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rfc:rfc8557

Internet Engineering Task Force (IETF) N. Finn Request for Comments: 8557 Huawei Technologies Co. Ltd Category: Informational P. Thubert ISSN: 2070-1721 Cisco

                                                              May 2019
             Deterministic Networking Problem Statement

Abstract

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

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are candidates for any level of Internet
 Standard; see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8557.

Copyright Notice

 Copyright (c) 2019 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Finn & Thubert Informational [Page 1] RFC 8557 Deterministic Networking Problem Statement May 2019

Table of Contents

 1. Introduction ....................................................2
 2. On Deterministic Networking .....................................4
 3. Problem Statement ...............................................6
    3.1. Supported Topologies .......................................6
    3.2. Flow Characterization ......................................6
    3.3. Centralized Path Computation and Installation ..............7
    3.4. Distributed Path Setup .....................................8
    3.5. Duplicated Data Format .....................................8
 4. Security Considerations .........................................9
 5. IANA Considerations .............................................9
 6. Informative References .........................................10
 Acknowledgments ...................................................11
 Authors' Addresses ................................................11

1. Introduction

 "Deterministic Networking Use Cases" [RFC8578] illustrates that
 beyond the classical case of Industrial Automation and Control
 Systems (IACSs) there are in fact multiple industries with strong,
 and relatively similar, needs for deterministic network services with
 latency guarantees and ultra-low packet loss.
 The generalization of the needs for more deterministic networks has
 led to the IEEE 802.1 Audio Video Bridging (AVB) Task Group becoming
 the Time-Sensitive Networking (TSN) [IEEE-802.1TSNTG] Task Group
 (TG), with a much-expanded constituency from the industrial and
 vehicular markets.
 Along with this expansion, the networks considered here are becoming
 larger and structured, requiring deterministic forwarding beyond the
 LAN boundaries.  For instance, an IACS segregates the network along
 the broad lines of the Purdue Enterprise Reference Architecture
 (PERA) [ISA95], typically using deterministic LANs for Purdue level 2
 control systems, whereas public infrastructures such as electricity
 automation require deterministic properties over the wide area.
 Implementers have come to realize that the convergence of IT and
 Operation Technology (OT) networks requires Layer 3, as well as
 Layer 2, capabilities.
 While the initial user base has focused almost entirely on Ethernet
 physical media and Ethernet-based bridging protocols from several
 Standards Development Organizations (SDOs), the need for Layer 3, as
 expressed above, must not be confined to Ethernet and Ethernet-like
 media.  While such media must be encompassed by any useful
 Deterministic Networking (DetNet) architecture, cooperation between
 the IETF and other SDOs must not be limited to the IEEE or the

Finn & Thubert Informational [Page 2] RFC 8557 Deterministic Networking Problem Statement May 2019

 IEEE 802 organizations.  Furthermore, while both completed and
 ongoing work in other SDOs, and in IEEE 802 in particular, provides
 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 this
 determinism in IT implementations.  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.  At any rate, 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
 flows.  Note: "Deterministic Networking Architecture" [DetNet-Arch]
 was produced by the DetNet Working Group to describe that model.
 At the time of this writing, it is expected that
 o  once the abstract model is agreed upon, the IETF will specify
    (1) the signaling elements to be used to establish a path and
    (2) the tagging elements to be used to identify the flows that are
    to be forwarded along that path
 o  the IETF will specify the necessary protocols or protocol
    additions, based on relevant IETF technologies, to implement the
    selected model
 A desirable outcome of the work is the ability to establish a
 multi-hop path over the IP or MPLS network for a particular flow with
 given timing and precise throughput requirements and to carry this
 particular flow along the multi-hop path with such characteristics as
 low latency and ultra-low jitter, reordering and/or replication 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 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.

Finn & Thubert Informational [Page 3] RFC 8557 Deterministic Networking Problem Statement May 2019

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, as well as 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 the ability to accelerate
 growth can be obtained by basing all of these disparate digital
 technologies on packet networks.
 The goals of Deterministic Networking are to (1) enable the migration
 of applications with critical timing and reliability issues that
 currently use special-purpose fieldbus technologies (High-Definition
 Multimedia Interface (HDMI), Controller Area Network (CAN bus),
 PROFIBUS [PROFIBUS], etc. ... even RS-232!) to packet technologies in
 general and to IP in particular and (2) support both these new
 applications and existing packet network applications over the same
 physical network.  In other words, a deterministic network is
 backwards compatible with (capable of transporting) statistically
 multiplexed traffic while preserving the properties of the accepted
 deterministic flows.
 [RFC8578] indicates that applications in multiple fields need 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 deterministic 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 10^-9 to 10^-12 or better

        on Ethernet and on the order of 10^-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).

Finn & Thubert Informational [Page 4] RFC 8557 Deterministic Networking Problem Statement May 2019

  • Cannot suffer throttling, congestion feedback, or any other

network-imposed transmission delay, although the flows can be

        meaningfully characterized by either (1) a fixed, repeating
        transmission schedule or (2) a maximum bandwidth and packet
        size.
 3.  Multiple methods for scheduling, shaping, limiting, and otherwise
     controlling the transmission of critical packets at each hop
     through the network data plane.
 4.  Robust defenses against misbehaving hosts, routers, or bridges,
     in both the data plane and the control plane, with guarantees
     that a critical flow within its guaranteed resources cannot be
     affected by other flows, whatever the pressures on the network.
     For more on the specific threats against DetNet, see
     "Deterministic Networking (DetNet) Security Considerations"
     [DetNet-Security].
 5.  One or more methods for reserving 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-1588], IEEE 802.1AS [IEEE-8021AS],
 and more.
 The needs related to multicast, latency, loss ratio, and throttling
 avoidance exist because the algorithms employed by the applications
 demand it.  They are not simply the transliteration of fieldbus needs
 to a packet-based fieldbus simulation; they also reflect fundamental
 mathematics of the control of a physical system.
 With classical forwarding of latency-sensitive 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 TSN TG 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.

Finn & Thubert Informational [Page 5] RFC 8557 Deterministic Networking Problem Statement May 2019

 Networking protocols commonly need robustness.  Note that robustness
 plays a particularly 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 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.

3. Problem Statement

3.1. Supported Topologies

 In some use cases, the end point that runs 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 such a 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 an ingress point and an egress router.  In any case, routers
 and switches in between should not need to be aware of whether the
 path is end to end or a tunnel.
 While it is clear that DetNet does not aim to set up deterministic
 paths over the global Internet, there is still a lack of clarity
 regarding the limits of a domain where a deterministic path can be
 set up.  These limits may depend on the technology that is used to
 set the path up, whether it is centralized or distributed.

3.2. Flow Characterization

 Deterministic forwarding can only apply to flows with such
 well-defined characteristics 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.

Finn & Thubert Informational [Page 6] RFC 8557 Deterministic Networking Problem Statement May 2019

3.3. Centralized Path Computation and Installation

 A centralized routing model, such as that provided with a Path
 Computation Element (PCE) (see [RFC4655]), enables global and
 per-flow optimizations.  This type of model is attractive, but a
 number of issues remain to be solved -- in particular:
 o  whether and how the path computation can be installed by
  • an end device or
  • a network management entity
    and
 o  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) models

 To enable a centralized model, DetNet should produce a description of
 the high-level interaction and data models to:
 o  report the topology and device capabilities to the central
    controller
 o  establish a direct interface between the centralized PCE and each
    device under its control in order to enable 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  provide support for life-cycle management for a path
    (instantiate/modify/update/delete)
 o  provide support for adaptability to cope with such various events
    as loss of a link
 o  expose the status of the path to the end devices (User-Network
    Interfaces (UNIs))

Finn & Thubert Informational [Page 7] RFC 8557 Deterministic Networking Problem Statement May 2019

 o  provide additional reliability through redundancy, particularly
    with Packet Replication, Elimination, and Ordering Functions
    (PREOF), where redundant paths may deliver packets out of order
    and PREOF may need to correct the ordering
 o  indicate the flows and packet sequences in-band with the flows.
    This is needed for flows that require PREOF in order to isolate
    duplicates and reorder packets at the end of the sequence

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, build
 upon Resource Reservation Protocol - TE (RSVP-TE) flows [RFC3209].
 But the focus of the work should be to deliver the centralized
 approach first.
 To enable functionality similar to that of RSVP-TE, the following
 steps would take place:
 1.  Neighbors and their capabilities would be discovered and exposed
     to compute a path that would fit the DetNet constraints --
     typically those of latency, time precision, and resource
     availability.
 2.  A constrained path would be calculated with an improved version
     of Constrained Shortest Path First (CSPF) that is aware of
     DetNet.
 3.  The path may be installed using a control protocol such as
     RSVP-TE, extended to enable flow identification and install new
     per-hop behavior such as Packet Replication, Elimination, and
     Ordering, and to reserve physical resources for the flow.  In
     that case, traffic flows could be transported through an MPLS-TE
     tunnel, using the reserved resources for this flow at each hop.

3.5. Duplicated Data Format

 In some cases, the duplication and elimination of packets over
 non-congruent paths are 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 of each) 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.

Finn & Thubert Informational [Page 8] RFC 8557 Deterministic Networking Problem Statement May 2019

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 of
 flows interacting and interfering with one another as they share
 physical resources such as Ethernet trunks and the radio spectrum.
 The requirement is that there is no possible data leak from and into
 a deterministic flow.  Stated more generally, 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 in time.  In that model, the
 time-sharing of physical resources becomes transparent to the
 individual flows, as these flows have no clue regarding whether or
 not the resources are used by other flows at other times.
 The overall security of a deterministic system must cover:
 o  the protection of the signaling protocol
 o  the authentication and authorization of the controlling nodes,
    including plug-and-play participating end systems
 o  the identification and shaping of the flows
 o  the isolation of flows from leakage and other influences from any
    activity sharing physical resources
 The specific threats against DetNet are further discussed in
 [DetNet-Security].

5. IANA Considerations

 This document has no IANA actions.

Finn & Thubert Informational [Page 9] RFC 8557 Deterministic Networking Problem Statement May 2019

6. Informative References

 [DetNet-Arch]
            Finn, N., Thubert, P., Varga, B., and J. Farkas,
            "Deterministic Networking Architecture", Work in
            Progress, draft-ietf-detnet-architecture-13, May 2019.
 [DetNet-Security]
            Mizrahi, T., Grossman, E., Ed., Hacker, A., Das, S.,
            Dowdell, J., Austad, H., Stanton, K., and N. Finn,
            "Deterministic Networking (DetNet) Security
            Considerations", Work in Progress,
            draft-ietf-detnet-security-04, March 2019.
 [IEEE-1588]
            IEEE, "IEEE Standard for a Precision Clock Synchronization
            Protocol for Networked Measurement and Control Systems",
            IEEE Standard 1588-2008, <https://standards.ieee.org/
            findstds/standard/1588-2008.html>.
 [IEEE-802.1TSNTG]
            IEEE Standards Association, "IEEE 802.1 Time-Sensitive
            Networking Task Group",
            <http://www.ieee802.org/1/pages/avbridges.html>.
 [IEEE-8021AS]
            IEEE, "IEEE Standard for Local and Metropolitan Area
            Networks - Timing and Synchronization for Time-Sensitive
            Applications in Bridged Local Area Networks",
            IEEE 802.1AS-2011,
            <http://www.ieee802.org/1/pages/802.1as.html>.
 [ISA95]    ANSI/ISA, "Enterprise-Control System Integration - Part 1:
            Models and Terminology", <https://www.isa.org/isa95/>.
 [PROFIBUS] IEC, "PROFIBUS Standard - DP Specification (IEC 61158
            Type 3)", <https://www.profibus.com/>.
 [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,
            <https://www.rfc-editor.org/info/rfc3209>.
 [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
            Computation Element (PCE)-Based Architecture", RFC 4655,
            DOI 10.17487/RFC4655, August 2006,
            <https://www.rfc-editor.org/info/rfc4655>.

Finn & Thubert Informational [Page 10] RFC 8557 Deterministic Networking Problem Statement May 2019

 [RFC7384]  Mizrahi, T., "Security Requirements of Time Protocols in
            Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
            October 2014, <https://www.rfc-editor.org/info/rfc7384>.
 [RFC8578]  Grossman, E., Ed., "Deterministic Networking Use Cases",
            RFC 8578, DOI 10.17487/RFC8578, May 2019,
            <https://www.rfc-editor.org/info/rfc8578>.

Acknowledgments

 The authors wish to thank Lou Berger, Pat Thaler, Jouni Korhonen,
 Janos Farkas, Stewart Bryant, Andrew Malis, Ethan Grossman, Patrick
 Wetterwald, Subha Dhesikan, Matthew Miller, Erik Nordmark, George
 Swallow, Rodney Cummings, Ines Robles, Shwetha Bhandari, Rudy Klecka,
 Anca Zamfir, David Black, Thomas Watteyne, Shitanshu Shah, Kiran
 Makhijani, Craig Gunther, Warren Kumari, Wilfried Steiner, Marcel
 Kiessling, Karl Weber, Alissa Cooper, and Benjamin Kaduk for their
 various contributions to this work.

Authors' Addresses

 Norman Finn
 Huawei Technologies Co. Ltd
 3755 Avocado Blvd.
 PMB 436
 La Mesa, California  91941
 United States of America
 Phone: +1 925 980 6430
 Email: norman.finn@mail01.huawei.com
 Pascal Thubert
 Cisco Systems, Inc.
 Building D, 45 Allee des Ormes - BP1200
 Mougins - Sophia Antipolis  06254
 France
 Phone: +33 4 97 23 26 34
 Email: pthubert@cisco.com

Finn & Thubert Informational [Page 11]

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