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Versions: (draft-matsuzono-nwcrg-nwc-ccn-reqs) 00 01 02

Network Coding Research Group                               K. Matsuzono
Internet-Draft                                                 H. Asaeda
Intended status: Informational                                      NICT
Expires: March 23, 2020                                      C. Westphal
                                                                  Huawei
                                                      September 20, 2019


 Network Coding for Content-Centric Networking / Named Data Networking:
                      Requirements and Challenges
                    draft-irtf-nwcrg-nwc-ccn-reqs-02

Abstract

   This document describes the current research outcomes regarding
   Network Coding (NC) for Content-Centric Networking (CCN) / Named Data
   Networking (NDN), and clarifies the requirements and challenges for
   applying NC into CCN/NDN.

Status of This Memo

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   This Internet-Draft will expire on March 23, 2020.

Copyright Notice

   Copyright (c) 2019 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
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  NDN/CCN Background  . . . . . . . . . . . . . . . . . . .   5
   3.  Advantages provided by NC and CCN/NDN . . . . . . . . . . . .   7
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Content Naming  . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Transport . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.2.1.  Scope of Network Coding . . . . . . . . . . . . . . .   9
       4.2.2.  Consumer Operation  . . . . . . . . . . . . . . . . .   9
       4.2.3.  Router Operation  . . . . . . . . . . . . . . . . . .   9
       4.2.4.  Publisher Operation . . . . . . . . . . . . . . . . .  10
       4.2.5.  Backward Compatibility  . . . . . . . . . . . . . . .  11
     4.3.  In-network Caching  . . . . . . . . . . . . . . . . . . .  11
     4.4.  Seamless Mobility . . . . . . . . . . . . . . . . . . . .  12
     4.5.  Security and Privacy  . . . . . . . . . . . . . . . . . .  12
   5.  Challenges  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  Adopting Convolutional Coding . . . . . . . . . . . . . .  13
     5.2.  Rate and Congestion Control . . . . . . . . . . . . . . .  13
     5.3.  Security and Privacy  . . . . . . . . . . . . . . . . . .  14
     5.4.  Routing Scalability . . . . . . . . . . . . . . . . . . .  15
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   Information-Centric Networks (ICN) in general, and Content-Centric
   Networking (CCN) [15] or Named Data Networking (NDN) [17] in
   particular, have emerged as a novel communication paradigm advocating
   to retrieve data through their names.  This paradigm pushes content
   awareness into the network layer.  It is expected to enable consumers
   to obtain the content they desire in a straightforward and efficient
   manner from the heterogenous networks they may be connected to.  The
   CCN/NDN architecture has introduced innovative ideas and has
   stimulated research in a variety of areas, such as in-network
   caching, name-based routing, multi-path transport, content security,
   and so on.  One key benefit of requesting content by name is that it
   removes the need to establish a session between the client and a
   specific server, and that content can thereby be retrieved from
   multiple sources.



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   In parallel, there has been a growing interest from both academia and
   industry to better understand fundamental aspects of Network Coding
   (NC) toward enhancing key system performance metrics such as data
   throughput, robustness and reduction in the required number of
   transmissions through connected networks, point-to-multipoint
   connections, etc.  Typically, NC is a technique mainly used to encode
   packets to recover lost source packets at the receiver, and to
   effectively get the desired information in a fully distributed
   manner.  In addition, NC can be used for security enhancements [2]
   [3] [4] [5].

   From the perspective of NC transport mechanism, NC is divided into
   two major categories: one is coherent NC, and the other is non-
   coherent NC [33].  In coherent NC, source and destination nodes
   exactly know network topology and coding operations at intermediate
   nodes.  When multiple consumers are trying to receive the same
   content such as live video streaming, coherent NC could enable the
   optimal throughput by making the content flow sent over the
   constructed optimal multicast trees [26].  However, it requires a
   fully adjustable and specific routing mechanism, and an intense
   computational task for central coordination.  In the case of non-
   coherent NC that often utilizes RLC, it is not required to know
   either network topology nor intermediate coding operations [27].
   Since non-coherent NC works in a completely independent and
   decentralized manner, this approach is more feasible especially in
   the large scale use cases.

   NC mixes multiple packets together with parts of the same content,
   and may do this at the source or at other nodes in the network.  As
   such, network coded packets are not connected to a specific server,
   as they may have been mixed within the network.  Since NC focuses on
   what information should be encoded in a network packet, rather than
   the specific host where it has been generated, it is in line with the
   CCN/NDN core networking layer.  NC has already been implemented for
   information/content dissemination (e.g. [6] [7] [8]).  Montpetit, et
   al., first suggested to exploit NC techniques to enhance key system
   performances in ICN [9].  NC provides CCN/NDN with the highly
   beneficial potential to effectively disseminate information in a
   completely independent and decentralized manner.

   In this document, we consider how NC can be applied to the CCN/NDN
   architecture and describe the requirements and potential challenges
   for making CCN/NDN-based communications better using the NC
   technology.  Please note that providing specific solutions (e.g., NC
   optimization methods) to enhance CCN/NDN performance metrics by
   exploiting NC is out of scope of this document.





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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

2.1.  Definitions

   The terminology regarding NC used in this document is described
   below.  It is aligned with RFCs produced by the FEC Framework
   (FECFRAME) IETF Working Groups as well as IRTF Coding for Efficient
   Network Communications Research Group (NWCRG)[20].

   o  Random Linear Coding (RLC): Particular case of Linear Coding using
      a set of random coding coefficients.

   o  Generation, or (IETF) Block: With Block Codes, the set of Source
      Symbols of the input Flow(s) that are logically grouped into a
      Block, before doing encoding.

   o  Generation Size, Code Dimension, or (IETF) Block Size: With Block
      Codes, the number of Source Symbols, k, belonging to a Block.

   o  Coding Vector: A set of Coding Coefficients used to generate a
      certain Repair Symbol through Linear Coding.  The number of
      nonzero coefficients in the Coding Vector defines its density

   o  Finite Field: Finite fields, used in Linear Codes, have the
      desired property of having all elements (except zero) invertible
      for + and * and all operations over any elements do not result in
      an overflow or underflow.  Examples of Finite Fields are prime
      fields {0..p^m-1}, where p is prime.  Most used fields use p=2 and
      are called binary extension fields {0..2^m-1}, where m often
      equals 1, 4 or 8 for practical reasons.

   o  Finite Field size: The number of elements in a finite field.  For
      example the binary extension field {0..2^m-1} has size q=2^m.

   o  Block Coding: Coding technique where the input Flow(s) must be
      first segmented into a sequence of blocks, FEC encoding and
      decoding being performed independently on a per-block basis.

   o  Sliding Window Coding or Convolutional Coding: General class of
      coding techniques that rely on a sliding encoding window.  This is
      an alternative solution to Block Coding.

   o  Fixed or Elastic Sliding Window Coding: Coding technique that
      generates repair data on-the-fly, from the set of source data



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      present in the sliding encoding window at that time, usually by
      using Linear Coding.  The sliding window may be either of fixed
      size or of variable size over the time (also known as "elastic
      sliding window").

   o  Feedback: Feedback information sent by a decoding node to a node
      (or from a consumer to a publisher in case of End-to-End Coding).
      The nature of information contained in a feedback packet varies,
      depending on the use-case.  It can provide reception and/or
      decoding statistics, or the list of available source packets
      received or decoded, or the list of lost source packets that
      should be retransmitted, or a number of additional repair packet
      needed to have a full rank linear system.

   Concerning CCN/NDN, the following terminology and definitions are
   used.

   o  Consumer: A node requesting content.  It initiates communication
      by sending an interest packets.

   o  Publisher: A node providing content.  It originally creates or
      owns the content.

   o  Forwarding Information Base (FIB): A lookup table in a content
      router containing the name prefix and corresponding destination
      interface to forward the interest packets.

   o  Pending Interest Table (PIT): A lookup table populated by the
      interest packets containing the name prefix of the requested data,
      and the outgoing interface used to forward the received data
      packets.

   o  Content Store (CS): A storage space for a router to cache content
      objects.  It is also known as in-network cache.

   o  Content Object: A unit of content data delivered through the CCN/
      NDN network.

   o  Content Flow: A sequence of content objects associated with the
      unique content name prefix.

2.2.  NDN/CCN Background

   Armed with the terminology above, we briefly explain the key concepts
   of CCN/NDN.  Both protocols are similar in principle, and different
   on some implementation choices.





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   In a CCN network, there are two types of packets at the network
   level: interest and data.  The consumer request a content by sending
   an "interest" message, that carries the name of the data.  On
   difference to note here in CCN and NDN is that in CCN [16], the
   interest must carry a full name, while in NDN [18] it may carry a
   name prefix (and receive in return any data with a name matching this
   prefix).

   Once a router receives an "interest" message, it performs a series of
   look-up: first it checks in the Content Store if it has a copy of the
   requested content available.  If it does, it returns the data and the
   transaction has successfully completed.

   If it does not, it performs a look-up of the PIT to see if there is
   already an outgoing request for the same data.  If there is not, then
   it creates an entry in the PIT that lists the name included in the
   interest, and the interfaces from which it received the interest.
   This is used later to send the data back, since interest packets do
   not carry a source field that identifies the requester.  If there is
   already a PIT entry for this name, then it is updated with the
   incoming interface of this new request and the interest is discarded.

   After the PIT look-up, the interest undergoes a FIB lookup to select
   an outgoing interface.  The FIB lists name prefixes and their
   corresponding forwarding interfaces, to send the interface towards a
   router that possesses a copy of the requested data.

   Once a copy of the data is retrieved, it is sent back to the
   requester(s) using the trail of PIT entries; intermediate nodes
   remove the PIT state every time that an interest is satisfied, and
   may store the data in their content store.

   Data packets carry some information to validate the data, in
   particular that the data is indeed the one that corresponds to the
   name.  This is required since authentication of the object is crucial
   in CCN/NDN.  However, this step is optional at intermediate routers,
   so as to speed up the processing.

   The key aspect of CCN/NDN is that the consumer of the content does
   not establish a session with a specific server.  Indeed, the node
   that returns the content is not aware of the network location of the
   requester and the requester is not aware of the network location of
   the node that provides the content.  This in theory allows the
   interests to follow different paths within a network, or even to be
   sent over totally different networks.






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3.  Advantages provided by NC and CCN/NDN

   Both NC for large scale content dissemination [7] and CCN/NDN can
   contribute to effective content/information delivery while working
   jointly.  They both bring similar benefits such as throughput/
   capacity gain and robustness enhancement.  The difference between
   their approaches is that, the former considers content flow as
   algebraic information to combine [19], while the latter focuses on
   content/information itself at the networking layer.  Because these
   approaches are complementary, it is natural to combine them.

   The CCN/NDN core abstraction at networking layer through name makes
   network stack simple as it enables applications to take maximum
   advantage of multiple simultaneous connectivities due to its simpler
   relationship with the layer 2 [15].  CCN/NDN itself, however, does
   not provide reliable and robust content dissemination by default.
   This requires some specific CCN/NDN transport (i.e., strategy layer)
   [15].  NC can enable the CCN/NDN transport system to effectively
   distribute and cache data associated with multi-path data retrieval
   [9].  Furthermore, NC can contribute to improving both caching
   performance and cache privacy that CCN/NDN newly poses at the
   networking layer [25].  Others also have considered NC in CCN/NDN use
   cases such as content dissemination with in-network caching [10] [12]
   [13], seamless mobility [11] [31], low-latency video streaming [14],
   etc.  In this context, it should be natural that there is much room
   for considering NC integration into CCN/NDN.

4.  Requirements

   This section presents the NC requirements for ICN/CCN in terms of
   network architecture and protocol.  The current document focuses on
   NC in a block coding manner.

4.1.  Content Naming

   Naming content objects is as important for CCN/NDN as naming hosts is
   for today's Internet [21].  Before performing network coding for
   specified content in CCN/NDN, the overall content should be split
   into small content objects to avoid packet fragmentation that could
   cause unnecessary packet processing and degrade throughput.  The size
   of content objects should be within the allowable packet size so as
   to avoid packet fragmentation in CCN/NDN network, and then network
   coding should be applied into a set of the content objects.

   Each coded packet MAY have a unique name as the original content
   object has in CCN/NDN, since PIT/CS operations typically need a
   unique name to identify the coded data.  As a way of naming coded
   packet, the coding vector and the identifier of generation can be



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   used as a part of the content object name [10].  For instance, when
   the block size (also called generation size) is k and the coding
   vector is [1,0,0,0], the name would be like /CCN.com/video-A/k/1000.
   This naming scheme is simple and can support the delivery of coded
   packets with exactly the same operations in the PIT/CS as for
   original source packets.  Since such a naming way enables consumer to
   specify coded packets to receive, it could shift the generation of
   the coding vector from the content producer onto the content
   requester (described in Section 4.2.2).

   If a naming schema such as above is used, it would be valuable to
   reconsider whether Interests should carry full names (as in CCN) or
   prefixes (as in NDN) as multiple network coded packets could match a
   response to a specific prefix for a given generation, such as
   /CCN.com/video-A/k.  In the latter case allowing partial name
   matching, the content requestor may not be able to obtain degrees of
   freedom.  Thus, extensions in the TLV header of the Interest would be
   used to specify further network coding information so as to limit
   coded packets to be received (for instance, by specifying the encoded
   vectors the content requestor receives (also called decoding matrix)
   as in [9]).  However, it may incur a largely increased size of TLV
   header, and thus it may be useful to use compression techniques for
   coding vectors [22] [23].  Without such coding information, the
   forwarding node would need to maintain some records regarding
   interest packets sent before (described in Section 4.2.3).

   Coded packet MAY have a name that indicates that it is a coded
   packet, and move the coding information into a metadata field in the
   payload (i.e., the name includes only data type, original or coded
   packet, etc).  It would not be beneficial for applications or
   services that may not need to understand the packet payload.  Due to
   the possibility that multiple coded packets may have a same name,
   some mechanism is needed for the content requestor to obtain
   innovative coded packets.  As described in Section 4.3, a mechanism
   to manage the multiple innovative packets in the CS would be required
   as well.  In addition, extra computational overhead would occur when
   the payload is being encrypted (described in Section 4.5).

4.2.  Transport

   The pull-based request-response feature of CCN/NDN is a fundamental
   principle of its transport layer; one Interest retrieves at most one
   Data packet.  It is believed that it is important to not violate this
   rule, as it would open denial of service attacks issues, and thus the
   following basic operation should be considered to apply NC to CCN/
   NDN.  In any case, such security considerations must be addressed if
   this rule were to be violated.




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4.2.1.  Scope of Network Coding

   It should be discussed whether the network can recode data packets
   that are being received in transit, or if only the data that matches
   an interest can be subject to network coding operations.  In the
   latter case, the network coding is performed on an end-to-end basis
   (where one end is the consumer, and the other end is any node that is
   able to respond to the Interest).  In the former case, NC happens
   anywhere in the network that is able to update the data.  As CCN/NDN
   has mechanisms in place to ensure the integrity of the data during
   transfer, NC in the network introduce complexities that would require
   special consideration for the integrity mechanisms to still work.

   Similarly, caching of network coded packets at intermediate node may
   be valuable, but may prevent the node caching the coded content to
   validate the content.

4.2.2.  Consumer Operation

   To obtain NC benefits associated with in-network caching, consumer
   needs to issue interests directing the router (or publisher) to
   forward innovative coded packets if available.  The reason why this
   directive is needed is that delay-sensitive applications such as
   live-video streaming may want to sequentially get original packets
   rather than coded packets cached in routers due to real-time
   constraint.  As described in Section 4.1, because coded packet can
   have a name explicitly different from original source packets,
   issuing such an interest is possible.

   When issuing interests specifying unique names with k and coding
   vectors for each coded packets, consumer appropriately receives
   innovative coded packets if they are available at some nodes and can
   be forwarded to the consumer.  However, consumer needs to know the
   naming structure (through a specific name resolution scheme for
   instance) in order for nodes to specify the exact name of generated
   coded data packet to retrieve it.  In the case of NC end-to-end
   approach, if consumer want to adjust some coding parameters at
   publisher, some specific scheme would be required.

4.2.3.  Router Operation

   Routers need to forward linearly independent coded packets toward
   downstream nodes if incoming interests for coded packets does not
   specify some coding parameters such as the coding vector to be used.
   Routers thus need to determine whether or not they can generate
   useful coded packets for consumers.  Assuming that the size of the
   Finite Field in use is not relatively small, re-encoding using enough
   cached independent packets has a strong probability of making



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   independent coded packets [26].  However, without enough cached
   packets, router needs to determine whether or not to an independent
   coded packet can be forwarded to the interface at which the interest
   arrived.  To deal with this issue, some proposed schemes [10] require
   that the router maintains a tally of the interests for a specific
   name, generation and the corresponding interface, so as to know how
   many degrees of freedom have been provided already for the NC
   packets.  Scalability and practicality of maintaining such scheme at
   intermediate routers should be considered.  In addition, some
   transport mechanism of in-network loss detection and recovery [31]
   [14] at router as well as consumer-driven mechanism could be
   indispensable in order to enable fast loss recovery and enhance NC
   gains.  After determining that independent coded packet cannot be
   provided, according to the FIB, the router relays received interests
   to upstream nodes to receive a new original or independent coded
   packet.  In this context, to effectively and quickly retrieve
   independent coded data, appropriately setting the FIB and efficient
   interest forwarding strategies should be also considered.

   In another possible case, when receiving interests for only original
   packets, routers may try to decode and get all the original packets
   and store them (if there are fully available cache capacity),
   enabling faster response to the interests.  Since re-encoding or
   decoding leads to extra computational overhead, routers need to
   determine how to response to receiving interests according to the use
   case (e.g., delay-sensitive or delay-tolerant application) and the
   router situation such as available cache space and computational
   capability.

4.2.4.  Publisher Operation

   The procedure for splitting an overall content into small content
   objects (described in Section 4.1) is the responsibility of the
   original publisher.  When applying NC for the content, the publisher
   performs NC over the content objects, and naming processing for the
   coded packets.  If the producer takes the lead in determining the
   used coding vectors and generating the coded packets, there are the
   two possible end-to-end cases; 1) content requestors obtain the names
   of coded packets through a certain mechanism, and send the correspond
   interests toward the publisher to get the coded packets already
   generated at the publisher, and 2) the publisher determines the
   coding vectors after receiving interests specifying them.  In the
   former case, although content requestors cannot flexibly specify an
   coding vector for generating the coded packet to retain, but the
   latency for getting the coded data can be reduced compared to the
   latter case where additional NC operations need after receiving
   interests.  The common benefit in such end-to-end cases is that if
   the publisher adds signature on the coded packets, data verification



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   can be possible throughout.  According to application requirement for
   latency, such NC operation strategy should be considered.

4.2.5.  Backward Compatibility

   Network Coding operations should be applied in addition to the
   regular network behavior.  As such, nodes should be able to not
   support network coding (either in forwarding the packets, but also in
   the caching mechanism).  Network Coding operations should function
   alongside regular network operations.  A network coding framework
   should be compatible with a regular framework, so as to allow
   backward compatibility and smooth migration from one framework to the
   other.

4.3.  In-network Caching

   Caching is an essential technique to improve throughput and latency
   in various applications.  In-network caching CCN/NDN essentially
   supports at network level is highly beneficial by exploiting NC to
   enable effective multicast transmission [32], multipath data
   retrieval [10] [11], fast loss recovery [14], and so on.  However,
   there are several issues to be considered.

   As a general issue, there are limitations of cache capacity, and
   caching policy affects on consumer's performances [24] [28] [29].  It
   is thus highly significant for routers to determine which packets
   should be cached and discarded.  Since delay-sensitive applications
   often do not require in-network cache for a long period due to their
   real-time constraints, routers have to know the necessity for caching
   received packets to save the caching volume.  This could be possible
   by putting a flag into optional header of data packets at publisher
   side.  When receiving data packets with the flag meaning no necessity
   for cache, routers just have to forward them to downstream nodes.  On
   the other hand, when receiving original packets or coded packets
   without the flag, router may cache them based on a specified
   replacement policy.

   One key aspect of in-network caching is whether or not intermediate
   nodes can cache NC packets without first decoding them.  They may be
   caching the coded packets without having the ability to perform
   validation of the content (described in Section 4.5).  Therefore,
   caching of coded packets would require some mechanism to validate
   coded packets.  In addition, when coded packets have a same name, it
   would also require some mechanism to identify them.







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4.4.  Seamless Mobility

   This subsection presents how NC can achieve seamless mobility [11]
   [31] and clarify the requirements.  A key feature of CCN/NDN is that
   it is sessionless and that multiple interests can be sent to
   different copies of the content in parallel.  CCN/NDN enables a
   consumer to retrieve the content from multiple copies that are
   distributed and asynchronous.  The key benefit is that the link
   between the consumer and the multiple copies acts as a virtual
   logical link, upon which rate adaptation mechanism (say, for video
   streaming) can be performed.

   In this context, NC adds a reliability layer network to CCN in a
   distributed and asynchronous manner, because NC provides a mechanism
   to ensure that the Interests sent to multiple copies of the content
   in parallel retrieve innovative packets, even in the case of packet
   losses on some of the paths/networks to these copies.  This naturally
   applies to mobility events, where the consumer may connect between
   multiple access points before a mobility event (make-before-break
   handoff).  In such mobility event, the consumer is connected first to
   the previous access point, then to both the previous and next access
   points, then finally only to the next access points.  With CCN, the
   consumer only sends interests on the available interfaces.  By
   combining NC with CCN, requesting coded packets ensures that during
   the phase where it is connected to the previous and the next APs at
   the same time, it does not receive duplicate data, but does not miss
   on any content either.  The consumer receives additional degrees of
   freedom with any innovative packet it receives on either interface.
   From this point of view, an effective interest forwarding strategy
   for obtaining innovative packets should be considered for consumer to
   achieve seamless mobility.

4.5.  Security and Privacy

   This subsection describes the requirement for security and privacy
   provided by NC in CCN/NDN, such as data integrity especially when
   intermediate nodes perform re-encoding, as in the case of hash
   restrictions for original data packets, and so on.

   Network coding impacts the security mechanisms of CCN/NDN.  In
   particular, CCN/NDN is designed to prevent modification of the Data
   packets.  Because Data packets for a specific name can be self-
   authenticated, they can be validated on the delivery path, and can
   also be cached at untrusted intermediate nodes.  Network coding may
   bring up issues if intermediate nodes are allowed to modify packets
   by performing additional network coding operations.  In addition, if
   in-network caches store coded packets, they need to be able to
   validate that the packets are not compromised, so as to avoid cache



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   pollution attacks.  Without having all the packets in a generation,
   the cache cannot decode the packets to check if it is authenticated.

   In CCN/NDN, content objects can be encrypted to support access
   control or privacy.  If the coding information of coded packet are
   encrypted together with the payload (for instance, at source coding),
   the content requestor or forwarding nodes would incur extra
   computational overhead for decryption of the packet to interpret the
   coding information.  With consideration for low computation overhead,
   some mechanism supporting both NC and access control/privacy should
   be considered.

5.  Challenges

   This section presents several primary challenges and research items
   to be considered when applying NC into CCN/NDN.

5.1.  Adopting Convolutional Coding

   Several block coding approaches have been proposed so far, but there
   is still no sufficient discussion and application of convolutional
   coding approach (e.g., sliding or elastic window coding) in CCN/NDN.
   Convolutional coding is often appropriate to situations where a fully
   or partially reliable delivery of continuous data flows is needed,
   especially when these data flows feature realtime constraints.  As in
   [34] on an end-to-end basis, it would be advantageous for continuous
   content flow to adopt sliding window coding in CCN/NDN.  In this
   case, the publisher needs to appropriately set coding parameters and
   let content requestor know the information, and content requestor
   needs to send interest (i.e., feedback information) about the data
   reception status.  Since CCN/NDN advocates hop-by-hop communication,
   it would be worth discussing and investigating how convolutional
   coding can be applied in a hop-by-hop fashion and the benefits.  In
   particular, assuming that NC could occur at intermediate nodes with
   some useful data packets stored in the CS as described in the
   previous section, both the encoding window and CS management would be
   required, and the feasibility and practicality should be considered.

5.2.  Rate and Congestion Control

   Adding redundancy using coded packets may cause further network
   congestion and adversely affect overall throughput performance.  In
   particular, in a situation where fair bandwidth sharing is more
   desirable, each streaming flow must adapt to the network conditions
   to fairly consume the available link bandwidth.  It is thus
   indispensable that each content flow cooperatively implements
   congestion control to adjust the consumed bandwidth to stabilize the
   network condition (i.e., to achieve low packet loss rate, delay, and



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   jitter).  From this point of view, a router supported approach would
   be effective, but an effective deployment scenario is needed.

   As described in Section 4.4, NC can contribute to seamless mobility
   by obtaining innovative packets without receiving duplicated packets
   through a virtual logical link to multiple copies of the content.  To
   achieve seamless mobility while improving overall throughput or
   latency, an effective rate adaptation mechanism upon the virtual
   logical link is also challenging.

5.3.  Security and Privacy

   CCN/NDN introduces new security and privacy issues at the networking
   layer different from IP network, such as cache poisoning and
   pollution attack, DoS attack using interest packets, and so on.

   NC could be utilized to mitigate some security or privacy issues CCN/
   NDN introduces.  For instance, assuming that consumers can utilize
   multipath data retrieval and caching in CCN/NDN with NC, cache
   privacy and anonymity set for consumers can be improved as well as
   caching performance due to the diversity of caching content along
   different paths.

   On the other hand, considering NC operations over CCN/NDN, the issues
   related to in-network caching add additional complexity.  In order to
   avoid cache poisoning attack which tries to fill routers cache with
   polluted content, router needs to check whether or not the content is
   validated.  However, in the case of performing NC and generating a
   new coded data at routers, a validation mechanism to accurately
   verify coded data as quickly as possible should be considered while
   maintaining in-network cache benefits (lower latency and network
   resource saving).  If router can cache some valid coded data, it
   needs to put a great deal of thought into the effectiveness with
   respect to cache pollution attack, since coded data newly generated
   may be unpopular.  Moreover, Denial of Service (DoS) attacks may
   target either the routers or the publishers performing NC to pose
   unnecessary coded data, impose higher NC computation load, and
   increase the number of PIT entries, which requires some careful
   considerations to avoid them.

   NC also offers a new surface of attack; for instance, if the coding
   vector is exposed at the network layer, it would have to be protected
   (and validated) so as to avoid modifications by an attacker (and
   allow for verification) on the path of the packet.

   In this context, from the perspective of both feasibility and
   practicability, a more effective approach with consideration for




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   security and privacy would be needed in order to accelerate the
   deployment of CCN/NDN with NC.

5.4.  Routing Scalability

   In CCN/NDN, a name-based routing protocol without a resolution
   process streamlines the routing process and reduces the overall
   latency.  As in IP routing, the growth in the routing table size has
   become a concern.  This may require a hierarchical naming scheme so
   as to improve the routing scalability by enabling aggregation of
   routing information.  Moreover, it is a challenge that content
   requestors efficiently obtain linearly independent coded packets
   using multipath retrieval in a fully distributed manner, in order to
   fully leverage NC over CCN/NDN to improve throughput or reduce
   latency.  This would require some efficient routing mechanism to
   appropriately set the FIB and also requires some efficient interest
   forwarding strategy.  Such routing coordination may create routing
   scalability issues.  From another NC perspective, as described
   Section 4.2.2, when issuing interests specifying unique names for
   each coded packet, consumers need in advance to know how to specify
   the names of the coded data through some specific name resolution
   scheme, and routers may need to appropriately set the FIBs.  In this
   context, it would be challenging to achieve effective and scalable
   routing for interests requesting coded data as well as to simplify
   the routing process.

6.  Security Considerations

   This document does not impact the security of the Internet.  Security
   considerations related to NC for CCN/NDN are described in the
   previous Section.

7.  References

7.1.  Normative References

   [1]        Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

7.2.  Informative References

   [2]        Cai, N. and R. Yeung, "Secure network coding", Proc.
              International Symposium on Information Theory
              (ISIT), IEEE, June 2002.





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   [3]        Lima, L., Gheorghiu, S., Barros, J., Mdard, M., and A.
              Toledo, "Secure Network Coding for Multi-Resolution
              Wireless Video Streaming", IEEE Journal of Selected Area
              (JSAC), vol. 28, no. 3, April 2002.

   [4]        Gkantsidis, C. and P. Rodriguez, "Cooperative Security for
              Network Coding File Distribution", Proc. Infocom, IEEE,
              April 2006.

   [5]        Vilea, J., Lima, L., and J. Barros, "Lightweight security
              for network coding", Proc. ICC, IEEE, May 2008.

   [6]        Dimarkis, A., Godfrey, P., Wu, Y., Wainwright, M., and K.
              Ramchandran, "Network Coding for Distributed Storage
              Systems", IEEE Trans. Information Theory, vol. 56, no.9,
              September 2010.

   [7]        Gkantsidis, C. and P. Rodriguez, "Network coding for large
              scale content distribution", Proc. Infocom, IEEE, March
              2005.

   [8]        Seferoglu, H. and A. Markopoulou, "Opportunistic Network
              Coding for Video Streaming over Wireless", Proc. Packet
              Video Workshop (PV), IEEE, November 2007.

   [9]        Montpetit, M., Westphal, C., and D. Trossen, "Network
              Coding Meets Information-Centric Networking: An
              Architectural Case for Information Dispersion Through
              Native Network Coding", Proc. Workshop on Emerging Name-
              Oriented Mobile Networking Design (NoM), ACM, June 2012.

   [10]       Saltarin, J., Bourtsoulatze, E., Thomos, N., and T. Braun,
              "NetCodCCN: a network coding approach for content-centric
              networks", Proc. Infocom, IEEE, April 2016.

   [11]       Ramakrishnan, A., Westphal, C., and J. Saltarin, "Adaptive
              Video Streaming over CCN with Network Coding for Seamless
              Mobility", Proc. International Symposium on Multimedia
              (ISM), IEEE, December 2016.

   [12]       Wang, J., Ren, J., Lu, K., Wang, J., Liu, S., and C.
              Westphal, "An Optimal Cache Management Framework for
              Information-Centric Networks with Network Coding", Proc.
              Networking Conference, IFIP/IEEE, June 2014.







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   [13]       Wang, J., Ren, J., Lu, K., Wang, J., Liu, S., and C.
              Westphal, "A Minimum Cost Cache Management Framework for
              Information-Centric Networks with Network Coding",
              Computer Networks, Elsevier, August 2016.

   [14]       Matsuzono, K., Asaeda, H., and T. Turletti, "Low Latency
              Low Loss Streaming using In-Network Coding and Caching",
              Proc. Infocom, IEEE, May 2017.

   [15]       Jacobson, V., Smetters, D., Thornton, J., Plass, M.,
              Briggs, N., and R. Braynard, "Networking Named Content",
              Proc. CoNEXT, ACM, December 2009.

   [16]       Mosko, M. and et al., "Content-Centric Networking (CCNx)
              Messages in TLV Format", RFC 8609, July 2019,
              <https://tools.ietf.org/html/rfc8609>.

   [17]       Zhang, L., Afanasyev, A., Burke, J., Jacobson, V., Claffy,
              K., Crowley, P., Papadopoulos, C., Wang, L., and B. Zhang,
              "Named data networking", ACM Comput. Commun. Rev., vol.
              44, no. 3, July 2014.

   [18]       NDN Packet Format, "NDN Packet Format Specification 0.3
              documentation", Sept. 2019,
              <https://named-data.net/doc/NDN-packet-spec/current/>.

   [19]       Koetter, R. and M. Medard, "An Algebraic Approach to
              Network Coding", IEEE/ACM Trans. on Networking, vol. 11,
              no 5, Oct. 2003.

   [20]       Adamson, B. and et al., "Taxonomy of Coding Techniques for
              Efficient Network Communications", RFC 8406, June 2018,
              <https://tools.ietf.org/html/rfc8406>.

   [21]       Kutscher, D. and et al., "Information-Centric Networking
              (ICN) Research Challenges", RFC 7927, July 2016.

   [22]       Thomos, N. and P. Frossard, "Toward one Symbol Network
              Coding Vectors", IEEE Communications letters, vol. 16, no.
              11, November 2012.

   [23]       Lucani, D., Pedersen, M., Heide, J., and F. Fitzek,
              "Fulcrum Network Codes: A Code for Fluid Allocation of
              Complexity",  available at http://arxiv.org/abs/1404.6620,
              April 2014.






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   [24]       Perino, D. and M. Varvello, "A reality check for content
              centric networking", Proc. SIGCOMM Workshop on
              Information-centric networking (ICN'11), ACM, August 2011.

   [25]       Wu, Q., Li, Z., Tyson, G., Uhlig, S., Kaafar, M., and G.
              Xie, "Privacy-Aware Multipath Video Caching for Content-
              Centric Networks", IEEE Journal of Selected Area
              (JSAC) vol. 38, no. 8, June 2016.

   [26]       Wu, Y., Chou, P., and K. Jain, "A comparison of network
              coding and tree packing", Proc. ISIT, IEEE, June 2004.

   [27]       Ho, T., Medard, M., Koetter, R., Karger, R., Effros, D.,
              Shi, M., and B. Leong, "A Random Linear Network Coding
              Approach to Multicast", IEEE Trans. Information
              Theory, vol. 52, no.10, October 2006.

   [28]       Podlipnig, S. and L. Osz, "A Survey of Web Cache
              Replacement Strategies", Proc. ACM Computing Surveys vol.
              35, no. 4, December 2003.

   [29]       Rossini, G. and D. Rossi, "Evaluating CCN multi-path
              interest forwarding strategies", Elsevier Computer
              Communication, vol.36, no. 7, April 2013.

   [30]       Chai, W., He, D., Psaras, I., and G. Pavlou, "Cache Less
              for More in Information-centric Networks", Journal
              Computer Communications, vol. 37. no. 7, April 2013.

   [31]       Carofiglio, G., Muscariello, L., Papalini, M., Rozhnova,
              N., and X. Zeng, "Leveraging ICN In-network Control for
              Loss Detection and Recovery in Wireless Mobile networks",
              Proc. ICN ACM, September 2016.

   [32]       Ali, M. and U. Niesen, "Coding for Caching: Fundamental
              Limits and Practical Challenges", IEEE Communications
              Magazine vol. 54, no. 8, August 2016.

   [33]       Koetter, R. and F. Kschischang, "An algebraic approach to
              network coding", IEEE Trans. Netw. vol.11, no.5, October
              2008.

   [34]       Tournoux, P., Lochin, E., Lacan, J., Bouabdallah, A., and
              V. Roca, "On-the-Fly Erasure Coding for Real-Time Video
              Applications", IEEE Trans. Multimeda vol.13, no.4, August
              2011.





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Authors' Addresses

   Kazuhisa Matsuzono
   National Institute of Information and Communications Technology
   4-2-1 Nukui-Kitamachi
   Koganei, Tokyo  184-8795
   Japan

   Email: matsuzono@nict.go.jp


   Hitoshi Asaeda
   National Institute of Information and Communications Technology
   4-2-1 Nukui-Kitamachi
   Koganei, Tokyo  184-8795
   Japan

   Email: asaeda@nict.go.jp


   Cedric Westphal
   Huawei
   2330 Central Expressway
   Santa Clara, California  95050
   USA

   Email: cedric.westphal@huawei.com
























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