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DetNet                                                           N. Finn
Internet-Draft                                                P. Thubert
Intended status: Standards Track                                   Cisco
Expires: September 10, 2015                                March 9, 2015


                 Deterministic Networking Architecture
                   draft-finn-detnet-architecture-00

Abstract

   Deterministic Networking (DetNet) provides a capability to carry
   specified unicast or multicast data streams for real-time
   applications with extremely low data loss rates and maximum latency.
   Techniques used include: 1) reserving data plane resources for
   individual (or aggregated) DetNet streams in some or all of the relay
   systems (bridges or routers) along the path of the stream; 2)
   providing fixed paths for DetNet streams that do not rapidly change
   with the network topology; and 3) sequentializing, replicating, and
   eliminating duplicate packets at various points to ensure the
   availability of at least one path.  The capabilities can be managed
   by configuration, or by manual or automatic network management.

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 http://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 10, 2015.

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of



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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Providing the DetNet Quality of Service . . . . . . . . . . .   5
     3.1.  Zero Congestion Loss  . . . . . . . . . . . . . . . . . .   6
     3.2.  Pinned-down paths . . . . . . . . . . . . . . . . . . . .   7
     3.3.  Seamless Redundancy . . . . . . . . . . . . . . . . . . .   7
   4.  DetNet Architecture . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  The Application Plane . . . . . . . . . . . . . . . . . .  11
     4.2.  The Controller Plane  . . . . . . . . . . . . . . . . . .  11
     4.3.  The Network Plane . . . . . . . . . . . . . . . . . . . .  12
     4.4.  Elements of DetNet Architecture . . . . . . . . . . . . .  13
     4.5.  DetNet streams  . . . . . . . . . . . . . . . . . . . . .  14
       4.5.1.  Talker guarantees . . . . . . . . . . . . . . . . . .  14
       4.5.2.  Incomplete Networks . . . . . . . . . . . . . . . . .  15
     4.6.  Data Flow Model through Systems . . . . . . . . . . . . .  16
     4.7.  Queuing, Shaping, Scheduling, and Preemption  . . . . . .  16
     4.8.  Coexistence with normal traffic . . . . . . . . . . . . .  16
     4.9.  Fault Mitigation  . . . . . . . . . . . . . . . . . . . .  16
     4.10. Protocol Stack Model  . . . . . . . . . . . . . . . . . .  17
     4.11. Advertising resources, capabilities and adjacencies . . .  17
     4.12. Provisioning model  . . . . . . . . . . . . . . . . . . .  17
       4.12.1.  Centralized Path Computation and Installation  . . .  17
       4.12.2.  Distributed Path Setup . . . . . . . . . . . . . . .  17
   5.  Related IETF work . . . . . . . . . . . . . . . . . . . . . .  18
     5.1.  Deterministic PHB . . . . . . . . . . . . . . . . . . . .  18
     5.2.  6TiSCH  . . . . . . . . . . . . . . . . . . . . . . . . .  18
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   Operational Technology (OT) refers to industrial networks that are
   typically used for monitoring systems and supporting control loops,
   as well as movement detection systems for use in process control
   (i.e., process manufacturing) and factory automation (i.e., discrete
   manufacturing).  Due to its different goals, OT has evolved in



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   parallel but in a manner that is radically different from IT/ICT,
   focusing on highly secure, reliable and deterministic networks, with
   limited scalability over a bounded area.

   The convergence of IT and OT technologies, also called the Industrial
   Internet, represents a major evolution for both sides.  The work has
   already started; in particular, the industrial automation space has
   been developing a number of Ethernet-based replacements for existing
   digital control systems, often not packet-based (fieldbus
   technologies).

   These replacements are meant to provide similar behavior as the
   incumbent protocols, and their common focus is to transport a fully
   characterized flow over a well-controlled environment (i.e., a
   factory floor), with a bounded latency, extraordinarily low frame
   loss, and a very narrow jitter.  Examples of such protocols include
   PROFINET, ODVA Ethernet/IP, and EtherCAT.

   In parallel, the need for determinism in professional and home audio/
   video markets drove the formation of the Audio/Video Bridging (AVB)
   standards effort of IEEE 802.1.  With the explosion of demand for
   connectivity and multimedia in transportation in general, the
   Ethernet AVB technology has become one of the hottest topics, in
   particular in the automotive connectivity.  It is finding application
   in all elements of the vehicle from head units, to rear seat
   entertainment modules, to amplifiers and camera modules.  While aimed
   at less critical applications than some industrial networks, AVB
   networks share the requirement for extremely low packet loss rates
   and ensured finite latency and jitter.

   Other instances of in-vehicle deterministic networks have arisen as
   well for control networks in cars, trains and buses, as well as
   avionics, with, for instance, the mission-critical "Avionics Full-
   Duplex Switched Ethernet" (AFDX) that was designed as part of the
   ARINC 664 standards.  Existing automotive control networks such as
   the LIN, CAN and FlexRay standards were not designed to cover these
   increasing demands in terms of bandwidth and scalability that we see
   with various kinds of Driver Assistance Systems (DAS) and new
   multiplexing technologies based on Ethernet are now getting traction.

   The generalization of the needs for more deterministic networks have
   led to the IEEE 802.1 AVB Task Group becoming the Time-Sensitive
   Networking (TSN) Task Group (TG), with a much-expanded constituency
   from the industrial and vehicular markets.  Along with this
   expansion, the networks in consideration are becoming larger and
   structured, requiring deterministic forwarding beyond the LAN
   boundaries.  For instance, Industrial Automation segregates the
   network along the broad lines of the Purdue Enterprise Reference



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   Architecture (PERA), using different technologies at each level, and
   public infrastructures such as Electricity Automation require
   deterministic properties over the Wide Area.  The realization is now
   coming that the convergence of IT and OT networks requires Layer-3,
   as well as Layer-2, capabilities.

   The present architecture is the result of a collaboration of the IETF
   and the IEEE and implements an abstract model that can be applicable
   both at Layer-2 and Layer-3, and along segments of different
   technologie.  With this new work, a path may span, for instance,
   across a (limited) number of 802.1 bridges and then a (limited)
   number of IP routers.  In that example, the IEEE 802.1 bridges may be
   operating at Layer-2 over Ethernet whereas the IP routers may be
   6TiSCH nodes operating at Layer-2 and/or Layer-3 over the IEEE
   802.15.4e MAC.

   Many applications of interest to 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 4.7 also require time synchronization among relay systems.
   The means used to achieve time synchronization are not addressed in
   this document.

2.  Terminology

   The follwing special terms are used in this document in order to
   avoid the assumption that a given element in the archetecture does or
   does not have Internet Protocol stack, functions as a router or a
   bridge, or otherwise plays a particular role at Layer-3 or higher:

   bridge
           A Customer Bridge as defined by IEEE 802.1Q
           [IEEE802.1Q-2011].

   circuit
           A trail of configuration from talker to listener(s) through
           relay systems associated with a DetNet stream, required to
           deliver the benefits of DetNet.

   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 talkers and listeners.

   listener
           An end system capable of sinking a DetNet stream.

   relay system



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           A router or a bridge.

   stream
           A DetNet stream is a sequence of packets from a single
           talker, through some number of relay systems to one or more
           listeners, that is limited by the talker in its maximum
           packet size and transmission rate, and can thus be ensured
           the DetNet Quality of Service (QoS) from the network.

   talker
           An end system capable of sourcing a DetNet stream.

3.  Providing the DetNet Quality of Service

   DetNet Quality of Service is expressed in terms of:

   o  Minimum and maximum end-to-end latency from talker to listener;

   o  Probability of loss of a packet, assuming the normal operation of
      the relay systems and links;

   o  Probability of loss of a packet in the event of the failure of a
      relay system or link.

   It is a distinction of DetNet that it is concerned solely with worst-
   case values for all of the above parameters.  Average, mean, or
   typical values are of no interest, because they do not affect the
   ability of a real-time system to perform its tasks.

   Three techniques are employed by DetNet to achieve these QoS
   parameters:

   a.  Zero congestion loss (Section 3.1).  Network resources such as
       link bandwidth, buffers, queues, shapers, and scheduled input/
       output slots are assigned in each relay system to the use of a
       specific DetNet stream or group of streams.  Note that, given a
       finite amount of buffer space), zero congestion loss necessarily
       ensures a maximum end-to-end latency.  Depending on the method
       employed, a minimum latency can also be achieved.

   b.  Pinned-down paths (Section 3.2).  Point-to-point paths or point-
       to-multipoint trees through the network from a talker to one or
       more listeners can be established, and DetNet streams assigned to
       follow a particular path or tree.

   c.  Packet replication and deletion (Section 3.3).  End systems and/
       or relay systems can sequence number, replicate, and eliminate
       replicated packets at multiple points in the network in order to



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       ensure that one (or more) equipment failure events still leave at
       least one path intact for a DetNet stream.

   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
   combinations:

   o  Pinned-down paths (a) plus packet replication (b) are exactly the
      techniques employed by [HSR-PRP].  Pinned-down paths are achieve
      by limiting the physical topology of the network, and the
      sequentialization, replication, and duplicate elimination
      facilitated by packet tags added at the front or the end of
      Ethernet frames.

   o  Zero congestion loss (a) alone is is offered by IEEE 802.1 Audio
      Video bridging [IEEE802.1BA-2011].  As long as the network suffers
      no failures, near-zero (at best, zero) congestion loss can be
      achieved through the use of a reservation protocol (MSRP) and
      shapers in every relay system (bridge).

   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.  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.

3.1.  Zero Congestion Loss

   The primary means by which DetNet achieves its QoS assurances is to
   completely eliminate congestion at an output port as a cause of
   packet loss.  Given that a DetNet stream cannot be throttled, this



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   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 talker, and
   every relay system along the path to the listener (or nearly every
   relay system -- see Section 4.5.2) be careful to regulate its output
   to not exceed the data rate for any stream, except for brief perios
   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
   stream.

   The low-level mechanisms described in Section 4.7 provide the
   necessary regulation of transmissions by an edge system or relay
   system to ensure zero congestion loss.  Of course, the reservation of
   the bandwidth and buffers for a stream requires the provisioning
   described in Section 4.12.

3.2.  Pinned-down paths

   In networks controlled by typical peer-to-peer protocols such as IEEE
   802.1 ISIS bridged networks or ETF OSPF routed networks, 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.  Thus, even redundant paths through a
   network, if controlled by the typical peer-to-peer protocols, do not
   eliminate the chances of brief losses of contact.  For this reason,
   many real-time networks rely on physical rings of two-port devices,
   with a relatively simple ring control protocol.  This both minimizes
   recovery time and easily supports redundant paths.  Of course, this
   comes at the cost 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 brief losses of connectivity, DetNet employs pinned-down
   paths, where the path taken by a given DetNet stream does not change,
   at least immediately, and likely not at all, in response to network
   topology events.  When combined with seamless redundancy
   (Section 3.3), this results in a high likelihood of continuous
   connectivity.

3.3.  Seamless Redundancy

   After congestion loss has been eliminated, the most important causes
   of packet loss are random media and/or memory faults and equipment
   failures.




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   Seamless redundancy involves three capabilities:

   o  Adding sequence numbers to the packets of a DetNet stream.

   o  Replicating these packets and, typically, sending them along at
      least two different paths to the listener(s).

   o  Discarding duplicated packets.

   In the simplest case, this amounts to replicating each packet in a
   talker that has two interfaces, and conveying them through the
   network, along separate paths, to the similarly dual-homed listeners,
   that discard the extras.  This ensures that one path (with zero
   congestion loss) remains, even if some relay system fails.

   Alternatively, relay systems 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 the following figure, where the two relay systems
   each replicate (R) the DetNet stream on input, sending the stream to
   both the other relay system and to the end system, and eliminated
   duplicates (E) on the output interface to the right-hand end system.
   Any one links in the network can fail, and the Detnet stream can
   still get through.  Furthermore, two links can fail, as long as they
   are in different segments of the network.

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

                                 Figure 1

4.  DetNet Architecture

   Traffic Engineering Architecture and Signaling (TEAS) [TEAS] defines
   traffic-engineering architectures for generic applicability across
   packet and non-packet networks.  From 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 pinned-down optimized
   paths, Deterministic Networking can be seen as a new, specialized



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   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 Software-Defined Networking (SDN): Layers
   and Architecture Terminology [RFC7426] which is represented below:












































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           SDN Layers and Architecture Terminology per RFC 7426

                     o--------------------------------o
                     |                                |
                     | +-------------+   +----------+ |
                     | | Application |   |  Service | |
                     | +-------------+   +----------+ |
                     |       Application Plane        |
                     o---------------Y----------------o
                                     |
       *-----------------------------Y---------------------------------*
       |           Network Services Abstraction Layer (NSAL)           |
       *------Y------------------------------------------------Y-------*
              |                                                |
              |               Service Interface                |
              |                                                |
       o------Y------------------o       o---------------------Y------o
       |      |    Control Plane |       | Management Plane    |      |
       | +----Y----+   +-----+   |       |  +-----+       +----Y----+ |
       | | Service |   | App |   |       |  | App |       | Service | |
       | +----Y----+   +--Y--+   |       |  +--Y--+       +----Y----+ |
       |      |           |      |       |     |               |      |
       | *----Y-----------Y----* |       | *---Y---------------Y----* |
       | | Control Abstraction | |       | | Management Abstraction | |
       | |     Layer (CAL)     | |       | |      Layer (MAL)       | |
       | *----------Y----------* |       | *----------Y-------------* |
       |            |            |       |            |               |
       o------------|------------o       o------------|---------------o
                    |                                 |
                    | CP                              | MP
                    | Southbound                      | Southbound
                    | Interface                       | Interface
                    |                                 |
       *------------Y---------------------------------Y----------------*
       |         Device and resource Abstraction Layer (DAL)           |
       *------------Y---------------------------------Y----------------*
       |            |                                 |                |
       |    o-------Y----------o   +-----+   o--------Y----------o     |
       |    | Forwarding Plane |   | App |   | Operational Plane |     |
       |    o------------------o   +-----+   o-------------------o     |
       |                       Network Device                          |
       +---------------------------------------------------------------+

                                 Figure 2







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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 Stream Management Entity, (SME) which may or may not
   be collocated with (one of) the end systems.

   At the Application Plane, a management interface enables the
   negotiation of streams between end systems.  An abstraction of the
   stream 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 relay systems.

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 refers to any device
   operating in that plane, whether is it a Path Computation entity or a
   Network Management entity (NME).  The Path Computation Element (PCE)
   [PCE] 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.

   One or more PCE(s) collaborate to implement the requests from the SME
   as Per-Stream Per-Hop Behaviors installed in the relay systems for
   each individual streams.  The PCEs place each stream along a
   deterministic sequence of relay systems so as to respect per-stream
   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.






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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.

   The network Plane comprises the Network Interface Cards (NIC) in the
   end systems, which are typically IP hosts, and relay systems, which
   are typically IP routers and switches.  Network-to-Network Interfaces
   such as used for Traffic Engineering path reservation in [RFC3209],
   as well as User-to-Network Interfaces (UNI) such as provided by the
   Local Management Interface (LMI) between network and end systems, are
   all part of the Network Plane.

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

                         Stream Management Entity

       End                                                     End
           System                                               System

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

                PCE         PCE              PCE              PCE

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

                  Relay      Relay      Relay      Relay
                  System     System     System     System
       NIC                                                     NIC
                  Relay      Relay      Relay      Relay
                  System     System     System     System

                                 Figure 3

   The relay systems (and eventually the end systems NIC) expose their
   capabilities and physical resources to the controller (the PCE), and
   update the PCE with their dynamic perception of the topology, across
   the Southbound Interface.  In return, the PCE(s) set the per-stream
   paths up, providing a Stream Characterization that is more tightly
   coupled to the relay system Operation than a TSpec.

   At the Network plane, relay systems exchange information regarding
   the state of the paths, between adjacent systems and eventually with
   the end systems, and forward packets within constraints associated to




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   each stream, or, when unable to do so, perform a last resort
   operation such as drop or declassify.

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

4.4.  Elements of DetNet Architecture

   The DetNet architecture has a number of elements, discussed in the
   following sections:

   a.  A model for the definition, identification, and operation of
       DetNet streams (Section 4.5), for use by relay systems to
       classify and process individual packets following per-stream
       rules.

   b.  A model for the flow of data from an end system or through a
       relay system that can be used to predict the bounds for that
       system's impact on the QoS of a DetNet stream, without
       significantly constraining the method of implementing that
       system, for use by the Controllers to configure policing and
       shaping engines in Network Systems over the Southbound interface.
       The model includes:

       1.  A model for queuing, transmission selection, shaping,
           preemption, and timing resources that can be used by an end
           system or relay system to control the selection of packets
           output on an interface.  These models must have sufficiently
           well-defined characteristics, both individually and in the
           aggregate, to give predictable results for the QoS for DetNet
           packets (Section 4.7).

       2.  A model for identifying misbehaving DetNet streams and
           mitigating their impact on properly functioning streams
           (Section 4.9).

   c.  A model for the relay system to inform the controller(s) of the
       information it needs for adequate path computations including:

       1.  Systems' individual capabilities (e.g. can do replication,
           can do precise time).

       2.  Link capabilities and resources (e.g. bandwidth, 0 delays,
           hardware deterministic support to the physical layer, ...)

       3.  hysical resources (total and available buffers, timers,
           queues, etc)




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       4.  Network Adjacencies (neighbors)

   d.  A model for the provision of a service, by end systems, or relay
       systems, to forward a DetNet stream over a simple or redundant
       path.  The model includes:

       1.  A model for an abstract relaying operation of either Routing
           or forwarding packets of a DetNet stream to a next-hop relay
           system, across Layer boundaries.

       2.  A model of next-hop(s) information for replicating the
           packets of a DetNet stream, typically at or near the talker,
           merging and/or re-replicating those packets at other points
           in the network, and finally eliminating the duplicates,
           typically at or near the listener(s), in order to provide
           high availability (Section 3.3).

   e.  The protocol stack model for an end system and/or a relay system
       should support the above elements in a manner that maximizes the
       applicability of existing standards and protocols to the DetNet
       problem, allows for the creation of new protocols where needed,
       thus making DetNet an add-on feature to existing networks, rather
       than a new way to do networking.  In particular this protocol
       stack supports networks in which the path from talker to
       listener(s) includes bridges and/or routers in any order
       (Section 4.10).

   f.  A variety of models for the provisioning of DetNet streams can be
       envisioned, including orchestration by a central controller or by
       a federation of controllers, provisioning by relay systems and
       end systems sharing peer-to-peer protocols, by off-line
       configuration, or by a combination of these methods.  The
       provisioning models are similar to existing Layer-2 and Layer-3
       models, in order to minimize the amount of innovation required in
       this area (Section 4.12).

4.5.  DetNet streams

4.5.1.  Talker guarantees

   DetNet streams can by synchronous or asynchronous.  The transmission
   of packets in synchronous DetNet streams uses time synchronization
   among the end and relay systems to control the flow of packets.
   Asynchronous DetNet streams are characterized by:

   o  A maximum packet size;

   o  An observation interval; and



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   o  A maximum number of transmissions during that observation
      interval.

   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
   stream can occupy the physical medium.

   The talker promises that these limits will not be exceeded.  If the
   talker transmits less data than this limit allows, the unused
   resources 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 streams would serve no purpose.  Those other
   streams have their own dedicated resources, on the assumption that
   all DetNet streams can use all of their resources over a long period
   of time.

   Note that there is no provision in DetNet for throttling streams; the
   assumption is that a DetNet stream, 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 extraordinarily infrequent.

   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 that 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) streams means that bridges and routers have to dedicate
   buffer resources to specific streams or to classes of streams.  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
   routers.

4.5.2.  Incomplete Networks

   The presence in the network of relay systems that are not fully
   capable of offering DetNet services complicates the ability of the
   relay systems and/or controller to allocate resources, as extra
   buffering, and thus extra latency, must be allocated at each point
   that is downstream from the non-DetNet relay system for some DetNet
   stream.




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4.6.  Data Flow Model through Systems

4.7.  Queuing, Shaping, Scheduling, and Preemption

   For this reason, the IEEE 802.1 Time-Sensitive Networking Task Group
   has defined a set of queuing, shaping, and scheduling algorithms that
   enable each bridge or router to compute the exact number of buffers
   to be allocated for each stream or class of streams.

4.8.  Coexistence with normal traffic

   A DetNet network supports the dedication of at least 75% of the
   network bandwidth to DetNet streams.  But, no matter how much is
   dedicated for DetNet streams, It is z goal of DetNet to not interfere
   excessively with existing QoS schemes.  It is also important that
   non-DetNet traffic not disrupt the DetNet stream, of course (see
   Section 4.9 and Section 6).  For these reasons:

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

   o  DetNet streams can be shaped, in order to ensure that the highest-
      priority non-DetNet packet also is ensured a maximum latency.

   o  When transmission opportunities for DetNet streams are scheduled
      in detail, then the algorithm constructing the schedule should
      leave sufficient opportunities for non-DetNet packets to satisfy
      the needs of the uses of the network.

   Ideally, the net effect of the presence of DetNet streams in a
   network on the non-DetNet packets is primarily a reductoin in the
   available bandwidth.

4.9.  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
   providing 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 disabling the offending packet,
   shutting down the offending DetNet stream, or shutting down the
   offending interface.

   It is also essential that filters and service remarking be employed
   to prevent non-DetNet packets from impinging on the resources
   allocated to DetNet packets.



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   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 systemd will have zero
   impact on well-behaved DetNet streams, except of course, for the
   receiving interface(s) immediately downstream of the misbehaving
   device.

4.10.  Protocol Stack Model

   This section will be further developed.  See [IEEE802.1CB], Annex C,
   for a description of the protocol stack.  This is very much a work in
   progress, not a standard.  See also [IEEE802.1Qcc].

4.11.  Advertising resources, capabilities and adjacencies

4.12.  Provisioning model

4.12.1.  Centralized Path Computation and Installation

   A centralized routing model, such as provided with a PCE (RFC 4655
   [RFC4655]), enables global and per-stream optimizations.  The model
   is attractive but a number of issues are left to be solved.  In
   particular:

   o  whether and how the path computation can be installed by 1) an end
      device or 2) a Network Management entity,

   o  and how the path is set up, either by installing state at each hop
      with a direct interaction between the forwarding device and the
      PCE, or along a path by injecting a source-routed request at one
      end of the path.

4.12.2.  Distributed Path Setup

   Whether a distributed alternative without a PCE can be valuable
   should be studied as well.  Such an alternative could for instance
   inherit from the Resource ReSerVation Protocol [RFC5127] (RSVP)
   flows.

   In a Layer-2 only environment, or as part of a layered approach to a
   mixed environment, IEEE 802.1 also has work, either completed or in
   progress.  [IEEE802.1Q-2011] Clause 35 describes SRP, a peer-to-peer
   protocol for Layer-2 roughly analogous to RSVP.  Almost complete is
   [IEEE802.1Qca], which defines how ISIS can provide multiple disjoint
   paths or distribution trees.  Also in progress is [IEEE802.1Qcc],
   which expands the capabilities of SRP.





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5.  Related IETF work

5.1.  Deterministic PHB

   [I-D.svshah-tsvwg-deterministic-forwarding] defines a Differentiated
   Services Per-Hop-Behavior (PHB) Group called Deterministic Forwarding
   (DF).  The document describes the purpose and semantics of this PHB.
   It also describes creation and forwarding treatment of the service
   class.  The document also describes how the code-point can be mapped
   into one of the aggregated Diffserv service classes [RFC5127].

5.2.  6TiSCH

   Industrial process control already leverages deterministic wireless
   Low power and Lossy Networks (LLNs) to interconnect critical
   resource-constrained devices and form wireless mesh networks, with
   standards such as [ISA100.11a] and [WirelessHART].

   These standards rely on variations of the [IEEE802154e] timeSlotted
   Channel Hopping (TSCH) [I-D.ietf-6tisch-tsch] Medium Access Control
   (MAC), and a form of centralized Path Computation Element (PCE), to
   deliver deterministic capabilities.

   The TSCH MAC benefits include high reliability against interference,
   low power consumption on characterized streams, and Traffic
   Engineering capabilities.  Typical applications are open and closed
   control loops, as well as supervisory control streams and management.

   The 6TiSCH Working Group focuses only on the TSCH mode of the IEEE
   802.15.4e standard.  The WG currently defines a framework for
   managing the TSCH schedule.  Future work will standardize
   deterministic operations over so-called tracks as described in
   [I-D.ietf-6tisch-architecture].  Tracks are an instance of a
   deterministic path, and the DetNet work is a prerequisite to specify
   track operations and serve process control applications.

   [RFC5673] and [I-D.ietf-roll-rpl-industrial-applicability] section
   2.1.3.  and next discusses application-layer paradigms, such as
   Source-sink (SS) that is a Multipeer to Multipeer (MP2MP) model that
   is primarily used for alarms and alerts, Publish-subscribe (PS, or
   pub/sub) that is typically used for sensor data, as well as Peer-to-
   peer (P2P) and Peer-to-multipeer (P2MP) communications.  Additional
   considerations on Duocast and its N-cast generalization are also
   provided for improved reliability.







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6.  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 bizarre
   errors such as can be coused by software failures.  Because there is
   essentiall 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 4.9.

   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 streams

7.  IANA Considerations

   This document does not require an action from IANA.

8.  Acknowledgements

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

9.  Informative References

   [AVnu]     http://www.avnu.org/, "The AVnu Alliance tests and
              certifies devices for interoperability, providing a simple
              and reliable networking solution for AV network
              implementation based on the Audio Video Bridging (AVB)
              standards.", .




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   [CCAMP]    IETF, "Common Control and Measurement Plane",
              <https://datatracker.ietf.org/doc/charter-ietf-ccamp/>.

   [HART]     www.hartcomm.org, "Highway Addressable Remote Transducer,
              a group of specifications for industrial process and
              control devices administered by the HART Foundation", .

   [HSR-PRP]  IEC, "High availability seamless redundancy (HSR) is a
              further development of the PRP approach, although HSR
              functions primarily as a protocol for creating media
              redundancy while PRP, as described in the previous
              section, creates network redundancy.  PRP and HSR are both
              described in the IEC 62439 3 standard.",
              <http://webstore.iec.ch/webstore/webstore.nsf/
              artnum/046615!opendocument>.

   [I-D.finn-detnet-problem-statement]
              Finn, N. and P. Thubert, "Deterministic Networking Problem
              Statement", draft-finn-detnet-problem-statement-01 (work
              in progress), October 2014.

   [I-D.ietf-6tisch-architecture]
              Thubert, P., Watteyne, T., Struik, R., and M. Richardson,
              "An Architecture for IPv6 over the TSCH mode of IEEE
              802.15.4e", draft-ietf-6tisch-architecture-05 (work in
              progress), January 2015.

   [I-D.ietf-6tisch-tsch]
              Watteyne, T., Palattella, M., and L. Grieco, "Using
              IEEE802.15.4e TSCH in an IoT context: Overview, Problem
              Statement and Goals", draft-ietf-6tisch-tsch-05 (work in
              progress), January 2015.

   [I-D.ietf-roll-rpl-industrial-applicability]
              Phinney, T., Thubert, P., and R. Assimiti, "RPL
              applicability in industrial networks", draft-ietf-roll-
              rpl-industrial-applicability-02 (work in progress),
              October 2013.

   [I-D.svshah-tsvwg-deterministic-forwarding]
              Shah, S. and P. Thubert, "Deterministic Forwarding PHB",
              draft-svshah-tsvwg-deterministic-forwarding-03 (work in
              progress), March 2015.

   [IEEE802.1AS-2011]
              IEEE, "Timing and Synchronizations (IEEE 802.1AS-2011)",
              2011, <http://standards.ieee.org/getIEEE802/
              download/802.1AS-2011.pdf>.



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   [IEEE802.1BA-2011]
              IEEE, "AVB Systems (IEEE 802.1BA-2011)", 2011,
              <http://standards.ieee.org/getIEEE802/
              download/802.1BA-2011.pdf>.

   [IEEE802.1CB]
              IEEE, "Seamless Redundancy (IEEE Draft P802.1CB)", 2015,
              <http://p8021:go_wildcats@www.ieee802.org/1/files/private/
              cb-drafts/>.

   [IEEE802.1Q-2011]
              IEEE, "MAC Bridges and VLANs (IEEE 802.1Q-2011", 2011,
              <http://standards.ieee.org/getIEEE802/
              download/802.1Q-2011.pdf>.

   [IEEE802.1Qat-2010]
              IEEE, "Stream Reservation Protocol (IEEE 802.1Qat-2010)",
              2010, <http://standards.ieee.org/getIEEE802/
              download/802.1Qat-2010.pdf>.

   [IEEE802.1Qav]
              IEEE, "Forwarding and Queuing (IEEE 802.1Qav-2009)", 2009,
              <http://standards.ieee.org/getIEEE802/
              download/802.1Qav-2009.pdf>.

   [IEEE802.1Qca]
              IEEE, "Path Control and Reservation", 2015,
              <http://p8021:go_wildcats@www.ieee802.org/1/files/private/
              ca-drafts/>.

   [IEEE802.1Qcc]
              IEEE, "Stream Reservation Protocol (SRP) Enhancements and
              Performance Improvements", 2015,
              <http://p8021:go_wildcats@www.ieee802.org/1/files/private/
              cc-drafts/>.

   [IEEE802.1TSNTG]
              IEEE Standards Association, "IEEE 802.1 Time-Sensitive
              Networks Task Group", 2013,
              <http://www.IEEE802.org/1/pages/avbridges.html>.

   [IEEE802154]
              IEEE standard for Information Technology, "IEEE std.
              802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
              and Physical Layer (PHY) Specifications for Low-Rate
              Wireless Personal Area Networks", June 2011.





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   [IEEE802154e]
              IEEE standard for Information Technology, "IEEE std.
              802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area
              Networks (LR-WPANs) Amendment 1: MAC sublayer", April
              2012.

   [ISA100.11a]
              ISA/IEC, "ISA100.11a, Wireless Systems for Automation,
              also IEC 62734", 2011, < http://www.isa100wci.org/en-
              US/Documents/PDF/3405-ISA100-WirelessSystems-Future-broch-
              WEB-ETSI.aspx>.

   [ODVA]     http://www.odva.org/, "The organization that supports
              network technologies built on the Common Industrial
              Protocol (CIP) including EtherNet/IP.", .

   [PCE]      IETF, "Path Computation Element",
              <https://datatracker.ietf.org/doc/charter-ietf-pce/>.

   [Profinet]
              http://us.profinet.com/technology/profinet/, "PROFINET is
              a standard for industrial networking in automation.",
              <http://us.profinet.com/technology/profinet/>.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

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

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

   [RFC5127]  Chan, K., Babiarz, J., and F. Baker, "Aggregation of
              Diffserv Service Classes", RFC 5127, February 2008.

   [RFC5673]  Pister, K., Thubert, P., Dwars, S., and T. Phinney,
              "Industrial Routing Requirements in Low-Power and Lossy
              Networks", RFC 5673, October 2009.

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







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

   [TEAS]     IETF, "Traffic Engineering Architecture and Signaling",
              <https://datatracker.ietf.org/doc/charter-ietf-teas/>.

   [WirelessHART]
              www.hartcomm.org, "Industrial Communication Networks -
              Wireless Communication Network and Communication Profiles
              - WirelessHART - IEC 62591", 2010.

Authors' Addresses

   Norm Finn
   Cisco Systems
   170 W Tasman Dr.
   San Jose, California  95134
   USA

   Phone: +1 408 526 4495
   Email: nfinn@cisco.com


   Pascal Thubert
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue de Roumanille
   Batiment T3
   Biot - Sophia Antipolis  06410
   FRANCE

   Phone: +33 4 97 23 26 34
   Email: pthubert@cisco.com
















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