Re: [Detnet] Rtgdir last call review of draft-ietf-detnet-bounded-latency-06

Mohammadpour Ehsan <ehsan.mohammadpour@epfl.ch> Wed, 01 September 2021 07:37 UTC

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From: Mohammadpour Ehsan <ehsan.mohammadpour@epfl.ch>
To: Tony Przygienda <prz@juniper.net>
CC: "rtg-dir@ietf.org" <rtg-dir@ietf.org>, DetNet WG <detnet@ietf.org>, "draft-ietf-detnet-bounded-latency.all@ietf.org" <draft-ietf-detnet-bounded-latency.all@ietf.org>, "last-call@ietf.org" <last-call@ietf.org>
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Subject: Re: [Detnet] Rtgdir last call review of draft-ietf-detnet-bounded-latency-06
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Dear Tony,

Thank you very much for the precise review! We have addressed the comments and updated the draft. A new version is available online: https://www.ietf.org/archive/id/draft-ietf-detnet-bounded-latency-07.html.


Best,
Ehsan



--
Ehsan Mohammadpour
PhD Candidate at Swiss Federal Institute of Technology (EPFL)
EPFL EDIC PhD student representative
IC IINFCOM, LCA2, INF 011, Station 14, 1015 Lausanne, Switzerland
https://people.epfl.ch/ehsan.mohammadpour<https://people.epfl.ch/ehsan.mohammadpour?lang=en>



On 24 Aug 2021, at 15:20, Tony Przygienda via Datatracker <noreply@ietf.org<mailto:noreply@ietf.org>> wrote:

Reviewer: Tony Przygienda
Review result: Has Nits

RtgDir review: draft-ietf-detnet-bounded-latency

I have been selected as the Routing Directorate reviewer for this draft.
The Routing Directorate seeks to review all routing or routing-related
drafts as they pass through IETF last call and IESG review, and
sometimes on special request. The purpose of the review is to provide
assistance to the Routing ADs. For more information about the Routing
Directorate, please see
​http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir

Although these comments are primarily for the use of the Routing ADs, it
would be helpful if you could consider them along with any other IETF
Last Call comments that you receive, and strive to resolve them through
discussion or by updating the draft.

Document: draft-ietf-detnet-bounded-latency
Reviewer: Tony Przygienda
Review Date: 08/24/21
Intended Status: Informational

Summary:

   The document is of high quality and basically ready for publication albeit
   it would benefit from some readability oriented explanations and
   clarifications that I marked up in the text below with [minor]. No defects
   were found in rough  retracing of the formulas and figures albeit some
   assumptions had to be extrapolated. The flow is laid out well and allows
   for natural sequential reading without too much backtracing.

Minor/Nits: expand some acronyms, provide reference or reasoning for some terse
assertions. Make some assumptions more explicit.

-----

Review DetNet Bounded Latency

DetNet                                                           N. Finn
Internet-Draft                               Huawei Technologies Co. Ltd
Intended status: Informational                            J-Y. Le Boudec
Expires: November 18, 2021                               E. Mohammadpour
                                                                   EPFL
                                                               J. Zhang
                                            Huawei Technologies Co. Ltd
                                                               B. Varga
                                                              J. Farkas
                                                               Ericsson
                                                           May 17, 2021

                        DetNet Bounded Latency
                 draft-ietf-detnet-bounded-latency-06

Abstract

  This document references specific queuing mechanisms, defined in
  other documents, that can be used to control packet transmission at
  each output port and achieve the DetNet qualities of service.  This
  document presents a timing model for sources, destinations, and the
  DetNet transit nodes that relay packets that is applicable to all of
  those referenced queuing mechanisms.  Using the model presented in
  this document, it should be possible for an implementor, user, or
  standards development organization to select a particular set of
  queuing mechanisms for each device in a DetNet network, and to select
  a resource reservation algorithm for that network, so that those
  elements can work together to provide the DetNet service.

Status of This Memo

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

  Internet-Drafts are working documents of the Internet Engineering
  Task Force (IETF).  Note that other groups may also distribute
  working documents as Internet-Drafts.  The list of current Internet-
  Drafts is at https://datatracker.ietf.org/drafts/current/.

  Internet-Drafts are draft documents valid for a maximum of six months
  and may be updated, replaced, or obsoleted by other documents at any
  time.  It is inappropriate to use Internet-Drafts as reference
  material or to cite them other than as "work in progress."

  This Internet-Draft will expire on November 18, 2021.

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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
  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  . . . . . . . . . . . . . . . . . . . . . . . .   3
  2.  Terminology and Definitions . . . . . . . . . . . . . . . . .   4
  3.  DetNet bounded latency model  . . . . . . . . . . . . . . . .   4
    3.1.  Flow admission  . . . . . . . . . . . . . . . . . . . . .   4
      3.1.1.  Static latency calculation  . . . . . . . . . . . . .   4
      3.1.2.  Dynamic latency calculation . . . . . . . . . . . . .   5
    3.2.  Relay node model  . . . . . . . . . . . . . . . . . . . .   6
  4.  Computing End-to-end Delay Bounds . . . . . . . . . . . . . .   8
    4.1.  Non-queuing delay bound . . . . . . . . . . . . . . . . .   8
    4.2.  Queuing delay bound . . . . . . . . . . . . . . . . . . .   9
      4.2.1.  Per-flow queuing mechanisms . . . . . . . . . . . . .   9
      4.2.2.  Aggregate queuing mechanisms  . . . . . . . . . . . .   9
    4.3.  Ingress considerations  . . . . . . . . . . . . . . . . .  10
    4.4.  Interspersed DetNet-unaware transit nodes . . . . . . . .  11
  5.  Achieving zero congestion loss  . . . . . . . . . . . . . . .  11
  6.  Queuing techniques  . . . . . . . . . . . . . . . . . . . . .  12
    6.1.  Queuing data model  . . . . . . . . . . . . . . . . . . .  13
    6.2.  Frame Preemption  . . . . . . . . . . . . . . . . . . . .  15
    6.3.  Time Aware Shaper . . . . . . . . . . . . . . . . . . . .  15
    6.4.  Credit-Based Shaper with Asynchronous Traffic Shaping . .  16
      6.4.1.  Delay Bound Calculation . . . . . . . . . . . . . . .  18
      6.4.2.  Flow Admission  . . . . . . . . . . . . . . . . . . .  19
    6.5.  Guaranteed-Service IntServ  . . . . . . . . . . . . . . .  20
    6.6.  Cyclic Queuing and Forwarding . . . . . . . . . . . . . .  21
  7.  Example application on DetNet IP network  . . . . . . . . . .  22
  8.  Security considerations . . . . . . . . . . . . . . . . . . .  24
  9.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  24
  10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
    10.1.  Normative References . . . . . . . . . . . . . . . . . .  24
    10.2.  Informative References . . . . . . . . . . . . . . . . .  25
  Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

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1.  Introduction

  The ability for IETF Deterministic Networking (DetNet) or IEEE 802.1
  Time-Sensitive Networking (TSN, [IEEE8021TSN]) to provide the DetNet
  services of bounded latency and zero congestion loss depends upon A)
  configuring and allocating network resources for the exclusive use of
  DetNet flows; B) identifying, in the data plane, the resources to be
  utilized by any given packet, and C) the detailed behavior of those
  resources, especially transmission queue selection, so that latency
  bounds can be reliably assured.

  As explained in [RFC8655], DetNet flows are characterized by 1) a
  maximum bandwidth, guaranteed either by the transmitter or by strict
  input metering; and 2) a requirement for a guaranteed worst-case end-
  to-end latency.  That latency guarantee, in turn, provides the
  opportunity for the network to supply enough buffer space to
  guarantee zero congestion loss.

  To be used by the applications identified in [RFC8578], it must be
  possible to calculate, before the transmission of a DetNet flow
  commences, both the worst-case end-to-end network latency, and the
  amount of buffer space required at each hop to ensure against
  congestion loss.

  This document references specific queuing mechanisms, defined in
  [RFC8655], that can be used to control packet transmission at each
  output port and achieve the DetNet qualities of service.  This
  document presents a timing model for sources, destinations, and the
  DetNet transit nodes that relay packets that is applicable to all of
  those referenced queuing mechanisms.  It furthermore provides end-to-
  end delay bound and backlog bound computations for such mechanisms
  that can be used by the control plane to provide DetNet QoS.

  Using the model presented in this document, it should be possible for
  an implementor, user, or standards development organization to select
  a particular set of queuing mechanisms for each device in a DetNet
  network, and to select a resource reservation algorithm for that
  network, so that those elements can work together to provide the
  DetNet service.  Section 7 provides an example application of this
  document to a DetNet IP network with combination of different queuing
  mechanisms.

  This document does not specify any resource reservation protocol or
  control plane function.  It does not describe all of the requirements
  for that protocol or control plane function.  It does describe
  requirements for such resource reservation methods, and for queuing
  mechanisms that, if met, will enable them to work together.

[minor] however, assumption should be stated that the path is fixed,
i.e. ECMP or loose next hops are not used since I do not see any
treatment of that subject (that needs probably to be voiced for both
IEEE & DetNet contexts)

[minor] it would be good to spell out that the document disregards
as well in-band packets that can be part of the stream such as OAM
or necessary retransmissions etc.

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2.  Terminology and Definitions

  This document uses the terms defined in [RFC8655].

3.  DetNet bounded latency model

3.1.  Flow admission

  This document assumes that following paradigm is used to admit DetNet
  flows:

  1.  Perform any configuration required by the DetNet transit nodes in
      the network for aggregates of DetNet flows.  This configuration
      is done beforehand, and not tied to any particular DetNet flow.

  2.  Characterize the new DetNet flow, particularly in terms of
      required bandwidth.

  3.  Establish the path that the DetNet flow will take through the
      network from the source to the destination(s).  This can be a
      point-to-point or a point-to-multipoint path.

  4.  Compute the worst-case end-to-end latency for the DetNet flow,
      using one of the methods, below (Section 3.1.1, Section 3.1.2).
      In the process, determine whether sufficient resources are
      available for the DetNet flow to guarantee the required latency
      and to provide zero congestion loss.

  5.  Assuming that the resources are available, commit those resources
      to the DetNet flow.  This may or may not require adjusting the
      parameters that control the filtering and/or queuing mechanisms
      at each hop along the DetNet flow's path.

  This paradigm can be implemented using peer-to-peer protocols or
  using a central controller.  In some situations, a lack of resources
  can require backtracking and recursing through this list.

  Issues such as service preemption of a DetNet flow in favor of
  another, when resources are scarce, are not considered, here.  Also
  not addressed is the question of how to choose the path to be taken
  by a DetNet flow.

3.1.1.  Static latency calculation

  The static problem:
          Given a network and a set of DetNet flows, compute an end-to-
          end latency bound (if computable) for each DetNet flow, and

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          compute the resources, particularly buffer space, required in
          each DetNet transit node to achieve zero congestion loss.

  In this calculation, all of the DetNet flows are known before the
  calculation commences.  This problem is of interest to relatively
  static networks, or static parts of larger networks.  It provides
  bounds on delay and buffer size.  The calculations can be extended to
  provide global optimizations, such as altering the path of one DetNet
  flow in order to make resources available to another DetNet flow with
  tighter constraints.

  The static latency calculation is not limited only to static
  networks; the entire calculation for all DetNet flows can be repeated
  each time a new DetNet flow is created or deleted.  If some already-
  established DetNet flow would be pushed beyond its latency
  requirements by the new DetNet flow, then the new DetNet flow can be
  refused, or some other suitable action taken.

  This calculation may be more difficult to perform than that of the
  dynamic calculation (Section 3.1.2), because the DetNet flows passing
  through one port on a DetNet transit node affect each others'
  latency.  The effects can even be circular, from a node A to B to C
  and back to A.  On the other hand, the static calculation can often
  accommodate queuing methods, such as transmission selection by strict
  priority, that are unsuitable for the dynamic calculation.

3.1.2.  Dynamic latency calculation

  The dynamic problem:
          Given a network whose maximum capacity for DetNet flows is
          bounded by a set of static configuration parameters applied
          to the DetNet transit nodes, and given just one DetNet flow,
          compute the worst-case end-to-end latency that can be
          experienced by that flow, no matter what other DetNet flows
          (within the network's configured parameters) might be created
          or deleted in the future.  Also, compute the resources,
          particularly buffer space, required in each DetNet transit
          node to achieve zero congestion loss.

  This calculation is dynamic, in the sense that DetNet flows can be
  added or deleted at any time, with a minimum of computation effort,
  and without affecting the guarantees already given to other DetNet
  flows.

  The choice of queuing methods is critical to the applicability of the
  dynamic calculation.  Some queuing methods (e.g.  CQF, Section 6.6)
  make it easy to configure bounds on the network's capacity, and to
  make independent calculations for each DetNet flow.  Some other

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  queuing methods (e.g. strict priority with the credit-based shaper
  defined in [IEEE8021Q] section 8.6.8.2) can be used for dynamic
  DetNet flow creation, but yield poorer latency and buffer space
  guarantees than when that same queuing method is used for static
  DetNet flow creation (Section 3.1.1).

3.2.  Relay node model

  A model for the operation of a DetNet transit node is required, in
  order to define the latency and buffer calculations.  In Figure 1 we
  see a breakdown of the per-hop latency experienced by a packet
  passing through a DetNet transit node, in terms that are suitable for
  computing both hop-by-hop latency and per-hop buffer requirements.

        DetNet transit node A            DetNet transit node B
     +-------------------------+       +------------------------+
     |              Queuing    |       |              Queuing   |
     |   Regulator subsystem   |       |   Regulator subsystem  |
     |   +-+-+-+-+ +-+-+-+-+   |       |   +-+-+-+-+ +-+-+-+-+  |
  -->+   | | | | | | | | | +   +------>+   | | | | | | | | | +  +--->
     |   +-+-+-+-+ +-+-+-+-+   |       |   +-+-+-+-+ +-+-+-+-+  |
     |                         |       |                        |
     +-------------------------+       +------------------------+
     |<->|<------>|<------->|<->|<---->|<->|<------>|<------>|<->|<--
  2,3  4      5        6      1    2,3   4      5        6     1   2,3
                  1: Output delay             4: Processing delay
                  2: Link delay               5: Regulation delay
                  3: Frame preemption delay   6: Queuing delay

                Figure 1: Timing model for DetNet or TSN

  In Figure 1, we see two DetNet transit nodes that are connected via a
  link.  In this model, the only queues, that we deal with explicitly,
  are attached to the output port; other queues are modeled as
  variations in the other delay times.  (E.g., an input queue could be
  modeled as either a variation in the link delay (2) or the processing
  delay (4).)  There are six delays that a packet can experience from
  hop to hop.

  1.  Output delay
     The time taken from the selection of a packet for output from a
     queue to the transmission of the first bit of the packet on the
     physical link.  If the queue is directly attached to the physical
     port, output delay can be a constant.  But, in many
     implementations, the queuing mechanism in a forwarding ASIC is
     separated from a multi-port MAC/PHY, in a second ASIC, by a
     multiplexed connection.  This causes variations in the output
     delay that are hard for the forwarding node to predict or control.

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  2.  Link delay
     The time taken from the transmission of the first bit of the
     packet to the reception of the last bit, assuming that the
     transmission is not suspended by a frame preemption event.  This
     delay has two components, the first-bit-out to first-bit-in delay
     and the first-bit-in to last-bit-in delay that varies with packet
     size.  The former is typically measured by the Precision Time
     Protocol and is constant (see [RFC8655]).  However, a virtual
     "link" could exhibit a variable link delay.

  3.  Frame preemption delay
     If the packet is interrupted in order to transmit another packet
     or packets, (e.g.  [IEEE8023] clause 99 frame preemption) an
     arbitrary delay can result.

  4.  Processing delay
     This delay covers the time from the reception of the last bit of
     the packet to the time the packet is enqueued in the regulator
     (Queuing subsystem, if there is no regulation).  This delay can be
     variable, and depends on the details of the operation of the
     forwarding node.

  5.  Regulator delay
     This is the time spent from the insertion of the last bit of a
     packet into a regulation queue until the time the packet is
     declared eligible according to its regulation constraints.  We
     assume that this time can be calculated based on the details of
     regulation policy.  If there is no regulation, this time is zero.

  6.  Queuing subsystem delay
     This is the time spent for a packet from being declared eligible
     until being selected for output on the next link.  We assume that
     this time is calculable based on the details of the queuing
     mechanism.  If there is no regulation, this time is from the
     insertion of the packet into a queue until it is selected for
     output on the next link.

  Not shown in Figure 1 are the other output queues that we presume are
  also attached to that same output port as the queue shown, and
  against which this shown queue competes for transmission
  opportunities.

  The initial and final measurement point in this analysis (that is,
  the definition of a "hop") is the point at which a packet is selected
  for output.  In general, any queue selection method that is suitable
  for use in a DetNet network includes a detailed specification as to
  exactly when packets are selected for transmission.  Any variations
  in any of the delay times 1-4 result in a need for additional buffers

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  in the queue.  If all delays 1-4 are constant, then any variation in
  the time at which packets are inserted into a queue depends entirely
  on the timing of packet selection in the previous node.  If the
  delays 1-4 are not constant, then additional buffers are required in
  the queue to absorb these variations.  Thus:

  o  Variations in output delay (1) require buffers to absorb that
     variation in the next hop, so the output delay variations of the
     previous hop (on each input port) must be known in order to
     calculate the buffer space required on this hop.

  o  Variations in processing delay (4) require additional output
     buffers in the queues of that same DetNet transit node.  Depending
     on the details of the queueing subsystem delay (6) calculations,
     these variations need not be visible outside the DetNet transit
     node.

4.  Computing End-to-end Delay Bounds

4.1.  Non-queuing delay bound

  End-to-end delay bounds can be computed using the delay model in
  Section 3.2.  Here, it is important to be aware that for several
  queuing mechanisms, the end-to-end delay bound is less than the sum
  of the per-hop delay bounds.  An end-to-end delay bound for one
  DetNet flow can be computed as

     end_to_end_delay_bound = non_queuing_delay_bound +
     queuing_delay_bound

  The two terms in the above formula are computed as follows.

  First, at the h-th hop along the path of this DetNet flow, obtain an
  upperbound per-hop_non_queuing_delay_bound[h] on the sum of the
  bounds over the delays 1,2,3,4 of Figure 1.  These upper bounds are
  expected to depend on the specific technology of the DetNet transit
  node at the h-th hop but not on the T-SPEC of this DetNet flow.  Then

[minor] refer where T-SPEC is defined.  RFC9016?

  set non_queuing_delay_bound = the sum of per-
  hop_non_queuing_delay_bound[h] over all hops h.

  Second, compute queuing_delay_bound as an upper bound to the sum of
  the queuing delays along the path.  The value of queuing_delay_bound
  depends on the T-SPEC of this DetNet flow and possibly of other flows
  in the network, as well as the specifics of the queuing mechanisms
  deployed along the path of this DetNet flow.  The computation of
  queuing_delay_bound is described in Section 4.2 as a separate
  section.

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4.2.  Queuing delay bound

  For several queuing mechanisms, queuing_delay_bound is less than the
  sum of upper bounds on the queuing delays (5,6) at every hop.  This
  occurs with (1) per-flow queuing, and (2) aggregate queuing with
  regulators, as explained in Section 4.2.1, Section 4.2.2, and
  Section 6.

  For other queuing mechanisms the only available value of
  queuing_delay_bound is the sum of the per-hop queuing delay bounds.
  In such cases, the computation of per-hop queuing delay bounds must
  account for the fact that the T-SPEC of a DetNet flow is no longer
  satisfied at the ingress of a hop, since burstiness increases as one
  flow traverses one DetNet transit node.

4.2.1.  Per-flow queuing mechanisms

  With such mechanisms, each flow uses a separate queue inside every
  node.  The service for each queue is abstracted with a guaranteed
  rate and a latency.  For every DetNet flow, a per-node delay bound as
  well as an end-to-end delay bound can be computed from the traffic
  specification of this DetNet flow at its source and from the values
  of rates and latencies at all nodes along its path.  The per-flow
  queuing is used in Guaranteed-Service IntServ.  Details of
  calculation for Guaranteed-Service IntServ are described in
  Section 6.5.

4.2.2.  Aggregate queuing mechanisms

  With such mechanisms, multiple flows are aggregated into macro-flows
  and there is one FIFO queue per macro-flow.  A practical example is
  the credit-based shaper defined in section 8.6.8.2 of [IEEE8021Q]
  where a macro-flow is called a "class".  One key issue in this
  context is how to deal with the burstiness cascade: individual flows
  that share a resource dedicated to a macro-flow may see their
  burstiness increase, which may in turn cause increased burstiness to
  other flows downstream of this resource.  Computing delay upper
  bounds for such cases is difficult, and in some conditions impossible
  [charny2000delay][bennett2002delay].  Also, when bounds are obtained,
  they depend on the complete configuration, and must be recomputed
  when one flow is added.  (The dynamic calculation, Section 3.1.2.)

  A solution to deal with this issue for the DetNet flows is to reshape
  them at every hop.  This can be done with per-flow regulators (e.g.
  leaky bucket shapers), but this requires per-flow queuing and defeats
  the purpose of aggregate queuing.  An alternative is the interleaved
  regulator, which reshapes individual DetNet flows without per-flow
  queuing ([Specht2016UBS], [IEEE8021Qcr]).  With an interleaved

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  regulator, the packet at the head of the queue is regulated based on
  its (flow) regulation constraints; it is released at the earliest
  time at which this is possible without violating the constraint.  One
  key feature of per-flow or interleaved regulator is that, it does not
  increase worst-case latency bounds [le_boudec2018theory].
  Specifically, when an interleaved regulator is appended to a FIFO
  subsystem, it does not increase the worst-case delay of the latter.

  Figure 2 shows an example of a network with 5 nodes, aggregate
  queuing mechanism and interleaved regulators as in Figure 1.  An end-
  to-end delay bound for DetNet flow f, traversing nodes 1 to 5, is
  calculated as follows:

     end_to_end_latency_bound_of_flow_f = C12 + C23 + C34 + S4

  In the above formula, Cij is a bound on the delay of the queuing
  subsystem in node i and interleaved regulator of node j, and S4 is a
  bound on the delay of the queuing subsystem in node 4 for DetNet flow
  f.  In fact, using the delay definitions in Section 3.2, Cij is a
  bound on sum of the delays 1,2,3,6 of node i and 4,5 of node j.
  Similarly, S4 is a bound on sum of the delays 1,2,3,6 of node 4.  A
  practical example of queuing model and delay calculation is presented
  Section 6.4.

                              f
                    ----------------------------->
                  +---+   +---+   +---+   +---+   +---+
                  | 1 |---| 2 |---| 3 |---| 4 |---| 5 |
                  +---+   +---+   +---+   +---+   +---+
                     \__C12_/\__C23_/\__C34_/\_S4_/

             Figure 2: End-to-end delay computation example

  REMARK: The end-to-end delay bound calculation provided here gives a
  much better upper bound in comparison with end-to-end delay bound
  computation by adding the delay bounds of each node in the path of a
  DetNet flow [TSNwithATS].

[minor] explain "better" in which sense, what metric is being compared?

4.3.  Ingress considerations

  A sender can be a DetNet node which uses exactly the same queuing
  methods as its adjacent DetNet transit node, so that the delay and
  buffer bounds calculations at the first hop are indistinguishable
  from those at a later hop within the DetNet domain.  On the other
  hand, the sender may be DetNet-unaware, in which case some
  conditioning of the DetNet flow may be necessary at the ingress
  DetNet transit node.

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  This ingress conditioning typically consists of a FIFO with an output
  regulator that is compatible with the queuing employed by the DetNet
  transit node on its output port(s).  For some queuing methods, simply
  requires added extra buffer space in the queuing subsystem.  Ingress
  conditioning requirements for different queuing methods are mentioned
  in the sections, below, describing those queuing methods.

4.4.  Interspersed DetNet-unaware transit nodes

  It is sometimes desirable to build a network that has both DetNet-
  aware transit nodes and DetNet-uaware transit nodes, and for a DetNet
  flow to traverse an island of DetNet-unaware transit nodes, while
  still allowing the network to offer delay and congestion loss
  guarantees.  This is possible under certain conditions.

  In general, when passing through a DetNet-unaware island, the island
  may cause delay variation in excess of what would be caused by DetNet
  nodes.  That is, the DetNet flow might be "lumpier" after traversing
  the DetNet-unaware island.  DetNet guarantees for delay and buffer
  requirements can still be calculated and met if and only if the
  following are true:

  1.  The latency variation across the DetNet-unaware island must be
      bounded and calculable.

  2.  An ingress conditioning function (Section 4.3) is required at the
      re-entry to the DetNet-aware domain.  This will, at least,
      require some extra buffering to accommodate the additional delay
      variation, and thus further increases the delay bound.

  The ingress conditioning is exactly the same problem as that of a
  sender at the edge of the DetNet domain.  The requirement for bounds
  on the latency variation across the DetNet-unaware island is
  typically the most difficult to achieve.  Without such a bound, it is
  obvious that DetNet cannot deliver its guarantees, so a DetNet-
  unaware island that cannot offer bounded latency variation cannot be
  used to carry a DetNet flow.

5.  Achieving zero congestion loss

  When the input rate to an output queue exceeds the output rate for a
  sufficient length of time, the queue must overflow.  This is
  congestion loss, and this is what deterministic networking seeks to
  avoid.

  To avoid congestion losses, an upper bound on the backlog present in
  the regulator and queuing subsystem of Figure 1 must be computed
  during resource reservation.  This bound depends on the set of flows

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  that use these queues, the details of the specific queuing mechanism
  and an upper bound on the processing delay (4).  The queue must
  contain the packet in transmission plus all other packets that are
  waiting to be selected for output.

  A conservative backlog bound, that applies to all systems, can be
  derived as follows.

  The backlog bound is counted in data units (bytes, or words of
  multiple bytes) that are relevant for buffer allocation.  Based on
  the que For every flow or an aggregate of flows, we need one buffer

[minor] English does not parse here

  space for the packet in transmission, plus space for the packets that
  are waiting to be selected for output.  Excluding transmission and
  frame preemption times, the packets are waiting in the queue since
  reception of the last bit, for a duration equal to the processing
  delay (4) plus the queuing delays (5,6).

  Let

  o  total_in_rate be the sum of the line rates of all input ports that
     send traffic to this output port.  The value of total_in_rate is
     in data units (e.g. bytes) per second.

  o  nb_input_ports be the number input ports that send traffic to this
     output port

  o  max_packet_length be the maximum packet size for packets that may
     be sent to this output port.  This is counted in data units.

  o  max_delay456 be an upper bound, in seconds, on the sum of the
     processing delay (4) and the queuing delays (5,6) for any packet
     at this output port.

  Then a bound on the backlog of traffic in the queue at this output
  port is

     backlog_bound = nb_input_ports * max_packet_length +
     total_in_rate* max_delay456

[minor] in_rate[space]*

6.  Queuing techniques

  In this section, for simplicity of delay computation, we assume that
  the T-SPEC or arrival curve [NetCalBook] for each DetNet flow at
  source is leaky bucket.  Also, at each Detnet transit node, the
  service for each queue is abstracted with a guaranteed rate and a
  latency.

[minor] guaranteed in which sense? avg. throughput, peak throughput

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6.1.  Queuing data model

  Sophisticated queuing mechanisms are available in Layer 3 (L3, see,
  e.g., [RFC7806] for an overview).  In general, we assume that "Layer
  3" queues, shapers, meters, etc., are precisely the "regulators"
  shown in Figure 1.  The "queuing subsystems" in this figure are not
  the province solely of bridges; they are an essential part of any
  DetNet transit node.  As illustrated by numerous implementation
  examples, some of the "Layer 3" mechanisms described in documents
  such as [RFC7806] are often integrated, in an implementation, with
  the "Layer 2" mechanisms also implemented in the same node.  An
  integrated model is needed in order to successfully predict the
  interactions among the different queuing mechanisms needed in a
  network carrying both DetNet flows and non-DetNet flows.

  Figure 3 shows the general model for the flow of packets through the
  queues of a DetNet transit node.  The DetNet packets are mapped to a
  number of regulators.  Here, we assume that the PREOF (Packet
  Replication, Elimination and Ordering Functions) functions are
  performed before the DetNet packets enter the regulators.  All
  Packets are assigned to a set of queues.

[minor] _p_ackets

  Queues compete for the
  selection of packets to be passed to queues in the queuing subsystem.
  Packets again are selected for output from the queuing subsystem.

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                                   |
  +--------------------------------V----------------------------------+
  |                          Queue assignment                         |
  +--+------+----------+---------+-----------+-----+-------+-------+--+
     |      |          |         |           |     |       |       |
  +--V-+ +--V-+     +--V--+   +--V--+     +--V--+  |       |       |
  |Flow| |Flow|     |Flow |   |Flow |     |Flow |  |       |       |
  |  0 | |  1 | ... |  i  |   | i+1 | ... |  n  |  |       |       |
  | reg| | reg|     | reg |   | reg |     | reg |  |       |       |
  +--+-+ +--+-+     +--+--+   +--+--+     +--+--+  |       |       |
     |      |          |         |           |     |       |       |
  +--V------V----------V--+   +--V-----------V--+  |       |       |
  |  Trans.  selection    |   | Trans. select.  |  |       |       |
  +----------+------------+   +-----+-----------+  |       |       |
             |                      |              |       |       |
          +--V--+                +--V--+        +--V--+ +--V--+ +--V--+
          | out |                | out |        | out | | out | | out |
          |queue|                |queue|        |queue| |queue| |queue|
          |  1  |                |  2  |        |  3  | |  4  | |  5  |
          +--+--+                +--+--+        +--+--+ +--+--+ +--+--+
             |                      |              |       |       |
  +----------V----------------------V--------------V-------V-------V--+
  |                      Transmission selection                       |
  +---------------------------------+---------------------------------+
                                    |
                                    V

             Figure 3: IEEE 802.1Q Queuing Model: Data flow

  Some relevant mechanisms are hidden in this figure, and are performed
  in the queue boxes:

  o  Discarding packets because a queue is full.

  o  Discarding packets marked "yellow" by a metering function, in
     preference to discarding "green" packets.

[minor] explain quickly "yellow" and "green". I understand that but
IETF is not very versant in shapers normally so minimal introduction of the
term is useful or reference needed.

  Ideally, neither of these actions are performed on DetNet packets.
  Full queues for DetNet packets should occur only when a DetNet flow
  is misbehaving, and the DetNet QoS does not include "yellow" service
  for packets in excess of committed rate.

  The queue assignment function can be quite complex, even in a bridge
  [IEEE8021Q], since the introduction of per-stream filtering and
  policing ([IEEE8021Q] clause 8.6.5.1).  In addition to the Layer 2
  priority expressed in the 802.1Q VLAN tag, a DetNet transit node can
  utilize any of the following information to assign a packet to a
  particular queue:

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  o  Input port.

  o  Selector based on a rotating schedule that starts at regular,
     time-synchronized intervals and has nanosecond precision.

  o  MAC addresses, VLAN ID, IP addresses, Layer 4 port numbers, DSCP.
     ([RFC8939], [RFC8964]) (Work items are expected to add MPC and
     other indicators.)

[minor] intoduce MPC or at least expand.

  o  The queue assignment function can contain metering and policing
     functions.

  o  MPLS and/or pseudowire ([RFC6658]) labels.

[minor] parentheses around references not necessary.

  The "Transmission selection" function decides which queue is to
  transfer its oldest packet to the output port when a transmission
  opportunity arises.

6.2.  Frame Preemption

  In [IEEE8021Q] and [IEEE8023], the transmission of a frame can be
  interrupted by one or more "express" frames, and then the interrupted
  frame can continue transmission.  The frame preemption is modeled as
  consisting of two MAC/PHY stacks, one for packets that can be
  interrupted, and one for packets that can interrupt the interruptible
  packets.  Only one layer of frame preemption is supported -- a
  transmitter cannot have more than one interrupted frame in progress.
  DetNet flows typically pass through the interrupting MAC.  For those
  DetNet flows with T-SPEC, latency bound can be calculated by the
  methods provided in the following sections that accounts for the
  affect of frame preemption, according to the specific queuing
  mechanism that is used in DetNet nodes.  Best-effort queues pass
  through the interruptible MAC, and can thus be preempted.

6.3.  Time Aware Shaper

  In [IEEE8021Q], the notion of time-scheduling queue gates is
  described in section 8.6.8.4.  On each node, the transmission
  selection for packets is controlled by time-synchronized gates; each
  output queue is associated with a gate.  The gates can be either open
  or close.  The states of the gates are determined by the gate control
  list (GCL).  The GCL specifies the opening and closing times of the
  gates.  The design of GCL should satisfy the requirement of latency
  upper bounds of all DetNet flows; therefore, those DetNet flows
  traverse a network should have bounded latency, if the traffic and
  nodes are conformant.

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  It should be noted that scheduled traffic service relies on a
  synchronized network and coordinated GCL configuration.  Synthesis of
  GCL on multiple nodes in network is a scheduling problem considering
  all DetNet flows traversing the network, which is a non-deterministic
  polynomial-time hard (NP-hard) problem.

[minor] ideally provide reference to proof.

Also, at this writing,
  scheduled traffic service supports no more than eight traffic queues,
  typically using up to seven priority queues and at least one best
  effort.

6.4.  Credit-Based Shaper with Asynchronous Traffic Shaping

  In the considered queuing model, we considered the four traffic
  classes (Definition 3.268 of [IEEE8021Q]): control-data traffic
  (CDT), class A, class B, and best effort (BE) in decreasing order of
  priority.  Flows of classes A and B are together referred as AVB
  flows.  This model is a subset of Time-Sensitive Networking as
  described next.

  Based on the timing model described in Figure 1, the contention
  occurs only at the output port of a DetNet transit node; therefore,
  the focus of the rest of this subsection is on the regulator and
  queuing subsystem in the output port of a DetNet transit node.  The
  input flows are identified using the information in (Section 5.1 of
  [RFC8939]).  Then they are aggregated into eight macro flows based on
  their service requirements; we refer to each macro flow as a class.
  The output port performs aggregate scheduling with eight queues
  (queuing subsystems): one for CDT, one for class A flows, one for
  class B flows, and five for BE traffic denoted as BE0-BE4.  The
  queuing policy for each queuing subsystem is FIFO.  In addition, each
  node output port also performs per-flow regulation for AVB flows
  using an interleaved regulator (IR), called Asynchronous Traffic
  Shaper [IEEE8021Qcr].  Thus, at each output port of a node, there is
  one interleaved regulator per-input port and per-class; the
  interleaved regulator is mapped to the regulator depicted in
  Figure 1.  The detailed picture of scheduling and regulation
  architecture at a node output port is given by Figure 4.  The packets
  received at a node input port for a given class are enqueued in the
  respective interleaved regulator at the output port.  Then, the
  packets from all the flows, including CDT and BE flows, are enqueued
  in queuing subsytem; there is no regulator for such classes.

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        +--+   +--+ +--+   +--+
        |  |   |  | |  |   |  |
        |IR|   |IR| |IR|   |IR|
        |  |   |  | |  |   |  |
        +-++XXX++-+ +-++XXX++-+
          |     |     |     |
          |     |     |     |
  +---+ +-v-XXX-v-+ +-v-XXX-v-+ +-----+ +-----+ +-----+ +-----+ +-----+
  |   | |         | |         | |Class| |Class| |Class| |Class| |Class|
  |CDT| | Class A | | Class B | | BE4 | | BE3 | | BE2 | | BE1 | | BE0 |
  |   | |         | |         | |     | |     | |     | |     | |     |
  +-+-+ +----+----+ +----+----+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+
    |        |           |         |       |       |       |       |
    |      +-v-+       +-v-+       |       |       |       |       |
    |      |CBS|       |CBS|       |       |       |       |       |
    |      +-+-+       +-+-+       |       |       |       |       |
    |        |           |         |       |       |       |       |
  +-v--------v-----------v---------v-------V-------v-------v-------v--+
  |                     Strict Priority selection                     |
  +--------------------------------+----------------------------------+
                                   |
                                   V

  Figure 4: The architecture of an output port inside a relay node with
       interleaved regulators (IRs) and credit-based shaper (CBS)

  Each of the queuing subsystems for classes A and B, contains Credit-
  Based Shaper (CBS).  The CBS serves a packet from a class according
  to the available credit for that class.  The credit for each class A
  or B increases based on the idle slope, and decreases based on the
  send slope, both of which are parameters of the CBS (Section 8.6.8.2
  of [IEEE8021Q]).

[minor] provide reference to "slope" or explain. Is that the same as
hysteresis "slopes"?

The CDT and BE0-BE4 flows are served by separate
  queuing subsystems.  Then, packets from all flows are served by a
  transmission selection subsystem that serves packets from each class
  based on its priority.  All subsystems are non-preemptive.
  Guarantees for AVB traffic can be provided only if CDT traffic is
  bounded; it is assumed that the CDT traffic has leaky bucket arrival
  curve with two parameters r_h as rate and b_h as bucket size, i.e.,
  the amount of bits entering a node within a time interval t is
  bounded by r_h t + b_h.

[minor] proably  r_h _*_ t + b_h

  Additionally, it is assumed that the AVB flows are also regulated at
  their source according to leaky bucket arrival curve.  At the source,
  the traffic satisfies its regulation constraint, i.e. the delay due
  to interleaved regulator at source is ignored.

  At each DetNet transit node implementing an interleaved regulator,
  packets of multiple flows are processed in one FIFO queue; the packet

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  at the head of the queue is regulated based on its leaky bucket
  parameters; it is released at the earliest time at which this is
  possible without violating the constraint.

  The regulation parameters for a flow (leaky bucket rate and bucket
  size) are the same at its source and at all DetNet transit nodes
  along its path in the case of that all clocks are perfect.  However,
  in reality there is clock nonideality thoughout the DetNet domain
  even with clock synchronization.  This phenomenon causes inaccuracy
  in the rates configured at the regulators that may lead to network
  instability.  To avoid that, when configuring the regulators, the
  rates are set as the source rates with some positive margin.
  [Thomas2020time] describes and provides solutions to this issue.

6.4.1.  Delay Bound Calculation

  A delay bound of the queuing subsystem ((4) in Figure 1) for an AVB
  flow of classes A or B can be computed if the following condition
  holds:

     sum of leaky bucket rates of all flows of this class at this
     transit node <= R, where R is given below for every class.

  If the condition holds, the delay bounds for a flow of class X (A or
  B) is d_X and calculated as:

     d_X = T_X + (b_t_X-L_min_X)/R_X - L_min_X/c

  where L_min_X is the minimum packet lengths of class X (A or B); c is
  the output link transmission rate; b_t_X is the sum of the b term
  (bucket size) for all the flows of the class X.  Parameters R_X and
  T_X are calculated as follows for class A and class B, separately:

  If the flow is of class A:

     R_A = I_A (c-r_h)/ c

     T_A = L_nA + b_h + r_h L_n/c)/(c-r_h)

[minor] introduce I_* already here as slopes otherwise the formula doesn't
parse here. Same for r_* leakiy bucket pars.

  where L_nA is the maximum packet length of class B and BE packets;
  L_n is the maximum packet length of classes A,B, and BE.

  If the flow is of class B:

     R_B = I_B (c-r_h)/ c

     T_B = (L_BE + L_A + L_nA I_A/(c_h-I_A) + b_h + r_h L_n/c)/(c-r_h)

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  where L_A is the maximum packet length of class A; L_BE is the
  maximum packet length of class BE.

  Then, an end-to-end delay bound of class X (A or B)is calculated by
  the formula Section 4.2.2, where for Cij:

     Cij = d_X

  More information of delay analysis in such a DetNet transit node is
  described in [TSNwithATS].

6.4.2.  Flow Admission

  The delay bound calculation requires some information about each
  node.  For each node, it is required to know the idle slope of CBS
  for each class A and B (I_A and I_B), as well as the transmission
  rate of the output link (c).  Besides, it is necessary to have the
  information on each class, i.e. maximum packet length of classes A,
  B, and BE.  Moreover, the leaky bucket parameters of CDT (r_h,b_h)
  should be known.  To admit a flow/flows of classes A and B, their
  delay requirements should be guaranteed not to be violated.  As
  described in Section 3.1, the two problems, static and dynamic, are
  addressed separately.  In either of the problems, the rate and delay
  should be guaranteed.  Thus,

  The static admission control:
          The leaky bucket parameters of all AVB flows are known,
          therefore, for each AVB flow f, a delay bound can be
          calculated.  The computed delay bound for every AVB flow
          should not be more than its delay requirement.  Moreover, the
          sum of the rate of each flow (r_f) should not be more than
          the rate allocated to each class (R).  If these two
          conditions hold, the configuration is declared admissible.

  The dynamic admission control:
          For dynamic admission control, we allocate to every node and
          class A or B, static value for rate (R) and maximum
          burstiness (b_t).

[minor] is that burstiness or is that bucket size? Please be consistent
in terminology. Generally, this is chokeful of symbols, a small glossary
for symbols @ beginning of chapter would make the reading much easier for
the average consumer.

In addition, for every node and every
          class A and B, two counters are maintained:

             R_acc is equal to the sum of the leaky-bucket rates of all
             flows of this class already admitted at this node; At all
             times, we must have:

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                R_acc <=R, (Eq. 1)

             b_acc is equal to the sum of the bucket sizes of all flows
             of this class already admitted at this node; At all times,
             we must have:

                b_acc <=b_t.  (Eq. 2)

          A new AVB flow is admitted at this node, if Eqs. (1) and (2)
          continue to be satisfied after adding its leaky bucket rate
          and bucket size to R_acc and b_acc.  An AVB flow is admitted
          in the network, if it is admitted at all nodes along its
          path.  When this happens, all variables R_acc and b_acc along
          its path must be incremented to reflect the addition of the
          flow.  Similarly, when an AVB flow leaves the network, all
          variables R_acc and b_acc along its path must be decremented
          to reflect the removal of the flow.

  The choice of the static values of R and b_t at all nodes and classes
  must be done in a prior configuration phase; R controls the bandwidth
  allocated to this class at this node, b_t affects the delay bound and
  the buffer requirement.  R must satisfy the constraints given in
  Annex L.1 of [IEEE8021Q].

6.5.  Guaranteed-Service IntServ

  Guaranteed-Service Integrated service (IntServ) is an architecture
  that specifies the elements to guarantee quality of service (QoS) on
  networks [RFC2212].

  The flow, at the source, has a leaky bucket arrival curve with two
  parameters r as rate and b as bucket size, i.e., the amount of bits
  entering a node within a time interval t is bounded by r t + b.

[minor] again, don't omit r _*_ t

  If a resource reservation on a path is applied, a node provides a
  guaranteed rate R and maximum service latency of T.  This can be
  interpreted in a way that the bits might have to wait up to T before
  being served with a rate greater or equal to R.  The delay bound of
  the flow traversing the node is T + b / R.

  Consider a Guaranteed-Service IntServ path including a sequence of
  nodes, where the i-th node provides a guaranteed rate R_i and maximum
  service latency of T_i.  Then, the end-to-end delay bound for a flow
  on this can be calculated as sum(T_i) + b / min(R_i).

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  The provided delay bound is based on a simple case of Guaranteed-
  Service IntServ where only a guaranteed rate and maximum service
  latency and a leaky bucket arrival curve are available.  If more
  information about the flow is known, e.g. the peak rate, the delay
  bound is more complicated; the detail is available in [RFC2212] and
  Section 1.4.1 of [NetCalBook].

6.6.  Cyclic Queuing and Forwarding

  Annex T of [IEEE8021Q] describes Cyclic Queuing and Forwarding (CQF),
  which provides bounded latency and zero congestion loss using the
  time-scheduled gates of [IEEE8021Q] section 8.6.8.4.  For a given
  class of DetNet flows, a set of two or more buffers is provided at
  the output queue layer of Figure 3.  A cycle time T_c is configured
  for each class of DetNet flows c, and all of the buffer sets in a
  class of DetNet flows swap buffers simultaneously throughout the
  DetNet domain at that cycle rate, all in phase.  In such a mechanism,
  the regulator, mentioned in Figure 1, is not required.

  In the case of two-buffer CQF, each class of DetNet flows c has two
  buffers, namely buffer1 and buffer2.  In a cycle (i) when buffer1
  accumulates received packets from the node's reception ports, buffer2
  transmits the already stored packets from the previous cycle (i-1).
  In the next cycle (i+1), buffer2 stores the received packets and
  buffer1 transmits the packets received in cycle (i).  The duration of
  each cycle is T_c.

  The per-hop latency is trivially determined by the cycle time T_c:
  the packet transmitted from a node at a cycle (i), is transmitted
  from the next node at cycle (i+1).  Hence, the maximum delay
  experienced by a given packet is from the beginning of cycle (i) to
  the end of cycle (i+1), or 2T_c; also, the minimum delay is from the
  end of cycle (i) to the beginning of cycle (i+1), i.e., zero.  Then,
  if the packet traverses h hops, the maximum delay is:

     (h+1) T_c

  and the minimum delay is:

     (h-1) T_c

  which gives a latency variation of 2T_c.

  The cycle length T_c should be carefully chosen; it needs to be large
  enough to accomodate all the DetNet traffic, plus at least one
  maximum interfering packet,

[minor] this would benefit from more explanation, why one? what is
"interfering"?

that can be received within one cycle.
  Also, the value of T_c includes a time interval, called dead time
  (DT), which is the sum of the delays 1,2,3,4 defined in Figure 1.

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  The value of DT guarantees that the last packet of one cycle in a
  node is fully delivered to a buffer of the next node is the same
  cycle.  A two-buffer CQF is recommended if DT is small compared to
  T_c.  For a large DT, CQF with more buffers can be used and a cycle
  identification label can be added to the packets.

  Ingress conditioning (Section 4.3) may be required if the source of a
  DetNet flow does not, itself, employ CQF.  Since there are no per-
  flow parameters in the CQF technique, per-hop configuration is not
  required in the CQF forwarding nodes.

7.  Example application on DetNet IP network

  This section provides an example application of this document on a
  DetNet-enabled IP network.  Consider Figure 5, taken from Section 3
  of [RFC8939], that shows a simple IP network:

  o  The end-system 1 implements Guaranteed-Service IntServ as in
     Section 6.5 between itself and relay node 1.

  o  Sub-network 1 is a TSN network.  The nodes in subnetwork 1
     implement credit-based shapers with asynchronous traffic shaping
     as in Section 6.4.

  o  Sub-network 2 is a TSN network.  The nodes in subnetwork 2
     implement cyclic queuing and forwarding with two buffers as in
     Section 6.6.

  o  The relay nodes 1 and 2 implement credit-based shapers with
     asynchronous traffic shaping as in Section 6.4.  They also perform
     the aggregation and mapping of IP DetNet flows to TSN streams
     (Section 4.4 of [I-D.ietf-detnet-ip-over-tsn]).

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   DetNet IP       Relay                        Relay       DetNet IP
   End-System      Node 1                       Node 2      End-System
       1                                                        2
  +----------+                                             +----------+
  |   Appl.  |<------------ End-to-End Service ----------->|   Appl.  |
  +----------+  ............                 ...........   +----------+
  | Service  |<-: Service  :-- DetNet flow --: Service  :->| Service  |
  +----------+  +----------+                 +----------+  +----------+
  |Forwarding|  |Forwarding|                 |Forwarding|  |Forwarding|
  +--------.-+  +-.------.-+                 +-.---.----+  +-------.--+
           : Link :       \      ,-----.      /     \   ,-----.   /
           +......+        +----[  Sub- ]----+       +-[  Sub- ]-+
                                [Network]              [Network]
                                 `--1--'                `--2--'

           |<--------------------- DetNet IP --------------------->|

  |<--- d1 --->|<--------------- d2_p --------------->|<-- d3_p -->|

    Figure 5: A Simple DetNet-Enabled IP Network, taken from RFC8939

  Consider a fully centeralized control plane for the network of
  Figure 5 as described in Section 3.2 of
  [I-D.ietf-detnet-controller-plane-framework].  Suppose end-system 1
  wants to create a DetNet flow with traffic specification destined to
  end-system 2 with end-to-end delay bound requirement D.  Therefore,
  the control plane receives a flow establishment request and
  calculates a number of valid paths through the network (Section 3.2
  of [I-D.ietf-detnet-controller-plane-framework]).  To select a proper
  path, the control plane needs to compute an end-to-end delay bound at
  every node of each selected path p.

  The end-to-end delay bound is d1 + d2_p + d3_p, where d1 is the delay
  bound from end-system 1 to the entrance of relay node 1, d2_p is the
  delay bound for path p from relay node 1 to entrance of the first
  node in sub-network 2, and d3_p the delay bound of path p from the
  first node in sub-network 2 to end-system 2.  The computation of d1
  is explained in Section 6.5.  Since the relay node 1, sub-network 1
  and relay node 2 implement aggregate queuing, we use the results in
  Section 4.2.2 and Section 6.4 to compute d2_p for the path p.
  Finally, d3_p is computed using the delay bound computation of
  Section 6.6.  Any path p such that d1 + d2_p + d3_p <= D satisfies
  the delay bound requirement of the flow.  If there is no such path,
  the control plane may compute new set of valid paths and redo the
  delay bound computation or do not admit the DetNet flow.

  As soon as the control plane selects a path that satisfies the delay
  bound constraint, it allocates and reserves the resources in the path

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  for the DetNet flow (Section 4.2
  [I-D.ietf-detnet-controller-plane-framework]).

8.  Security considerations

  Detailed security considerations for DetNet are cataloged in
  [I-D.ietf-detnet-security], and more general security considerations
  are described in [RFC8655].

  Security aspects that are unique to DetNet are those whose aim is to
  provide the specific QoS aspects of DetNet, specifically bounded end-
  to-end delivery latency and zero congestion loss.  Achieving such
  loss rates and bounded latency may not be possible in the face of a
  highly capable adversary, such as the one envisioned by the Internet
  Threat Model of BCP 72 [RFC3552] that can arbitrarily drop or delay
  any or all traffic.  In order to present meaningful security
  considerations, we consider a somewhat weaker attacker who does not
  control the physical links of the DetNet domain but may have the
  ability to control a network node within the boundary of the DetNet
  domain.

  A security consideration for this document is to secure the resource
  reservation signaling for DetNet flows.  Any forge or manipulation of
  packets during reservation may lead the flow not to be admitted or
  face delay bound violation.  Security mitigation for this issue is
  describedd in Section 7.6 of [I-D.ietf-detnet-security].

9.  IANA considerations

  This document has no IANA actions.

10.  References

10.1.  Normative References

  [RFC2212]  Shenker, S., Partridge, C., and R. Guerin, "Specification
             of Guaranteed Quality of Service", RFC 2212,
             DOI 10.17487/RFC2212, September 1997,
             <https://www.rfc-editor.org/info/rfc2212>.

  [RFC6658]  Bryant, S., Ed., Martini, L., Swallow, G., and A. Malis,
             "Packet Pseudowire Encapsulation over an MPLS PSN",
             RFC 6658, DOI 10.17487/RFC6658, July 2012,
             <https://www.rfc-editor.org/info/rfc6658>.

  [RFC7806]  Baker, F. and R. Pan, "On Queuing, Marking, and Dropping",
             RFC 7806, DOI 10.17487/RFC7806, April 2016,
             <https://www.rfc-editor.org/info/rfc7806>.

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  [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
             "Deterministic Networking Architecture", RFC 8655,
             DOI 10.17487/RFC8655, October 2019,
             <https://www.rfc-editor.org/info/rfc8655>.

  [RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
             Bryant, "Deterministic Networking (DetNet) Data Plane:
             IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,
             <https://www.rfc-editor.org/info/rfc8939>.

  [RFC8964]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
             S., and J. Korhonen, "Deterministic Networking (DetNet)
             Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
             2021, <https://www.rfc-editor.org/info/rfc8964>.

10.2.  Informative References

  [bennett2002delay]
             J.C.R. Bennett, K. Benson, A. Charny, W.F. Courtney, and
             J.-Y. Le Boudec, "Delay Jitter Bounds and Packet Scale
             Rate Guarantee for Expedited Forwarding",
             <https://dl.acm.org/citation.cfm?id=581870>.

  [charny2000delay]
             A. Charny and J.-Y. Le Boudec, "Delay Bounds in a Network
             with Aggregate Scheduling", <https://link.springer.com/
             chapter/10.1007/3-540-39939-9_1>.

  [I-D.ietf-detnet-controller-plane-framework]
             A. Malis, X. Geng, M. Chen, F. Qin, and B. Varga,
             "Deterministic Networking (DetNet) Controller Plane
             Framework draft-ietf-detnet-controller-plane-framework-
             00", <https://datatracker.ietf.org/doc/html/draft-ietf-
             detnet-controller-plane-framework>.

  [I-D.ietf-detnet-ip-over-tsn]
             B. Varga, J. Farkas, A. Malis, and S. Bryant, "DetNet Data
             Plane: IP over IEEE 802.1 Time Sensitive Networking (TSN)
             draft-ietf-detnet-ip-over-tsn-07",
             <https://datatracker.ietf.org/doc/html/draft-ietf-detnet-
             ip-over-tsn-07>.

  [I-D.ietf-detnet-security]
             E. Grossman, T. Mizrahi, and A. Hacker, "Deterministic
             Networking (DetNet) Security Considerations draft-ietf-
             detnet-security-16", <https://datatracker.ietf.org/doc/
             draft-ietf-detnet-security/>.

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  [IEEE8021Q]
             IEEE 802.1, "IEEE Std 802.1Q-2018: IEEE Standard for Local
             and metropolitan area networks - Bridges and Bridged
             Networks", 2018,
             <http://ieeexplore.ieee.org/document/8403927>.

  [IEEE8021Qcr]
             IEEE 802.1, "IEEE P802.1Qcr: IEEE Draft Standard for Local
             and metropolitan area networks - Bridges and Bridged
             Networks - Amendment: Asynchronous Traffic Shaping", 2017,
             <http://www.ieee802.org/1/files/private/cr-drafts/>.

  [IEEE8021TSN]
             IEEE 802.1, "IEEE 802.1 Time-Sensitive Networking (TSN)
             Task Group", <http://www.ieee802.org/1/>.

  [IEEE8023]
             IEEE 802.3, "IEEE Std 802.3-2018: IEEE Standard for
             Ethernet", 2018,
             <http://ieeexplore.ieee.org/document/8457469>.

  [le_boudec2018theory]
             J.-Y. Le Boudec, "A Theory of Traffic Regulators for
             Deterministic Networks with Application to Interleaved
             Regulators",
             <https://ieeexplore.ieee.org/document/8519761>.

  [NetCalBook]
             J.-Y. Le Boudec and P. Thiran, "Network calculus: a theory
             of deterministic queuing systems for the internet", 2001,
             <https://ica1www.epfl.ch/PS_files/NetCal.htm>.

  [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
             Text on Security Considerations", BCP 72, RFC 3552,
             DOI 10.17487/RFC3552, July 2003,
             <https://www.rfc-editor.org/info/rfc3552>.

  [RFC8578]  Grossman, E., Ed., "Deterministic Networking Use Cases",
             RFC 8578, DOI 10.17487/RFC8578, May 2019,
             <https://www.rfc-editor.org/info/rfc8578>.

  [Specht2016UBS]
             J. Specht and S. Samii, "Urgency-Based Scheduler for Time-
             Sensitive Switched Ethernet Networks",
             <https://ieeexplore.ieee.org/abstract/document/7557870>.

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  [Thomas2020time]
             L. Thomas and J.-Y. Le Boudec, "On Time Synchronization
             Issues in Time-Sensitive Networks with Regulators and
             Nonideal Clocks",
             <https://dl.acm.org/doi/10.1145/3393691.3394206>.

  [TSNwithATS]
             E. Mohammadpour, E. Stai, M. Mohiuddin, and J.-Y. Le
             Boudec, "End-to-end Latency and Backlog Bounds in Time-
             Sensitive Networking with Credit Based Shapers and
             Asynchronous Traffic Shaping",
             <https://arxiv.org/abs/1804.10608/>.

Authors' Addresses

  Norman Finn
  Huawei Technologies Co. Ltd
  3101 Rio Way
  Spring Valley, California  91977
  US

  Phone: +1 925 980 6430
  Email: nfinn@nfinnconsulting.com<mailto:nfinn@nfinnconsulting.com>

  Jean-Yves Le Boudec
  EPFL
  IC Station 14
  Lausanne EPFL  1015
  Switzerland

  Email: jean-yves.leboudec@epfl.ch<mailto:jean-yves.leboudec@epfl.ch>

  Ehsan Mohammadpour
  EPFL
  IC Station 14
  Lausanne EPFL  1015
  Switzerland

  Email: ehsan.mohammadpour@epfl.ch<mailto:ehsan.mohammadpour@epfl.ch>

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  Jiayi Zhang
  Huawei Technologies Co. Ltd
  Q27, No.156 Beiqing Road
  Beijing  100095
  China

  Email: zhangjiayi11@huawei.com<mailto:zhangjiayi11@huawei.com>

  Balazs Varga
  Ericsson
  Konyves Kalman krt. 11/B
  Budapest  1097
  Hungary

  Email: balazs.a.varga@ericsson.com<mailto:balazs.a.varga@ericsson.com>

  Janos Farkas
  Ericsson
  Konyves Kalman krt. 11/B
  Budapest  1097
  Hungary

  Email: janos.farkas@ericsson.com<mailto:janos.farkas@ericsson.com>

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