Subject: Re: [6tisch] [Detnet] comments on draft-finn-detnet-architecture-00

From: "Norman Finn (nfinn)" <[email-masked]>
Date: Fri, 3 Apr 2015 21:45:22 +0000

Thanks, Thomas.  I tend to agree with Pascal to leave that to 6TiSCH.

— Norm

From: Thomas Watteyne <[email-masked]<mailto:[email-masked]>>
Date: Monday, March 23, 2015 at 09:44 AM
To: "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>
Subject: [Detnet] comments on draft-finn-detnet-architecture-00

Norm, Pascal,

Please find below a number of comment on draft-finn-detnet-architecture-00.

Overall, the draft is very well written and highlights important points for deterministic networking.

My general comments are:
- in the context of a low-power wireless network (e.g. 6TiSCH), I wonder what you thoughts are on reserving a fixed path. Maybe some extra text on redundancy is needed?
- would it make sense to discuss the difference between hard and soft real-time, also wrt wireless systems?

Thomas

---

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.
TW> it looks like you aim for 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
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   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,
TW> define IT and ICT at first use
   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
TW> "on transporting"?
   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.
TW> It might be good to quantify the target latency, packet loss and jitter.
TW> I appreciate this is not easy, but one representatve example might help
   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
TW> ":"
   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.
TW> ensure -> guarantee?

   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
TW> would TTP/C fit in this list?
   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.
TW> typo
   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.
TW> add somethind like "possibly wireless" somewhere?
   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.
TW> why this 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
TW> typo
   special terms are used in this document in order to
   avoid the assumption that a given element in the archetecture
TW> typo
   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:
TW> I don't get the sentence above

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

   circuit
           A trail of configuration from talker to listener(s)
TW> sender and receiver might be more common at the IETF?
           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.

TW> maybe add "layer 2 bridge" and "layer 3 router" for clarity?

   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.
TW> Would it make sense to discuss hard and soft real-time here, in
TW> particular in the context of a wireless system?

   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/
TW> add 6TiSCH cells?
       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)
TW> extra ")"
   , 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.
TW> Using a single path in a wireless system will fail, I would recommend
TW> discussing here path redundancy, for example through DAGs

   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.
TW> and the provision the sufficient link bandwidth?

   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
TW> typo
   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.
TW> this has some energy cost associated?

   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
TW> typo
   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
TW> I don't understand what R and E means

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):
TW> double ":"
   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.

TW> could you define NME, SME and PCE in the terminology?

   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.
TW> how is a packet "labeled" as part of stream?

   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
TW> typo
           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
TW> typo
   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
TW> typo
   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
TW> please define "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
TW> typo
   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
TW> typo
   by software failures.  Because there is
   essentiall
TW> typo
   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<http://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:[email-masked]/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:[email-masked]/1/files/private/
              ca-drafts/>.

   [IEEE802.1Qcc]
              IEEE, "Stream Reservation Protocol (SRP) Enhancements and
              Performance Improvements", 2015,
              <http://p8021:[email-masked]/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<http://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<tel:%2B1%20408%20526%204495>
   Email: [email-masked]<mailto:[email-masked]>

   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<tel:%2B33%204%2097%2023%2026%2034>
   Email: [email-masked]<mailto:[email-masked]>

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---

From: "Patrick Wetterwald (pwetterw)" <[email-masked]>
Date: Thu, 9 Apr 2015 09:03:25 +0000

Norm, Pascal,

Some other comments:

  *   If you look at https://tools.ietf.org/html/draft-wetterwald-detnet-utilities-reqs you will see that for some important use cases, the jitter should very close to zero. In the architecture draft, you are mainly focussing on the maximum value of the latency and the packet loss (at least in the text). This is not sufficient for power automation and tele protection use case. We need to be able to deploy deterministic network with Jitter = 0.
  *   Second: may be good to reference the requirement drafts in the doc. :-)

Thanks,

Patrick

From: Thomas Watteyne <[email-masked]<mailto:[email-masked]>>
Date: Monday 23 March 2015 18:44
To: "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>
Subject: [Detnet] comments on draft-finn-detnet-architecture-00

Norm, Pascal,

My general comments are:

Thomas

---

DetNet                                                           N. Finn

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1.  Introduction

2.  Terminology

   The follwing
TW> typo

   bridge

   circuit

   end system

   listener

   relay system

           A router or a bridge.

   stream

   talker

3.2.  Pinned-down paths

3.3.  Seamless Redundancy

   end    R +                   v | ^                  + E end
   system   +                   v | ^                  +   system

                                 Figure 1

4.  DetNet Architecture

                                 Figure 2

4.3.  The Network Plane

                         Stream Management Entity

       End                                                     End
           System                                               System

                PCE         PCE              PCE              PCE

                  Relay      Relay      Relay      Relay

                                 Figure 3

       3.  hysical
TW> typo

4.5.  DetNet streams

4.5.1.  Talker guarantees

   o  A maximum packet size;

4.9.  Fault Mitigation

4.12.  Provisioning model

5.  Related IETF work

5.1.  Deterministic PHB

5.2.  6TiSCH

   Security must cover:

7.  IANA Considerations

8.  Acknowledgements

   [I-D.ietf-6tisch-tsch]

   [IEEE802.1AS-2011]

   [IEEE802.1BA-2011]

   [IEEE802.1CB]

   [IEEE802.1Q-2011]

   [IEEE802.1Qat-2010]

   [IEEE802.1Qav]

   [IEEE802.1Qca]

   [IEEE802.1Qcc]

   [IEEE802.1TSNTG]

   [IEEE802154]

   [IEEE802154e]

   [ISA100.11a]

   [Profinet]

   [WirelessHART]

Authors' Addresses

   Norm Finn
   Cisco Systems
   170 W Tasman Dr.

   Pascal Thubert
   Cisco Systems

---

From: Qin Wang <[email-masked]>
Date: Thu, 9 Apr 2015 15:09:41 +0000 (UTC)

Hi Patrick,
I don't understand why communication jitter = 0 is so important. Assume DetNet can guarantee the maximum end-to-end latency, and there is a well designed buffer in the Listener device, then I think the Listener can consume data just on time, in another word, from application point of view, jitter =0. Please point out if I'm wrong.
ThanksQin 

     On Thursday, April 9, 2015 5:03 PM, Patrick Wetterwald (pwetterw) <[email-masked]> wrote:

 Norm, Pascal,
Some other comments:
   
   - If you look at https://tools.ietf.org/html/draft-wetterwald-detnet-utilities-reqs you will see that for some important use cases, the jitter should very close to zero. In the architecture draft, you are mainly focussing on the maximum value of the latency and the packet loss (at least in the text). This is not sufficient for power automation and tele protection use case. We need to be able to deploy deterministic network with Jitter = 0.
   - Second: may be good to reference the requirement drafts in the doc. :-)
Thanks,
Patrick

From: Thomas Watteyne <[email-masked]>
Date: Monday 23 March 2015 18:44
To: "[email-masked]" <[email-masked]>, "[email-masked]" <[email-masked]>
Subject: [Detnet] comments on draft-finn-detnet-architecture-00

Norm, Pascal,
Please find below a number of comment on draft-finn-detnet-architecture-00.
Overall, the draft is very well written and highlights important points for deterministic networking.
My general comments are:- in the context of a low-power wireless network (e.g. 6TiSCH), I wonder what you thoughts are on reserving a fixed path. Maybe some extra text on redundancy is needed?- would it make sense to discuss the difference between hard and soft real-time, also wrt wireless systems?
Thomas
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DetNet                                                           N. FinnInternet-Draft                                                P. ThubertIntended status: Standards Track                                   CiscoExpires: 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.TW> it looks like you aim for 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,TW> define IT and ICT at first use   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 transportTW> "on transporting"?   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.TW> It might be good to quantify the target latency, packet loss and jitter.TW> I appreciate this is not easy, but one representatve example might help   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 vehicleTW> ":"   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.TW> ensure -> guarantee?
   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 andTW> would TTP/C fit in this list?   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.TW> typo   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.TW> add somethind like "possibly wireless" somewhere?   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.TW> why this 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 follwingTW> typo   special terms are used in this document in order to   avoid the assumption that a given element in the archetectureTW> typo   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:TW> I don't get the sentence above
   bridge           A Customer Bridge as defined by IEEE 802.1Q           [IEEE802.1Q-2011].
   circuit           A trail of configuration from talker to listener(s)TW> sender and receiver might be more common at the IETF?           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.           TW> maybe add "layer 2 bridge" and "layer 3 router" for clarity?   
   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.TW> Would it make sense to discuss hard and soft real-time here, inTW> particular in the context of a wireless system?   
   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/TW> add 6TiSCH cells?       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)TW> extra ")"   , 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.TW> Using a single path in a wireless system will fail, I would recommendTW> discussing here path redundancy, for example through DAGs
   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.TW> and the provision the sufficient link bandwidth?
   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 periosTW> typo   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.TW> this has some energy cost associated?      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 linksTW> typo   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 1TW> I don't understand what R and E means
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): TW> double ":"   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.

TW> could you define NME, SME and PCE in the terminology?      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.TW> how is a packet "labeled" as part of stream?
   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.  hysicalTW> typo           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 zTW> typo   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 reductoinTW> typo   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 remarkingTW> please define "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 systemdTW> typo   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 cousedTW> typo   by software failures.  Because there is   essentiallTW> typo   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:[email-masked]/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:[email-masked]/1/files/private/              ca-drafts/>.
   [IEEE802.1Qcc]              IEEE, "Stream Reservation Protocol (SRP) Enhancements and              Performance Improvements", 2015,              <http://p8021:[email-masked]/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.

Finn & Thubert         Expires September 10, 2015              [Page 22]Internet-Draft    Deterministic Networking Architecture       March 2015

   [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: [email-masked]

   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: [email-masked]

_______________________________________________
6tisch mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/6tisch

---

From: Tom Phinney <[email-masked]>
Date: Thu, 09 Apr 2015 21:05:05 -0700

Qin,

I believe that you are correct. Communications jitter would directly
affect a system only if either the source or destination (or perhaps
both) had no buffering. If a microphone output is digitized and
streamed immediately to a distant speaker, then jitter IN THE
COMMUNICATIONS would be apparent. Otherwise it is the end-to-end
jitter between the clocked periodic input to the source buffer and
the clocked periodic output of the sink buffer that is significant.

In most closed-loop control systems, it is important that data that
is sampled from the controlled process in epoch N be delivered to
the computational element that computes the closed-loop correction
in epoch N+j, and that the output of that computation be delivered
to the controlled effector element (e.g., a valve) in epoch N+k.
Usually j and k are equal to zero, but the same logic holds when
they are very small integers, 0 <= j <=k.

It is important that the data not be delivered in the wrong epoch,
because it is possible to destabilize a control loop without
spoofing or losing or reordering any data simply by deliberately
jittering the arrival epoch. Honeywell demonstrated this years ago.

However, communications jitter that causes the data to arrive
slightly earlier in one epoch than in another is not relevant,
provided that the jitter is not so much as to cause the data to
arrive in the wrong epoch.

-Tom

====

On 2015.04.09 08:09, Qin Wang wrote:

Hi
Patrick,

I don't
understand why communication jitter = 0 is so important.
Assume DetNet can guarantee the maximum end-to-end latency,
and there is a well designed buffer in the Listener device,
then I think the Listener can consume data just on time, in
another word, from application point of view, jitter =0.
Please point out if I'm wrong.

Thanks

Qin

On Thursday,
April 9, 2015 5:03 PM, Patrick Wetterwald (pwetterw)
<[email-masked]> wrote:

Norm, Pascal,

Some other comments:

If you look at https://tools.ietf.org/html/draft-wetterwald-detnet-utilities-reqs you
will see that for some important use cases, the
jitter should very close to zero. In the
architecture draft, you are mainly focussing on
the maximum value of the latency and the packet
loss (at least in the text). This is not
sufficient for power automation and tele
protection use case. We need to be able to
deploy deterministic network with Jitter = 0.

Second: may be good to reference the
requirement drafts in the doc. :-)

Thanks,

Patrick

From: Thomas
Watteyne <[email-masked]>

Date: Monday
23 March 2015 18:44

To: "[email-masked]"
<[email-masked]>,
"[email-masked]"
<[email-masked]>

Subject: [Detnet]
comments on draft-finn-detnet-architecture-00

Norm, Pascal,

Please find below a number of comment
on draft-finn-detnet-architecture-00.

Overall, the draft is very well
written and highlights important points
for deterministic networking.

My general comments are:

- in the context of a low-power
wireless network (e.g. 6TiSCH), I wonder
what you thoughts are on reserving a
fixed path. Maybe some extra text on
redundancy is needed?

- would it make sense to discuss the
difference between hard and soft
real-time, also wrt wireless systems?

Thomas

---

DetNet

N. Finn

Internet-Draft

P. Thubert

Intended
status: Standards Track
Cisco

Expires:
September 10, 2015
March 9, 2015

Deterministic
Networking Architecture

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.

TW>
it looks like you aim for 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

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,

TW>
define IT and ICT at first use

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

TW>
"on transporting"?

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.

TW>
It might be good to quantify the
target latency, packet loss and
jitter.

TW>
I appreciate this is not easy, but
one representatve example might help

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

TW>
":"

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.

TW>
ensure -> guarantee?

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

TW>
would TTP/C fit in this list?

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,

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.

TW>
typo

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.

TW>
add somethind like "possibly
wireless" somewhere?

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.

TW>
why this 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

TW>
typo

special terms are used in this
document in order to

avoid the assumption that a given
element in the archetecture

TW>
typo

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:

TW>
I don't get the sentence above

bridge

A Customer Bridge as
defined by IEEE 802.1Q

[IEEE802.1Q-2011].

circuit

A trail of configuration
from talker to listener(s)

TW>
sender and receiver might be more
common at the IETF?

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.

TW>
maybe add "layer 2 bridge" and
"layer 3 router" for clarity?

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

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.

TW>
Would it make sense to discuss hard
and soft real-time here, in

TW>
particular in the context of a
wireless system?

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/

TW>
add 6TiSCH cells?

output slots are assigned in
each relay system to the use of a

specific DetNet stream or group
of streams.  Note that, given a

TW>
extra ")"

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.

TW>
Using a single path in a wireless
system will fail, I would recommend

TW>
discussing here path redundancy, for
example through DAGs

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

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

TW>
and the provision the sufficient
link bandwidth?

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

TW>
typo

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

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).

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.

TW>
this has some energy cost
associated?

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

TW>
typo

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

TW>
I don't understand what R and E
means

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):

TW>
double ":"

Layers

and Architecture Terminology
[RFC7426] which is represented
below:

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SDN Layers and Architecture
Terminology per RFC 7426

|
|

| +-------------+
+----------+ |

| | Application |
|  Service | |

| +-------------+
+----------+ |

|
Application Plane        |

|

|           Network Services
Abstraction Layer (NSAL)           |

|
|

|               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

|
|

|         Device and resource
Abstraction Layer (DAL)           |

|            |
|                |

|    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

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.

TW>
could you define NME, SME and PCE in
the terminology?

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

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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

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

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.

TW>
how is a packet "labeled" as part of
stream?

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

TW>
typo

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

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

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;

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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

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

TW>
typo

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

TW>
typo

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

TW>
please define "service remarking"

be employed

to prevent non-DetNet packets from
impinging on the resources

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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

TW>
typo

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

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

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
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

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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

TW>
typo

by software failures.  Because
there is

essentiall

TW>
typo

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",

[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.",

Finn, N. and P. Thubert,
"Deterministic Networking Problem

Statement",
draft-finn-detnet-problem-statement-01
(work

in progress), October
2014.

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.

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-03
(work in

progress), March 2015.

[IEEE802.1AS-2011]

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

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[IEEE802.1BA-2011]

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

[IEEE802.1CB]

IEEE, "Seamless
Redundancy (IEEE Draft P802.1CB)",
2015,

cb-drafts/>.

[IEEE802.1Q-2011]

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

[IEEE802.1Qat-2010]

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

[IEEE802.1Qav]

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

[IEEE802.1Qca]

IEEE, "Path Control and
Reservation", 2015,

ca-drafts/>.

[IEEE802.1Qcc]

IEEE, "Stream
Reservation Protocol (SRP)
Enhancements and

Performance
Improvements", 2015,

cc-drafts/>.

[IEEE802.1TSNTG]

IEEE Standards
Association, "IEEE 802.1
Time-Sensitive

Networks Task Group",
2013,

[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-

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",

[Profinet]

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.

[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.

Finn
& Thubert         Expires
September 10, 2015
[Page 22]

Internet-Draft
Deterministic Networking
Architecture       March 2015

[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",

[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.

USA

Phone:
+1 408 526 4495

Email:
[email-masked]

Pascal Thubert

Cisco Systems

Batiment T3

FRANCE

Phone:
+33 4 97 23 26 34

Email:
[email-masked]

Finn
& Thubert         Expires
September 10, 2015
[Page 23]

6tisch mailing list

[email-masked]

---

From: "Norman Finn (nfinn)" <[email-masked]>
Date: Thu, 9 Apr 2015 20:44:09 +0000

Good points.  I’ll work on that for the next edit.

— Norm

From: "Patrick Wetterwald (pwetterw)" <[email-masked]<mailto:[email-masked]>>
Date: Thursday, April 9, 2015 at 02:03 AM
To: Thomas Watteyne <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>
Subject: Re: [Detnet] comments on draft-finn-detnet-architecture-00

Norm, Pascal,

Some other comments:

Thanks,

Patrick

Norm, Pascal,

My general comments are:

Thomas

---

DetNet                                                           N. Finn

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1.  Introduction

2.  Terminology

   The follwing
TW> typo

   bridge

   circuit

   end system

   listener

   relay system

           A router or a bridge.

   stream

   talker

3.2.  Pinned-down paths

3.3.  Seamless Redundancy

   end    R +                   v | ^                  + E end
   system   +                   v | ^                  +   system

                                 Figure 1

4.  DetNet Architecture

                                 Figure 2

4.3.  The Network Plane

                         Stream Management Entity

       End                                                     End
           System                                               System

                PCE         PCE              PCE              PCE

                  Relay      Relay      Relay      Relay

                                 Figure 3

       3.  hysical
TW> typo

4.5.  DetNet streams

4.5.1.  Talker guarantees

   o  A maximum packet size;

4.9.  Fault Mitigation

4.12.  Provisioning model

5.  Related IETF work

5.1.  Deterministic PHB

5.2.  6TiSCH

   Security must cover:

7.  IANA Considerations

8.  Acknowledgements

   [I-D.ietf-6tisch-tsch]

   [IEEE802.1AS-2011]

   [IEEE802.1BA-2011]

   [IEEE802.1CB]

   [IEEE802.1Q-2011]

   [IEEE802.1Qat-2010]

   [IEEE802.1Qav]

   [IEEE802.1Qca]

   [IEEE802.1Qcc]

   [IEEE802.1TSNTG]

   [IEEE802154]

   [IEEE802154e]

   [ISA100.11a]

   [Profinet]

   [WirelessHART]

Authors' Addresses

   Norm Finn
   Cisco Systems
   170 W Tasman Dr.

   Pascal Thubert
   Cisco Systems

---

From: "Norman Finn (nfinn)" <[email-masked]>
Date: Thu, 9 Apr 2015 20:53:17 +0000

There are (at least!) two basic models in use, today, for running real time applications over ethernet:

 1. Do what the packet says to do when you get the packet.
    That allows a maximally-stupid end node, but constrains the network to have near-0 jitter, or things can happen at the wrong time.  This is not trivial for the network to do, can require considerable buffering capability, especially applied to multicasts, and VERY quickly ceases to scale.
 2. Synchronize your clock with everyone else's, then do what the packet says to do when the packet says to do it.
    That requires a somewhat smarter end node, but means that the network only has to guarantee a worst-case maximum latency, not a worst-case minimum latency.

If I were designing a new application, I would lean towards the second scheme.  But, one size definitely doesn’t fit all.

— Norm

From: Qin Wang <[email-masked]<mailto:[email-masked]>>
Reply-To: Qin Wang <[email-masked]<mailto:[email-masked]>>
Date: Thursday, April 9, 2015 at 08:09 AM
To: "Patrick Wetterwald (pwetterw)" <[email-masked]<mailto:[email-masked]>>, Thomas Watteyne <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>
Subject: Re: [Detnet] [6tisch] comments on draft-finn-detnet-architecture-00

Hi Patrick,

Thanks
Qin

On Thursday, April 9, 2015 5:03 PM, Patrick Wetterwald (pwetterw) <[email-masked]<mailto:[email-masked]>> wrote:

Norm, Pascal,

Some other comments:

Thanks,

Patrick

Norm, Pascal,

My general comments are:

Thomas

---

DetNet                                                           N. Finn

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1.  Introduction

2.  Terminology

   The follwing
TW> typo

   bridge

   circuit

   end system

   listener

   relay system

           A router or a bridge.

   stream

   talker

3.2.  Pinned-down paths

3.3.  Seamless Redundancy

   end    R +                   v | ^                  + E end
   system   +                   v | ^                  +   system

                                 Figure 1

4.  DetNet Architecture

                                 Figure 2

4.3.  The Network Plane

                         Stream Management Entity

       End                                                     End
           System                                               System

                PCE         PCE              PCE              PCE

                  Relay      Relay      Relay      Relay

                                 Figure 3

       3.  hysical
TW> typo

4.5.  DetNet streams

4.5.1.  Talker guarantees

   o  A maximum packet size;

4.9.  Fault Mitigation

4.12.  Provisioning model

5.  Related IETF work

5.1.  Deterministic PHB

5.2.  6TiSCH

   Security must cover:

7.  IANA Considerations

8.  Acknowledgements

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

   [I-D.ietf-6tisch-tsch]

   [IEEE802.1AS-2011]

   [IEEE802.1BA-2011]

   [IEEE802.1CB]

   [IEEE802.1Q-2011]

   [IEEE802.1Qat-2010]

   [IEEE802.1Qav]

   [IEEE802.1Qca]

   [IEEE802.1Qcc]

   [IEEE802.1TSNTG]
              IEEE Standards Association, "IEEE 802.1 Time-Sensitive
              Networks Task Group", 2013,
              <http://www.IEEE802.org/1/pages/avbridges.html<http://www.ieee802.org/1/pages/avbridges.html>>.

   [IEEE802154]

   [IEEE802154e]

   [ISA100.11a]

   [Profinet]

   [WirelessHART]
              www.hartcomm.org<http://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.

   Phone: +1 408 526 4495

   Pascal Thubert
   Cisco Systems

   Phone: +33 4 97 23 26 34

_______________________________________________
6tisch mailing list
[email-masked]<mailto:[email-masked]>
https://www.ietf.org/mailman/listinfo/6tisch

---

From: "Patrick Wetterwald (pwetterw)" <[email-masked]>
Date: Fri, 10 Apr 2015 08:27:31 +0000

Hi Qin,

Norm is right and for utilities and specifically the tele protection use case (one of the most important for them) we are in the case 1 of Norm’s answer.
Just, I’m not sure to call the tele protection IED a maximally-stupid end node :-) as it is probably a few 100 of thousand dollars product which is dealing with 750 KV electrical lines.

The goal of utilities is to increase the load of their existing transmission lines (electrical). Getting a few % more on those lines is a gain which is measured in Millions or Billions of dollars (it can avoid deploying a new HV transmission line over a country if demand increases). Decreasing latency and zeroing the jitter will give them this flexibility.
Basically, they are calibrating the IEDs on both ends of the line by eliminating the effect of the latency.  Then the remaining part is the jitter. If the jitter is too big, you can get false information and IEDs can decide to disconnect the 750KV line which can completely destabilize your grid. This is real time and buffering is not an option.

I hope this answers your question.

Patrick

From: "Norman Finn (nfinn)" <[email-masked]<mailto:[email-masked]>>
Date: Thursday 9 April 2015 22:53
To: Qin Wang <[email-masked]<mailto:[email-masked]>>, pwetterw <[email-masked]<mailto:[email-masked]>>, Thomas Watteyne <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>, "[email-masked]<mailto:[email-masked]>" <[email-masked]<mailto:[email-masked]>>
Subject: Re: [Detnet] [6tisch] comments on draft-finn-detnet-architecture-00

— Norm

Hi Patrick,

Thanks
Qin

Norm, Pascal,

Some other comments:

Thanks,

Patrick

Norm, Pascal,

My general comments are:

Thomas

---

DetNet                                                           N. Finn

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1.  Introduction

2.  Terminology

   The follwing
TW> typo

   bridge

   circuit

   end system

   listener

   relay system

           A router or a bridge.

   stream

   talker

3.2.  Pinned-down paths

3.3.  Seamless Redundancy

   end    R +                   v | ^                  + E end
   system   +                   v | ^                  +   system

                                 Figure 1

4.  DetNet Architecture

                                 Figure 2

4.3.  The Network Plane

                         Stream Management Entity

       End                                                     End
           System                                               System

                PCE         PCE              PCE              PCE

                  Relay      Relay      Relay      Relay

                                 Figure 3

       3.  hysical
TW> typo

4.5.  DetNet streams

4.5.1.  Talker guarantees

   o  A maximum packet size;

4.9.  Fault Mitigation

4.12.  Provisioning model

5.  Related IETF work

5.1.  Deterministic PHB

5.2.  6TiSCH

   Security must cover:

7.  IANA Considerations

8.  Acknowledgements

   [I-D.ietf-6tisch-tsch]

   [IEEE802.1AS-2011]

   [IEEE802.1BA-2011]

   [IEEE802.1CB]

   [IEEE802.1Q-2011]

   [IEEE802.1Qat-2010]

   [IEEE802.1Qav]

   [IEEE802.1Qca]

   [IEEE802.1Qcc]

   [IEEE802.1TSNTG]

   [IEEE802154]

   [IEEE802154e]

   [ISA100.11a]

   [Profinet]

   [WirelessHART]

Authors' Addresses

   Norm Finn
   Cisco Systems
   170 W Tasman Dr.

   Phone: +1 408 526 4495

   Pascal Thubert
   Cisco Systems

   Phone: +33 4 97 23 26 34

---

From: John Grant <[email-masked]>
Date: Fri, 10 Apr 2015 09:59:41 +0100

> I don't understand why communication jitter = 0 is so important. Assume DetNet can guarantee the maximum end-to-end latency, and there is a well designed buffer in the Listener device, then I think…

For streams with medium to high bit rates, such as video and uncompressed audio, buffer space can be an issue. For implementations in FPGA, the jitter spec can make the difference between buffering the data in internal block RAM or having to send it out to external memory and then get it back again. Similarly with microcontrollers.

Many IoT applications will require controlled latency, and you can't assume IoT devices will all have the same amounts of memory as PCs and smartphones..

John Grant
Nine Tiles, Cambridge, England
+44 1223 862599 and +44 1223 511455
http://www.ninetiles.com

---

From: Christian Boiger <[email-masked]>
Date: Fri, 10 Apr 2015 11:32:00 +0000

Actually the packet delay variation is not only important for the applications, it is also an important factor to a achieve really low deterministic latency. In networks where the packet delay variation for a packet grows at each hop it gets very hard to guarantee a very low latency. AVB is working that way and this has its limitations, especially in arbitrary big and complex networks (and the goal of AVB was only 2ms over 7 hops). In order to get much smaller latencies and simpler ways to calculate the worst case latency in a network, a small and bounded (not only bounded by the worst case latency) packet delay variation is very important.

Regards
Christian

Von: detnet [mailto:[email-masked]] Im Auftrag von Norman Finn (nfinn)
Gesendet: Donnerstag, 9. April 2015 22:53
An: Qin Wang; Patrick Wetterwald (pwetterw); Thomas Watteyne; [email-masked]; [email-masked]
Betreff: Re: [Detnet] [6tisch] comments on draft-finn-detnet-architecture-00

— Norm

Hi Patrick,

Thanks
Qin

Norm, Pascal,

Some other comments:

Patrick

Norm, Pascal,

My general comments are:

Thomas

---

DetNet                                                           N. Finn

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1.  Introduction

2.  Terminology

   The follwing
TW> typo

   bridge

   circuit

   end system

   listener

   relay system

           A router or a bridge.

   stream

   talker

3.2.  Pinned-down paths

3.3.  Seamless Redundancy

   end    R +                   v | ^                  + E end
   system   +                   v | ^                  +   system

                                 Figure 1

4.  DetNet Architecture

                                 Figure 2

4.3.  The Network Plane

                         Stream Management Entity

       End                                                     End
           System                                               System

                PCE         PCE              PCE              PCE

                  Relay      Relay      Relay      Relay

                                 Figure 3

       3.  hysical
TW> typo

4.5.  DetNet streams

4.5.1.  Talker guarantees

   o  A maximum packet size;

4.9.  Fault Mitigation

4.12.  Provisioning model

5.  Related IETF work

5.1.  Deterministic PHB

5.2.  6TiSCH

   Security must cover:

7.  IANA Considerations

8.  Acknowledgements

   [I-D.ietf-6tisch-tsch]

   [IEEE802.1AS-2011]

   [IEEE802.1BA-2011]

   [IEEE802.1CB]

   [IEEE802.1Q-2011]

   [IEEE802.1Qat-2010]

   [IEEE802.1Qav]

   [IEEE802.1Qca]

   [IEEE802.1Qcc]

   [IEEE802.1TSNTG]

   [IEEE802154]

   [IEEE802154e]

   [ISA100.11a]

   [Profinet]

   [WirelessHART]

Authors' Addresses

   Norm Finn
   Cisco Systems
   170 W Tasman Dr.

   Phone: +1 408 526 4495

   Pascal Thubert
   Cisco Systems

   Phone: +33 4 97 23 26 34

---

From: Rodney Cummings <[email-masked]>
Date: Fri, 10 Apr 2015 09:01:44 -0500

I agree with Norm's conclusion, but you are correct that this is a 
tradeoff in complexity (and therefore to some degree cost).

As a baseline assumption, I take it as a given that every host is synced 
in time (e.g. IEEE 1588). Power does this, industrial does this, and 
automotive is doing it.

Let's also assume that the application requires zero jitter. Both Option 1 
and 2 meet that requirement. 

Option 1 is simply what Norm says... use the packet at the point when your 
application's jitter is zero in synced time. In the host (end-station), 
this requires a buffer per DetNet (zero-jitter) flow, and the ability to 
identify each flow. That is not rocket science, even for an FPGA. For 
large topologies, the tradeoff is that there is some complex math to 
figure out the worst-case latency, but let's be clear... that's just 
math... not higher cost hardware. There are ways to mitigate this math 
using certain techniques in the network... in the same direction as you go 
with Option 2, but not "full blown" (not zero jitter at every hop).

Option 2 sounds appealing at first, but it implies identification and 
buffering of each DetNet flow at every hop. You are essentially moving a 
minor requirement for the host to every switch/router in the network, 
which greatly expands the overall complexity. You also don't avoid the 
math problem, because now there is a complex calculation to figure out the 
schedule for every flow at every hop.

The main difference is that Option 2 is more complex to implement, 
probably by order(s) of magnitude. I agree with Norm. If you are designing 
a new application for zero jitter, Option 1 is the way to go.

All of this being said, 802.1 TSN is providing hooks to enable either 
option. Option 1 is the baseline assumption for most applications, but 
Option 2 is certainly do-able. Hopefully IETF DetNet will move in the same 
direction.

From:   Christian Boiger <[email-masked]>
To:     "Norman Finn (nfinn)" <[email-masked]>, Qin Wang 
<[email-masked]>, "Patrick Wetterwald (pwetterw)" 
<[email-masked]>, Thomas Watteyne <[email-masked]>, 
"[email-masked]" <[email-masked]>, "[email-masked]" <[email-masked]>, 
Date:   04/10/2015 06:32 AM
Subject:        Re: [Detnet] [6tisch] comments on 
draft-finn-detnet-architecture-00
Sent by:        "detnet" <[email-masked]>

Actually the packet delay variation is not only important for the 
applications, it is also an important factor to a achieve really low 
deterministic latency. In networks where the packet delay variation for a 
packet grows at each hop it gets very hard to guarantee a very low 
latency. AVB is working that way and this has its limitations, especially 
in arbitrary big and complex networks (and the goal of AVB was only 2ms 
over 7 hops). In order to get much smaller latencies and simpler ways to 
calculate the worst case latency in a network, a small and bounded (not 
only bounded by the worst case latency) packet delay variation is very 
important.
 
Regards
Christian

Von: detnet [mailto:[email-masked]] Im Auftrag von Norman Finn 
(nfinn)
Gesendet: Donnerstag, 9. April 2015 22:53
An: Qin Wang; Patrick Wetterwald (pwetterw); Thomas Watteyne; 
[email-masked]; [email-masked]
Betreff: Re: [Detnet] [6tisch] comments on 
draft-finn-detnet-architecture-00
 
There are (at least!) two basic models in use, today, for running real 
time applications over ethernet:
 
 1. Do what the packet says to do when you get the packet.
    That allows a maximally-stupid end node, but constrains the network to 
have near-0 jitter, or things can happen at the wrong time.  This is not 
trivial for the network to do, can require considerable buffering 
capability, especially applied to multicasts, and VERY quickly ceases to 
scale.
 2. Synchronize your clock with everyone else's, then do what the packet 
says to do when the packet says to do it.
    That requires a somewhat smarter end node, but means that the network 
only has to guarantee a worst-case maximum latency, not a worst-case 
minimum latency.
 
If I were designing a new application, I would lean towards the second 
scheme.  But, one size definitely doesn’t fit all.
 
— Norm
 
From: Qin Wang <[email-masked]>
Reply-To: Qin Wang <[email-masked]>
Date: Thursday, April 9, 2015 at 08:09 AM
To: "Patrick Wetterwald (pwetterw)" <[email-masked]>, Thomas Watteyne 
<[email-masked]>, "[email-masked]" <[email-masked]>, "
[email-masked]" <[email-masked]>
Subject: Re: [Detnet] [6tisch] comments on 
draft-finn-detnet-architecture-00
 
Hi Patrick,
 
I don't understand why communication jitter = 0 is so important. Assume 
DetNet can guarantee the maximum end-to-end latency, and there is a well 
designed buffer in the Listener device, then I think the Listener can 
consume data just on time, in another word, from application point of 
view, jitter =0. Please point out if I'm wrong.
 
Thanks
Qin

On Thursday, April 9, 2015 5:03 PM, Patrick Wetterwald (pwetterw) <
[email-masked]> wrote:
 
Norm, Pascal,
 
Some other comments:
 
If you look at 
https://tools.ietf.org/html/draft-wetterwald-detnet-utilities-reqs you 
will see that for some important use cases, the jitter should very close 
to zero. In the architecture draft, you are mainly focussing on the 
maximum value of the latency and the packet loss (at least in the text). 
This is not sufficient for power automation and tele protection use case. 
We need to be able to deploy deterministic network with Jitter = 0.
Second: may be good to reference the requirement drafts in the doc. :-)
Thanks,
 
Patrick

From: Thomas Watteyne <[email-masked]>
Date: Monday 23 March 2015 18:44
To: "[email-masked]" <[email-masked]>, "[email-masked]" <
[email-masked]>
Subject: [Detnet] comments on draft-finn-detnet-architecture-00
 
Norm, Pascal,
 
Please find below a number of comment on 
draft-finn-detnet-architecture-00.
 
Overall, the draft is very well written and highlights important points 
for deterministic networking.
 
My general comments are:
- in the context of a low-power wireless network (e.g. 6TiSCH), I wonder 
what you thoughts are on reserving a fixed path. Maybe some extra text on 
redundancy is needed?
- would it make sense to discuss the difference between hard and soft 
real-time, also wrt wireless systems?
 
Thomas
 
---

DetNet                                                           N. Finn

Abstract

Status of This Memo

 

Copyright Notice

 

Table of Contents

1.  Introduction

 

 
TW> It might be good to quantify the target latency, packet loss and 
TW> I appreciate this is not easy, but one representatve example might 
help

 

 
 
2.  Terminology
 
   The follwing
TW> typo
 
   bridge
 
   circuit
 
   end system
 
   listener
 
   relay system

           A router or a bridge.

   stream
 
   talker

 

 

 

 

 

 

 

 

3.2.  Pinned-down paths

 
3.3.  Seamless Redundancy

 

 

 

 
   end    R +                   v | ^                  + E end
   system   +                   v | ^                  +   system
 
                                 Figure 1
 
4.  DetNet Architecture

 

 

 

 

 

 

 

 

 
 
                                 Figure 2

 

 

 

 

 

4.3.  The Network Plane

 
 
                         Stream Management Entity
 
       End                                                     End
           System                                               System

                PCE         PCE              PCE              PCE

                  Relay      Relay      Relay      Relay
 
                                 Figure 3

 

 

 

 

 
 
       3.  hysical
TW> typo

 

 

 
 
4.5.  DetNet streams
 
4.5.1.  Talker guarantees

   o  A maximum packet size;

 

 

 

 

 

 

 

4.9.  Fault Mitigation

 

 

4.12.  Provisioning model

 

 

 

5.  Related IETF work
 
5.1.  Deterministic PHB

5.2.  6TiSCH

 

 

 

 
 
   Security must cover:

 
 
7.  IANA Considerations

8.  Acknowledgements

 

 

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

 
 
   [I-D.ietf-6tisch-tsch]

 
   [IEEE802.1AS-2011]

   [IEEE802.1BA-2011]
 
   [IEEE802.1CB]
 
   [IEEE802.1Q-2011]
 
   [IEEE802.1Qat-2010]
 
   [IEEE802.1Qav]
 
   [IEEE802.1Qca]
 
   [IEEE802.1Qcc]
 
   [IEEE802.1TSNTG]
 
   [IEEE802154]

   [IEEE802154e]
 
   [ISA100.11a]

 
   [Profinet]

 

 

 

 
 
   [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.
 
   Phone: +1 408 526 4495
   Email: [email-masked]

   Pascal Thubert
   Cisco Systems
 
   Phone: +33 4 97 23 26 34
   Email: [email-masked]

 

 

 
 
_______________________________________________
6tisch mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/6tisch
 _______________________________________________
detnet mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/detnet

---

From: Rodney Cummings <[email-masked]>
Date: Fri, 10 Apr 2015 09:09:48 -0500

Oops. My apologies... I just realized that I flipped the option 1 and 2 
numbers. Corrected below.

From:   Rodney Cummings/AUS/NIC
To:     "[email-masked]" <[email-masked]>, 
Cc:     "[email-masked]" <[email-masked]>, "Norman Finn (nfinn)" 
<[email-masked]>, "Patrick Wetterwald (pwetterw)" <[email-masked]>, 
Qin Wang <[email-masked]>, Thomas Watteyne 
<[email-masked]>, Christian Boiger 
<[email-masked]>
Date:   04/10/2015 09:01 AM
Subject:        Re: [Detnet] [6tisch] comments on 
draft-finn-detnet-architecture-00

Option 2 is simply what Norm says... use the packet at the point when your 
application's jitter is zero in synced time. In the host (end-station), 
this requires a buffer per DetNet (zero-jitter) flow, and the ability to 
identify each flow. That is not rocket science, even for an FPGA. For 
large topologies, the tradeoff is that there is some complex math to 
figure out the worst-case latency, but let's be clear... that's just 
math... not higher cost hardware. There are ways to mitigate this math 
using certain techniques in the network... in the same direction as you go 
with Option 1, but not "full blown" (not zero jitter at every hop).

Option 1 sounds appealing at first, but it implies identification and 

The main difference is that Option 1 is more complex to implement, 
probably by order(s) of magnitude. I agree with Norm. If you are designing 
a new application for zero jitter, Option 2 is the way to go.

All of this being said, 802.1 TSN is providing hooks to enable either 
option. Option 2 is the baseline assumption for most applications, but 
Option 1 is certainly do-able. Hopefully IETF DetNet will move in the same 
direction.

 
Regards
Christian

 

— Norm

Hi Patrick,

Thanks
Qin

Norm, Pascal,
 
Some other comments:
 
If you look at 
 
Patrick

Norm, Pascal,

 
My general comments are:
 
Thomas
 
---

DetNet                                                           N. Finn

Abstract

Status of This Memo

 

Copyright Notice

 

Table of Contents

1.  Introduction

 

 

 

 
 
2.  Terminology
 
   The follwing
TW> typo
 
   bridge
 
   circuit
 
   end system
 
   listener
 
   relay system

           A router or a bridge.

   stream
 
   talker

 

 

 

 

 

 

 

 

3.2.  Pinned-down paths

 
3.3.  Seamless Redundancy

 

 

 

 
   end    R +                   v | ^                  + E end
   system   +                   v | ^                  +   system
 
                                 Figure 1
 
4.  DetNet Architecture

 

 

 

 

 

 

 

 

 
 
                                 Figure 2

 

 

 

 

 

4.3.  The Network Plane

 
 
                         Stream Management Entity
 
       End                                                     End
           System                                               System

                PCE         PCE              PCE              PCE

                  Relay      Relay      Relay      Relay
 
                                 Figure 3

 

 

 

 

 
 
       3.  hysical
TW> typo

 

 

 
 
4.5.  DetNet streams
 
4.5.1.  Talker guarantees

   o  A maximum packet size;

 

 

 

 

 

 

 

4.9.  Fault Mitigation

 

 

4.12.  Provisioning model

 

 

 

5.  Related IETF work
 
5.1.  Deterministic PHB

5.2.  6TiSCH

 

 

 

 
 
   Security must cover:

 
 
7.  IANA Considerations

8.  Acknowledgements

 

 

 

 
   [I-D.ietf-6tisch-tsch]

 
   [IEEE802.1AS-2011]

   [IEEE802.1BA-2011]
 
   [IEEE802.1CB]
 
   [IEEE802.1Q-2011]
 
   [IEEE802.1Qat-2010]
 
   [IEEE802.1Qav]
 
   [IEEE802.1Qca]
 
   [IEEE802.1Qcc]
 
   [IEEE802.1TSNTG]
 
   [IEEE802154]

   [IEEE802154e]
 
   [ISA100.11a]

 
   [Profinet]

 

 

 

 
 
   [WirelessHART]
 
Authors' Addresses
 
   Norm Finn
   Cisco Systems
   170 W Tasman Dr.
 
   Phone: +1 408 526 4495
   Email: [email-masked]

   Pascal Thubert
   Cisco Systems
 
   Phone: +33 4 97 23 26 34

---

From: [email-masked]
Date: Mon, 13 Apr 2015 15:33:47 +0530

Hi,

The math for Option 1 can really get interesting if we combine zero jitter
pursuit with seamless redundancy to improve the message reliability.
Different paths can present dissimilar jitter to the "virtual" end-point
which is expected to give jitter-free stream to the listener, apart from
removing duplicates. With more path diversity comes more complexity in
smoothening the stream.

Anand

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