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

From: Tony Przygienda via Datatracker <[email-masked]>
Date: Tue, 24 Aug 2021 06:20:07 -0700

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: [email-masked]

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

   Email: [email-masked]

   Ehsan Mohammadpour
   EPFL
   IC Station 14
   Lausanne EPFL  1015
   Switzerland

   Email: [email-masked]

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

   Email: [email-masked]

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

   Email: [email-masked]

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

   Email: [email-masked]

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