Considerations in the development of a QoS Architecture for CCNx-like ICN protocols
draft-oran-icnrg-qosarch-02

Versions: 00 01 02                                                      
ICNRG                                                            D. Oran
Internet-Draft                       Network Systems Research and Design
Intended status: Informational                           August 27, 2019
Expires: February 28, 2020


 Considerations in the development of a QoS Architecture for CCNx-like
                             ICN protocols
                      draft-oran-icnrg-qosarch-01

Abstract

   This is a position paper.  It documents the author's personal views
   on how Quality of Service (QoS) capabilities ought to be accommodated
   in ICN protocols like CCNx or NDN which employ flow-balanced
   Interest/Data exchanges and hop-by-hop forwarding state as their
   fundamental machinery.  It argues that such protocols demand a
   substantially different approach to QoS from that taken in TCP/IP,
   and proposes specific design patterns to achieve both classification
   and differentiated QoS treatment on both a flow and aggregate basis.
   It also considers the effect of caches as a resource in addition to
   memory, CPU and link bandwidth that should be subject to explicitly
   un-fair resource allocation.  The proposed methods are intended to
   operate purely at the network layer, providing the primitives needed
   to achieve both transport and higher layer QoS objectives.  It
   explicitly excludes any discussion of Quality of Experience (QoE)
   which can only be assessed and controlled at the application layer or
   above.

Status of This Memo

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   This Internet-Draft will expire on February 28, 2020.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Some background on the nature and properties of Quality of
       Service in network protocols  . . . . . . . . . . . . . . . .   4
     3.1.  Congestion Control basics relevant to ICN . . . . . . . .   5
   4.  What can we control to achieve QoS in ICN?  . . . . . . . . .   6
   5.  How does this relate to QoS in TCP/IP?  . . . . . . . . . . .   8
   6.  Why is ICN Different? Can we do Better? . . . . . . . . . . .   9
   7.  A strawman set of principles to guide QoS architecture for
       ICN . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     10.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   The TCP/IP protocol suite used on today's Internet has over 30 years
   of accumulated research and engineering into the provision of Quality
   of Service machinery, employed with varying success in different
   environments.  ICN protocols like Named Data Networking (NDN [NDN])
   and Content-Centric Networking (CCNx [RFC8569],[RFC8609]) have an
   accumulated 10 years of research and very little deployment.  We
   therefore have the opportunity to either recapitulate the approaches
   take with TCP/IP (e.g.  IntServ [RFC2998] and Diffserv [RFC2474]) or
   design a new architecture and associated mechanisms aligned with the
   properties of ICN protocols which differ substantially from those of
   TCP/IP.  This position paper advocates the latter approach and
   comprises the author's personal views on how Quality of Service (QoS)



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   capabilities ought to be accommodated in ICN protocols like CCNx or
   NDN.  Specifically, these protocols differ in fundamental ways from
   TCP/IP.  These differences are summarized in the following table:

   +---------------------------------+---------------------------------+
   |              TCP/IP             |           CCNx or NDN           |
   +---------------------------------+---------------------------------+
   |       Stateless forwarding      |       Stateful forwarding       |
   |          Simple Packets         |    Object model with optional   |
   |                                 |             caching             |
   |       Pure datagram model       |      Request-response model     |
   |        Asymmetric Routing       |        Symmetric Routing        |
   |   Independent flow directions   |           Flow balance          |
   |  Flows grouped by IP prefix and |   Flows grouped by name prefix  |
   |               port              |                                 |
   |  End-to-end congestion control  |  Hop-by-hop congestion control  |
   +---------------------------------+---------------------------------+

   Table 1: Differences between IP and ICN relevant to QoS architecture

   This document proposes specific design patterns to achieve both flow
   classification and differentiated QoS treatment for ICN on both a
   flow and aggregate basis.  It also considers the effect of caches as
   a resource in addition to memory, CPU and link bandwidth that should
   be subject to explicitly un-fair resource allocation.  The proposed
   methods are intended to operate purely at the network layer,
   providing the primitives needed to achieve both transport and higher
   layer QoS objectives.  It does not propose detailed protocol
   machinery to achieve these goals; it leaves these to supplementary
   specifications, such as [I-D.moiseenko-icnrg-flowclass].  It
   explicitly excludes any discussion of Quality of Experience (QoE)
   which can only be assessed and controlled at the application layer or
   above.

   Much of this document is derived from presentations the author has
   given at ICNRG meetings over the last few years that are available
   through the IETF datatracker (see, for example [Oran2018QoSslides]).

2.  Requirements Language

   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 [RFC2119].








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3.  Some background on the nature and properties of Quality of Service
    in network protocols

   Much of this background material is tutorial, and can be simply
   skipped by readers familiar with the long and checkered history of
   quality of service in packet networks.  Other parts of it are
   polemical yet serve to illuminate the author's personal biases and
   technical views.

   All networking systems provide some degree of "quality of service" in
   that they exhibit non-zero utility when offered traffic to carry.
   The term therefore is used to describe systems that control the
   allocation of various resources in order to achieve _managed
   unfairness_.  Absent explicit mechanisms to decide what traffic to be
   unfair to, most systems try to achieve some form of "fairness" in the
   allocation of resources, optimizing the overall utility delivered to
   all demand under the constraint of available resources.  From this it
   should be obvious that you cannot use QoS mechanisms to create or
   otherwise increase resource capacity!  In fact, all known QoS schemes
   have non-zero overhead and hence may (albeit slightly) decrease to
   total esources available to carry user traffic.

   Further, accumulated experience seems to indicate that QoS is helpful
   in a fairly narrow range of network conditions:

   o  If your resources are lightly loaded, you don't need it, as
      neither congestive loss nor substantial queueing delay occurs

   o  If your resources are heavily oversubscribed, it doesn't save you.
      So many users will be unhappy that you are probably not delivering
      a viable service

   o  Failures can rapidly shift your state from the first above to the
      second, in which case either:

      *  your QoS machinery cannot respond quickly enough to maintain
         the advertised service quality continuously, or

      *  resource allocations are sufficiently conservative to result in
         substantial wasted capacity under non-failure conditions

   Nevertheless, though not universally deployed, QoS is advantageous at
   least for some applications and some network environments.  Some
   examples include:

   o  applications with steep utility functions [Shenker2006], such as
      real-time multimedia




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   o  applications with safety-critical operational constraints, such as
      avionics or industrial automation

   o  dedicated or tightly managed networks whose economics depend on
      strict adherence to challenging service level agreements (SLAs)

   Another factor in the design and deployment of QoS is the scalability
   and scope over which the desired service can be achieved.  Here there
   are two major considerations, one technical, the other economic/
   political:

   o  Some signaled QoS schemes, such as RSVP [RFC2205], maintain state
      in routers for each flow, which scales linearly with the number of
      flows.  For core routers through which pass millions to billions
      of flows, the memory required is infeasible to provide.

   o  The Internet is comprised of many minimally cooperating autonomous
      systems [AS].  There are practically no successful examples of QoS
      deployments crossing the AS boundaries of multiple service
      providers.  This in almost all cases limits the applicability of
      QoS capabilities to be intra-domain.

   Finally, the relationship between QoS and either accounting or
   billing is murky.  Some schemes can accurately account for resource
   consumption and ascertain to which user to allocate the usage.
   Others cannot.  While the choice of mechanism may have important
   practical economic and political consequences for cost and workable
   business models, this document considers none of those things and
   discusses QoS in the context of providing managed unfairness only.

   Some further background on congestion control for ICN is below.

3.1.  Congestion Control basics relevant to ICN

   Congestion control is necessary in any packet network that
   multiplexes traffic among multiple sources and destinations in order
   to:

   1.  Prevent collapse of utility due to overload, where the total
       offered service declines as load increases, perhaps
       precipitously, rather than increasing or remaining flat.

   2.  Avoid starvation of some traffic due to excessive demand by other
       traffic.

   3.  Beyond the basic protections against starvation, achieve
       "fairness" among competing traffic.  Two common objective
       functions are [minmaxfairness] and [proportionalfairness] both of



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       which have been implemented and deployed successfully on packet
       networks for many years.

   Before moving on to QoS, it is useful to consider how congestion
   control works in NDN or CCNx.  Unlike the IP protocol family, which
   relies exclusively on end-to-end congestion control (e.g.
   TCP[RFC0793], DCCP[RFC4340], SCTP[RFC4960],
   QUIC[I-D.ietf-quic-transport]), CCNx and NDN employ hop-by-hop
   congestion control.  There is per-Interest/Data state at every hop of
   the path and therefore for each outstanding Interest, bandwidth for
   data returning on the inverse path can be allocated.  In current
   designs, this allocation is often done using Interest counting.  By
   accepting one Interest packet from a downstream node, implicitly this
   provides a guarantee (either hard or soft) that there is sufficient
   bandwidth on the inverse direction of the link to send back one Data
   packet.  A number of congestion control schemes have been developed
   for ICN that operate in this fashion, for example [Wang2013],
   [Mahdian2016], [Song2018], [Carofiglio2012].  Other schemes, like
   [Schneider2016] neither count nor police interests, but instead
   monitor queues using AQM (active queue management) to mark returning
   Data packets that have experienced congestion.  This later class of
   schemes is similar to those used on IP in the sense that it depends
   on consumers adequately reducing their rate of Interest injection to
   avoid Data packet drops due to buffer overflow in forwarders.  The
   former class of schemes is (arguably) more robust against mis-
   behavior by consumers.

4.  What can we control to achieve QoS in ICN?

   QoS is achieved through managed unfairness in the allocation of
   resources in network elements, particularly in the routers doing
   forwarding of ICN packets.  So, a first order question is what
   resources need to be allocated, and how to ascertain which traffic
   gets what allocations.  In the case of CCNx or NDN the important
   network element resources are:
















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   +-----------------------------+-------------------------------------+
   |           Resource          | ICN Usage                           |
   +-----------------------------+-------------------------------------+
   | Communication Link capacity | buffering for queued packets        |
   |    Content Store capacity   | to hold cached data                 |
   |       Forwarder memory      | for the Pending Interest Table      |
   |                             | (PIT)                               |
   |       Compute capacity      | for forwarding packets, including   |
   |                             | the cost of Forwarding Information  |
   |                             | Base (FIB) lookups.                 |
   +-----------------------------+-------------------------------------+

              Table 2: ICN-related Network Element Resources

   For these resources, any QoS scheme has to specify two things:

   1.  How do you create _equivalence classes_ (a.k.a. flows) of traffic
       to which different QoS treatments are applied?

   2.  What are the possible treatments and how are those mapped to the
       resource allocation algorithms?

   Two critical facts of life come into play when designing a QoS
   scheme.  First, the number of equivalence classes that can be
   simultaneously tracked in a network element is bounded by both memory
   and processing capacity to do the necessary lookups.  One can allow
   very fine-grained equivalence classes, but not be able to employ them
   globally because of scaling limits of core routers.  That means it is
   wise to either restrict the range of equivalence classes, or allow
   them to be _aggregated_, trading off accuracy in policing traffic
   against ability to scale.

   The second is how flexible is the set of treatments that are defined.
   The ability to encode the treatment requests in the protocol can be
   limited (as it is for IP - there are only 6 of the TOS bits available
   for Diffserv treatments), but as or more important is whether there
   are practical traffic policing, queuing, and pacing algorithms that
   can be combined to support a rich set of QoS treatments.

   The two considerations above in combination can easily be
   substantially more expressive than can be achieved in practice with
   the available number of queues on real network interfaces or the
   amount of per-packet computation needed to enque or dequeue a packet.








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5.  How does this relate to QoS in TCP/IP?

   TCP/IP has fewer resource types to manage than ICN, and in some cases
   the allocation methods are simpler, as shown in the following table:

   +-----------------------------+-------------+-----------------------+
   |           Resource          | IP Relevant | TCP/IP Usage          |
   +-----------------------------+-------------+-----------------------+
   | Communication Link capacity |     YES     | buffering for queued  |
   |                             |             | packets               |
   |    Content Store capacity   |      NO     | no content store in   |
   |                             |             | IP                    |
   |       Forwarder memory      |    MAYBE    | not needed for        |
   |                             |             | output-buffered       |
   |                             |             | designs               |
   |       Compute capacity      |     YES     | for forwarding        |
   |                             |             | packets, but arguably |
   |                             |             | much cheaper than ICN |
   +-----------------------------+-------------+-----------------------+

               Table 3: IP-related Network Element Resources

   For these resources, IP has specified three fundamental things, as
   shown in the following table:

   +----------------+--------------------------------------------------+
   |      What      | How                                              |
   +----------------+--------------------------------------------------+
   |  *Equivalence  | subset+prefix match on IP 5-tuple                |
   |    classes*    | {SA,DA,SP,DP,PT}                                 |
   |   *Diffserv    | (very) small number of globally-agreed traffic   |
   |  treatments*   | classes                                          |
   |    *Intserv    | per-flow parameterized _Controlled Load_ and     |
   |  treatments*   | _Guaranteed_ service classes                     |
   +----------------+--------------------------------------------------+

     Table 4: Fundamental protocol elements to achieve QoS for TCP/IP

   Equivalence classes for IP can be pairwise, by matching against both
   source and destination address+port, pure group using only
   destination address+port, or source-specific multicast with source
   adress+port and destination multicast address+port.

   With Intserv, the signaling protocol RSVP [RFC2205] carries two data
   structures, the FLOWSPEC and the TSPEC.  The former fulfills the
   requirement to identify the equivalence class to which the QoS being
   signaled applies.  The latter comprises the desired QoS treatment
   along with a description of the dynamic character of the traffic



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   (e.g. average bandwidth and delay, peak bandwidth, etc.).  Both of
   these encounter substantial scaling limits, which has meant that
   Intserv has historically been limited to confined topologies, and/or
   high-value usages, like traffic engineering.

   With Diffserv, the protocol encoding (6 bits in the TOS field of the
   IP header) artificially limits the number of classes one can specify.
   These are documented in [RFC4594].  Nonetheless, when used with fine-
   grained equivalence classes, one still runs into limits on the number
   of queues required.

6.  Why is ICN Different?  Can we do Better?

   While one could adopt an approach to QoS mirroring the extensive
   experience with TCP/IP, this would, in the author's view, be a
   mistake.  The implementation and deployment of QoS in IP networks has
   been spotty at best.  There are of course economic and political
   reasons as well as technical reasons for these mixed results, but
   there are several architectural choices in ICN that make it a
   potentially much better protocol base to enhance with QoS machinery.
   This section discusses those difference and their consequences.

   First and foremost, hierarchical names are a much richer basis for
   specifying equivalence classes than IP 5-tuples.  The IP address (or
   prefix) can only separate traffic by topology to the granularity of
   hosts, and not express actual computational instances nor sets of
   data.  Ports give some degree of per-instance demultiplexing, but
   this tends to be both coarse and ephemeral, while confounding the
   demultiplexing function with the assignment of QoS treatments to
   particular subsets of the data.  Some degree of finer granularity is
   possible with IPv6 by exploiting the ability to use up to 64 bits of
   address for classifying traffic.  In fact, the hICN project
   ([I-D.muscariello-intarea-hicn]), while adopting the request-response
   model of CCNx, uses IPv6 addresses as the available namespace, and
   IPv6 packets (plus "fake" TCP headers) as the wire format.

   Nonetheless, the flexibility of tokenized, variable length,
   hierarchical names allows one to directly associate classes of
   traffic for QoS purposes with the structure of an application
   namespace.  The classification can be as coarse or fine-grained as
   desired by the application.  While not _always_ the case, there is
   typically a straightforward association between how objects are
   named, and how they are grouped together for common treatment.
   Examples abound; a number can be conveniently found in
   [I-D.moiseenko-icnrg-flowclass].

   In ICN, QoS is not pre-bound to topology since names are non-
   topological, unlike unicast IP addresses.  This allows QoS to be



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   applied to multi-destination and multi-path environments in a
   straightforward manner, rather than requiring either multicast with
   coarse class-based scheduling or complex signaling like that in RSVP-
   TE [RFC3209] that is needed to make point-to-multipoint MPLS work.

   Because of IP's stateless forwarding model, complicated by the
   ubiquity of asymmetric routes, any flow-based QoS requires state that
   is decoupled from the actual arrival of traffic and hence must be
   maintained, at least as soft-state, even during quiescent periods.
   Intserv, for example, requires flow signaling with state O(#flows).
   ICN, even worst case, requires state O(#active interest/data
   exchanges), since state can be instantiated on arrival of an
   Interest, and removed lazily once the data hase been returned.

   Unlike Intserv, Difserv eschews signaling in favor of class-based
   configuration of resources and queues in network elements.  However,
   Diffserv limits traffic treatments to a few bits taken from the ToS
   field of IP.  No such wire encoding limitations exist for NDN or
   CCNx, as the protocol is completely TLV-based, and one (or even more
   than one) new field can be easily defined to carry QoS treatment
   information.

   Therefore, there are greenfield possibilities for more powerful QoS
   treatment options in ICN.  For example, IP has no way to express a
   QoS treatment like "try hard to deliver reliably, even at the expense
   of delay or bandwidth".  Such a QoS treatment for ICN could invoke
   native ICN mechanisms, none of which are present in IP, such as:

   o  In-network retransmission in response to hop-by-hop errors
      returned from upstream forwarders

   o  Trying multiple paths to multiple content sources either in
      parallel or serially

   o  Higher precedence for short-term caching to recover from
      downstream errors

   Such mechanisms are typically described in NDN and CCNx as
   _forwarding strategies_. However, little or no guidance is given for
   what application actions or protocol machinery is used to decide
   which forwarding strategy to use for which Interests that arrive at a
   forwarder.  See [BenAbraham2018] for an investigation of these
   issues.  Associating forwarding strategies with the equivalence
   classes and QoS treatments directly can make them more accessible and
   useful to implement and deploy.

   IP has three forwarding semantics, with different QoS needs (Unicast,
   Anycast, Multicast).  ICN has the single forwarding semantic, so any



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   QoS machinery can be uniformly applied across any request/response
   invocation, whether it employs dynamic destination routing, multi-
   destination parallel requests, or even localized flooding (e.g.
   directly on L2 multicast mechanisms).  Additionally, the pull-based
   model of ICN avoids a number of thorny multicast QoS problems that IP
   has ([Wang2000], [RFC3170], [Tseng2003]).

   The Multi-destination/multi-path forwarding model in ICN changes
   resource allocation needs in a fairly deep way.  IP treats all
   endpoints as open-loop packet sources, whereas NDN and CCNx have
   strong asymmetry between producers and consumers as packet sources.

   IP has no caching in routers, whereas ICN needs ways to allocate
   cache resources.  Treatments to control caching operation are
   unlikely to look much like the treatments used to control link
   resources.  NDN and CCNx already have useful cache control directives
   associated with Data messages.  The CCNx controls include

   ExpiryTime  time after which a cached Content Object is considered
      expired and MUST no longer be used to respond to an Interest from
      a cache.

   Recommended Cache Time  time after which the publisher considers the
      Content Object to be of low value to cache.

   (See [RFC8569] for the formal definitions)

   ICN flow classifiers, such as those in
   [I-D.moiseenko-icnrg-flowclass] can be used to achieve soft or hard
   partitioning of cache resources in the content store of an ICN
   forwarder.  For example, cached content for a given equivalence class
   can be considered _fate shared_ in a cache whereby objects from the
   same equivalence class are purged as a group rather than
   individually.  This can recover cache space more quickly and at lower
   overhead than pure per-object replacement.  In addition, since the
   forwarder remembers the QoS treatment for each pending Interest in
   its PIT, the above cache controls can be augmented by policy to
   prefer retention of cached content for some equivalence classes as
   part of the cache replacement algorithm.

   Stateless forwarding and asymmetric routing in IP limits available
   state/feedback to manage link resources.  In contrast, NDN or CCNx
   forwarding allows all link resource allocation to occur as part of
   Interest forwarding, potentially simplifying things considerably.
   For example, with symmetric routing, producers have no control over
   the paths their data packets traverse, and hence any QoS treatments
   intended to affect routing paths will have no effect.




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7.  A strawman set of principles to guide QoS architecture for ICN

   Based on the observations made in the earlier sections, this summary
   section captures the author's ideas for clear and actionable
   architectural principals for how to incorporate QoS machinery into
   ICN protocols like NDN and CCNx.  Hopefully, they can guide further
   work and focus effort on portions of the giant design space for QoS
   that have the best tradeoffs in terms of flexibility, simplicity, and
   deployability.

   *Define equivalence classes using the name hierarchy rather than
   creating an independent traffic class definition*. This directly
   associates the specification of equivalence classes of traffic with
   the structure of the application namespace.  It can allow
   hierarchical decomposition of equivalence classes in a natural way
   because of the way hierarchical ICN names are constructed.  Two
   practical mechanisms are presented in [I-D.moiseenko-icnrg-flowclass]
   with different tradeoffs between security and the ability to
   aggregate flows.  Either prefix-based (EC3) or explicit name
   component based (ECNT) or both could be adopted as the part of the
   QoS architecture for defining equivalence classes.

   *Put consumers in control of Link and Forwarding resource
   allocation*. Do _all_ link buffering and forwarding (both memory and
   CPU) resource allocations based on Interest arrivals.  This is
   attractive because it provides early congestion feedback to
   consumers, and allows scheduling the reverse link direction ahead of
   time for carrying the matching data.  This makes enforcement of QoS
   treatments a single-ended rather than a double-ended problem and can
   avoid wasting resources on fetching data that will wind up dropped
   when it arrives at a bottleneck link.

   *Allow producers to influence the allocation of of cache resources*.
   Producers want to affect caching decisions in order to:

   o  Shed load by having Interests served by content stores in
      forwarders before reaching the producer itself.

   o  Survive transient outages of either the producer or links close to
      the producer.

   For caching to be effective, individual Data objects in an
   equivalence classes need to have similar treatment; otherwise well-
   known cache thrashing pathologies due to self-interference emerge.
   Producers have the most direct control over caching policies through
   the caching directives in Data messages.  It therefore makes sense to
   put the producer, rather than the consumer or network operator in
   charge of specifying these equivalence classes.



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   See [I-D.moiseenko-icnrg-flowclass] for specific mechanisms to
   achieve this.

   *Allow consumers to influence the allocation of of cache resources*.
   Consumers want to affect caching decisions in order to:

   o  Reduce latency for retrieving data

   o  Survive transient outages of either a producer or links close to
      the consumer

   Consumers can have indirect control over caching by specifying QoS
   treatments in their Interests.  Consider the following potential QoS
   treatments by consumers that can drive caching policies:

   o  A QoS treatment requesting better robustness against transient
      disconnection can be used by a forwarder close to the consumer (or
      downstream of an unreliable link) to preferentially cache the
      corresponding data.

   o  Conversely a QoS treatment together with, or in addition to a
      request for short latency, to indicate that new data will be
      requested soon enough that caching the current data being
      requested would be ineffective and hence to only pay attention to
      the caching preferences of the producer.

   o  A QoS treatment indicating a mobile consumer likely to incur a
      mobility event within an RTT (or a few RTTs).  Such a treatment
      would allow a mobile network operator to preferentially cache the
      data at a forwarder positioned at a _join point_ or _rendezvous
      point_ of their topology

   Network operators, whether closely tied administratively to producer
   or consumer, or constituting an independent transit administration,
   provide the storage resources in the ICN forwarders.  Therefore, they
   are the ultimate arbiters of how the cache resources are managed.  In
   addition to any local policies they may enforce, the cache behavior
   from the QoS standpoint emerges from how the producer-specified
   equivalence classes map onto cache space availability, including
   whether cache entries are treated individually, or fate-shared.
   Forwarders also determine how the consumer-specified QoS treatments
   map to the precedence used for retaining Data objects in the cache.

   Besides utilizing cache resources to meet the QoS goals of individual
   producers and consumers, network operators also want to manage their
   cache resources in order to:





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   o  Amerliorate congestion hotspots by reducing load converging on
      producers they host on their network.

   o  Improve Interest satisfaction rates by utilizing caches as short-
      term retransmission buffers to recover from link errors or
      outages.

   o  Improve both latency and reliability in environments when
      consumers move in the operator's topology.

   *Re-think how to specify traffic treatments - don't just copy
   Diffserv*. Some of the Diffserv classes may form a good starting
   point, as their mapping onto queuing algorithms for managing link
   buffering are well understood.  However, Diffserv alone does not
   allow one to express latency versus reliability tradeoffs or other
   useful QoS treatments.  Nor does it permit "TSPEC"-style traffic
   descriptions as are allowed in a signaled QoS scheme (despite neither
   having nor needing a separate signaling protocol given the state
   carried in the ICN data plane by forwarders).  Here are some
   examples:

   o  A "burst" treatment, where an initial Interest gives an aggregate
      data size to request allocation of link capacity for a large burst
      of Interest/Data exchanges.  The Interest can be rejected at any
      hop if the resources are not available.  Such a treatment can also
      accomodate Data implosion produced by the discovery procedures of
      management protocols like [I-D.irtf-icnrg-ccninfo].

   o  A "reliable" treatment, which affects preference for allocation of
      PIT space for the Interest and Content Store space for the data in
      order to improve the robustness of IoT data delivery in
      constrained environment, as is described in
      [I-D.gundogan-icnrg-iotqos].

   o  A "search" treatment, which, within the specified Interest
      Lifetime, tries many paths either in parallel or serial to
      potentially many content sources, to maximize the probability that
      the requested item will be found.  This is done at the expense of
      the extra bandwidth of both forwarding Interests and receiving
      multiple responses upstream of an aggregation point.  The
      treatment can encode a value expressing tradeoffs like breadth-
      first versus depth-first search, and bounds on the total resource
      expenditure.  Such a treatment would be useful for instrumentation
      protocols like [I-D.mastorakis-icnrg-icntraceroute].

   As an aside, loose latency control can be achieved by bounding
   Interest Lifetime as long as it is not also used as an application
   mechanism to provide subscriptions or establish path traces for



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   producer mobility.  See [Krol2018] for a discussion of the network
   versus application timescale issues in ICN protocols.

8.  IANA Considerations

   This document does not require any IANA actions

9.  Security Considerations

   There are a few ways in which QoS for ICN interacts with security and
   privacy issues.  Since QoS addresses relationships among traffic
   rather than the inherent characteristics of traffic, it neither
   enhances nor deteriorates the security and privacy properties of the
   data being carried, as long as the machinery does not alter or
   otherwise compromise the basic security properties of the associated
   protocols.  The QoS approaches advocated here for ICN can serve to
   amplify existing threats to network traffic however:

   o  An attacker able to manipulate the QoS treatments of traffic can
      mount a more focused (and potentially more effective) denial of
      service attack by suppressing performance on traffic the attacker
      is targeting.  Since the architcture here assumes QoS treatments
      are manipulable hop-by-hop, any on-path adversary can wreak havoc.
      Note however, that in basic ICN, and on-path attacker can do this
      and more by dropping, delaying, or mis-routing traffic independent
      of any particular QoS machinery in use.

   o  By explicitly revealing equivalence classes of traffic via either
      names or other fields in packets, an attacker has yet one more
      handle to use to discover linkability of multiple requests.

10.  References

10.1.  Normative References

   [RFC2119]  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>.

   [RFC8569]  Mosko, M., Solis, I., and C. Wood, "Content-Centric
              Networking (CCNx) Semantics", RFC 8569,
              DOI 10.17487/RFC8569, July 2019,
              <https://www.rfc-editor.org/info/rfc8569>.







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   [RFC8609]  Mosko, M., Solis, I., and C. Wood, "Content-Centric
              Networking (CCNx) Messages in TLV Format", RFC 8609,
              DOI 10.17487/RFC8609, July 2019,
              <https://www.rfc-editor.org/info/rfc8609>.

10.2.  Informative References

   [AS]       "Autonomous System (Internet)", no date,
              <https://en.wikipedia.org/wiki/
              Autonomous_system_(Internet)>.

   [BenAbraham2018]
              Ben Abraham, H., Parwatikar, J., DeHart, J., Dresher, A.,
              and P. Crowley, "Decoupling Information and Connectivity
              via Information-Centric Transport, in 5th ACM Conference
              on Information-Centric Networking (ICN '18), September
              21-23, 2018, Boston, MA, USA",
              DOI 10.1145/3267955.3267963, September 2018,
              <https://conferences.sigcomm.org/acm-icn/2018/proceedings/
              icn18-final31.pdf>.

   [Carofiglio2012]
              Carofiglio, G., Gallo, M., and L. Muscariello, "Joint hop-
              by-hop and receiver-driven interest control protocol for
              content-centric networks, in ICN Workshop at SIGcomm
              2012", DOI 10.1145/2377677.2377772, 2102,
              <http://conferences.sigcomm.org/sigcomm/2012/paper/icn/
              p37.pdf>.

   [I-D.gundogan-icnrg-iotqos]
              Gundogan, C., Schmidt, T., Waehlisch, M., Frey, M., Shzu-
              Juraschek, F., and J. Pfender, "Quality of Service for ICN
              in the IoT", draft-gundogan-icnrg-iotqos-01 (work in
              progress), July 2019.

   [I-D.ietf-quic-transport]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-22 (work
              in progress), July 2019.

   [I-D.irtf-icnrg-ccninfo]
              Asaeda, H., Ooka, A., and X. Shao, "CCNinfo: Discovering
              Content and Network Information in Content-Centric
              Networks", draft-irtf-icnrg-ccninfo-02 (work in progress),
              July 2019.






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   [I-D.mastorakis-icnrg-icntraceroute]
              Mastorakis, S., Gibson, J., Moiseenko, I., Droms, R., and
              D. Oran, "ICN Traceroute Protocol Specification", draft-
              mastorakis-icnrg-icntraceroute-05 (work in progress),
              August 2019.

   [I-D.moiseenko-icnrg-flowclass]
              Moiseenko, I. and D. Oran, "Flow Classification in
              Information Centric Networking", draft-moiseenko-icnrg-
              flowclass-04 (work in progress), July 2019.

   [I-D.muscariello-intarea-hicn]
              Muscariello, L., Carofiglio, G., Auge, J., and M.
              Papalini, "Hybrid Information-Centric Networking", draft-
              muscariello-intarea-hicn-02 (work in progress), June 2019.

   [Krol2018]
              Krol, M., Habak, K., Oran, D., Kutscher, D., and I.
              Psaras, "RICE: Remote Method Invocation in ICN, in
              Proceedings of the 5th ACM Conference on Information-
              Centric Networking - ICN '18",
              DOI 10.1145/3267955.3267956, September 2018,
              <https://conferences.sigcomm.org/acm-icn/2018/proceedings/
              icn18-final9.pdf>.

   [Mahdian2016]
              Mahdian, M., Arianfar, S., Gibson, J., and D. Oran,
              "MIRCC: Multipath-aware ICN Rate-based Congestion Control,
              in Proceedings of the 3rd ACM Conference on Information-
              Centric Networking", DOI 10.1145/2984356.2984365, 2016,
              <http://conferences2.sigcomm.org/acm-icn/2016/proceedings/
              p1-mahdian.pdf>.

   [minmaxfairness]
              "Max-min Fairness", no date,
              <https://en.wikipedia.org/wiki/Max-min_fairness>.

   [NDN]      "Named Data Networking", various,
              <https://named-data.net/project/execsummary/>.

   [Oran2018QoSslides]
              Oran, D., "Thoughts on Quality of Service for NDN/CCN-
              style ICN protocol architectures, presented at ICNRG
              Interim Meeting, Cambridge MA", September 2018,
              <https://datatracker.ietf.org/meeting/interim-2018-icnrg-
              03/materials/slides-interim-2018-icnrg-03-sessa-thoughts-
              on-qos-for-ndnccn-style-icn-protocol-architectures>.




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   [proportionalfairness]
              "Proportionally Fair", no date,
              <https://en.wikipedia.org/wiki/Proportionally_fair>.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <https://www.rfc-editor.org/info/rfc2205>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

   [RFC2998]  Bernet, Y., Ford, P., Yavatkar, R., Baker, F., Zhang, L.,
              Speer, M., Braden, R., Davie, B., Wroclawski, J., and E.
              Felstaine, "A Framework for Integrated Services Operation
              over Diffserv Networks", RFC 2998, DOI 10.17487/RFC2998,
              November 2000, <https://www.rfc-editor.org/info/rfc2998>.

   [RFC3170]  Quinn, B. and K. Almeroth, "IP Multicast Applications:
              Challenges and Solutions", RFC 3170, DOI 10.17487/RFC3170,
              September 2001, <https://www.rfc-editor.org/info/rfc3170>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC4340]  Kohler, E., Handley, M., and S. Floyd, "Datagram
              Congestion Control Protocol (DCCP)", RFC 4340,
              DOI 10.17487/RFC4340, March 2006,
              <https://www.rfc-editor.org/info/rfc4340>.

   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration
              Guidelines for DiffServ Service Classes", RFC 4594,
              DOI 10.17487/RFC4594, August 2006,
              <https://www.rfc-editor.org/info/rfc4594>.

   [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              RFC 4960, DOI 10.17487/RFC4960, September 2007,
              <https://www.rfc-editor.org/info/rfc4960>.




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   [Schneider2016]
              Schneider, K., Yi, C., Zhang, B., and L. Zhang, "A
              Practical Congestion Control Scheme for Named Data
              Networking, in Proceedings of the 2016 conference on 3rd
              ACM Conference on Information-Centric Networking - ACM-ICN
              '16", DOI 10.1145/2984356.2984369, 2016,
              <http://conferences2.sigcomm.org/acm-icn/2016/proceedings/
              p21-schneider.pdf>.

   [Shenker2006]
              Shenker, S., "Fundamental Design Issues for the Future
              Internet, in IEEE Journal on Selected Areas in
              Communications", DOI 10.1109/49.414637, 2006,
              <https://dl.acm.org/citation.cfm?id=2316898>.

   [Song2018]
              Song, J., Lee, M., and T. Kwon, "SMIC: Subflow-level
              Multi-path Interest Control for Information Centric
              Networking, in 5th ACM Conference on Information-Centric
              Networking", DOI 10.1145/3267955.3267971, 2018,
              <https://conferences.sigcomm.org/acm-icn/2018/proceedings/
              icn18-final62.pdf>.

   [Tseng2003]
              Tseng, CH., "The performance of QoS-aware IP multicast
              routing protocols, in Networks, Vol:42, No:2",
              DOI 10.1002/net.10084, September 2003,
              <https://onlinelibrary.wiley.com/doi/abs/10.1002/
              net.10084>.

   [Wang2000]
              Wang, B. and J. Hou, "Multicast routing and its QoS
              extension: problems, algorithms, and protocols, in IEEE
              Network, Vol:14, No:1", DOI 10.1109/65.819168, Jan/Feb
              2000, <https://ieeexplore.ieee.org/
              document/819168?arnumber=819168>.

   [Wang2013]
              Wang, Y., Rozhnova, N., Narayanan, A., Oran, D., and I.
              Rhee, "An Improved Hop-by-hop Interest Shaper for
              Congestion Control in Named Data Networking, in ACM
              SIGCOMM Workshop on Information-Centric Networking",
              DOI 10.1145/2534169.2491233, 2013,
              <http://conferences.sigcomm.org/sigcomm/2013/papers/icn/
              p55.pdf>.






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Author's Address

   Dave Oran
   Network Systems Research and Design
   4 Shady Hill Square
   Cambridge, MA  02138
   USA

   Email: daveoran@orandom.net










































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