DetNet                                                           N. Finn
Internet-Draft                                                    Huawei
Intended status: Standards Track                              P. Thubert
Expires: December 30, 2018 February 4, 2019                                          Cisco
                                                                B. Varga
                                                               J. Farkas
                                                           June 28,
                                                          August 3, 2018

                 Deterministic Networking Architecture


   Deterministic Networking (DetNet) provides a capability to carry
   specified unicast or multicast data flows for real-time applications
   with extremely low data loss rates and bounded latency.  Techniques
   used include: 1) reserving data plane resources for individual (or
   aggregated) DetNet flows in some or all of the intermediate nodes
   (e.g., bridges or routers) along the path of the flow; 2) providing
   explicit routes for DetNet flows that do not immediately change with
   the network topology; and 3) distributing data from DetNet flow
   packets over time and/or space to ensure delivery of each packet's
   data in spite of the loss of a path.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Terms used in this document . . . . . . . . . . . . . . .   4
     2.2.  IEEE 802.1 TSN to DetNet dictionary . . . . . . . . . . .   6
   3.  Providing the DetNet Quality of Service . . . . . . . . . . .   7
     3.1.  Primary goals defining the DetNet QoS . . . . . . . . . .   7
     3.2.  Mechanisms to achieve DetNet QoS  . . . . . . . . . . . .   9
       3.2.1.  Congestion protection . . . . . . . . . . . . . . . .   9  Eliminate congestion loss . . . . . . . . . . . .   9  Jitter Reduction  . . . . . . . . . . . . . . . .  10
       3.2.2.  Service Protection  . . . . . . . . . . . . . . . . .  11  In-Order Delivery . . . . . . . . . . . . . . . .  11  Packet Replication and Elimination  . . . . . . .  11  Packet encoding for service protection  . . . . .  13
       3.2.3.  Explicit routes . . . . . . . . . . . . . . . . . . .  13
     3.3.  Secondary goals for DetNet  . . . . . . . . . . . . . . .  14
       3.3.1.  Coexistence with normal traffic . . . . . . . . . . .  14
       3.3.2.  Fault Mitigation  . . . . . . . . . . . . . . . . . .  15
   4.  DetNet Architecture . . . . . . . . . . . . . . . . . . . . .  16
     4.1.  DetNet stack model  . . . . . . . . . . . . . . . . . . .  16
       4.1.1.  Representative Protocol Stack Model . . . . . . . . .  16
       4.1.2.  DetNet Data Plane Overview  . . . . . . . . . . . . .  18
       4.1.3.  Network reference model . . . . . . . . . . . . . . .  20
     4.2.  DetNet systems  . . . . . . . . . . . . . . . . . . . . .  21
       4.2.1.  End system  . . . . . . . . . . . . . . . . . . . . .  21
       4.2.2.  DetNet edge, relay, and transit nodes . . . . . . . .  22
     4.3.  DetNet flows  . . . . . . . . . . . . . . . . . . . . . .  23
       4.3.1.  DetNet flow types . . . . . . . . . . . . . . . . . .  23
       4.3.2.  Source transmission behavior  . . . . . . . . . . . .  23
       4.3.3.  Incomplete Networks . . . . . . . . . . . . . . . . .  25
     4.4.  Traffic Engineering for DetNet  . . . . . . . . . . . . .  25
       4.4.1.  The Application Plane . . . . . . . . . . . . . . . .  25
       4.4.2.  The Controller Plane  . . . . . . . . . . . . . . . .  26
       4.4.3.  The Network Plane . . . . . . . . . . . . . . . . . .  26
     4.5.  Queuing, Shaping, Scheduling, and Preemption  . . . . . .  27
     4.6.  Service instance  . . . . . . . . . . . . . . . . . . . .  28
     4.7.  Flow identification at technology borders . . . . . . . .  29  30
       4.7.1.  Exporting flow identification . . . . . . . . . . . .  29  30
       4.7.2.  Flow attribute mapping between layers . . . . . . . .  31
       4.7.3.  Flow-ID mapping examples  . . . . . . . . . . . . . .  32
     4.8.  Advertising resources, capabilities and adjacencies . . .  34
     4.9.  Scaling to larger networks  . . . . . . . . . . . . . . .  34  35
     4.10. Compatibility with Layer-2  . . . . . . . . . . . . . . .  34  35
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  35
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  35  36
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  35  36
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  35  36
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  36  37
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  39  40

1.  Introduction

   Deterministic Networking (DetNet) is a service that can be offered by
   a network to DetNet flows.  DetNet provides these flows with
   extremely low packet loss rates and assured maximum end-to-end
   delivery latency.  This is accomplished by dedicating network
   resources such as link bandwidth and buffer space to DetNet flows
   and/or classes of DetNet flows, and by replicating packets along
   multiple paths.  Unused reserved resources are available to non-
   DetNet packets.

   The Deterministic Networking Problem Statement
   [I-D.ietf-detnet-problem-statement] introduces Deterministic
   Networking, and Deterministic Networking Use Cases
   [I-D.ietf-detnet-use-cases] summarizes the need for it.  See
   [I-D.ietf-detnet-dp-sol-mpls] and [I-D.ietf-detnet-dp-sol-ip] for
   specific techniques that can be used to identify DetNet Flows flows and
   assign them to specific paths through a network.

   A goal of DetNet is a converged network in all respects.  That is,
   the presence of DetNet flows does not preclude non-DetNet flows, and
   the benefits offered DetNet flows should not, except in extreme
   cases, prevent existing QoS mechanisms from operating in a normal
   fashion, subject to the bandwidth required for the DetNet flows.  A
   single source-destination pair can trade both DetNet and non-DetNet
   flows.  End systems and applications need not instantiate special
   interfaces for DetNet flows.  Networks are not restricted to certain
   topologies; connectivity is not restricted.  Any application that
   generates a data flow that can be usefully characterized as having a
   maximum bandwidth should be able to take advantage of DetNet, as long
   as the necessary resources can be reserved.  Reservations can be made
   by the application itself, via network management, by an applications
   application's controller, or by other means, e.g., a dynamic control
   plane (e.g., [RFC2205]).

   Many applications, applications that are intended to be served by Deterministic
   Networking require the ability to synchronize the clocks in end
   systems to a sub-microsecond accuracy.  Some of the queue control
   techniques defined in Section 4.5 also require time synchronization
   among relay and transit nodes.  The means used to achieve time
   synchronization are not addressed in this document.  DetNet should can
   accommodate various time synchronization techniques and profiles that
   are defined elsewhere to solve exchange time in address the needs of different market

2.  Terminology

2.1.  Terms used in this document

   The following terms are used in the context of DetNet in this

           Resources are dedicated to support a DetNet flow.  Depending
           on an implementation, the resource may be reused by non-
           DetNet flows when it is not used by the DetNet flow.

           The native format of a DetNet flow.

   DetNet destination
           An end system capable of terminating a DetNet flow.

   DetNet domain
           The portion of a network that is DetNet aware.  It includes
           end systems and other DetNet nodes.

   DetNet flow
           A DetNet flow is a sequence of packets to which the DetNet
           service is to be provided.

   DetNet compound flow and DetNet member flow
           A DetNet compound flow is a DetNet flow that has been
           separated into multiple duplicate DetNet member flows for
           service protection at the DetNet service layer.  Member flows
           are merged back into a single DetNet compound flow such that
           there are no duplicate packets.  "Compound" and "member" are
           strictly relative to each other, not absolutes; a DetNet
           compound flow comprising multiple DetNet member flows can, in
           turn, be a member of a higher-order compound.

   DetNet intermediate node
           A DetNet relay node or transit node.

   DetNet edge node
           An instance of a DetNet relay node that acts as a source and/
           or destination at the DetNet service layer.  For example, it
           can include a DetNet service layer proxy function for DetNet
           service protection (e.g., the addition or removal of packet
           sequencing information) for one or more end systems, or
           starts or terminates congestion protection at the DetNet
           transport layer, or aggregates DetNet services into new
           DetNet flows.  It is analogous to a Label Edge Router (LER)
           or a Provider Edge (PE) router.

           User-to-Network Interface with DetNet specific
           functionalities.  It is a packet-based reference point and
           may provide multiple functions like encapsulation, status,
           synchronization, etc.

   end system
           Commonly called a "host" in IETF documents, and an "end
           station" is IEEE 802 documents.  End systems of interest to
           this document are either sources or destinations of DetNet
           flows.  And end system may or may not be DetNet transport
           layer aware or DetNet service layer aware.

           A connection between two DetNet nodes.  It may be composed of
           a physical link or a sub-network technology that can provide
           appropriate traffic delivery for DetNet flows.

   DetNet system
           A DetNet aware end system, transit node, or relay node.
           "DetNet" may be omitted in some text.

   DetNet relay node
           A DetNet node including a service layer function that
           interconnects different DetNet transport layer paths to
           provide service protection.  A DetNet relay node can be a
           bridge, a router, a firewall, or any other system that
           participates in the DetNet service layer.  It typically
           incorporates DetNet transport layer functions as well, in
           which case it is collocated with a transit node.

   PEF     A Packet Elimination Function (PEF) eliminates duplicate
           copies of packets to prevent excess packets flooding the
           network or duplicate packets being sent out of the DetNet
           domain.  PEF can be implemented by an edge node, a relay
           node, or an end system.

   PRF     A Packet Replication Function (PRF) replicates DetNet flow
           packets and forwards them to one or more next hops in the
           DetNet domain.  The number of packet copies sent to each next
           hop is a DetNet flow specific parameter at the node doing the
           replication.  PRF can be implemented by an edge node, a relay
           node, or an end system.

   PREOF   Collective name for Packet Replication, Elimination, and
           Ordering Functions.

   POF     A Packet Ordering Function (POF) re-orders packets within a
           DetNet flow that are received out of order.  This function
           can be implemented by an edge node, a relay node, or an end

           The set of resources allocated between a source and one or
           more destinations through transit nodes and subnets
           associated with a DetNet flow, to provide the expected provisioned
           Service. service.

   DetNet service layer
           The layer at which A DetNet Service, such as congestion or service, e.g., service protection
           is provided.

   DetNet service proxy
           Maps between App-flows and DetNet flows.

   DetNet source
           An end system capable of originating a DetNet flow.

   DetNet transit node
           A node operating at the DetNet transport layer, that utilizes
           link layer and/or network layer switching across multiple
           links and/or sub-networks to provide paths for DetNet service
           layer functions.  Typically provides congestion protection
           over those paths.  An MPLS LSR is an example of a DetNet
           transit node.

   DetNet transport layer
           The layer that optionally provides congestion protection for
           DetNet flows over paths provided by the underlying network.

2.2.  IEEE 802.1 TSN to DetNet dictionary

   This section also serves as a dictionary for translating from the
   terms used by the Time-Sensitive Networking (TSN) Task Group
   [IEEE802.1TSNTG] of the IEEE 802.1 WG to those of the DetNet WG.

           The IEEE 802.1 term for a destination of a DetNet flow.

   relay system
           The IEEE 802.1 term for a DetNet intermediate node.

           The IEEE 802.1 term for a DetNet flow.

           The IEEE 802.1 term for the source of a DetNet flow.

   bridged path
           A VLAN bridge uses the VLAN ID and the destination MAC
           address to select the outbound port hence the path for a

3.  Providing the DetNet Quality of Service

3.1.  Primary goals defining the DetNet QoS

   The DetNet Quality of Service can be expressed in terms of:

   o  Minimum and maximum end-to-end latency from source to destination;
      timely delivery, and bounded jitter (packet delay variation)
      derived from these constraints.

   o  Probability of  Packet loss of a packet, ratio, under various assumptions as to the operational
      states of the nodes and links.  If packet
      replication is used to reduce the probability of packet loss, then
      a related property is the probability (may be zero) of delivery of
      a duplicate packet.  Duplicate packet delivery is an inherent risk
      in highly reliable and/or broadcast transmissions.

   o  An upper bound on out-of-order packet delivery.  It is worth
      noting that some DetNet applications are unable to tolerate any
      out-of-order delivery.

   It is a distinction of DetNet that it is concerned solely with worst-
   case values for the end-to-end latency, jitter, and misordering.
   Average, mean, or typical values are of little interest, because they
   do not affect the ability of a real-time system to perform its tasks.
   In general, a trivial priority-based queuing scheme will give better
   average latency to a data flow than DetNet, but of course, the worst-
   case latency can be essentially unbounded.

   Three techniques are used by DetNet to provide these qualities of

   o  Congestion protection (Section 3.2.1).

   o  Service protection (Section 3.2.2).

   o  Explicit routes (Section 3.2.3).

   Congestion protection operates by allocating resources along the path
   of a DetNet Flow, flow, e.g., buffer space or link bandwidth.  Congestion
   protection greatly reduces, or even eliminates entirely, packet loss
   due to output packet congestion within the network, but it can only
   be supplied to a DetNet flow that is limited at the source to a
   maximum packet size and transmission rate.  Note that congestion
   protection provided via congestion detection and notification is
   explicitly excluded from consideration in DetNet, as it serves a
   different set of applications.

   Congestion protection addresses two of the DetNet QoS requirements:
   latency and packet loss.  Given that DetNet nodes have a finite
   amount of buffer space, congestion protection necessarily results in
   a maximum end-to-end latency.  It also addresses the largest
   contribution to packet loss, which is buffer congestion.

   After congestion, the most important contributions to packet loss are
   typically from random media errors and equipment failures.  Service
   protection is the name for the mechanisms used by DetNet to address
   these losses.  The mechanisms employed are constrained by the
   requirement to meet the users' latency requirements.  Packet
   replication and elimination (Section 3.2.2) and packet encoding
   (Section are described in this document to provide service
   protection; others may be found.  For instance, packet encoding can
   be used to provide service protection against random media errors,
   packet replication and elimination can be used to provide service
   protection against equipment failures.  This mechanism distributes
   the contents of DetNet flows over multiple paths in time and/or
   space, so that the loss of some of the paths does need not cause the
   loss of any packets.

   The paths are typically (but not necessarily) explicit routes, so
   that they do not normally suffer temporary interruptions caused by
   the convergence of routing or bridging protocols.

   These three techniques can be applied independently, giving eight
   possible combinations, including none (no DetNet), although some
   combinations are of wider utility than others.  This separation keeps
   the protocol stack coherent and maximizes interoperability with
   existing and developing standards in this (IETF) and other Standards
   Development Organizations.  Some examples of typical expected

   o  Explicit routes plus service protection are exactly the techniques
      employed by seamless redundancy mechanisms applied on a ring
      topology as described, e.g., in [IEEE802.1CB]. [IEC62439-3-2016].  In this case,
      example, explicit routes are achieved by limiting the physical
      topology of the network to a ring.  Sequentialization,
      replication, and duplicate elimination are facilitated by packet
      tags added at the front or the end of Ethernet frames.  [RFC8227]
      provides another example in the context of MPLS.

   o  Congestion protection alone is offered by IEEE 802.1 Audio Video
      bridging [IEEE802.1BA].  As long as the network suffers no
      failures, zero congestion loss can be achieved through the use of
      a reservation protocol (MSRP [IEEE802.1Q]), [IEEE802.1Q-2018]), shapers in every
      bridge, and proper dimensioning.

   o  Using all three together gives maximum protection.

   There are, of course, simpler methods available (and employed, today)
   to achieve levels of latency and packet loss that are satisfactory
   for many applications.  Prioritization and over-provisioning is one
   such technique.  However, these methods generally work best in the
   absence of any significant amount of non-critical traffic in the
   network (if, indeed, such traffic is supported at all), or work only
   if the critical traffic constitutes only a small portion of the
   network's theoretical capacity, or work only if all systems are
   functioning properly, or in the absence of actions by end systems
   that disrupt the network's operations.

   There are any number of methods in use, defined, or in progress for
   accomplishing each of the above techniques.  It is expected that this
   DetNet Architecture will assist various vendors, users, and/or
   "vertical" Standards Development Organizations (dedicated to a single
   industry) to make selections among the available means of
   implementing DetNet networks.

3.2.  Mechanisms to achieve DetNet QoS

3.2.1.  Congestion protection  Eliminate congestion loss

   The primary means by which DetNet achieves its QoS assurances is to
   reduce, or even completely eliminate, congestion within a node as a
   cause of packet loss.  Given that a DetNet flow cannot be throttled,
   this can be achieved only by the provision of sufficient buffer
   storage at each hop through the network to ensure that no packets are
   dropped due to a lack of buffer storage.

   Ensuring adequate buffering requires, in turn, that the source, and
   every intermediate node along the path to the destination (or nearly
   every node, see Section 4.3.3) be careful to regulate its output to
   not exceed the data rate for any DetNet flow, except for brief
   periods when making up for interfering traffic.  Any packet sent
   ahead of its time potentially adds to the number of buffers required
   by the next hop and may thus exceed the resources allocated for a
   particular DetNet flow.

   The low-level mechanisms described in Section 4.5 provide the
   necessary regulation of transmissions by an end system or
   intermediate node to provide congestion protection.  The allocation
   of the bandwidth and buffers for a DetNet flow requires provisioning
   A DetNet node may have other resources requiring allocation and/or
   scheduling, that might otherwise be over-subscribed and trigger the
   rejection of a reservation.  Jitter Reduction

   A core objective of DetNet is to enable the convergence of sensitive
   non-IP networks onto a common network infrastructure.  This requires
   the accurate emulation of currently deployed mission-specific
   networks, which for example rely on point-to-point analog (e.g.,
   4-20mA modulation) and serial-digital cables (or buses) for highly
   reliable, synchronized and jitter-free communications.  While the
   latency of analog transmissions is basically the speed of light,
   legacy serial links are usually slow (in the order of Kbps) compared
   to, say, GigE, and some latency is usually acceptable.  What is not
   acceptable is the introduction of excessive jitter, which may, for
   instance, affect the stability of control systems.

   Applications that are designed to operate on serial links usually do
   not provide services to recover the jitter, because jitter simply
   does not exist there.  DetNet flows are generally expected to be
   delivered in-order and the precise time of reception influences the
   processes.  In order to converge such existing applications, there is
   a desire to emulate all properties of the serial cable, such as clock
   transportation, perfect flow isolation and fixed latency.  While
   minimal jitter (in the form of specifying minimum, as well as
   maximum, end-to-end latency) is supported by DetNet, there are
   practical limitations on packet-based networks in this regard.  In
   general, users are encouraged to use, instead of, "do this when you
   get the packet," a combination of:

   o  Sub-microsecond time synchronization among all source and
      destination end systems, and

   o  Time-of-execution fields in the application packets.

   Jitter reduction is provided by the mechanisms described in
   Section 4.5 that also provide congestion protection.

3.2.2.  Service Protection

   Service protection aims to mitigate or eliminate packet loss due to
   equipment failures, random media and/or memory faults.  These types
   of packet loss can be greatly reduced by spreading the data over
   multiple disjoint forwarding paths.  Various service protection
   methods are described in [RFC6372], e.g., 1+1 linear protection.
   This section describes the functional details of an additional method
   in Section, which can be implemented as described in
   Section or as specified in [I-D.ietf-detnet-dp-sol-mpls] in
   order to provide 1+n hitless protection.  The appropriate service
   protection mechanism depends on the scenario and the requirements.  In-Order Delivery

   Out-of-order packet delivery can be a side effect of service
   protection.  Packets delivered out-of-order impact the amount of
   buffering needed at the destination to properly process the received
   data.  Such packets also influence the jitter of a flow.  The DetNet
   service includes maximum allowed misordering as a constraint.  Zero
   misordering would be a valid service constraint to reflect that the
   end system(s) of the flow cannot tolerate any out-of-order delivery.
   Service protection may provide a mechanism
   DetNet Packet Ordering Functionality (POF) (Section can be
   used to support provide in-order delivery.  Packet Replication and Elimination

   This section describes a service protection method that sends copies
   of the same packets over multiple paths.

   The DetNet service layer includes the packet replication (PRF), the
   packet elimination (PEF), and the packet ordering functionality (POF)
   for use in DetNet edge, relay node, and end system packet processing.
   Either of these functions can be enabled in a DetNet edge node, relay
   node or end system.  The collective name for all three functions is
   PREOF.  The packet replication and elimination service protection
   method altogether involves four capabilities:

   o  Providing sequencing information to the packets of a DetNet
      compound flow.  This may be done by adding a sequence number or
      time stamp as part of DetNet, or may be inherent in the packet,
      e.g., in a transport protocol, or associated to other physical
      properties such as the precise time (and radio channel) of
      reception of the packet.  This is typically done once, at or near
      the source.

   o  The Packet Replication Function (PRF) replicates these packets
      into multiple DetNet member flows and typically sends them along
      multiple different paths to the destination(s), e.g., over the
      explicit routes of Section 3.2.3.  The location within a node, and
      the mechanism used for the PRF is implementation specific.

   o  The Packet Elimination Function (PEF) eliminates duplicate packets
      of a DetNet flow based on the sequencing information and a history
      of received packets.  The output of the PEF is always a single
      packet.  This may be done at any node along the path to save
      network resources further downstream, in particular if multiple
      Replication points exist.  But the most common case is to perform
      this operation at the very edge of the DetNet network, preferably
      in or near the receiver.  The location within a node, and
      mechanism used for the PEF is implementation specific.

   o  The Packet Ordering Function (POF) uses the sequencing information
      to re-order a DetNet flow's packets that are received out of

   The order in which a node applies PEF, POF, and PRF to a DetNet flow
   is implementation specific.

   Some service protection mechanisms rely on switching from one flow to
   another when a failure of a flow is detected.  Contrarily, packet
   replication and elimination combines the DetNet member flows sent
   along multiple different paths, and performs a packet-by-packet
   selection of which to discard, e.g., based on sequencing information.

   In the simplest case, this amounts to replicating each packet in a
   source that has two interfaces, and conveying them through the
   network, along separate (disjoint non-SRLG) paths, to the similarly
   dual-homed destinations, that discard the extras.  This ensures that
   one path (with zero congestion loss) remains, even if some
   intermediate node fails.  The sequencing information can also be used
   for loss detection and for re-ordering.

   DetNet relay nodes in the network can provide replication and
   elimination facilities at various points in the network, so that
   multiple failures can be accommodated.

   This is shown in Figure 1, where the two relay nodes each replicate
   (R) the DetNet flow on input, sending the DetNet member flows to both
   the other relay node and to the end system, and eliminate duplicates
   (E) on the output interface to the right-hand end system.  Any one
   link in the network can fail, and the DetNet compound flow can still
   get through.  Furthermore, two links can fail, as long as they are in
   different segments of the network.

                > > > > > > > > > relay > > > > > > > >
               > /------------+ R node E +------------\ >
              > /                  v + ^               \ >
      end    R +                   v | ^                + E end
      system   +                   v | ^                +   system
              > \                  v + ^               / >
               > \------------+ R relay E +-----------/ >
                > > > > > > > > >  node > > > > > > > >

               Figure 1: Packet replication and elimination

   Packet replication and elimination does not react to and correct
   failures; it is entirely passive.  Thus, intermittent failures,
   mistakenly created packet filters, or misrouted data is handled just
   the same as the equipment failures that are handled by typical
   routing and bridging protocols.

   If packet replication and elimination is used over paths providing
   congestion protection (Section 3.2.1), and member flows that take
   different-length paths through the network are combined, a merge
   point may require extra buffering to equalize the delays over the
   different paths.  This equalization ensures that the resultant
   compound flow will not exceed its contracted bandwidth even after one
   or the other of the paths is restored after a failure.  The extra
   buffering can be also used to provide in-order delivery.  Packet encoding for service protection

   There are methods for using multiple paths to provide service
   protection that involve encoding the information in a packet
   belonging to a DetNet flow into multiple transmission units,
   combining information from multiple packets into any given
   transmission unit.  Such techniques, also known as "network coding",
   can be used as a DetNet service protection technique.

3.2.3.  Explicit routes

   In networks controlled by typical dynamic control protocols such as
   IS-IS or OSPF, a network topology event in one part of the network
   can impact, at least briefly, the delivery of data in parts of the
   network remote from the failure or recovery event.  Even the use of
   redundant paths through a network defined, e.g., as defined by
   [RFC6372] do not eliminate the chances of packet loss.  Furthermore,
   out-of-order packet delivery can be a side effect of route changes.

   Many real-time networks rely on physical rings or chains of two-port devices,
   with a relatively simple ring control protocol.  This supports
   redundant paths for service protection with a minimum of wiring.  As
   an additional benefit, ring topologies can often utilize different
   topology management protocols than those used for a mesh network,
   with a consequent reduction in the response time to topology changes.
   Of course, this comes at some cost in terms of increased hop count,
   and thus latency, for the typical path.

   In order to get the advantages of low hop count and still ensure
   against even very brief losses of connectivity, DetNet employs
   explicit routes, where the path taken by a given DetNet flow does not
   change, at least immediately, and likely not at all, in response to
   network topology events.  Service protection (Section 3.2.2 or
   Section over explicit routes provides a high likelihood of
   continuous connectivity.  Explicit routes can be established in
   various ways, e.g., with RSVP-TE [RFC3209], with Segment Routing (SR)
   [RFC8402], via a Software Defined Networking approach [RFC7426], with
   IS-IS [RFC7813], etc.  Explicit routes are typically used in MPLS TE

   Out-of-order packet delivery can be a side effect of distributing a
   single flow over multiple paths especially when there is a change
   from one path to another when combining the flow.  This is
   irrespective of the distribution method used, and also applies to
   service protection over explicit routes.  As described in
   Section, out-of-order packets influence the jitter of a flow
   and impact the amount of buffering needed to process the data;
   therefore, DetNet service includes maximum allowed misordering as a
   constraint.  The use of explicit routes helps to provide in-order
   delivery because there is no immediate route change with the network
   topology, but the changes are plannable as they are between the
   different explicit routes.

3.3.  Secondary goals for DetNet

   Many applications require DetNet to provide additional services,
   including coexistence with other QoS mechanisms Section 3.3.1 and
   protection against misbehaving transmitters Section 3.3.2.

3.3.1.  Coexistence with normal traffic

   A DetNet network supports the dedication of a high proportion (e.g.
   75%) of the network bandwidth to DetNet flows.  But, no matter how
   much is dedicated for DetNet flows, it is a goal of DetNet to coexist
   with existing Class of Service schemes (e.g., DiffServ).  It is also
   important that non-DetNet traffic not disrupt the DetNet flow, of
   course (see Section 3.3.2 and Section 5).  For these reasons:

   o  Bandwidth (transmission opportunities) not utilized by a DetNet
      flow are is available to non-DetNet packets (though not to other
      DetNet flows).

   o  DetNet flows can be shaped or scheduled, in order to ensure that
      the highest-priority non-DetNet packet is also ensured a worst-
      case latency (at any given hop).

   o  When transmission opportunities for DetNet flows are scheduled in
      detail, then the algorithm constructing the schedule should leave
      sufficient opportunities for non-DetNet packets to satisfy the
      needs of the users of the network.  Detailed scheduling can also
      permit the time-shared use of buffer resources by different DetNet

   Ideally, the net effect of the presence of DetNet flows in a network
   on the non-DetNet packets is primarily a reduction in the available

3.3.2.  Fault Mitigation

   One key to building robust real-time systems is to reduce the
   infinite variety of possible failures to a number that can be
   analyzed with reasonable confidence.  DetNet aids in the process by
   allowing for filters and policers to detect DetNet packets received
   on the wrong interface, or at the wrong time, or in too great a
   volume, and to then take actions such as discarding the offending
   packet, shutting down the offending DetNet flow, or shutting down the
   offending interface.

   It is also essential that filters and service remarking be employed
   at the network edge to prevent non-DetNet packets from being mistaken
   for DetNet packets, and thus impinging on the resources allocated to
   DetNet packets.

   There exist techniques, at present and/or in various stages of
   standardization, that can perform these fault mitigation tasks that
   deliver a high probability that misbehaving systems will have zero
   impact on well-behaved DetNet flows, except of course, for the
   receiving interface(s) immediately downstream of the misbehaving
   device.  Examples of such techniques include traffic policing
   functions (e.g.  [RFC2475]) and separating flows into per-flow rate-
   limited queues.

4.  DetNet Architecture

4.1.  DetNet stack model

   DetNet functionality (Section 3) is implemented in two adjacent
   layers in the protocol stack: the DetNet service layer and the DetNet
   transport layer.  The DetNet service layer provides DetNet service,
   e.g., service protection, to higher layers in the protocol stack and
   applications.  The DetNet transport layer supports DetNet service in
   the underlying network, e.g., by providing explicit routes and
   congestion protection to DetNet flows.

4.1.1.  Representative Protocol Stack Model

   Figure 2 illustrates a conceptual DetNet data plane layering model.
   One may compare it to that in [IEEE802.1CB], Annex C.

             |  packets going  |        ^  packets coming   ^
             v down the stack  v        |   up the stack    |
           +----------------------+   +-----------------------+
           |        Source        |   |      Destination      |
           +----------------------+   +-----------------------+
           |    Service layer:    |   |     Service layer:    |
           |  Packet sequencing   |   | Duplicate elimination |
           |  Flow replication    |   |      Flow merging     |
           |   Packet encoding    |   |    Packet decoding    |
           +----------------------+   +-----------------------+
           |   Transport layer:   |   |    Transport layer:   |
           |   Congestion prot.   |   |    Congestion prot.   |
           |   Explicit routes    |   |    Explicit routes    |
           +----------------------+   +-----------------------+
           |     Lower layers     |   |     Lower layers      |
           +----------------------+   +-----------------------+
                      v                           ^

                Figure 2: DetNet data plane protocol stack

   Not all layers are required for any given application, or even for
   any given network.  The functionality shown in Figure 2 is:

           Shown as "source" and "destination" in the diagram.

   Packet sequencing
           As part of DetNet service protection, supplies the sequence
           number for packet replication and elimination
           (Section 3.2.2).  Peers with Duplicate elimination.  This
           layer is not needed if a higher-layer transport protocol is
           expected to perform any packet sequencing and duplicate
           elimination required by the DetNet flow replication.

   Duplicate elimination
           As part of the DetNet service layer, based on the sequenced
           number supplied by its peer, packet sequencing, Duplicate
           elimination discards any duplicate packets generated by
           DetNet flow replication.  It can operate on member flows,
           compound flows, or both.  The replication may also be
           inferred from other information such as the precise time of
           reception in a scheduled network.  The duplicate elimination
           layer may also perform resequencing of packets to restore
           packet order in a flow that was disrupted by the loss of
           packets on one or another of the multiple paths taken.

   Flow replication
           As part of DetNet service protection, packets that belong to
           a DetNet compound flow are replicated into two or more DetNet
           member flows.  This function is separate from packet
           sequencing.  Flow replication can be an explicit replication
           and remarking of packets, or can be performed by, for
           example, techniques similar to ordinary multicast
           replication, albeit with resource allocation implications.
           Peers with DetNet flow merging.

   Flow merging
           As part of DetNet service protection, merges DetNet member
           flows together for packets coming up the stack belonging to a
           specific DetNet compound flow.  Peers with DetNet flow
           replication.  DetNet flow merging, together with packet
           sequencing, duplicate elimination, and DetNet flow
           replication perform packet replication and elimination
           (Section 3.2.2).

   Packet encoding
           As part of DetNet service protection, as an alternative to
           packet sequencing and flow replication, packet encoding
           combines the information in multiple DetNet packets, perhaps
           from different DetNet compound flows, and transmits that
           information in packets on different DetNet member Flows.
           Peers with Packet decoding.

   Packet decoding
           As part of DetNet service protection, as an alternative to
           flow merging and duplicate elimination, packet decoding takes
           packets from different DetNet member flows, and computes from
           those packets the original DetNet packets from the compound
           flows input to packet encoding.  Peers with Packet encoding.

   Congestion protection
           The DetNet transport layer provides congestion protection.
           See Section 4.5.  The actual queuing and shaping mechanisms
           are typically provided by underlying subnet layers, these can
           be closely associated with the means of providing paths for
           DetNet flows (e.g., MPLS LSPs or bridged paths), flows, the path and the congestion protection are
           conflated in this figure.

   Explicit routes
           The DetNet transport layer provides mechanisms to ensure that
           fixed paths are provided for DetNet flows.  These explicit
           paths avoid the impact of network convergence.

   Operations, Administration, and Maintenance (OAM) leverages in-band
   and out-of-band signaling that validates whether the service is
   effectively obtained within QoS constraints.  OAM is not shown in
   Figure 2; it may reside in any number of the layers.  OAM can involve
   specific tagging added in the packets for tracing implementation or
   network configuration errors; traceability enables to find whether a
   packet is a replica, which relay node performed the replication, and
   which segment was intended for the replica.  Active and hybrid OAM
   methods require additional bandwidth to perform fault management and
   performance monitoring of the DetNet domain.  OAM may, for instance,
   generate special test probes or add OAM information into the data

   The packet sequencing and replication elimination functions at the
   source and destination ends of a DetNet compound flow may be
   performed either in the end system or in a DetNet relay node.

4.1.2.  DetNet Data Plane Overview

   A "Deterministic Network" will be composed of DetNet enabled end
   systems and nodes, i.e., edge nodes, relay nodes and collectively
   deliver DetNet services.  DetNet enabled nodes are interconnected via
   transit nodes (e.g., LSRs) which support DetNet, but are not DetNet
   service aware.  All DetNet enabled nodes are connected to sub-
   networks, where a point-to-point link is also considered as a simple
   sub-network.  These sub-networks will provide DetNet compatible
   service for support of DetNet traffic.  Examples of sub-networks
   include MPLS TE, IEEE 802.1 TSN and OTN.  Of course, multi-layer
   DetNet systems may also be possible, where one DetNet appears as a
   sub-network, and provides service to, a higher layer DetNet system.
   A simple DetNet concept network is shown in Figure 3.

   TSN              Edge          Transit        Relay        DetNet
   End System       Node            Node         Node         End System

   +---------+   +.........+                                 +---------+
   |  Appl.  |<--:Svc Proxy:-- End to End Service ---------->|  Appl.  |
   +---------+   +---------+                   +---------+   +---------+
   |   TSN   |   |TSN| |Svc|<-- DetNet flow ---: Service :-->| Service |
   +---------+   +---+ +---+    +---------+    +---------+   +---------+
   |Transport|   |Trp| |Trp|    |Transport|    |Trp| |Trp|   |Transport|
   +-------.-+   +-.-+ +-.-+    +--.----.-+    +-.-+ +-.-+   +---.-----+
           :  Link :    /  ,-----.  \   :  Link  :    /  ,-----.  \
           +.......+    +-[  Sub  ]-+   +........+    +-[  Sub  ]-+
                           [Network]                     [Network]
                            `-----'                       `-----'

                 Figure 3: A Simple DetNet Enabled Network

   Distinguishing the function of two DetNet data plane layers, the
   DetNet service layer and the DetNet transport layer, helps to explore
   and evaluate various combinations of the data plane solutions
   available, some are illustrated in Figure 4.  This separation of
   DetNet layers, while helpful, should not be considered as formal
   requirement.  For example, some technologies may violate these strict
   layers and still be able to deliver a DetNet service.

              |  Service  | PW, UDP, GRE
              | Transport | IPv6, IPv4, MPLS TE LSPs, MPLS SR

                 Figure 4: DetNet adaptation to data plane

   In some networking scenarios, the end system initially provides a
   DetNet flow encapsulation, which contains all information needed by
   DetNet nodes (e.g., Real-time Transport Protocol (RTP) [RFC3550]
   based DetNet flow transported over a native UDP/IP network or
   PseudoWire).  In other scenarios, the encapsulation formats might
   differ significantly.

   There are many valid options to create a data plane solution for
   DetNet traffic by selecting a technology approach for the DetNet
   service layer and also selecting a technology approach for the DetNet
   transport layer.  There are a high number of valid combinations.

   One of the most fundamental differences between different potential
   data plane options is the basic headers used by DetNet nodes.  For
   example, the basic service can be delivered based on an MPLS label or
   an IP header.  This decision impacts the basic forwarding logic for
   the DetNet service layer.  Note that in both cases, IP addresses are
   used to address DetNet nodes.  The selected DetNet transport layer
   technology also needs to be mapped to the sub-net technology used to
   interconnect DetNet nodes.  For example, DetNet flows will need to be
   mapped to TSN Streams.

4.1.3.  Network reference model

   Figure 5 shows another view of the DetNet service related reference
   points and main components.

   DetNet                                                     DetNet
   end system                                                 end system
      _                                                             _
     / \     +----DetNet-UNI (U)                                   / \
    /App\    |                                                    /App\
   /-----\   |                                                   /-----\
   | NIC |   v         ________                                  | NIC |
   +--+--+   _____    /        \             DetNet-UNI (U) --+  +--+--+
      |     /     \__/          \                             |     |
      |    / +----+    +----+    \_____                       |     |
      |   /  |    |    |    |          \_______               |     |
      +------U PE +----+ P  +----+             \          _   v     |
          |  |    |    |    |    |              |     ___/ \        |
          |  +--+-+    +----+    |       +----+ |    /      \_      |
          \     |                |       |    | |   /         \     |
           \    |   +----+    +--+-+  +--+PE  |------         U-----+
            \   |   |    |    |    |  |  |    | |   \_      _/
             \  +---+ P  +----+ P  +--+  +----+ |     \____/
              \___  |    |    |    |           /
                  \ +----+__  +----+     DetNet-1    DetNet-2
      |            \_____/  \___________/                           |
      |                                                             |
      |      |     End-to-End-Service     End-to-End service         |     |         |     |
      |      |     DetNet-Service     DetNet service             |     |         |     |
      |      <------------------------------------------------>     |
      |      |                                |     |         |     |

          Figure 5: DetNet Service Reference Model (multi-domain)

   DetNet-UNIs ("U" in Figure 5) are assumed in this document to be
   packet-based reference points and provide connectivity over the
   packet network.  A DetNet-UNI may provide multiple functions, e.g.,
   it may add networking technology specific encapsulation to the DetNet
   flows if necessary; it may provide status of the availability of the
   resources associated with a reservation; it may provide a
   synchronization service for the end system; it may carry enough
   signaling to place the reservation in a network without a controller,
   or if the controller only deals with the network but not the end
   systems.  Internal reference points of end systems (between the
   application and the NIC) are more challenging from control
   perspective and they may have extra requirements (e.g., in-order
   delivery is expected in end system internal reference points, whereas
   it is considered optional over the DetNet-UNI).

4.2.  DetNet systems

4.2.1.  End system

   The native data flow between the source/destination end systems is
   referred to as application-flow (App-flow).  The traffic
   characteristics of an App-flow can be CBR (constant bit rate) or VBR
   (variable bit rate) and can have L1 or L2 or L3 encapsulation (e.g.,
   TDM (time-division multiplexing), Ethernet, IP).  These
   characteristics are considered as input for resource reservation and
   might be simplified to ensure determinism during transport (e.g.,
   making reservations for the peak rate of VBR traffic, etc.).

   An end system may or may not be DetNet transport layer aware or
   DetNet service layer aware.  That is, an end system may or may not
   contain DetNet specific functionality.  End systems with DetNet
   functionalities may have the same or different transport layer as the
   connected DetNet domain.  Categorization of end systems are shown in
   Figure 6.

                End system
                    |  DetNet aware ?
                   / \
           +------<   >------+
        NO |       \ /       | YES
           |        v        |
    DetNet unaware           |
      End system             |
                             | Service/
                             | Transport
                            / \  aware ?
                  +--------<   >-------------+
          t-aware |         \ /              | s-aware
                  |          v               |
                  |          | both          |
                  |          |               |
          DetNet t-aware     |        DetNet s-aware
            End system       |         End system
                       DetNet st-aware
                         End system

                  Figure 6: Categorization of end systems

   Note some known use case examples for end systems:

   o  DetNet unaware: The classic case requiring service proxies.

   o  DetNet t-aware: An extant TSN A DetNet transport-aware system.  It knows about
      some TSN functions (e.g., reservation), but not about service

   o  DetNet s-aware: An extant IEC 62439-3 A DetNet service-aware system.  It supplies
      sequence numbers, but doesn't know about zero congestion loss.

   o  DetNet st-aware: A full functioning DetNet end system, it has
      DetNet functionalities and usually the same forwarding paradigm as
      the connected DetNet domain.  It can be treated as an integral
      part of the DetNet domain.

4.2.2.  DetNet edge, relay, and transit nodes

   As shown in Figure 3, DetNet edge nodes providing proxy service and
   DetNet relay nodes providing the DetNet service layer are DetNet-
   aware, and DetNet transit nodes need only be aware of the DetNet
   transport layer.

   In general, if a DetNet flow passes through one or more DetNet-
   unaware network nodes between two DetNet nodes providing the DetNet
   transport layer for that flow, there is a potential for disruption or
   failure of the DetNet QoS.  A network administrator needs to ensure
   that the DetNet-unaware network nodes are configured to minimize the
   chances of packet loss and delay, and provision enough extra buffer
   space in the DetNet transit node following the DetNet-unaware network
   nodes to absorb the induced latency variations.

4.3.  DetNet flows

4.3.1.  DetNet flow types

   A DetNet flow can have different formats while it is transported
   between the peer end systems.  Therefore, the following possible
   types / formats of a DetNet flow are distinguished in this document:

   o  App-flow: native format of the data carried over a DetNet flow.
      It does not contain any DetNet related attributes.

   o  DetNet-t-flow: specific format of a DetNet flow.  Only requires
      the congestion / latency features provided by the DetNet transport

   o  DetNet-s-flow: specific format of a DetNet flow.  Only requires
      the service protection feature ensured by the DetNet service

   o  DetNet-st-flow: specific format of a DetNet flow.  It requires
      both DetNet service layer and DetNet transport layer functions
      during forwarding.

4.3.2.  Source transmission behavior

   For the purposes of congestion protection, DetNet flows can be
   synchronous or asynchronous.  In synchronous DetNet flows, at least
   the intermediate nodes (and possibly the end systems) are closely
   time synchronized, typically to better than 1 microsecond.  By
   transmitting packets from different DetNet flows or classes of DetNet
   flows at different times, using repeating schedules synchronized
   among the intermediate nodes, resources such as buffers and link
   bandwidth can be shared over the time domain among different DetNet
   flows.  There is a tradeoff among techniques for synchronous DetNet
   flows between the burden of fine-grained scheduling and the benefit
   of reducing the required resources, especially buffer space.

   In contrast, asynchronous DetNet flows are not coordinated with a
   fine-grained schedule, so relay and end systems must assume worst-
   case interference among DetNet flows contending for buffer resources.
   Asynchronous DetNet flows are characterized by:

   o  A maximum packet size;

   o  An observation interval; and

   o  A maximum number of transmissions during that observation

   These parameters, together with knowledge of the protocol stack used
   (and thus the size of the various headers added to a packet), limit
   the number of bit times per observation interval that the DetNet flow
   can occupy the physical medium.

   The source is required not to exceed these limits in order to obtain
   DetNet service.  If the source transmits less data than this limit
   allows, the unused resource such as link bandwidth can be made
   available by the system to non-DetNet packets.  However, making those
   resources available to DetNet packets in other DetNet flows would
   serve no purpose.  Those other DetNet flows have their own dedicated
   resources, on the assumption that all DetNet flows can use all of
   their resources over a long period of time.

   There is no provision in DetNet for throttling DetNet flows (reducing
   end-to-end transmission rate via any explicit congestion
   notification); the assumption is that a DetNet flow, to be useful,
   must be delivered in its entirety.  That is, while any useful
   application is written to expect a certain number of lost packets,
   the real-time applications of interest to DetNet demand that the loss
   of data due to the network is an extraordinarily event.

   Although DetNet strives to minimize the changes required of an
   application to allow it to shift from a special-purpose digital
   network to an Internet Protocol network, one fundamental shift in the
   behavior of network applications is impossible to avoid: the
   reservation of resources before the application starts.  In the first
   place, a network cannot deliver finite latency and practically zero
   packet loss to an arbitrarily high offered load.  Secondly, achieving
   practically zero packet loss for unthrottled (though bandwidth
   limited) DetNet flows means that bridges and routers have to dedicate
   buffer resources to specific DetNet flows or to classes of DetNet
   flows.  The requirements of each reservation have to be translated
   into the parameters that control each system's queuing, shaping, and
   scheduling functions and delivered to the hosts, bridges, and

4.3.3.  Incomplete Networks

   The presence in the network of transit nodes or subnets that are not
   fully capable of offering DetNet services complicates the ability of
   the intermediate nodes and/or controller to allocate resources, as
   extra buffering must be allocated at points downstream from the non-
   DetNet intermediate node for a DetNet flow.  This extra buffering may
   increase latency and/or jitter.

4.4.  Traffic Engineering for DetNet

   Traffic Engineering Architecture and Signaling (TEAS) [TEAS] defines
   traffic-engineering architectures for generic applicability across
   packet and non-packet networks.  From a TEAS perspective, Traffic
   Engineering (TE) refers to techniques that enable operators to
   control how specific traffic flows are treated within their networks.

   Because if its very nature of establishing explicit optimized paths,
   Deterministic Networking can be seen as a new, specialized branch of
   Traffic Engineering, and inherits its architecture with a separation
   into planes.

   The Deterministic Networking architecture is thus composed of three
   planes, a (User) Application Plane, a Controller Plane, and a Network
   Plane, which echoes that of Figure 1 of Software-Defined Networking
   (SDN): Layers and Architecture Terminology [RFC7426].:

4.4.1.  The Application Plane

   Per [RFC7426], the Application Plane includes both applications and
   services.  In particular, the Application Plane incorporates the User
   Agent, a specialized application that interacts with the end user /
   operator and performs requests for Deterministic Networking services
   via an abstract Flow Management Entity, (FME) which may or may not be
   collocated with (one of) the end systems.

   At the Application Plane, a management interface enables the
   negotiation of flows between end systems.  An abstraction of the flow
   called a Traffic Specification (TSpec) provides the representation.
   This abstraction is used to place a reservation over the (Northbound)
   Service Interface and within the Application plane.  It is associated
   with an abstraction of location, such as IP addresses and DNS names,
   to identify the end systems and eventually specify intermediate

4.4.2.  The Controller Plane

   The Controller Plane corresponds to the aggregation of the Control
   and Management Planes in [RFC7426], though Common Control and
   Measurement Plane (CCAMP) [CCAMP] makes an additional distinction
   between management and measurement.  When the logical separation of
   the Control, Measurement and other Management entities is not
   relevant, the term Controller Plane is used for simplicity to
   represent them all, and the term controller plane entity (CPE) Controller Plane Function (CPF)
   refers to any device operating in that plane, whether is it a Path
   Computation entity, Element (PCE) [RFC4655], or a Network Management entity (NME)),
   (NME), or a distributed control plane.  The Path Computation Element (PCE)
   [RFC4655] CPF is a core element of
   a controller, in charge of computing Deterministic paths to be
   applied in the Network Plane.

   A (Northbound) Service Interface enables applications in the
   Application Plane to communicate with the entities in the Controller
   Plane as illustrated in Figure 7.

   One or more PCE(s) CPF(s) collaborate to implement the requests from the FME
   as Per-Flow Per-Hop Behaviors installed in the intermediate nodes for
   each individual flow.  The PCEs CPFs place each flow along a deterministic
   sequence of intermediate nodes so as to respect per-flow constraints
   such as security and latency, and optimize the overall result for
   metrics such as an abstract aggregated cost.  The deterministic
   sequence can typically be more complex than a direct sequence and
   include redundancy path, with one or more packet replication and
   elimination points.

4.4.3.  The Network Plane

   The Network Plane represents the network devices and protocols as a
   whole, regardless of the Layer at which the network devices operate.
   It includes Forwarding Plane (data plane), Application, and
   Operational Plane (control plane) (e.g., OAM) aspects.

   The network Plane comprises the Network Interface Cards (NIC) in the
   end systems, which are typically IP hosts, and intermediate nodes,
   which are typically IP routers and switches.  Network-to-Network
   Interfaces such as used for Traffic Engineering path reservation in
   [RFC5921], as well as User-to-Network Interfaces (UNI) such as
   provided by the Local Management Interface (LMI) between network and
   end systems, are both part of the Network Plane, both in the control
   plane and the data plane.

   A Southbound (Network) Interface enables the entities in the
   Controller Plane to communicate with devices in the Network Plane as
   illustrated in Figure 7.  This interface leverages and extends TEAS
   to describe the physical topology and resources in the Network Plane.

       End                                                     End
       System                                               System

      -+-+-+-+-+-+-+ Northbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

                CPE         CPE              CPE              CPE

                CPF         CPF              CPF              CPF

      -+-+-+-+-+-+-+ Southbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

              intermediate  intermed.   intermed.  intermed.
                  Node       Node       Node       Node
       NIC                                                     NIC
              intermediate  intermed.   intermed.  intermed.
                  Node       Node       Node       Node

              Figure 7: Northbound and Southbound interfaces

   The intermediate nodes (and eventually the end systems NIC) expose
   their capabilities and physical resources to the controller (the
   CPF), and update the CPEs CPFs with their dynamic perception of the
   topology, across the Southbound Interface.  In return, the CPEs CPFs set
   the per-flow paths up, providing a Flow Characterization that is more
   tightly coupled to the intermediate node Operation than a TSpec.

   At the Network plane, intermediate nodes may exchange information
   regarding the state of the paths, between adjacent systems and
   eventually with the end systems, and forward packets within
   constraints associated to each flow, or, when unable to do so,
   perform a last resort operation such as drop or declassify.

   This document focuses on the Southbound interface and the operation
   of the Network Plane.

4.5.  Queuing, Shaping, Scheduling, and Preemption

   DetNet achieves congestion protection and bounded delivery latency by
   reserving bandwidth and buffer resources at every hop along the path
   of the DetNet flow.  The reservation itself is not sufficient,
   however.  Implementors and users of a number of proprietary and
   standard real-time networks have found that standards for specific
   data plane techniques are required to enable these assurances to be
   made in a multi-vendor network.  The fundamental reason is that
   latency variation in one system results in the need for extra buffer
   space in the next-hop system(s), which in turn, increases the worst-
   case per-hop latency.

   Standard queuing and transmission selection algorithms allow a
   central controller to compute the latency contribution of each
   transit node to the end-to-end latency, to compute the amount of
   buffer space required in each transit node for each incremental
   DetNet flow, and most importantly, to translate from a flow
   specification to a set of values for the managed objects that control
   each relay or end system.  For example, the IEEE 802.1 WG has
   specified (and is specifying) a set of queuing, shaping, and
   scheduling algorithms that enable each transit node (bridge or
   router), and/or a central controller, to compute these values.  These
   algorithms include:

   o  A credit-based shaper [IEEE802.1Q] Clause 34. [IEEE802.1Qav] (superseded by

   o  Time-gated queues governed by a rotating time schedule,
      synchronized among all transit nodes [IEEE802.1Qbv]. [IEEE802.1Qbv] (superseded by

   o  Synchronized double (or triple) buffers driven by synchronized
      time ticks.  [IEEE802.1Qch].  [IEEE802.1Qch] (superseded by [IEEE802.1Q-2018]).

   o  Pre-emption of an Ethernet packet in transmission by a packet with
      a more stringent latency requirement, followed by the resumption
      of the preempted packet [IEEE802.1Qbu], [IEEE802.3br]. [IEEE802.1Qbu] (superseded by
      [IEEE802.1Q-2018]), [IEEE802.3br] (superseded by

   While these techniques are currently embedded in Ethernet [IEEE802.3]
   [IEEE802.3-2018] and bridging standards, we can note that they are
   all, except perhaps for packet preemption, equally applicable to
   other media than Ethernet, and to routers as well as bridges.  Other
   media may have its own methods, see, e.g.,
   [I-D.ietf-6tisch-architecture], [RFC7554].  DetNet may include such
   definitions in the future, or may define how these techniques can be
   used by DetNet nodes.

4.6.  Service instance

   A Service instance represents all the functions required on a node to
   allow the end-to-end service between the UNIs.

   The DetNet network general reference model is shown in Figure 8 for a
   DetNet service scenario (i.e., between two DetNet-UNIs).  In this
   figure, end systems ("A" and "B") are connected directly to the edge
   nodes of an IP/MPLS network ("PE1" and "PE2").  End systems
   participating in DetNet communication may require connectivity before
   setting up an App-flow that requires the DetNet service.  Such a
   connectivity related service instance and the one dedicated for
   DetNet service share the same access.  Packets belonging to a DetNet
   flow are selected by a filter configured on the access ("F1" and
   "F2").  As a result, data flow specific access ("access-A + F1" and
   "access-B + F2") are terminated in the flow specific service instance
   ("SI-1" and "SI-2").  A tunnel is used to provide connectivity
   between the service instances.

   The tunnel is used to transport exclusively the packets of the DetNet
   flow between "SI-1" and "SI-2".  The service instances are configured
   to implement DetNet functions and a flow specific DetNet transport.
   The service instance and the tunnel may or may not be shared by
   multiple DetNet flows.  Sharing the service instance by multiple
   DetNet flows requires properly populated forwarding tables of the
   service instance.

             access-A                                     access-B
              <----->    <-------- tunnel ---------->     <----->

                 +---------+        ___  _        +---------+
   End system    |  +----+ |       /   \/ \_      | +----+  | End system
       "A" -------F1+    | |      /         \     | |    +F2----- "B"
                 |  |    +========+ IP/MPLS +=======+    |  |
                 |  |SI-1| |      \__  Net._/     | |SI-2|  |
                 |  +----+ |         \____/       | +----+  |
                 |PE1      |                      |      PE2|
                 +---------+                      +---------+

             Figure 8: DetNet network general reference model

   The tunnel between the service instances may have some special
   characteristics.  For example, in case of a DetNet L3 service, there
   are differences in the usage of the PW for DetNet traffic compared to
   the network model described in [RFC6658].  In the DetNet scenario,
   the PW is likely to be used exclusively by the DetNet flow, whereas
   [RFC6658] states: "The packet PW appears as a single point-to-point
   link to the client layer.  Network-layer adjacency formation and
   maintenance between the client equipment will follow the normal
   practice needed to support the required relationship in the client
   layer ... This packet pseudowire PseudoWire is used to transport all of the
   required Layer-2 and Layer-3 protocols between LSR1 and LSR2".
   Further details are network technology specific and can be found in
   [I-D.ietf-detnet-dp-sol-mpls] and [I-D.ietf-detnet-dp-sol-ip].

4.7.  Flow identification at technology borders

4.7.1.  Exporting flow identification

   A DetNet node may need to map specific flows to lower layer flows (or
   Streams) in order to provide specific queuing and shaping services
   for specific flows.  For example:

   o  A non-IP, strictly L2 source end system X may be sending multiple
      flows to the same L2 destination end system Y.  Those flows may
      include DetNet flows with different QoS requirements, and may
      include non-DetNet flows.

   o  A router may be sending any number of flows to another router.
      Again, those flows may include DetNet flows with different QoS
      requirements, and may include non-DetNet flows.

   o  Two routers may be separated by bridges.  For these bridges to
      perform any required per-flow queuing and shaping, they must be
      able to identify the individual flows.

   o  A Label Edge Router (LER) may have a Label Switched Path (LSP) set
      up for handling traffic destined for a particular IP address
      carrying only non-DetNet flows.  If a DetNet flow to that same
      address is requested, a separate LSP may be needed, in order that
      all of the Label Switch Routers (LSRs) along the path to the
      destination give that flow special queuing and shaping.

   The need for a lower-layer node to be aware of individual higher-
   layer flows is not unique to DetNet.  But, given the endless
   complexity of layering and relayering over tunnels that is available
   to network designers, DetNet needs to provide a model for flow
   identification that is better than packet inspection.  That is not to
   say that packet inspection to layer 4 or 5 addresses will not be
   used, or the capability standardized; but, there are alternatives.

   A DetNet relay node can connect DetNet flows on different paths using
   different flow identification methods.  For example:

   o  A single unicast DetNet flow passing from router A through a
      bridged network to router B may be assigned a TSN Stream
      identifier that is unique within that bridged network.  The
      bridges can then identify the flow without accessing higher-layer
      headers.  Of course, the receiving router must recognize and
      accept that TSN Stream.

   o  A DetNet flow passing from LSR A to LSR B may be assigned a
      different label than that used for other flows to the same IP

   In any of the above cases, it is possible that an existing DetNet
   flow can be an aggregate carrying multiple other DetNet flows.  (Not
   to be confused with DetNet compound vs. member flows.)  Of course,
   this requires that the aggregate DetNet flow be provisioned properly
   to carry the aggregated flows.

   Thus, rather than packet inspection, there is the option to export
   higher-layer information to the lower layer.  The requirement to
   support one or the other method for flow identification (or both) is
   a complexity that is part of DetNet control models.

4.7.2.  Flow attribute mapping between layers

   Transport of DetNet flows over multiple technology domains may
   require that lower layers are aware of specific flows of higher
   layers.  Such an "exporting of flow identification" is needed each
   time when the forwarding paradigm is changed on the transport path
   (e.g., two LSRs are interconnected by a L2 bridged domain, etc.).
   The three representative forwarding methods considered for
   deterministic networking are:

   o  IP routing

   o  MPLS label switching

   o  Ethernet bridging

   A packet with corresponding Flow-IDs is illustrated in Figure 9. 9,
   which also indicates where each Flow-ID can be added or removed.

       add/remove     add/remove
       Eth Flow-ID    IP Flow-ID
           |             |
           v             v
        |      |      |      |                                      |
        | Eth  | MPLS |  IP  |     Application data                 |
        |      |      |      |                                      |
             MPLS Flow-ID

                  Figure 9: Packet with multiple Flow-IDs

   The additional (domain specific) Flow-ID can be

   o  created by a domain specific function or

   o  derived from the Flow-ID added to the App-flow.

   The Flow-ID must be unique inside a given domain.  Note that the
   Flow-ID added to the App-flow is still present in the packet, but
   transport nodes may lack the function to recognize it; that's why the
   additional Flow-ID is added.

4.7.3.  Flow-ID mapping examples

   IP nodes and MPLS nodes are assumed to be configured to push such an
   additional (domain specific) Flow-ID when sending traffic to an
   Ethernet switch (as shown in the examples below).

   Figure 10 shows a scenario where an IP end system ("IP-A") is
   connected via two Ethernet switches ("ETH-n") to an IP router ("IP-

                                     IP domain

           +======+                                       +======+
           |L3-ID |                                       |L3-ID |
           +======+  /\                           +-----+ +======+
                    /  \       Forward as         |     |
                   /IP-A\      per ETH-ID         |IP-1 |      Recognize
   Push  ------>  +-+----+         |              +---+-+  <----- ETH-ID
   ETH-ID           |         +----+-----+            |
                    |         v          v            |
                    |      +-----+    +-----+         |
                    +------+     |    |     +---------+
           +......+        |ETH-1+----+ETH-2|           +======+
           .L3-ID .        +-----+    +-----+           |L3-ID |
           +======+             +......+                +======+
           |ETH-ID|             .L3-ID .                |ETH-ID|
           +======+             +======+                +------+

                             Ethernet domain

         Figure 10: IP nodes interconnected by an Ethernet domain

   End system "IP-A" uses the original App-flow specific ID ("L3-ID"),
   but as it is connected to an Ethernet domain it has to push an
   Ethernet-domain specific flow-ID ("VID + multicast MAC address",
   referred as "ETH-ID") before sending the packet to "ETH-1" node.
   Ethernet switch "ETH-1" can recognize the data flow based on the
   "ETH-ID" and it does forwarding toward "ETH-2".  "ETH-2" switches the
   packet toward the IP router.  "IP-1" must be configured to receive
   the Ethernet Flow-ID specific multicast flow, but (as it is an L3
   node) it decodes the data flow ID based on the "L3-ID" fields of the
   received packet.

   Figure 11 shows a scenario where MPLS domain nodes ("PE-n" and "P-m")
   are connected via two Ethernet switches ("ETH-n").

                                    MPLS domain

       +=======+                                  +=======+
       |MPLS-ID|                                  |MPLS-ID|
       +=======+  +-----+                 +-----+ +=======+ +-----+
                  |     |   Forward as    |     |           |     |
                  |PE-1 |   per ETH-ID    | P-2 +-----------+ PE-2|
   Push   ----->  +-+---+        |        +---+-+           +-----+
   ETH-ID           |      +-----+----+       |  \ Recognize
                    |      v          v       |   +-- ETH-ID
                    |   +-----+    +-----+    |
                    +---+     |    |     +----+
           +.......+    |ETH-1+----+ETH-2|   +=======+
           .MPLS-ID.    +-----+    +-----+   |MPLS-ID|
           +=======+                         +=======+
           |ETH-ID |         +.......+       |ETH-ID |
           +=======+         .MPLS-ID.       +-------+
                             |ETH-ID |
                          Ethernet domain

        Figure 11: MPLS nodes interconnected by an Ethernet domain

   "PE-1" uses the MPLS specific ID ("MPLS-ID"), but as it is connected
   to an Ethernet domain it has to push an Ethernet-domain specific
   flow-ID ("VID + multicast MAC address", referred as "ETH-ID") before
   sending the packet to "ETH-1".  Ethernet switch "ETH-1" can recognize
   the data flow based on the "ETH-ID" and it does forwarding toward
   "ETH-2".  "ETH-2" switches the packet toward the MPLS node ("P-2").
   "P-2" must be configured to receive the Ethernet Flow-ID specific
   multicast flow, but (as it is an MPLS node) it decodes the data flow
   ID based on the "MPLS-ID" fields of the received packet.

   One can appreciate from the above example that, when the means used
   for DetNet flow identification is altered or exported, the means for
   encoding the sequence number information must similarly be altered or

4.8.  Advertising resources, capabilities and adjacencies

   There are three classes of information that a central controller or
   distributed control plane needs to know that can only be obtained
   from the end systems and/or nodes in the network.  When using a peer-
   to-peer control plane, some of this information may be required by a
   system's neighbors in the network.

   o  Details of the system's capabilities that are required in order to
      accurately allocate that system's resources, as well as other
      systems' resources.  This includes, for example, which specific
      queuing and shaping algorithms are implemented (Section 4.5), the
      number of buffers dedicated for DetNet allocation, and the worst-
      case forwarding delay and misordering.

   o  The dynamic state of a node's DetNet resources.

   o  The identity of the system's neighbors, and the characteristics of
      the link(s) between the systems, including the length (in
      nanoseconds) of the link(s).

4.9.  Scaling to larger networks

   Reservations for individual DetNet flows require considerable state
   information in each transit node, especially when adequate fault
   mitigation (Section 3.3.2) is required.  The DetNet data plane, in
   order to support larger numbers of DetNet flows, must support the
   aggregation of DetNet flows.  Such aggregated flows can be viewed by
   the transit nodes' data plane largely as individual DetNet flows.
   Without such aggregation, the per-relay system may limit the scale of
   DetNet networks.  Example techniques that may be used include MPLS
   hierarchy and IP DiffServ Code Points (DSCPs).

4.10.  Compatibility with Layer-2

   Standards providing similar capabilities for bridged networks (only)
   have been and are being generated in the IEEE 802 LAN/MAN Standards
   Committee.  The present architecture describes an abstract model that
   can be applicable both at Layer-2 and Layer-3, and over links not
   defined by IEEE 802.

   DetNet enabled end systems and intermediate nodes can be
   interconnected by sub-networks, i.e., Layer-2 technologies.  These
   sub-networks will provide DetNet compatible service for support of
   DetNet traffic.  Examples of sub-networks include MPLS TE, 802.1 TSN,
   and a point-to-point OTN link.  Of course, multi-layer DetNet systems
   may be possible too, where one DetNet appears as a sub-network, and
   provides service to, a higher layer DetNet system.

5.  Security Considerations

   Security in the context of Deterministic Networking has an added
   dimension; the time of delivery of a packet can be just as important
   as the contents of the packet, itself.  A man-in-the-middle attack,
   for example, can impose, and then systematically adjust, additional
   delays into a link, and thus disrupt or subvert a real-time
   application without having to crack any encryption methods employed.
   See [RFC7384] for an exploration of this issue in a related context.

   Furthermore, in a control system where millions of dollars of
   equipment, or even human lives, can be lost if the DetNet QoS is not
   delivered, one must consider not only simple equipment failures,
   where the box or wire instantly becomes perfectly silent, but complex
   errors such as can be caused by software failures.  Because there is
   essential no limit to the kinds of failures that can occur,
   protecting against realistic equipment failures is indistinguishable,
   in most cases, from protecting against malicious behavior, whether
   accidental or intentional.  See also Section 3.3.2.

   Security must cover:

   o  the protection of the signaling protocol

   o  the authentication and authorization of the controlling systems

   o  the identification and shaping of the DetNet flows

6.  Privacy Considerations

   DetNet is provides a Quality of Service (QoS), and as such, does not
   directly raise any new privacy considerations.

   However, the requirement for every (or almost every) node along the
   path of a DetNet flow to identify DetNet flows may present an
   additional attack surface for privacy, should the DetNet paradigm be
   found useful in broader environments.

7.  IANA Considerations

   This document does not require an action from IANA.

8.  Acknowledgements

   The authors wish to thank Lou Berger, David Black, Stewart Bryant,
   Rodney Cummings, Ethan Grossman, Craig Gunther, Marcel Kiessling,
   Rudy Klecka, Jouni Korhonen, Erik Nordmark, Shitanshu Shah, Wilfried
   Steiner, George Swallow, Michael Johas Teener, Pat Thaler, Thomas
   Watteyne, Patrick Wetterwald, Karl Weber, Anca Zamfir, for their
   various contribution with this work.

9.  Informative References

   [CCAMP]    IETF, "Common Control and Measurement Plane Working

              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-14 (work
              in progress), April 2018.

              Korhonen, J. and B. Varga, "DetNet IP Data Plane
              Encapsulation", draft-ietf-detnet-dp-sol-ip-00 (work in
              progress), July 2018,
              draft-ietf-detnet-dp-sol-ip/>. 2018.

              Korhonen, J. and B. Varga, "DetNet MPLS Data Plane
              Encapsulation", draft-ietf-detnet-dp-sol-mpls-00 (work in
              progress), July 2018,
              draft-ietf-detnet-dp-sol-mpls/>. 2018.

              Finn, N. and P. Thubert, "Deterministic Networking Problem
              Statement", draft-ietf-detnet-problem-statement-05 draft-ietf-detnet-problem-statement-06 (work
              in progress), June July 2018.

              Grossman, E., "Deterministic Networking Use Cases", draft-
              ietf-detnet-use-cases-17 (work in progress), June 2018.

              Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
              Litkowski, S.,

              International Electrotechnical Commission (IEC) TC 65/SC
              65C - Industrial networks, "IEC 62439-3:2016 Industrial
              communication networks - High availability automation
              networks - Part 3: Parallel Redundancy Protocol (PRP) and R. Shakir, "Segment Routing
              Architecture", draft-ietf-spring-segment-routing-15 (work
              in progress), January 2018.
              High-availability Seamless Redundancy (HSR)", 2016,

              IEEE Standards Association, "IEEE Std 802.1BA-2011 Audio
              Video Bridging (AVB) Systems", 2011,

              IEEE Standards Association, "IEEE Std 802.1CB 802.1CB-2017 Frame
              Replication and Elimination for Reliability", 2017,


              IEEE Standards Association, "IEEE Std 802.1Q-2018 Bridges
              and Bridged Networks", 2018,

              IEEE Standards Association, "IEEE Std 802.1Qav-2009
              Bridges and Bridged Networks - Amendment 12: Forwarding
              and Queuing Enhancements for Time-Sensitive Streams",
              2009, <>.

              IEEE Standards Association, "IEEE Std 802.1Qbu-2016
              Bridges and Bridged Networks - Amendment 26: Frame
              Preemption", 2016,

              IEEE Standards Association, "IEEE Std 802.1Qbv-2015
              Bridges and Bridged Networks - Amendment 25: Enhancements
              for Scheduled Traffic", 2015,

              IEEE Standards Association, "IEEE Std 802.1Qbv-2015 802.1Qch-2017
              Bridges and Bridged Networks - Amendment 29: Cyclic
              Queuing and Forwarding", 2017,

              IEEE Standards Association, "IEEE 802.1 Time-Sensitive
              Networking Task Group", 2013,


              IEEE Standards Association, "IEEE Std 802.3-2015 802.3-2018 Standard
              for Ethernet", 2015,
              <>. 2018, <

              IEEE Standards Association, "IEEE Std 802.3br-2016
              Standard for Ethernet Amendment 5: Specification and
              Management Parameters for Interspersing Express Traffic",
              2016, <>.

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

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <>.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,

   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,

   [RFC6372]  Sprecher, N., Ed. and A. Farrel, Ed., "MPLS Transport
              Profile (MPLS-TP) Survivability Framework", RFC 6372,
              DOI 10.17487/RFC6372, September 2011,

   [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,

   [RFC7384]  Mizrahi, T., "Security Requirements of Time Protocols in
              Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
              October 2014, <>.

   [RFC7426]  Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
              Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
              Defined Networking (SDN): Layers and Architecture
              Terminology", RFC 7426, DOI 10.17487/RFC7426, January
              2015, <>.

   [RFC7554]  Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
              IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
              Internet of Things (IoT): Problem Statement", RFC 7554,
              DOI 10.17487/RFC7554, May 2015,

   [RFC7813]  Farkas, J., Ed., Bragg, N., Unbehagen, P., Parsons, G.,
              Ashwood-Smith, P., and C. Bowers, "IS-IS Path Control and
              Reservation", RFC 7813, DOI 10.17487/RFC7813, June 2016,

   [RFC8227]  Cheng, W., Wang, L., Li, H., van Helvoort, H., and J.
              Dong, "MPLS-TP Shared-Ring Protection (MSRP) Mechanism for
              Ring Topology", RFC 8227, DOI 10.17487/RFC8227, August
              2017, <>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <>.

   [TEAS]     IETF, "Traffic Engineering Architecture and Signaling
              Working Group",

Authors' Addresses

   Norman Finn
   3755 Avocado Blvd.
   PMB 436
   La Mesa, California  91941

   Phone: +1 925 980 6430
   Pascal Thubert
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis  06410

   Phone: +33 4 97 23 26 34

   Balazs Varga
   Magyar tudosok korutja 11
   Budapest  1117


   Janos Farkas
   Magyar tudosok korutja 11
   Budapest  1117