D., Mueller, C., and C. Timmerer, "Video Adaptation in
              Limited/Zero Network Coverage", CCNxCon 2013, Palo Alto
              Research Center (PARC), September 2013.

   [Detti11]  Detti, A., Blefari-Melazzi, N., Salsano, S., and M.
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              S., and A. Bragagnini, "Offloading cellular networks with
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   [Detti13]  Detti, A., Ricci, B., and N. Blefari-Melazzi, "Peer-To-
              Peer Live Adaptive Video Streaming for Information Centric
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              Communications (PIMRC), DOI 10.1109/PIMRC.2013.6666771,
              September 2013.

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              Cryptology - CRYPTO '93 Proceedings, Lecture Notes in
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              Hellwagner, "An Experimental Analysis of Dynamic Adaptive
              Streaming over HTTP in Content Centric Networks", 2013
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              Electronics, Massachusetts Institute of Technology, March

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              AppLications", 2010, <http://www.ict-medieval.eu>.

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              Matijasevic, "Social video consumption: Synchronized
              viewing experiences across devices and networks", 2013
              IEEE International Conference on Communications Workshops
              (ICC), pp. 286-290, DOI 10.1109/ICCW.2013.6649245, 2013.

              Montpetit, M., Westphal, C., and D. Trossen, "Network
              Coding Meets Information-Centric Networking: An
              Architectural Case for Information Dispersion Through
              Native Network Coding", Proceedings of the 1st ACM
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              DOI 10.1145/2248361.2248370, June 2013.

              Mueller, C., Lederer, S., and C. Timmerer, "A Proxy Effect
              Analysis and Fair Adaptation Algorithm for Multiple
              Competing Dynamic Adaptive Streaming over HTTP Clients",
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              Content Chunks", Proceedings of the 8th International
              Workshop on Secure Network Protocols (NPSec '13),
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   [RFC7476]  Pentikousis, K., Ed., Ohlman, B., Corujo, D., Boggia, G.,
              Tyson, G., Davies, E., Molinaro, A., and S. Eum,
              "Information-Centric Networking: Baseline Scenarios",
              RFC 7476, DOI 10.17487/RFC7476, March 2015,

   [RFC7846]  Cruz, R., Nunes, M., Xia, J., Huang, R., Ed., Taveira, J.,
              and D. Lingli, "Peer-to-Peer Streaming Tracker Protocol
              (PPSTP)", RFC 7846, DOI 10.17487/RFC7846, May 2016,

   [Su14]     Su, K. and C. Westphal, "On the Benefit of Information
              Centric Networks for Traffic Engineering", 2014 IEEE
              International Conference on Communications (ICC),
              DOI 10.1109/ICC.2014.6883810, June 2014.


   This work was supported in part by the European Community in the
   context of the SocialSensor (FP7-ICT-287975) project and partly
   performed in the Lakeside Labs research cluster at AAU.  SocialSensor
   receives research funding from the European Community's Seventh
   Framework Programme.  The work for this document was also partially
   performed in the context of the FP7/NICT EU-JAPAN GreenICN project,
   <http://www.greenicn.org>.  Apart from this, the European Commission
   has no responsibility for the content of this document.  The
   information in this document is provided as is and no guarantee or
   warranty is given that the information is fit for any particular
   purpose.  The user, thereof, uses the information at its sole risk
   and liability.

Authors' Addresses

   Cedric Westphal (editor)

   Email: Cedric.Westphal@huawei.com

   Stefan Lederer
   Alpen-Adria University Klagenfurt

   Email: stefan.lederer@itec.aau.at

   Daniel Posch
   Alpen-Adria University Klagenfurt

   Email: daniel.posch@itec.aau.at

   Christian Timmerer
   Alpen-Adria University Klagenfurt

   Email: christian.timmerer@itec.aau.at

   Aytac Azgin

   Email: aytac.azgin@huawei.com

   Will (Shucheng) Liu

   Email: liushucheng@huawei.com

   Christopher Mueller

   Email: christopher.mueller@bitmovin.net

   Andrea Detti
   University of Rome Tor Vergata

   Email: andrea.detti@uniroma2.it

   Daniel Corujo
   Instituto de Telecomunicacoes Aveiro

   Email: dcorujo@av.it.pt

   Jianping Wang
   City University of Hong Kong

   Email: jianwang@cityu.edu.hk

   Marie-Jose Montpetit

   Email: marie@mjmontpetit.com

   Niall Murray
   Athlone Institute of Technology

   Email: nmurray@research.ait.ie


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