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DetNet                                                           N. Finn
Internet-Draft                               Huawei Technologies Co. Ltd
Intended status: Standards Track                          J-Y. Le Boudec
Expires: September 6, 2018                                          EPFL
                                                                B. Varga
                                                               J. Farkas
                                                                Ericsson
                                                           March 5, 2018


                         DetNet Bounded Latency
                  draft-finn-detnet-bounded-latency-00

Abstract

   This document presents a parameterized timing model for Deterministic
   Networking so that existing and future standards can achieve bounded
   latency and zero congestion loss.

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 September 6, 2018.

Copyright Notice

   Copyright (c) 2018 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



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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Terminology and Definitions . . . . . . . . . . . . . . . . .   4
   4.  DetNet bounded latency model  . . . . . . . . . . . . . . . .   4
     4.1.  Flow creation . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  End-to-end model  . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Relay system model  . . . . . . . . . . . . . . . . . . .   5
   5.  Computing End-to-end Latency Bounds . . . . . . . . . . . . .   7
     5.1.  Examples of Computations  . . . . . . . . . . . . . . . .   8
   6.  Achieving zero congestion loss  . . . . . . . . . . . . . . .   8
     6.1.  A General Formula . . . . . . . . . . . . . . . . . . . .   8
   7.  Queuing model . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Queuing data model  . . . . . . . . . . . . . . . . . . .   9
     7.2.  IEEE 802.1 Queuing Model  . . . . . . . . . . . . . . . .  11
       7.2.1.  Queuing Data Model with Preemption  . . . . . . . . .  11
       7.2.2.  Transmission Selection Model  . . . . . . . . . . . .  12
     7.3.  Other queuing models, e.g. IntServ  . . . . . . . . . . .  14
   8.  Parameters for the bounded latency model  . . . . . . . . . .  14
     8.1.  Sender parameters . . . . . . . . . . . . . . . . . . . .  14
     8.2.  Relay system parameters . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   The ability for IETF Deterministic Networking (DetNet) or IEEE 802.1
   Time-Sensitive Networking (TSN) 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/TSN
   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.  Thus, DetNet is an example of an
   INTSERV Guaranteed Quality of Service [RFC2212]

   As explained in [I-D.ietf-detnet-architecture], 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 of use to the



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   applications identified in [I-D.ietf-detnet-use-cases], 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.

   Rather than defining, in great detail, specific mechanisms to be used
   to control packet transmission at each output port, this document
   presents a timing model for sources, destinations, and the network
   nodes that relay packets.  The parameters specified in this model:

   o  Characterize a DetNet flow in a way that provides externally
      measureable verification that the sender is conforming to its
      promised maximum, can be implemented reasonably easily by a
      sending device, and does not require excessive over-allocation of
      resources by the network.

   o  Enable resonably accurate computation of worst-case end-to-end
      latency, in a way that requires as little detailed knowledge as
      possible of the behavior of the Quality of Service (QoS)
      algorithms implemented in each devince, including queuing,
      shaping, metering, policing, and transmission selection
      techniques.

   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 QoS algorithms 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.

   This document does not specify any resource reservation protocol or
   server.  It does not describe all of the requirements for that
   protocol or server.  It does describe a set of requirements for
   resource reservation algorithms and for QoS algorithms that, if met,
   will enable them to work together.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   The lowercase forms with an initial capital "Must", "Must Not",
   "Shall", "Shall Not", "Should", "Should Not", "May", and "Optional"
   in this document are to be interpreted in the sense defined in
   [RFC2119], but are used where the normative behavior is defined in
   documents published by SDOs other than the IETF.



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3.  Terminology and Definitions

   This document uses the terms defined in
   [I-D.ietf-detnet-architecture].

4.  DetNet bounded latency model

4.1.  Flow creation

   The bounded latency model assusmes the use of the following paradigm
   for provisioning a particular DetNet flow:

   1.  Perform any onfiguration required by the relay systems in the
       network for the classes of service to be offered, including one
       or more classes of DetNet service.  This configuration is
       general; it is not tied to any particular flow.

   2.  Characterize the DetNet flow in terms of limitations on the
       sender Section 8.1 and flow requirements Section 8.2.

   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.  Select one of the DetNet classes of service for the DetNet flow.

   5.  Compute the worst-case end-to-end latency for the DetNet flow.
       In the process, determine whether sufficient resources are
       available for that flow to guarantee the required latency and
       provide zero congestion loss.

   6.  Assuming that the resources are available, commit those resources
       to the flow.  This may or may not require adjusting the
       parameters that control the QoS algorithms at each hop along the
       flow's path.

   This paradigm can be static and/or dynamic, and can be implemented
   using peer-to-peer protocols or with a central server model.  In some
   situations, backtracking and recursing through this list may be
   necessary.

   Issues such as un-provisioning a DetNet flow in favor of another when
   resources are scarce are not considered.  How the path to be taken by
   a DetNet flow is chosen is not considered in this document.







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4.2.  End-to-end model

   [Suggestion: This is the introduction to network calculus.  The
   starting point is a model in which a relay system is a black box.]

4.3.  Relay system model

   [NWF I think that at least some of this will be useful.  We won't
   know until we see what J-Y has to say in Section 4.2.  I'm especially
   interested in whether J-Y thinks that the "output delay" in Figure 1
   is useful in determining the number of buffers needed in the next
   hop.  It is possible that we can define the parameters we need
   without this section.]

   In Figure 1 we see a breakdown of the per-hop latency experienced by
   a packet passing through a relay system, in terms that are suitable
   for computing both hop-by-hop latency and per-hop buffer
   requirements.

              DetNet relay node A        DetNet relay node B
              +-----------------+        +-----------------+
              |        Queue    |        |        Queue    |
              |       +-+-+-+   |        |       +-+-+-+   |
           -->+       | | | +   +------->+       | | | +   +--->
              |       +-+-+-+   |        |       +-+-+-+   |
              |                 |        |                 |
              +-----------------+        +-----------------+
              |<----->|<--->|<->|<------>|<----->|<--->|<->|<--
           2,3    4      5    1    2,3       4      5    1   2,3
                  1: Output delay       3: Preemption delay
                  2: Link delay         4: Processing delay
                  5: Queuing delay

                 Figure 1: Timing model for DetNet or TSN

   In Figure 1, we see two DetNet relay nodes (typically, bridges or
   routers), with a wired link between them.  In this model, the only
   queues 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 five 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



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      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.

   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 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 [I-D.ietf-detnet-architecture]).
      However, a virtual "link" could exhibit a variable link delay.

   3.  Preemption delay
      If the packet is interrupted (e.g.  [IEEE8023br] preemption) in
      order to transmit another packet or packets, an arbitrary delay
      can result.

   4.  Processing delay
      This delay covers the time from the reception of the last bit of
      the packet to that packet being eligible, if there were no other
      packets in the queue, for selection for output.  This delay can be
      variable, and depends on the details of the operation of the
      forwarding node.

   5.  Queuing delay
      This is the time spent from the insertion of the packet into a
      queue until the packet is selected for output on the next link.
      We assume that this time is calculable based on the details of the
      queuing mechanism.

   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
   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




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   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 relay node.  Depending
      on the details of the queueing delay (5) calculations, these
      variations need not be visible outside the DetNet relay node.

5.  Computing End-to-end Latency Bounds

   End-to-end latency bounds can be computed using the delay model in
   Section 4.3.  Here it is important to be aware that for several
   queuing mechanisms, the worst-case end-to-end delay is less than the
   sum of the per-hop worst-case delays.  An end-to-end latency bound
   for one detnet flow can be computed as

      end_to_end_latency_bound = non_queuing_latency + queuing_latency

   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 upper
   bound per-hop_non_queuing_latency[h] on the sum of delays 1,2,3,4 of
   Figure 1.  These upper-bounds are expected to depend on the specific
   technology of the node at the h-th hop but not on the T-SPEC of this
   detnet flow.  Then set non_queuing_latency = the sum of per-
   hop_non_queuing_latency[h] over all hops h.

   Second, compute queuing_latency as an upper bound to the sum of the
   queuing delays along the path.  The value of queuing_latency depends
   on the T-SPEC of this flow and possibly of other flows in the
   network, as well as the specifics of the queuing mechanisms deployed
   along the path of this flow.

   For several queuing mechanisms, queuing_latency is less than the sum
   of upper bounds on the queuing delay (5) at every hop.  Section 5.1
   gives such practical computation examples.

   For other queuing mechanisms the only available value of
   queuing_latency 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 node.




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5.1.  Examples of Computations

   [[ JYLB: THIS IS WHERE DETAILS OF END-TO-END LATENCY COMPUTATION ARE
   GIVEN FOR PER-FLOW QUEUING AND FOR TSN WITH ATS]]

6.  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.

6.1.  A General Formula

   To avoid congestion losses, an upper bound on the backlog present in
   the queue of Figure 1 must be computed during path computation.  This
   bound depends on the set of flows that use this queue, 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.  For every
   class we need one buffer space for the packet in transmission, plus
   space for the packets that are waiting to be selected for output.
   Excluding transmission and 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 delay (5).

   Let

   o  nb_classes be the number of classes of traffic that may use this
      output port

   o  total_in_rate be the sum of the line rates of all input ports that
      send traffic of any class 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 of any
      class to this output port

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




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   o  max_delay45 be an upper bound, in seconds, on the sum of the
      processing delay (4) and the queuing delay (5) for a packet of any
      class at this ouput port.

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

      backlog_bound = ( nb_classes + nb_input_ports ) *
      max_packet_length + total_in_rate* max_delay45

7.  Queuing model

   [[ JYLB: THIS IS WHERE DETAILS OF END-TO-END LATENCY COMPUTATION ARE
   GIVEN FOR PER-FLOW QUEUING AND FOR TSN WITH ATS]]

7.1.  Queuing data model

   Sophisticated QoS 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 instantiated hierarchically
   above the "Layer 2" queuing mechanisms, among which packets compete
   for opportunities to be transmitted on a physical (or sometimes,
   logical) medium.  These "Layer 2 queuing mechanisms" are not the
   province solely of bridges; they are an essential part of any DetNet
   relay node.  As illustrated by numerous implementation examples, the
   "Layer 3" some of mechanisms described in documents such as [RFC7806]
   are often integrated, in an implementation, with the "Layer 2"
   mechanisms also implemented in the same system.  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 2 shows the (very simple) model for the flow of packets
   through the queues of an IEEE 802.1Q bridge.  Packets are assigned to
   a class of service.  The classes of service are mapped to some number
   of physical FIFO queues.  IEEE 802.1Q allows a maximum of 8 classes
   of service, but it is more common to implement 2 or 4 queues on most
   ports.













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                                    |
                     +--------------V---------------+
                     |  Class of Service Assignment |
                     +--+-------+---------------+---+
                        |       |               |
                     +--V--+ +--V--+         +--V--+
                     |Class| |Class|         |Class|
                     |  0  | |  1  |  . . .  |  n  |
                     |queue| |queue|         |queue|
                     +--+--+ +--+--+         +--+--+
                        |       |               |
                     +--V-------V---------------V--+
                     |   Transmission selection    |
                     +--------------+--------------+
                                    |
                                    V

              Figure 2: IEEE 802.1Q Queuing Model: Data flow

   Some relevant mechanisms are hidden in this figure, and are performed
   in the "Class n queue" box:

   o  Discarding packets because a queue is full.

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

   The Class of Service Assignment function can be quite complex, since
   the introduction of [IEEE802.1Qci].  In addition to the Layer 2
   priority expressed in the 802.1Q VLAN tag, a bridge can utilize any
   of the following information to assign a packet to a particular class
   of service (queue):

   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.
      (Work items expected to add MPC and other indicators.)

   o  The Class of Service Assignment function can contain metering and
      policing functions.

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




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7.2.  IEEE 802.1 Queuing Model

7.2.1.  Queuing Data Model with Preemption

   Figure 2 must be modified if the output port supports preemption
   ([IEEE8021Qbu] and [IEEE8023br]).  This modification is shown in
   Figure 3.

                                  |
   +------------------------------V------------------------------+
   |                Class of Service Assignment                  |
   +--+-------+-------+-------+-------+-------+-------+-------+--+
      |       |       |       |       |       |       |       |
   +--V--+ +--V--+ +--V--+ +--V--+ +--V--+ +--V--+ +--V--+ +--V--+
   |Class| |Class| |Class| |Class| |Class| |Class| |Class| |Class|
   |  a  | |  b  | |  c  | |  d  | |  e  | |  f  | |  g  | |  h  |
   |queue| |queue| |queue| |queue| |queue| |queue| |queue| |queue|
   +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+ +--+--+
      |       |       |       +-+     |       |       |       |
      |       |       |         |     |       |       |       |
   +--V-------V-------V------+ +V-----V-------V-------V-------V--+
   | Interrupted xmit select | |     Preempting xmit select      | 802.1
   +-------------+-----------+ +----------------+----------------+
                 |                              |                 ======
   +-------------V-----------+ +----------------V----------------+
   |    Preemptible MAC      | |         Express MAC             | 802.3
   +--------+----------------+ +----------------+----------------+
            |                                   |
   +--------V-----------------------------------V----------------+
   |                     MAC merge sublayer                      |
   +--------------------------+----------------------------------+
                              |
   +--------------------------V----------------------------------+
   |                 PHY (unaware of preemption)                 |
   +--------------------------+----------------------------------+
                              |
                              V

      Figure 3: IEEE 802.1Q Queuing Model: Data flow with preemption

   From Figure 3, we can see that, in the IEEE 802 model, the preemption
   feature 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.  The Class of Service (queue)
   determines which packets are which.  In Figure 3, the classes of
   service are marked "a, b, ..." instead of with numbers, in order to
   avoid any implication about which numeric Layer 2 priority values
   correspond to preemptible or preempting queues.  Although it shows



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   three queues going to the preemptible MAC/PHY, any assignment is
   possible.

7.2.2.  Transmission Selection Model

   In Figure 4, we expand the "Transmission selection" function of
   Figure 3.

   Figure 4 does NOT show the data path.  It shows an example of a
   configuration of the IEEE 802.1Q transmission selection box shown in
   Figure 2 and Figure 3.  Each queue m presents a "Class m Ready"
   signal.  These signals go through various logic, filters, and state
   machines, until a single queue's "not empty" signal is chosen for
   presentation to the underlying MAC/PHY.  When the MAC/PHY is ready to
   take another output packet, then a packet is selected from the one
   queue (if any) whose signal manages to pass all the way through the
   transmission selection function.


































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   +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
   |Class| |Class| |Class| |Class| |Class| |Class| |Class| |Class|
   |  1  | |  0  | |  4  | |  5  | |  6  | |  7  | |  2  | |  3  |
   |Ready| |Ready| |Ready| |Ready| |Ready| |Ready| |Ready| |Ready|
   +--+--+ +--+--+ +--+--+ +-XXX-+ +--+--+ +--+--+ +--+--+ +--+--+
      |       |       |               |       |       |       |
      |    +--V--+ +--V--+ +--+--+ +--V--+    |    +--V--+ +--V--+
      |    |Prio.| |Prio.| |Prio.| |Prio.|    |    |Sha- | |Sha- |
      |    |  0  | |  4  | |  5  | |  6  |    |    |  per| |  per|
      |    | PFC | | PFC | | PFC | | PFC |    |    |  A  | |  B  |
      |    +--+--+ +--+--+ +-XXX-+ +-XXX-+    |    +--+--+ +-XXX-+
      |       |       |                       |       |
   +--V--+ +--V--+ +--V--+ +--+--+ +--+--+ +--V--+ +--V--+ +--+--+
   |Time | |Time | |Time | |Time | |Time | |Time | |Time | |Time |
   | Gate| | Gate| | Gate| | Gate| | Gate| | Gate| | Gate| | Gate|
   |  1  | |  0  | |  4  | |  5  | |  6  | |  7  | |  2  | |  3  |
   +--+--+ +-XXX-+ +--+--+ +--+--+ +-XXX-+ +--+--+ +-XXX-+ +--+--+
      |               |                       |
   +--V-------+-------V-------+--+            |
   |802.1Q Enhanced Transmission |            |
   | Selection (ETS) = Weighted  |            |
   | Fair Queuing (WFQ)          |            |
   +--+-------+------XXX------+--+            |
      |                                       |
   +--V-------+-------+-------+-------+-------V-------+-------+--+
   |         Strict Priority selection (rightmost first)         |
   +-XXX------+-------+-------+-------+-------+-------+-------+--+
                                              |
                                              V

                  Figure 4: 802.1Q Transmission Selection

   The following explanatory notes apply to Figure 4

   o  The numbers in the "Class n Ready" boxes are the values of the
      Layer 2 priority that are assigned to that Class of Service in
      this example.  The rightmost CoS is the most important, the
      leftmost the least.  Classes 2 and 3 are made the most important,
      because they carry DetNet flows.  It is all right to make them
      more important than the priority 7 queue, which typically carries
      critical network control protocols such as spanning tree or IS-IS,
      because the shaper ensures that the highest priority best-effort
      queue (7) will get reasonable access to the MAC/PHY.  Note that
      Class 5 has no Ready signal, indicating that that queue is empty.

   o  Below the Class Ready signals are shown the Priority Flow Control
      gates (IEEE Std 802.1Qbb-2011 Priority-based Flow Control, now
      [IEEE8021Q] clause 36) on Classes of Service 1, 0, 4, and 5, and



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      two 802.1Q shapers, A and B.  Perhaps shaper A conforms to the
      IEEE Std 802.1Qav-2009 (now [IEEE8021Q] clause 34) credit-based
      shaper, and shaper B conforms to [IEEE8021Qcr] Asynchronous
      Traffic Shaper.  Any given Class of Service can have either a PFC
      function or a shaper, but not both.

   o  Next are the IEEE Std 802.1Qbv time gates ([IEEE8021Qbv]).  Each
      one of the 8 Classes of Service has a time gate.  The gates are
      controlled by a repeating schedule that restarts periodically, and
      can be programmed to turn any combination of gates on or off with
      nanosecond precision.  (Although the implementation is not
      necessarily that accurate.)

   o  Following the time gates, any number of Classes of Service can be
      linked to one ore more instances of the Enhanced Transmission
      Selection function.  This does weighted fair queuing among the
      members of its group.

   o  A final selection of the one queue to be selected for output is
      made by strict priority.  Note that the priority is determined not
      by the Layer 2 priority, but by the Class of Service.

   o  An "XXX" in the lower margin of a box (e.g.  "Prio. 5 PFC"
      indicates that the box has blocked the "Class n Ready" signal.

   o  IEEE 802.1Qch Cyclic Queuing and Forwarding [IEEE802.1Qch] is
      accomplished using two or three queues (e.g. 2 and 3 in the
      figure), using sophisticated time-based schedules in the Class of
      Service Assignment function, and using the IEEE 802.1Qbv time
      gates [IEEE8021Qbv] to swap between the output buffers.

7.3.  Other queuing models, e.g.  IntServ

   [[NWF More sections that discuss specific models]]

8.  Parameters for the bounded latency model

8.1.  Sender parameters

8.2.  Relay system parameters

   [[NWF This section talks about the paramters that must be passed hop-
   by-hop (T-SPEC?  F-SPEC?) by a resoure reservation protocol.]]








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9.  References

9.1.  Normative References

   [I-D.ietf-detnet-architecture]
              Finn, N. and P. Thubert, "Deterministic Networking
              Architecture", draft-ietf-detnet-architecture-00 (work in
              progress), September 2016.

   [I-D.ietf-detnet-dp-alt]
              Korhonen, J., Farkas, J., Mirsky, G., Thubert, P.,
              Zhuangyan, Z., and L. Berger, "DetNet Data Plane Protocol
              and Solution Alternatives", draft-ietf-detnet-dp-alt-00
              (work in progress), October 2016.

   [I-D.ietf-detnet-use-cases]
              Grossman, E., "Deterministic Networking Use Cases", draft-
              ietf-detnet-use-cases-14 (work in progress), February
              2018.

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

   [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>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [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>.

9.2.  Informative References







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   [IEEE802.1Qch]
              IEEE, "IEEE Std 802.1Qch-2017 IEEE Standard for Local and
              metropolitan area networks - Bridges and Bridged Networks
              Amendment 29: Cyclic Queuing and Forwarding (amendment to
              802.1Q-2014)", 2017,
              <http://www.ieee802.org/1/files/private/ch-drafts/>.

   [IEEE802.1Qci]
              IEEE, "IEEE Std 802.1Qci-2017 IEEE Standard for Local and
              metropolitan area networks - Bridges and Bridged Networks
              - Amendment 30: Per-Stream Filtering and Policing", 2017,
              <http://www.ieee802.org/1/files/private/ci-drafts/>.

   [IEEE8021Q]
              IEEE 802.1, "IEEE Std 802.1Q-2014: IEEE Standard for Local
              and metropolitan area networks - Bridges and Bridged
              Networks", 2014, <http://standards.ieee.org/getieee802/
              download/802-1Q-2014.pdf>.

   [IEEE8021Qbu]
              IEEE, "IEEE Std 802.1Qbu-2016 IEEE Standard for Local and
              metropolitan area networks - Bridges and Bridged Networks
              - Amendment 26: Frame Preemption", 2016,
              <http://standards.ieee.org/getieee802/
              download/802.1Qbu-2016.zip>.

   [IEEE8021Qbv]
              IEEE 802.1, "IEEE Std 802.1Qbv-2015: IEEE Standard for
              Local and metropolitan area networks - Bridges and Bridged
              Networks - Amendment 25: Enhancements for Scheduled
              Traffic", 2015, <http://standards.ieee.org/getieee802/
              download/802.1Qbv-2015.zip>.

   [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 802.3-2015: IEEE Standard for Local
              and metropolitan area networks - Ethernet", 2015,
              <http://standards.ieee.org/getieee802/
              download/802.3-2015.zip>.



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   [IEEE8023br]
              IEEE 802.3, "IEEE Std 802.3br-2016: IEEE Standard for
              Local and metropolitan area networks - Ethernet -
              Amendment 5: Specification and Management Parameters for
              Interspersing Express Traffic", 2016,
              <http://standards.ieee.org/getieee802/
              download/802.3br-2016.pdf>.

Authors' Addresses

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

   Phone: +1 925 980 6430
   Email: norman.finn@mail01.huawei.com


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

   Email: jean-yves.leboudec@epfl.ch


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

   Email: balazs.a.varga@ericsson.com


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

   Email: janos.farkas@ericsson.com






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