detnet                                                           N. Finn
Internet-Draft                                                P. Thubert
Intended status: Standards Track                                   Cisco
Expires: April 26, 2015                                 October 23, 2014

               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 April 26, 2015.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  On Deterministic Networking . . . . . . . . . . . . . . . . .   4
   4.  Related IETF work . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Deterministic PHB . . . . . . . . . . . . . . . . . . . .   6
     4.2.  6TiSCH  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Flow Characterization . . . . . . . . . . . . . . . . . .   7
     5.2.  Centralized Path Computation and Installation . . . . . .   7
     5.3.  Distributed Path Setup  . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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
   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

   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

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   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 guaranteed 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
   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.

   In order to serve this extended requirement, the IETF and the IEEE
   must collaborate and define an abstract model that can be applicable
   both at Layer-2 and Layer-3, and along segments of different
   technologies.  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 IEEE802.1 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
   IEEE802.15.4e MAC.

   The proposed model should enable a fully scheduled operation
   orchestrated by a central controller, as well as 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.

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   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
   such as PCE, MPLS and 6TiSCH, 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 precise timing
   and 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.
   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, and an existing path may be moved
   or removed.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  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

   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],[AVnu], [Profinet],[HSR-PRP],
   etc...) has shown that these applications need a some or all of a
   suite of features that includes:

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   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;

       *  Need a packet loss ratio in the range of 1.0e-9 to 1.0e-12, or

       *  Can, in total, absorb more than half of the network's
          available bandwidth (that is, 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.

   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.

   When 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

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   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 set of queuing,
   shaping, and scheduling algorithms (:::reference to section, below
   :::) that enable each bridge or router to compute the exact number of
   buffers to be allocated for each flow or class of flows.  The present
   authors assume that these techniques will be used by the DetNet
   Working Group.

   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 unthrottled
   (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.

4.  Related IETF work

4.1.  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].

4.2.  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].

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   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 flows, and Traffic Engineering
   capabilities.  Typical applications are open and closed control
   loops, as well as supervisory control flows and management.

   The 6TiSCH Working Group focuses only on the TSCH mode of the
   IEEE802.15.4e 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.

5.  Problem Statement

5.1.  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.

5.2.  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

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      PCE, or along a path by injecting a source-routed request at one
      end of the path.

5.3.  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)

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.

   Security must cover:

   o  the protection of the signaling protocol

   o  the authentication and authorisation of the controlling nodes

   o  the identification and shaping of the flows

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.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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9.2.  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 Audio Video Bridging (AVB)
              standards.", .

   [HART], "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.", .

              Thubert, P., Watteyne, T., and R. Assimiti, "An
              Architecture for IPv6 over the TSCH mode of IEEE
              802.15.4e", draft-ietf-6tisch-architecture-03 (work in
              progress), July 2014.

              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-02 (work in
              progress), October 2014.

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

              Shah, S. and P. Thubert, "Deterministic Forwarding PHB",
              draft-svshah-tsvwg-deterministic-forwarding-02 (work in
              progress), September 2014.

              IEEE, "Timing and Synchronizations (IEEE 802.1AS-2011)",
              2011, <

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              IEEE, "AVB Systems (IEEE 802.1BA-2011)", 2011,

              IEEE, "MAC Bridges and VLANs (IEEE 802.1Q-2011", 2011,

              IEEE, "Stream Reservation Protocol (IEEE 802.1Qat-2010)",
              2010, <

              IEEE, "Forwarding and Queuing (IEEE 802.1Qav-2009)", 2009,

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

              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.

              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

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

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

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

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

   [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.

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

Authors' Addresses

   Norm Finn
   Cisco Systems
   510 McCarthy Blvd
   Milpitas, California  95035

   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

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