\
Transport Area Working Group                               G. White, Ed.
Internet-Draft                                                 CableLabs
Intended status: Informational                         February 22, 2021
Expires: August 26, 2021


       Operational Guidance for Deployment of L4S in the Internet
                      draft-white-tsvwg-l4sops-02

Abstract

   This document is intended to provide additional guidance to operators
   of end-systems, operators of networks, and researchers beyond that
   provided in [I-D.ietf-tsvwg-ecn-l4s-id] and
   [I-D.ietf-tsvwg-aqm-dualq-coupled] in order to ensure successful
   deployment of L4S [I-D.ietf-tsvwg-l4s-arch] in the Internet.  The
   focus of this document is on potential interactions between L4S flows
   and Classic ECN ([RFC3168]) flows in Classic ECN bottleneck links.
   The document discusses the potential outcomes of these interactions,
   describes mechanisms to detect the presence of [RFC3168] bottlenecks,
   and identifies opportunites to prevent and/or detect and resolve
   fairness problems in such networks.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on August 26, 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Per-Flow Fairness . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Detection of Classic ECN Bottlenecks  . . . . . . . . . . . .   6
   4.  Operator of an L4S host . . . . . . . . . . . . . . . . . . .   6
     4.1.  Edge Servers  . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  Other hosts . . . . . . . . . . . . . . . . . . . . . . .   9
   5.  Operator of a Network Employing RFC3168 FIFO Bottlenecks  . .   9
     5.1.  Configure AQM to treat ECT(1) as NotECT . . . . . . . . .   9
     5.2.  ECT(1) Tunnel Bypass  . . . . . . . . . . . . . . . . . .  10
     5.3.  Configure Non-Coupled Dual Queue  . . . . . . . . . . . .  10
     5.4.  WRED with ECT(1) Differentation . . . . . . . . . . . . .  11
     5.5.  Disable RFC3168 ECN Marking . . . . . . . . . . . . . . .  11
     5.6.  Re-mark ECT(1) to NotECT Prior to AQM . . . . . . . . . .  11
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Low-latency, low-loss, scalable throughput (L4S)
   [I-D.ietf-tsvwg-l4s-arch] traffic is designed to provide lower
   queuing delay than conventional traffic via a new network service
   based on a modified Explicit Congestion Notification (ECN) response
   from the network.  L4S traffic is identified by the ECT(1) codepoint,
   and network bottlenecks that support L4S should congestion-mark
   ECT(1) packets to enable L4S congestion feedback.  However, L4S
   traffic is also expected to coexist well with classic congestion
   controlled traffic even if the bottleneck queue does not support L4S.
   This includes paths where the bottleneck link utilizes packet drops
   in response to congestion (either due to buffer overrun or active
   queue management), as well as paths that implement a 'flow-queuing'
   scheduler such as fq_codel [RFC8290].  A potential area of poor
   interoperability lies in network bottlenecks employing a shared queue
   that implements an Active Queue Management (AQM) algorithm that
   provides Explicit Congestion Notification signaling according to
   [RFC3168].  Although RFC3168 has been updated (via [RFC8311]) to
   reserve ECT(1) for experimental use only (also see [IANA-ECN]), and



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   its use for L4S has been specified in [I-D.ietf-tsvwg-ecn-l4s-id],
   not all deployed queues have been updated accordingly.  It has been
   demonstrated ([Fallback]) that when a set of long-running flows
   comprising both classic congestion controlled flows and L4S-compliant
   congestion controlled flows compete for bandwidth in such a legacy
   shared RFC3168 queue, the classic congestion controlled flows may
   achieve lower throughput than they would have if all of the flows had
   been classic congestion controlled flows.  This 'unfairness' between
   the two classes is more pronounced on longer RTT paths (e.g. 50ms and
   above) and/or at higher link rates (e.g. 50 Mbps and above).  The
   lower the capacity per flow, the less pronounced the problem becomes.
   Thus the imbalance is most significant when the slowest flow rate is
   still high in absolute terms.

   The root cause of the unfairness is that a legacy RFC3168 queue does
   not differentiate between packets marked ECT(0) (used by classic
   senders) and those marked ECT(1) (used by L4S senders), and provides
   an identical congestion signal (CE marks) to both types, while the
   L4S architecture redefines the CE mark and congestion response in the
   case of ECT(1) marked packets.  The result is that the two classes
   respond differently to the CE congestion signal.  The classic senders
   expect that CE marks are sent very rarely (e.g. approximately 1 CE
   mark every 200 round trips on a 50 Mbps x 50ms path) while the L4S
   senders expect very frequent CE marking (e.g. approximately 2 CE
   marks per round trip).  The result is that the classic senders
   respond to the CE marks provided by the bottleneck by yielding
   capacity to the L4S flows.  The resulting rate imbalance can be
   demonstrated, and could be a cause of concern in some cases.

   This concern primarily relates to single-queue (FIFO) bottleneck
   links that implement legacy RFC3168 ECN, but the situation can also
   potentially occur in fq_codel [RFC8290] bottlenecks when flow
   isolation is imperfect due to hash collisions or VPN tunnels.

   While the above mentioned unfairness has been demonstrated in
   laboratory testing, it has not been observed in operational networks,
   in part because members of the Transport Working group are not aware
   of any deployments of single-queue Classic ECN bottlenecks in the
   Internet.  Additionally, this issue was considered and is discussed
   in Appendix B.1 of [I-D.ietf-tsvwg-ecn-l4s-id].  It was recognized
   that compromises would have to be made because IP header space is
   extremely limited.  A number of alternative codepoint schemes were
   compared for their ability to traverse most Internet paths, to work
   over tunnels, to work at lower layers, to work with TCP, etc.  It was
   decided to progress on the basis that robust performance in presence
   of these single-queue RFC3168 bottlenecks is not the most critical
   issue, since it was believed that they are rare.  Nonetheless, there
   is the possibility that such deployments exist, and hence an interest



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   in providing guidance to ensure that measures can be taken to address
   the potential issues, should they arise in practice.

2.  Per-Flow Fairness

   There are a number of factors that influence the relative rates
   achieved by a set of users or a set of applications sharing a queue
   in a bottleneck link.  Notably the response that each application has
   to congestion signals (whether loss or explicit signaling) can play a
   large role in determining whether the applications share the
   bandwidth in an equitable manner.  In the Internet, ISPs typically
   control capacity sharing between their customers using a scheduler at
   the access bottleneck rather than relying on the congestion responses
   of end-systems.  So in that context this question primarily concerns
   capacity sharing between the applications used by one customer.
   Nonetheless, there are many networks on the Internet where capacity
   sharing relies, at least to some extent, on congestion control in the
   end-systems.  The traditional norm for congestion response has been
   that it is handled on a per-connection basis, and that (all else
   being equal) it results in each connection in the bottleneck
   achieving a data rate inversely proportional to the average RTT of
   the connection.  The end result (in the case of steady-state behavior
   of a set of like connections) is that each user or application
   achieves a data rate proportional to N/RTT, where N is the number of
   simultaneous connections that the user or application creates, and
   RTT is the harmonic mean of the average round-trip-times for those
   connections.  Thus, users or applications that create a larger number
   of connections and/or that have a lower RTT achieve a larger share of
   the bottleneck link rate than others.

   While this may not be considered fair by many, it nonetheless has
   been the typical starting point for discussions around fairness.  In
   fact it has been common when evaluating new congestion responses to
   actually set aside N & RTT as variables in the equation, and just
   compare per-flow rates between flows with the same RTT.  For example
   [RFC5348] defines the congestion response for a flow to be
   '"reasonably fair" if its sending rate is generally within a factor
   of two of the sending rate of a [Reno] TCP flow under the same
   conditions.'  Given that RTTs can vary by roughly two orders of
   magnitude and flow counts can vary by at least an order of magnitude
   between applications, it seems that the accepted definition of
   reasonable fairness leaves quite a bit of room for different levels
   of performance between users or applications, and so perhaps isn't
   the gold standard, but is rather a metric that is used because of its
   convenience.

   In practice, the effect of this RTT dependence has historically been
   muted by the fact that many networks were deployed with very large



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   ("bloated") drop-tail buffers that would introduce queuing delays
   well in excess of the base RTT of the flows utilizing the link, thus
   equalizing (to some degree) the effective RTTs of those flows.
   Recently, as network equipment suppliers and operators have worked to
   improve the latency performance of the network by the use of smaller
   buffers and/or AQM algorithms, this has had the side-effect of
   uncovering the inherent RTT bias in classic congestion control
   algorithms.

   The L4S architecture aims to significantly improve this situation, by
   requiring senders to adopt a congestion response that eliminates RTT
   bias as much as possible (see [I-D.ietf-tsvwg-ecn-l4s-id]).  As a
   result, L4S promotes a level of per-flow fairness beyond what is
   ordinarily considered for classic senders, the legacy RFC3168 issue
   notwithstanding.

   It is also worth noting that the congestion control algorithms
   deployed currently on the internet tend toward (RTT-weighted)
   fairness only over long timescales.  For example, the cubic algorithm
   can take minutes to converge to fairness when a new flow joins an
   existing flow on a link [Cubic].  Since the vast majority of TCP
   connections don't last for minutes, it is unclear to what degree per-
   flow, same-RTT fairness, even when demonstrated in the lab,
   translates to the real world.

   So, in real networks, where per-application, per-end-host or per-
   customer fairness may be more important than long-term, same-RTT,
   per-flow fairness, it may not be that instructive to focus on the
   latter as being a necessary end goal.

   Nonetheless, situations in which the presence of an L4S flow has the
   potential to cause harm [Harm] to classic flows need to be
   understood.  Most importantly, if there are situations in which the
   introduction of L4S traffic would degrade classic traffic performance
   significantly, i.e. to the point that it would be considered
   starvation, these situations need to be understood and either
   remedied or avoided.

   Aligned with this context, the guidance provided in this document is
   aimed not at monitoring the relative performance of L4S senders
   compared against classic senders on a per-flow basis, but rather at
   identifying instances where RFC3168 bottlenecks are deployed so that
   operators of L4S senders can have the opportunity to assess whether
   any actions need to be taken.  Additionally this document provides
   guidance for network operators around configuring any RFC3168
   bottlenecks to minimize the potential for negative interactions
   between L4S and classic senders.




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3.  Detection of Classic ECN Bottlenecks

   The IETF encourages researchers, end system deployers and network
   operators to conduct experiments to identify to what degree legacy
   RFC3168 bottlecks exist in networks.  These types of measurement
   campaigns, even if each is conducted over a limited set of paths,
   could be useful to further understand the scope of any potential
   issues, to guide end system deployers on where to examine performance
   more closely (or possibly delay L4S deployment), and to help network
   operators identify nodes where remediation may be necessary to
   provide the best performance.

   The design of such experiments should consider not only the detection
   of RFC3168 ECN marking, but also the determination whether the
   bottleneck AQM is a single queue (FIFO) or a flow-queuing system.  It
   is believed that the vast majority, if not all, of the RFC3168 AQMs
   in use at bottleneck links are flow-queuing systems (e.g. fq_codel
   [RFC8290] or [COBALT]).  When flow isolation is successful, the FQ
   scheduling of such queues isolates classic congestion control traffic
   from L4S traffic, and thus eliminates the potential for unfairness.
   But, these systems are known to sometimes result in imperfect
   isolation, either due to hash collisions (see Section 5.3 of
   [RFC8290]) or because of VPN tunneling (see Section 6.2 of
   [RFC8290]).  It is believed that the majority of fq_codel deployments
   in bottleneck links today (e.g.  [Cake]) employ hashing algorithms
   that virtually eliminate the possibility of collisions, making this a
   non-issue for those deployments.  But, VPN tunnels remain an issue
   for fq_codel deployments, and the introduction of L4S traffic raises
   the possibility that tunnels containing mixed classic and L4S traffic
   would exist, in which case fq_codel implementations that have not
   been updated to be L4S-aware could exhibit similar unfairness
   properties as single queue AQMs.  Until such queues are upgraded to
   support L4S or treat ECT(1) as not-ECT traffic, end-host mitigations
   such as separating L4S and Classic traffic into distinct VPN tunnels
   could be employed.

   [Fallback] contains recommendations on some of the mechanisms that
   can be used to detect legacy RFC3168 bottlenecks.  TODO: summarize
   the main ones here.

4.  Operator of an L4S host

   From a host's perspective, support for L4S involves both endpoints:
   ECT(1) marking & L4S-compatible congestion control at the sender, and
   ECN feedback at the receiver.  Between these two entities, it is
   primarily incumbent upon the sender to evaluate the potential for
   presence of legacy RFC3168 FIFO bottlenecks and make decisions
   whether or not to use L4S congestion control.  A general purpose



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   receiver is not expected to perform any testing or monitoring for
   RFC3168, and is also not expected to invoke any active response in
   the case that such a bottleneck exists.  That said, it is certainly
   possible for receivers to disable L4S functionality by not
   negotiating ECN support with the sender.

   Prior to deployment of any new technology, it is commonplace for the
   parties involved in the deployment to validate the performance of the
   new technology, via lab testing, limited field testing, large scale
   field testing, etc.  The same is expected for deployers of L4S
   technology.  As part of that validation, it is recommended that
   deployers consider the issue of RFC3168 FIFO bottlenecks and conduct
   experiments as described in the previous section, or otherwise assess
   the impact that the L4S technology will have in the networks in which
   it is to be deployed, and take action as is described further in this
   section.

   If pre-deployment testing raises concerns about issues with RFC3168
   bottlenecks, the actions taken may depend on the server type:

   o  General purpose servers (e.g. web servers)

      *  Active testing could be performed by the server.  For example,
         a javascript application could run simultaneous downloads
         during page reading time in order to survey for presence of
         legacy RFC3168 FIFO bottlenecks on paths to users.

      *  Passive testing could be built in to the transport protocol
         implementation at the sender in order to perform detection (see
         [Fallback]).

      *  Taking action based on the detection of RFC3168 FIFO
         bottlenecks is likely not needed for short transactional
         transfers (e.g. sub 10 seconds) since these are unlikely to
         achieve the steady-state conditions where unfairness has been
         observed.

      *  For longer file transfers, it may be possible to fall-back to
         Classic behavior in real-time, or to simply disable L4S for
         future long file transfers to clients where legacy RFC3168 has
         been detected.

   o  Specialized servers handling long-running sessions (e.g. cloud
      gaming)

      *  Active testing could be performed at each session startup





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      *  Active testing could be integrated into a "pre-validation" of
         the service, done when the user signs up, and periodically
         thereafter

      *  In-band detection as described in [Fallback] could be performed
         during the session

   In addition, the responsibilities of and actions taken by a sender
   may depend on the environment in which it is deployed.  The following
   sub-sections discuss two scenarios: senders serving a limited known
   target audience and those that serve an unknown target audience.

4.1.  Edge Servers

   Some hosts (such as CDN leaf nodes and servers internal to an ISP)
   are deployed in environments in which they serve content to a
   constrained set of networks or clients.  The operator of such hosts
   may be able to determine whether there is the possibility of
   [RFC3168] FIFO bottlenecks being present, and utilize this
   information to make decisions on selectively deploying L4S and/or
   disabling it (e.g. bleaching ECN).  Furthermore, such an operator may
   be able to determine the likelihood of an L4S bottleneck being
   present, and use this information as well.

   For example, if a particular network is known to have deployed legacy
   [RFC3168] FIFO bottlenecks, deployment of L4S for that network should
   be delayed until those bottlenecks can be upgraded to mitigate any
   potential issues as discussed in the next section.

   Prior to deploying L4S on edge servers a server operator should:

   o  Consult with network operators on presence of legacy [RFC3168]
      FIFO bottlenecks

   o  Consult with network operators on presence of L4S bottlenecks

   o  Perform pre-deployment testing per network

   If a particular network offers connectivity to other networks (e.g.
   in the case of an ISP offering service to their customer's networks),
   the lack of RFC3168 FIFO bottleneck deployment in the ISP network
   can't be taken as evidence that RFC3168 FIFO bottlenecks don't exist
   end-to-end (because one may have been deployed by the end-user
   network).  In these cases, deployment of L4S will need to take
   appropriate steps to detect the presence of such bottlenecks.  At
   present, it is believed that the vast majority of RFC3168 bottlenecks
   in end-user networks are implementations that utilize fq_codel or
   Cake, where the unfairness problem is less likely to be a concern.



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   While this doesn't completely eliminate the possibility that a legacy
   [RFC3168] FIFO bottleneck could exist, it nonetheless provides useful
   information that can be utilized in the decision making around the
   potential risk for any unfairness to be experienced by end users.

4.2.  Other hosts

   Hosts that are deployed in locations that serve a wide variety of
   networks face a more difficult prospect in terms of handling the
   potential presence of RFC3168 FIFO bottlenecks.  Nonetheless, the
   steps listed in the ealier section (based on server type) can be
   taken to minimize the risk of unfairness.

   Since existing studies have hinted that RFC3168 FIFO bottlenecks are
   rare, detections using these techniques may also prove to be rare.
   Therefore, it may be possible for a host to cache a list of end host
   ip addresses where a RFC3168 bottleneck has been detected.  Entries
   in such a cache would need to age-out after a period of time to
   account for IP address changes, path changes, equipment upgrades,
   etc.

   It has been suggested that a public blacklist of domains that
   implement RFC3168 FIFO bottlenecks or a public whitelist of domains
   that are participating in the L4S experiment could be maintained.
   There are a number of significant issues that would seem to make this
   idea infeasible, not the least of which is the fact that presence of
   RFC3168 FIFO bottlenecks or L4S bottlenecks is not a property of a
   domain, it is the property of a path between two endpoints.

5.  Operator of a Network Employing RFC3168 FIFO Bottlenecks

   While it is, of course, preferred for networks to deploy L4S-capable
   high fidelity congestion signaling, and while it is more preferable
   for L4S senders to detect problems themselves, a network operator who
   has deployed equipment in a likely bottleneck link location (i.e. a
   link that is expected to be fully saturated) that is configured with
   a leagcy [RFC3168] FIFO AQM can take certain steps in order to
   improve rate fairness between classic traffic and L4S traffic, and
   thus enable L4S to be deployed in a greater number of paths.

   Some of the options listed in this section may not be feasible in all
   networking equipment.

5.1.  Configure AQM to treat ECT(1) as NotECT

   If equipment is configurable in such as way as to only supply CE
   marks to ECT(0) packets, and treat ECT(1) packets identically to




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   NotECT, or is upgradable to support this capability, doing so will
   eliminate the risk of unfairness.

5.2.  ECT(1) Tunnel Bypass

   Using an [RFC6040] compatibility mode tunnel, tunnel ECT(1) traffic
   through the [RFC3168] bottleneck with the outer header indicating
   Not-ECT.

   Two variants exist for this approach

   1.  per-domain: tunnel ECT(1) pkts to domain edge towards dst

   2.  per-dst: tunnel ECT(1) pkts to dst

5.3.  Configure Non-Coupled Dual Queue

   Equipment supporting [RFC3168] may be configurable to enable two
   parallel queues for the same traffic class, with classification done
   based on the ECN field.

   Option 1:

   o  Configure 2 queues, both with ECN; 50:50 WRR scheduler

      *  Queue #1: ECT(1) & CE packets - Shallow immediate AQM target

      *  Queue #2: ECT(0) & NotECT packets - Classic AQM target

   o  Outcome in the case of n L4S flows and m long-running Classic
      flows

      *  if m & n are non-zero, flows get 1/2n and 1/2m of the capacity,
         otherwise 1/n or 1/m

      *  never < 1/2 each flow's rate if all had been Classic

   This option would allow L4S flows to achieve low latency, low loss
   and scalable throughput, but would sacrifice the more precise flow
   balance offered by [I-D.ietf-tsvwg-aqm-dualq-coupled].  This option
   would be expected to result in some reordering of previously CE
   marked packets sent by Classic ECN senders, which is a trait shared
   with [I-D.ietf-tsvwg-aqm-dualq-coupled].  As is discussed in
   [I-D.ietf-tsvwg-ecn-l4s-id], this reordering would be either zero
   risk or very low risk.

   Option 2:




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   o  Configure 2 queues, both with AQM; 50:50 WRR scheduler

      *  Queue #1: ECT(1) & NotECT packets - ECN disabled

      *  Queue #2: ECT(0) & CE packets - ECN enabled

   o  Outcome

      *  ECT(1) treated as NotECT

      *  Flow balance for the 2 queues the same as in option 1

   This option would not allow L4S flows to achieve low latency, low
   loss and scalable throughput in this bottleneck link.  As a result it
   is a less prefered option.

5.4.  WRED with ECT(1) Differentation

   This configuration is similar to Option 2 in the previous section,
   but uses a single queue with WRED functionality.

   o  Configure the queue with two WRED classes

   o  Class #1: ECT(1) & NotECT packets - ECN disabled

   o  Class #2: ECT(0) & CE packets - ECN enabled

5.5.  Disable RFC3168 ECN Marking

   Disabling [RFC3168] ECN marking eliminates the unfairness issue.
   Clearly a downside to this approach is that classic senders will no
   longer get the benefits of Explict Congestion Notification.

5.6.  Re-mark ECT(1) to NotECT Prior to AQM

   While not a recommended alternative, remarking ECT(1) packets as
   NotECT (i.e. bleaching ECT(1)) ensures that they are treated
   identically to classic NotECT senders.  However, this also eliminates
   the possibility of downstream L4S bottlenecks providing high fidelity
   congestion signals.

6.  Contributors

   Thanks to Bob Briscoe, Jake Holland, Koen De Schepper, Olivier
   Tilmans, Tom Henderson, Asad Ahmed, and members of the TSVWG mailing
   list for their contributions to this document.





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7.  IANA Considerations

   None.

8.  Security Considerations

   For further study.

9.  Informative References

   [Cake]     Hoiland-Jorgensen, T., Taht, D., and J. Morton, "Piece of
              CAKE: A Comprehensive Queue Management Solution for Home
              Gateways", 2018, <https://arxiv.org/abs/1804.07617>.

   [COBALT]   Palmei, J. and et al., "Design and Evaluation of COBALT
              Queue Discipline", IEEE International Symposium on Local
              and Metropolitan Area Networks 2019, 2019,
              <https://ieeexplore.ieee.org/abstract/document/8847054>.

   [Cubic]    Ha, S., Rhee, I., and L. Xu, "CUBIC: A New TCP-Friendly
              High-Speed TCP Variant", ACM SIGOPS Operating Systems
              Review , 2008,
              <https://www.cs.princeton.edu/courses/archive/fall16/
              cos561/papers/Cubic08.pdf>.

   [Fallback]
              Briscoe, B. and A. Ahmed, "TCP Prague Fall-back on
              Detection of a Classic ECN AQM", ArXiv , Feb 2021,
              <https://arxiv.org/abs/1911.00710>.

   [Harm]     Ware, R., Mukerjee, M., Seshan, S., and J. Sherry, "Beyond
              Jain's Fairness Index: Setting the Bar For The Deployment
              of Congestion Control Algorithms", Hotnets'19 , 2019,
              <https://www.cs.cmu.edu/~rware/assets/pdf/ware-
              hotnets19.pdf>.

   [I-D.ietf-tsvwg-aqm-dualq-coupled]
              Schepper, K., Briscoe, B., and G. White, "DualQ Coupled
              AQMs for Low Latency, Low Loss and Scalable Throughput
              (L4S)", draft-ietf-tsvwg-aqm-dualq-coupled-13 (work in
              progress), November 2020.

   [I-D.ietf-tsvwg-ecn-l4s-id]
              Schepper, K. and B. Briscoe, "Identifying Modified
              Explicit Congestion Notification (ECN) Semantics for
              Ultra-Low Queuing Delay (L4S)", draft-ietf-tsvwg-ecn-l4s-
              id-12 (work in progress), November 2020.




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Internet-Draft          L4S Operational Guidance           February 2021


   [I-D.ietf-tsvwg-l4s-arch]
              Briscoe, B., Schepper, K., Bagnulo, M., and G. White, "Low
              Latency, Low Loss, Scalable Throughput (L4S) Internet
              Service: Architecture", draft-ietf-tsvwg-l4s-arch-08 (work
              in progress), November 2020.

   [IANA-ECN]
              Internet Assigned Numbers Authority, "IANA ECN Field
              Assignments", 2018, <https://www.iana.org/assignments/
              dscp-registry/dscp-registry.xhtml#ecn-field>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <https://www.rfc-editor.org/info/rfc3168>.

   [RFC5348]  Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
              Friendly Rate Control (TFRC): Protocol Specification",
              RFC 5348, DOI 10.17487/RFC5348, September 2008,
              <https://www.rfc-editor.org/info/rfc5348>.

   [RFC6040]  Briscoe, B., "Tunnelling of Explicit Congestion
              Notification", RFC 6040, DOI 10.17487/RFC6040, November
              2010, <https://www.rfc-editor.org/info/rfc6040>.

   [RFC8290]  Hoeiland-Joergensen, T., McKenney, P., Taht, D., Gettys,
              J., and E. Dumazet, "The Flow Queue CoDel Packet Scheduler
              and Active Queue Management Algorithm", RFC 8290,
              DOI 10.17487/RFC8290, January 2018,
              <https://www.rfc-editor.org/info/rfc8290>.

   [RFC8311]  Black, D., "Relaxing Restrictions on Explicit Congestion
              Notification (ECN) Experimentation", RFC 8311,
              DOI 10.17487/RFC8311, January 2018,
              <https://www.rfc-editor.org/info/rfc8311>.

Author's Address

   Greg White (editor)
   CableLabs

   Email: g.white@cablelabs.com









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