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

From: "Pascal Thubert (pthubert)" <[email-masked]>
Date: Mon, 23 Mar 2015 22:51:38 +0000

Hello Thomas:

I think that this should come from 6TiSCH based on experience from TSCH 
deployments, and be pushed to DetNet as requirements from the LLN/TSCH side.

It is my hope that something like 
https://tools.ietf.org/html/draft-wang-6tisch-track-use-cases-00 evolves in 
that direction...

Makes sense ?

Pascal

From: detnet [mailto:[email-masked]] On Behalf Of Thomas Watteyne
Sent: lundi 23 mars 2015 10:44
To: [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

                   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 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, "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, "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]

   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]

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