Deterministic Networking Problem Statement

detnet                                                           N. Finn
Internet-Draft                                                    Huawei
Intended status: Informational                                P. Thubert
Expires: March 20, 2018                                            Cisco
                                                      September 16, 2017

               Deterministic Networking Problem Statement


   This paper documents the needs in various industries to establish
   multi-hop paths for characterized flows with deterministic properties

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   This Internet-Draft will expire on March 20, 2018.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  On Deterministic Networking . . . . . . . . . . . . . . . . .   3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Supported topologies  . . . . . . . . . . . . . . . . . .   6
     3.2.  Flow Characterization . . . . . . . . . . . . . . . . . .   6
     3.3.  Centralized Path Computation and Installation . . . . . .   6
     3.4.  Distributed Path Setup  . . . . . . . . . . . . . . . . .   7
     3.5.  Duplicated data format  . . . . . . . . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Deterministic Networking Use Cases [I-D.ietf-detnet-use-cases]
   document illustrates that beyond the classical case of industrial
   automation and control systems (IACS), there are in fact multiple
   industries with strong and yet relatively similar needs for
   deterministic network services with latency guarantees and ultra-low
   packet loss.

   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) [IEEE802.1TSNTG] 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, IACS segregates the network along the
   broad lines of the Purdue Enterprise Reference Architecture (PERA)
   [ISA95], typically using deterministic local area networks for level
   2 control systems, whereas public infrastructures such as Electricity
   Automation require deterministic properties over the Wide Area.  The
   realization is now coming that the convergence of IT and Operational
   Technology (OT) networks requires Layer-3, as well as Layer-2,

   While the initial user base has focused almost entirely on Ethernet
   physical media and Ethernet-based bridging protocol (from several
   Standards Development Organizations), the need for Layer-3 expressed
   above, must not be confined to Ethernet and Ethernet-like media, and
   while such media must be encompassed by any useful DetNet
   architecture, cooperation between IETF and other SDOs must not be
   limited to IEEE or IEEE 802.  Furthermore, while the work completed

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   and ongoing in other SDOs, and in IEEE 802 in particular, provide an
   obvious starting point for a DetNet architecture, we must not assume
   that these other SDOs' work confines the space in which the DetNet
   architecture progresses.

   The properties of deterministic networks will have specific
   requirements for the use of routed networks to support these
   applications and a new model must be proposed to integrate
   determinism in IT technology.  The proposed model should enable a
   fully scheduled operation orchestrated by a central controller, and
   may support a more distributed operation with probably lesser
   capabilities.  In any fashion, the model should not compromise the
   ability of a network to keep carrying the sorts of traffic that is
   already carried today in conjunction with new, more deterministic

   Once the abstract model is agreed upon, the IETF will need to specify
   the signaling elements to be used to establish a path and the tagging
   elements to be used identify the flows that are to be forwarded along
   that path.  The IETF will also need to specify the necessary
   protocols, or protocol additions, based on relevant IETF
   technologies, to implement the selected model.

   As a result of this work, it will be possible to establish a multi-
   hop path over the IP network, for a particular flow with given timing
   and precise throughput requirements, and carry this particular flow
   along the multi-hop path with such characteristics as low latency and
   ultra-low jitter, duplication and elimination of packets over non-
   congruent paths for a higher delivery ratio, and/or zero congestion
   loss, regardless of the amount of other flows in the network.

   Depending on the network capabilities and on the current state,
   requests to establish a path by an end-node or a network management
   entity may be granted or rejected, an existing path may be moved or
   removed, and DetNet flows exceeding their contract may face packet
   declassification and drop.

2.  On Deterministic Networking

   The Internet is not the only digital network that has grown
   dramatically over the last 30-40 years.  Video and audio
   entertainment, and control systems for machinery, manufacturing
   processes, and vehicles are also ubiquitous, and are now based almost
   entirely on digital technologies.  Over the past 10 years, engineers
   in these fields have come to realize that significant advantages in
   both cost and in the ability to accelerate growth can be obtained by
   basing all of these disparate digital technologies on packet

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   The goals of Deterministic Networking are to enable the migration of
   applications that use special-purpose fieldbus technologies (HDMI,
   CANbus, ProfiBus, etc... even RS-232!) to packet technologies in
   general, and the Internet Protocol in particular, and to support both
   these new applications, and existing packet network applications,
   over the same physical network.

   Considerable experience ([ODVA]/[EIP],[AVnu],
   [Profinet],[HART],[IEC62439], [ISA100.11a] and [WirelessHART],
   etc...) has shown that these applications need a some or all of a
   suite of features that includes:

   1.  Time synchronization of all host and network nodes (routers and/
       or bridges), accurate to something between 10 nanoseconds and 10
       microseconds, depending on the application.

   2.  Support for critical packet flows that:

       *  Can be unicast or multicast;

       *  Need absolute guarantees of minimum and maximum latency end-
          to-end across the network; sometimes a tight jitter is
          required as well;

       *  Need a packet loss ratio beyond the classical range for a
          particular medium, in the range of 1.0e-9 to 1.0e-12, or
          better, on Ethernet, and in the order of 1.0e-5 in Wireless
          Sensor mesh Networks;

       *  Can, in total, absorb more than half of the network's
          available bandwidth (that is, massive over-provisioning is
          ruled out as a solution);

       *  Cannot suffer throttling, congestion feedback, or any other
          network-imposed transmission delay, although the flows can be
          meaningfully characterized either by a fixed, repeating
          transmission schedule, or by a maximum bandwidth and packet

   3.  Multiple methods to schedule, shape, limit, and otherwise control
       the transmission of critical packets at each hop through the
       network data plane;

   4.  Robust defenses against misbehaving hosts, routers, or bridges,
       both in the data and control planes, with guarantees that a
       critical flow within its guaranteed resources cannot be affected
       by other flows whatever the pressures on the network;

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   5.  One or more methods to reserve resources in bridges and routers
       to carry these flows.

   Time synchronization techniques need not be addressed by an IETF
   Working Group; there are a number of standards available for this
   purpose, including IEEE 1588, IEEE 802.1AS, and more.

   The multicast, latency, loss ratio, and non-throttling needs are made
   necessary by the algorithms employed by the applications.  They are
   not simply the transliteration of fieldbus needs to a packet-based
   fieldbus simulation, but reflect fundamental mathematics of the
   control of a physical system.

   With classical forwarding latency- and loss-sensitive packets across
   a network, interactions among different critical flows introduce
   fundamental uncertainties in delivery schedules.  The details of the
   queuing, shaping, and scheduling algorithms employed by each bridge
   or router to control the output sequence on a given port affect the
   detailed makeup of the output stream, e.g. how finely a given flow's
   packets are mixed among those of other flows.

   This, in turn, has a strong effect on the buffer requirements, and
   hence the latency guarantees deliverable, by the next bridge or
   router along the path.  For this reason, the IEEE 802.1 Time-
   Sensitive Networking Task Group has defined a new 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 flow
   or class of flows.

   Robustness is a common need for networking protocols, but plays a
   more important part in real-time control networks, where expensive
   equipment, and even lives, can be lost due to misbehaving equipment.

   Reserving resources before packet transmission is the one fundamental
   shift in the behavior of network applications that is impossible to
   avoid.  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 un-throttled
   (though bandwidth limited) flows means that bridges and routers have
   to dedicate buffer resources to specific flows or to classes of
   flows.  The requirements of each reservation have to be translated
   into the parameters that control each host's, bridge's, and router's
   queuing, shaping, and scheduling functions and delivered to the
   hosts, bridges, and routers.

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3.  Problem Statement

3.1.  Supported topologies

   In some use cases, the end point which run the application is
   involved in the deterministic networking operation, for instance by
   controlling certain aspects of its throughput such as rate or precise
   time of emission.  In that case, the deterministic path is end-to-end
   from application host to application host.

   On the other end, the deterministic portion of a path may be a tunnel
   between and ingress and an egress router.  In any case, routers and
   switches in between should not need to be aware whether the path is
   end-to-end of a tunnel.

   While it is clear that DetNet does not aim at setting up
   deterministic paths over the global Internet, there is still a lack
   of clarity on the limits of a domain where a deterministic path can
   be set up.  These limits may depend in the technology that is used to
   seu th epath up, whether it is centralized or distributed.

3.2.  Flow Characterization

   Deterministic forwarding can only apply on flows with well-defined
   characteristics such as periodicity and burstiness.  Before a path
   can be established to serve them, the expression of those
   characteristics, and how the network can serve them, for instance in
   shaping and forwarding operations, must be specified.

3.3.  Centralized Path Computation and Installation

   A centralized routing model, such as provided with a PCE, enables
   global and per-flow 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 following classical Traffic Engineering (TE)

   To enable a centralized model, DetNet should produce the complete SDN
   architecture with describes at a high level the interaction and data
   models to:

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   o  report the topology and device capabilities to the central

   o  establish a direct interface between the centralized PCE to each
      device under its control in order to enable a vertical signaling

   o  request a path setup for a new flow with particular
      characteristics over the service interface and control it through
      its life cycle;

   o  support for life cycle management for a path

   o  support for adaptability to cope with various events such as loss
      of a link, etc...

   o  expose the status of the path to the end devices (UNI interface)

   o  provide additional reliability through redundancy, in particular
      with packet replication and elimination;

   o  indicate the flows and packet sequences in-band with the flows;

3.4.  Distributed Path Setup

   Whether a distributed alternative without a PCE can be valuable could
   be studied as well.  Such an alternative could for instance inherit
   from the Resource ReSerVation Protocol [RFC3209] (RSVP-TE) flows.
   But the focus of the work should be to deliver the centralized
   approach first.

   To enable a RSVP-TE like functionality, the following steps would
   take place:

   1.  Neighbors and their capabilities are discovered and exposed to
       compute a path that fits the DetNet constraints, typically of
       latency, time precision and resource availability.

   2.  A constrained path is calculated with an improved version of CSPF
       that is aware of DetNet.

   3.  The path is installed using RSVP-TE, associated with flow
       identification, per-hop behavior such as replication and
       elimination, blocked resources, and flow timing information.

   4.  Traffic flows are transported through the MPLS-TE tunnel, using
       the reserved resources for this flow at each hop.

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3.5.  Duplicated data format

   In some cases the duplication and elimination of packets over non-
   congruent paths is required to achieve a sufficiently high delivery
   ratio to meet application needs.  In these cases, a small number of
   packet formats and supporting protocols are required (preferably,
   just one) to serialize the packets of a DetNet stream at one point in
   the network, replicate them at one or more points in the network, and
   discard duplicates at one or more other points in the network,
   including perhaps the destination host.  Using an existing solution
   would be preferable to inventing a new one.

4.  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.

   Typical control networks today rely on complete physical isolation to
   prevent rogue access to network resources.  DetNet enables the
   virtualization of those networks over a converged IT/OT
   infrastructure.  Doing so, DetNet introduces an additional risk that
   flows interact and interfere with one another as they share physical
   resources such as Ethernet trunks and radio spectrum.  The
   requirement is that there is no possible data leak from and into a
   deterministic flow, and in a more general fashion there is no
   possible influence whatsoever from the outside on a deterministic
   flow.  The expectation is that physical resources are effectively
   associated with a given flow at a given point of time.  In that
   model, Time Sharing of physical resources becomes transparent to the
   individual flows which have no clue whether the resources are used by
   other flows at other times.

   Security must cover:

   o  the protection of the signaling protocol

   o  the authentication and authorization of the controlling nodes

   o  the identification and shaping of the flows

   o  the isolation of flows from leakage and other influences from any
      activity sharing physical resources.

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5.  IANA Considerations

   This document does not require an action from IANA.

6.  Acknowledgments

   The authors wish to thank Lou Berger, 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, Patrick
   Wetterwald, Subha Dhesikan, Rudy Klecka and Pat Thaler for their
   various contribution to this work.

7.  Informative References

   [AVnu], "The AVnu Alliance tests and
              certifies devices for interoperability, providing a simple
              and reliable networking solution for AV network
              implementation based on the IEEE Audio Video Bridging
              (AVB) and Time-Sensitive Networking (TSN) standards.".

   [EIP], "EtherNet/IP provides users with the
              network tools to deploy standard Ethernet technology (IEEE
              802.3 combined with the TCP/IP Suite) for industrial
              automation applications while enabling Internet and
              enterprise connectivity data anytime, anywhere.",

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

              Grossman, E., Gunther, C., Thubert, P., Wetterwald, P.,
              Raymond, J., Korhonen, J., Kaneko, Y., Das, S., Zha, Y.,
              Varga, B., Farkas, J., Goetz, F., Schmitt, J., Vilajosana,
              X., Mahmoodi, T., Spirou, S., and P. Vizarreta,
              "Deterministic Networking Use Cases", draft-ietf-detnet-
              use-cases-12 (work in progress), April 2017.

              IEC, "Industrial communication networks - High
              availability automation networks - Part 3: Parallel
              Redundancy Protocol (PRP) and High-availability Seamless
              Redundancy (HSR) - IEC62439-3", 2012,

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

              ISA/IEC, "ISA100.11a, Wireless Systems for Automation,
              also IEC 62734", 2011, <

   [ISA95]    ANSI/ISA, "Enterprise-Control System Integration Part 1:
              Models and Terminology", 2000,

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

    , "PROFINET is
              a standard for industrial networking in automation.",

   [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,

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

    , "Industrial Communication Networks -
              Wireless Communication Network and Communication Profiles
              - WirelessHART - IEC 62591", 2010.

Authors' Addresses

   Norman Finn
   3101 Rio Way
   Spring Valley, California  91977

   Phone: +1 925 980 6430

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   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

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