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Requirements for Reliable Wireless Industrial Services
draft-ietf-detnet-raw-industrial-req-01

Document Type Active Internet-Draft (detnet WG)
Authors Rute C. Sofia , Paulo Mendes , Carlos J. Bernardos , Eve Schooler
Last updated 2024-07-08
Replaces draft-ietf-raw-industrial-requirements
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draft-ietf-detnet-raw-industrial-req-01
Deterministic Networking Working Group                        R.S. Sofia
Internet-Draft                                              fortiss GmbH
Intended status: Informational                                 P. Mendes
Expires: 9 January 2025                                           Airbus
                                                      CJ. Bernardos, Ed.
                                                                    UC3M
                                                             E. Schooler
                                                    University of Oxford
                                                             8 July 2024

         Requirements for Reliable Wireless Industrial Services
                draft-ietf-detnet-raw-industrial-req-01

Abstract

   This document provides an overview of the communication requirements
   for handling reliable wireless services in the context of industrial
   environments.  The aim of the draft is to raise awareness of the
   communication requirements of current and future wireless industrial
   services; how they can coexist with wired infrastructures; the key
   drivers for reliable wireless integration; the relevant communication
   requirements to be considered; the current and future challenges
   arising from the use of wireless services; and the potential benefits
   of wireless communication.

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 https://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 9 January 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions used in this document . . . . . . . . . . . . . .   4
   3.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Wireless Industrial Services today  . . . . . . . . . . . . .   4
     4.1.  Equipment and Process Control Services  . . . . . . . . .   6
     4.2.  Quality Control Services  . . . . . . . . . . . . . . . .   9
     4.3.  Factory Resource Management Services  . . . . . . . . . .  10
     4.4.  Display Services  . . . . . . . . . . . . . . . . . . . .  11
     4.5.  Human Safety Services . . . . . . . . . . . . . . . . . .  12
     4.6.  Mobile Robotics Services  . . . . . . . . . . . . . . . .  13
     4.7.  Power Grid Control  . . . . . . . . . . . . . . . . . . .  14
     4.8.  Wireless Avionics Intra-communication . . . . . . . . . .  14
   5.  Additional Reliable Wireless Industrial Services  . . . . . .  15
     5.1.  AR/VR Services within Flexible Factories  . . . . . . . .  16
       5.1.1.  Description . . . . . . . . . . . . . . . . . . . . .  16
       5.1.2.  Recommendations related to wireless determinism and
               reliability . . . . . . . . . . . . . . . . . . . . .  16
       5.1.3.  Requirements Considerations . . . . . . . . . . . . .  17
     5.2.  Decentralised Shop-floor Communication Services . . . . .  18
       5.2.1.  Description . . . . . . . . . . . . . . . . . . . . .  18
       5.2.2.  Recommendations related to wireless determinism and
               reliability . . . . . . . . . . . . . . . . . . . . .  18
       5.2.3.  Requirements Considerations . . . . . . . . . . . . .  19
     5.3.  Autonomous Airborne Services  . . . . . . . . . . . . . .  19
       5.3.1.  Recommendations related to wireless determinism and
               reliability . . . . . . . . . . . . . . . . . . . . .  20
       5.3.2.  Requirements Considerations . . . . . . . . . . . . .  21
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  22
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

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1.  Introduction

   In industrial environments, short-range wireless standards such as
   IEEE 802.11ax are gaining momentum as the need for flexibility in
   infrastructure design and process support increases.

   Wireless, and in particular the latest evolution of Wi-Fi, has
   reached a level of maturity where the technology can support the
   stringent requirements of industrial environments, while being
   compatible with traditional fixed core networks.  Wireless
   technologies bring flexibility, lower operating costs and higher
   availability to industrial systems at the edge in scenarios that
   require support for mobility or large-scale integration of sensing
   devices.

   However, there are barriers to the integration of wireless in
   industrial environments.  Firstly, as wireless is a shared medium, it
   faces challenges such as interference and signal strength variability
   depending on the environment.  These characteristics raise questions
   about the availability, resilience and security support of critical
   services.  Secondly, wireless relies on probabilistic Quality of
   Service (QoS) and therefore requires tuning to support time-sensitive
   traffic with limited latency, low jitter and zero congestion loss.

   Still, recent advances in OFDMA-based wireless in the context of IEEE
   802.11 standards, such as 802.11ax and 802.11be, bring interesting
   features in the context of supporting critical industrial
   applications and services, such as a greater degree of flexibility in
   terms of resource management; frequency allocation aspects that can
   provide better traffic isolation; or even mechanisms that can support
   tighter time synchronisation across wireless environments, thus
   providing the means to better support traffic in converged networks.

   To address the communication challenges that exist in industrial
   domains, it is necessary to have a better understanding of the
   communication requirements that current and future industrial
   applications may attain.

   Therefore, the focus of this draft is to discuss the requirements of
   current and future industrial applications and how best to support
   time-sensitive applications and services within converged industrial
   networks.

   To this end, the draft addresses issues related to industrial
   wireless services, gathered from relevant normative and informational
   references in the industrial domain; discusses key drivers for
   wireless integration; identifies specific wireless mechanisms that
   can support such integration and the challenges they face; and

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   elaborates specific requirements to be considered for both current
   wireless services and a subset of future industrial wireless
   services.

2.  Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].
   In this document, these words will appear with that interpretation
   only when in ALL CAPS.  Lower case uses of these words are not to be
   interpreted as carrying significance described in RFC 2119.

3.  Definitions

   *  Latency (also known as bounded latency) refers to the end-to-end
      transmission delay between a sender and a receiver when a traffic
      flow is initiated by an application.  By definition, latency
      corresponds to the time interval between the sending of the first
      packet of a flow from a source to a destination and the time at
      which the last packet of that flow is received.

   *  "Periodicity" indicates whether or not the data transmission is
      periodic and, where possible, the specific periodicity per unit of
      time has been specified.

   *  "Transmit data size" corresponds to the data payload in bytes.

   *  "Packet loss tolerance" is shown as 0 (zero congestion loss);
      tolerant (the application is tolerant of packet loss).  Packet
      loss occurs when packets fail to reach a particular destination on
      a network.  Packet loss is usually measured as a percentage of
      packets lost relative to the total number of packets sent.  In the
      context of deterministic networking, and in particular Time-
      sensitive Networking (TSN), a packet is lost if it is not received
      within a specified time.

   *  "Time sync" refers to the need to ensure IEEE 1588
      synchronization.

   *  "Node Density" gives an indication (where available) of the number
      of end nodes per 20mx20m.

4.  Wireless Industrial Services today

   This section describes industrial applications where wireless
   technologies (mostly IEEE 802.11) are already being used, derived
   from an analysis of related work.

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   Industrial wireless services focused on empowering industrial
   manufacturing environments have been extensively documented via the
   IEEE Nendica group [NENDICA], the Internet Industrial Consortium
   [IIC], the OPC FLC working group [OPCFLC].  The IEEE Nendica 2020
   report [NENDICA] includes several end-to-end use-cases and a
   technical analysis of the identified features and functions supported
   by wireless/wired deterministic environments.  Based on surveys to
   industry, the report provides a first characterisation of wireless
   services in factories (Wi-Fi 5), describing the scenarios in terms of
   aspects such as as payload size in bytes, communication rate, arrival
   time tolerance, node density.

   The IEEE 802.11 RTA report [IEEERTA] provides additional input on
   supporting wireless for time-sensitive and real-time applications.
   For each category of application, the report provides a description,
   basic information concerning topology and packet flow/traffic model,
   and summarises the problem statement (key challenges).  The
   industrial applications in this report are a subset and have also
   considered sources such as IEEE Nendica, IEC/IEEE 60802 Use-cases, as
   well as 3GPP TR 22.804.  The report groups the different services
   into 3 classes (A,B,C) and provides communication requirements for
   each class categorised as: bounded latency (worst-case one-way
   latency measured at the application layer); reliability (defined as
   the percentage of packets expected to be received within the bounded
   latency); time synchronisation requirements (in the order of micro/
   milliseconds); throughput requirements (high, medium, low).  The
   report concludes with guidelines on implementation aspects, e.g.,
   traffic classification aspects and new capabilities to support real-
   time applications.

   The Avnu Alliance provides a white paper describing the steps for
   integrating TSN over Wi-Fi [AVNU2020], briefly describing the
   integration of Wi-Fi in specific applications such as: closed loop
   control, mobile robots, power grid control, professional audio/video,
   gaming, AR/VR.  The document also raises awareness to the possibility
   of wireless replacing or complementing wired systems in connected
   cabines, i.e., in regards to the wiring harness in vehicles (cars,
   airplanes, trains), which is currently expensive and requires complex
   onboarding.  Wireless can help reduce costs if it can be adapted to
   the critical latency, safety requirements and regulations.  According
   to Avnu, such cases would require 100 micosecond level cycles.
   Communication requirements are summarised in terms of whether or not
   IEEE 1588 synchronisation is required; the typical packet size (data
   payload); bounded latency; reliability.

   Manufacturing wireless use-cases have also been discussed in the
   context of 5G ACIA [ACIA], NICT [NICT], and IETF Deterministic
   Networking [RFC8578].  These sources provide an overview on user

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   stories, and discuss the challenges posed by wireless integration.
   However, the communication requirements are not systematically
   presented.  Finally, IETF RFC9450 provides an initial overview on the
   challenges of wireless industrial use-cases [RFC9450].

   Derived from the analysis of the above sources, this section provides
   a description of service categories and their communication
   requirements.  The following application categories, which cover most
   of the areas today and also span a broad range of requirements, are
   addressed:

   *  Equipment and process control.

   *  Quality supervision.

   *  Factory resource management.

   *  Display.

   *  Human safety.

   *  Industrial systems.

   *  Mobile robots.

   *  Drones/UAV control.

   *  Power grid control.

   *  Communication-based train networks.

   *  Mining industry.

   *  Connected cabin.

   The communication requirements selected and presented for each
   service category have been extracted from the various available
   related works.  The parameters are: bounded latency; periodicity;
   transmitted data size; packet loss tolerance; time synchronisation
   requirements; node density characterisation.

4.1.  Equipment and Process Control Services

   This category of industrial wireless services refers to the data
   exchange required to send commands to, for example, mobile robots/
   vehicles, production equipment, and to receive status information.
   Reasons for wireless integration are: flexibility of use,
   reconfigurability, mobility, reduction of maintenance costs.

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   In this category, examples of services and their communication
   requirements are:

   *  Control of machines and robots.

      -  Bounded latency: below 10 ms.

      -  Periodic.

      -  Transmit data size (bytes): 10-400 (small).

      -  Tolerance to packet loss: 0.

      -  Time synchronization: IEEE 1588.

      -  Node density: 1 to 20 (per 20mx20m area).

   *  AGVs with rails

      -  Bounded latency: 10 ms-100ms.

      -  Periodic, once per minute.

      -  Transmit data size (bytes): 10-400 (small).

      -  Tolerance to packet loss: 0.

      -  Time synchronization: IEEE 1588.

      -  Node density: 1 to 20 (per 20mx20m area).

   *  AGVs without rails

      -  Bounded latency:1 s.

      -  Periodic, once per minute.

      -  Transmit data size (bytes): 10-400 (small).

      -  Tolerance to packet loss: 0.

      -  Time synchronization: IEEE 1588.

      -  Node density: 1 to 20 (per 20mx20m area).

   *  Hard-real time isochronous control, motion control

      -  Bounded latency: 250us - 1ms.

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      -  Periodic.

      -  Transmit data size (bytes): 10-400 (small).

      -  Tolerance to packet loss: 0.

      -  Time synchronization: IEEE 1588.

      -  Node density: 1 to 20 (per 20mx20m area).

   *  Printing, packaging

      -  Bounded latency: below 2 ms.

      -  Transmit data size (bytes): 10-400 (small).

      -  Tolerance to packet loss: 0.

      -  Time synchronization: IEEE 1588.

      -  Node density: over 50 to 100.

   *  PLC to PLC communication

      -  Bounded latency: 100 us-50 ms.

      -  Transmit data size (bytes): 100-700.

      -  Tolerance to packet loss: 0.

      -  Time synchronization: IEEE 1588.

   *  Interactive video

      -  Bounded latency: 50 -10 ms.

      -  Time synchronization: 10-1 "U+00B5" s.

   *  Mobile robotics

      -  Bounded latency: 50-10 ms.

   *  AR/VR, remote HMI

      -  Bounded latency: 10 - 1 ms.

      -  Time synchronization: ~1 "U+00B5" s.

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      -  Time synchronization: 10-1 "U+00B5" s.

   *  Machine, production line controls

      -  Bounded latency: 10 - 1 ms.

4.2.  Quality Control Services

   Quality control includes industrial services that collect and
   evaluate information about products and machine conditions during
   production.  Reasons for wireless integration: flexibility of use,
   reduction of maintenance costs.

   Examples of services in this category, and their communication
   requirements are:

   *  Inline inspection

      -  Bounded latency: bellow 10ms.

      -  Time synchronization: 10-1 "U+00B5"s.

      -  Periodic, once per second.

      -  Transmit data size (bytes): 64-1M.

      -  Tolerance to packet loss: 0.

      -  Node density: 1-10 (per 20mx20m).

   *  Machine operation recording

      -  Bounded latency: over 100 s.

      -  Time synchronization: 10-1 "U+00B5"s.

      -  Periodic, once per second.

      -  Transmit data size (bytes): 64-1M.

      -  Tolerance to packet loss: 0.

      -  Node density: 1-10 (per 20mx20m).

   *  Logging

      -  Bounded latency: over 100s.

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      -  Time synchronization: 10-1 "U+00B5"s.

      -  Transmit data size (bytes): 64-1M.

      -  Tolerance to packet loss: 0.

      -  Node density: 1-10 (per 20mx20m).

4.3.  Factory Resource Management Services

   Refers to the collection of information on whether production is
   taking place in the correct environmental conditions, and whether
   people and equipment contributing to increased productivity are being
   managed appropriately.  Reasons for wireless integration include:
   flexibility of use, reconfigurability, reduction in maintenance
   costs.

   The applications discussed in this context are:

   *  Machine monitoring

      -  Bounded latency: 100ms-10s.

      -  Periodic.

      -  Time synchronization: 10-1 "U+00B5" s.

      -  Transmit data size (bytes): 10-10M.

      -  Tolerance to packet loss: 0.

      -  Node density: 1-30.

   *  Preventive maintenance

      -  Bounded latency: over 100ms.

      -  Periodic, once per event.

   *  Positioning, motion analysis

      -  Bounded latency: 50ms-10s.

      -  Periodic, once per second.

   *  Inventory control

      -  Bounded latency: 50ms-10s.

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      -  Periodic, once per second.

   *  Facility control environment

      -  Bounded latency: 1s-50s.

      -  Periodic, once per minute.

   *  Checking status of material, small equipment

      -  Bounded latency: 100ms-1s.

      -  Sporadic, 1 to 10 times per 30 minutes.

4.4.  Display Services

   This category of services is aimed at workers, enabling them to
   obtain the support information they require.  It also targets
   managers in terms of monitoring production status and processes.
   Reasons for wireless integration are: scalability, flexibility of
   deployment, support for mobility.  Examples of services are:

   *  Work commands, e.g., wearable displays

      -  Bounded latency: 1-10s.

      -  Sporadic, once per 10s-1m.

      -  Transmit data size (bytes): 10-6K.

      -  Tolerance to packet loss: yes.

      -  Node density: 1-30

   *  Display information

      -  Bounded latency: 10s.

      -  Sporadic, once per hour.

      -  Transmit data size (bytes): 10-6K.

      -  Tolerance to packet loss: yes.

      -  Node density: 1-30.

   *  Supporting maintenance (video, audio)

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      -  Bounded latency: 500ms.

      -  Sporadic, once per 100ms.

      -  Transmit data size (bytes): 10-6K.

      -  Tolerance to packet loss: yes.

      -  Node density: 1-30.

4.5.  Human Safety Services

   Refers to industrial wireless services concerned with the collection
   of data to infer potential hazards to workers in industrial
   environments.  The need for wireless integration concerns: support
   for pervasive deployment; mobility.

   Examples of services are:

   *  Detection of dangerous situations/operations

      -  Bounded latency: 1s.

      -  Periodic, 10 per second (10 fps).

      -  Transmit data size (bytes): 2-100K.

      -  Tolerance to packet loss: yes.

      -  Node density: 1-50.

   *  Vital sign monitoring, dangerous behaviour detection

      -  Bounded latency: 1s-50s.

      -  Periodic, once per minute.

      -  Transmit data size (bytes): 2-100K.

      -  Tolerance to packet loss: 0.

      -  Node density: 1-30.

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4.6.  Mobile Robotics Services

   Refers to services that support the communication between robots,
   e.g., task sharing; guidance control including data processing, AV,
   alerts.  Reasons for considering wireless integration are: the need
   to support mobility and reconfigurability.

   *  Video operated remote control

      -  Bounded latency: 10-100ms.

      -  Transmit data size (bytes): 15-150K.

      -  Tolerance to packet loss: yes.

      -  Node density: 2-100.

   *  Assembly of robots or milling machines

      -  Bounded latency: 4-8ms.

      -  Transmit data size (bytes): 40-250.

      -  Tolerance to packet loss: yes.

      -  Node density: 2-100.

   *  Operation of mobile cranes

      -  Bounded latency: 12ms.

      -  Periodic, once per 2-5ms.

      -  Transmit data size (bytes): 40-250.

      -  Tolerance to packet loss: yes.

      -  Node density: 2-100.

   *  Drone/UAV air monitoring

      -  Bounded latency: 100ms.

      -  Tolerance to packet loss: yes.

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4.7.  Power Grid Control

   Grid control refers to services that support communication links for
   predictive maintenance and fault isolation on high-voltage lines,
   transformers, reactors, etc.  Reasons for wireless integration
   include: reducing the cost of wire replacement maintenance.

   *  Bounded latency: 1-10ms.

   *  Transmit data size (bytes): 20-50.

   *  Time synchronization: IEEE 1588.

   *  Tolerance to packet loss: yes.

   *  Node density: 2-100.

4.8.  Wireless Avionics Intra-communication

   Wireless integration is also relevant to industrial environments in
   the context of cabling replacement.  Within the context of avionics
   [AVIONICS], _Wireless Avionics Intra-communication (WAIC)_ systems
   [WAIC] are expected to benefit significantly from deterministic
   communication due to their higher criticality.  For example, flight
   control systemswhich integrate a large number of endpoints (sensors
   and actuators), require high reliability and bounded latency to help
   estimate and control the state of the aircraft.  Real-time data must
   be delivered with strict deadlines for most control systems.

   The WAIC standardisation process is still ongoing, with no clear
   indication of the frequencies that would be reserved for such
   systems, although the frequency band 4.2 GHz to 4.4 GHz seems to be
   the most popular at the moment.  Nevertheless, regardless of the
   allocated frequency bands, the deterministic guarantees required by
   WAIC services can be achieved by integrating functionality developed
   in current wireless standards.

   However, the following requirements are expected to be supported by
   wireless technology in order to ensure the deterministic operation of
   WAIC systems:

   *  MUST provide deterministic behaviour in short radio ranges (<
      100m).

   *  MUST use low transmit power levels for low rate (10mW) and high
      rate (50mW) applications.

   *  MUST ensure good system reconfigurability.

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   *  MUST support dissimilar redundancy.

   Specific communication needs can be identified in terms of potential
   KPIs:

   *  Latency: 20-40ms [PARK2020].

   *  Packet payload: small (e.g., 50 bytes) and variable bit rate
      [PARK2020].

   *  Support between 125 to 4150 nodes [AVIONICS].

   *  Maximum distance between transmitter and receiver: 15m [AVIONICS].

   *  Aggregate average data rate of network (kbit/s): 394 to 18385
      [AVIONICS].

   *  Latency: below 5s for High data rate Inside (HI) applications
      [AVIONICS].

   *  Jitter: below 50ms for HI applications [AVIONICS].

   An example of current standards that may support the deterministic
   requirements of the WAIC system is IEEE 802.11ax, which is being
   devised to operate between 1 and 7GHz (in addition to 2.4 GHz and
   5GHz).  The WAIC requirement for high reliability and bounded latency
   can be supported by IEEE 802.11ax's ability to split the spectrum in
   frequency Resource Units (RUs), which are assigned to stations for
   reception and transmission by a central coordinating entity, the
   wireless Access Point.  Reliability could be explored, for example,
   by assigning more than one RU to the same station, an aspect that is
   not covered by IEEE 802.11ax but already under discussion for IEEE
   802.11be.  By centraly scheduling RUs, contention overhead can be
   avoided, increasing efficiency in dense deployment scenarios such as
   WAIC applications.  In this context, OFDMA and the concept of spatial
   reuse are relevant to support large-scale simultaneous transmission
   while avoiding collision and interference and ensuring high
   throughput [ROBOTS1].

5.  Additional Reliable Wireless Industrial Services

   This section provides examples of additional wireless industrial
   services, that could be deployed (to a larger extent) in the future,
   and that would significantly benefit from some deterministic and
   reliability characteristics.  This set of servuces complement the
   related use cases documented in [RFC8578] and [RFC9450].  We have
   specifically selected three different examples of such use-cases,
   based on their specific relevance to wireless deterministic

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   networking and reliability: i) remote AR/VR for maintenance and
   control; ii) decentralised shop floor communication; and iii)
   wireless in-cab communication.  Based on these examples,
   recommendations for deployment with wireless determinism and
   reliability are discussed and a list of specific requirements is
   provided.

5.1.  AR/VR Services within Flexible Factories

5.1.1.  Description

   While video is now being integrated into industrial automation
   systems and used on the shop floor to assist workers, the integration
   of AR/VR on the shop floor in industrial environments is still in its
   initial stages.  However, it is being used in the electrical industry
   to improve worker productivity and safety, and to overlay real-time
   metadata on equipment being serviced or operated.

   In this context, it is important to ensure that the AR/VR traffic
   does not interfere with the critical traffic of the production
   system, i.e. performance characteristics such as latency and jitter
   for the critical traffic must be independent of disturbances.  It is
   also important to provide the AR/VR application with low latency,
   even at the edge of mobility.

5.1.2.  Recommendations related to wireless determinism and reliability

   The support of AR/AV in the context of remote maintenance
   environments is bound to increase in industrial environments, given
   its relevance in terms of remote maintenance and equipment operation.
   It is also important to consider its use in the context of worker
   safety, and it is foreseeable that in the future AV-based remote
   maintenance will be supported by mobile devices carried by workers on
   the move.  Wireless is therefore a key communications asset for this
   type of application.  In terms of traffic on a converged network, AR/
   AV is a real-time, bandwidth-intensive service.  It therefore
   requires special treatment (other than Best Effort, BE).  In
   addition, AR/AV traffic flows must not cause interference when
   transmitted over wireless links.  Traffic isolation is therefore an
   important aspect to ensure for this type of traffic profile.

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   A third aspect to be addressed in the future is the fact that there
   will most likely be a need to support multiple AR/AV streams from
   different end-users within a single Wireless Local Area Network
   (WLAN), increasing the need for traffic isolation.  A fourth issue is
   that VR systems, if not properly supported, will lead to VR sickness.
   Specific network and non-network requirements have already been
   identified by IEEE 802, MPEG, 3GPP.  Such requirements include
   support for higher frame rates, reduction of motion-to-photon
   latency, higher data rates, low jitter, etc.

5.1.3.  Requirements Considerations

   Based on the former recommendations, the following list of
   requirements is identified for wireless determinism and reliability
   and availability:

   *  The AR/AV traffic MUST be isolated in order to prevent
      interference, i.e., it SHOULD have a specific CoS assigned
      (downlink and uplink).

   *  Between the wireless devices (stations) and the AP, it is
      necessary to ensure that the AR/AV traffic is handled in a way
      that does not interfere with critical traffic.

   *  Low mobility SHOULD be supported.

   *  Multi-user support SHOULD be provided.

   *  VR sickness MUST be prevented [IEEERTA].

   *  Tight integration of AR/VR systems with production systems SHOULD
      be addressed in a way that is compatible with the deterministic
      wired infrastructure.  For example, Audio Video Bridging (AVB) in
      the wired TSN infrastructure.  Specifically, AVB is typically
      blocked by the time-sensitive shaper and affected by TAS, CBS,
      FIFO and FPNS (fixed priority non-preemptive scheduling).

   *  A software-based mechanism on the AP SHOULD support appropriate
      mapping of CoS to the wireless QoS (e.g., EDCA UPs).

   *  MAC layer contention MUST be mitigated for all wireless stations
      in the area (within the range of the same AP or not).

   Specific communication requirements to be considered are:

   *  Latency: 3-10ms [IEEERTA].

   *  Bandwidth, 0.1-2Gbps [IEEERTA].

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   *  Data payload, over 4Kbytes [IEEERTA].

5.2.  Decentralised Shop-floor Communication Services

5.2.1.  Description

   The increasing automation of industrial environments implies an
   increase in the number of integrated nodes, including mobile nodes.
   For example, wireless is a key driver for scenarios involving mobile
   vehicles [NICT].  NICT also describes production environments,
   especially those with high temperatures, where wireless communication
   is used to support worker safety and remote monitoring of production
   status.  Such environments include different applications (e.g.,
   worker safety, mobile robots, factory resource management) and debate
   on the interconnection of different wireless technologies and
   devices, from PLCs, to autonomous mobile robots, e.g., UAVs, AGVs.
   Wireless/wired integration mechanisms have also been discussed in the
   cost of self-organising production lines [DIETRICH2018].  Therefore,
   the concept of flexible and heterogeneous shop-floor communication is
   already present in industrial environments, based on hybrid wired/
   wireless systems and the integration of multi-AP environments.

5.2.2.  Recommendations related to wireless determinism and reliability

   Previous related work discusses centralised communication
   architectures (infrastructure mode), and for this case, the
   connectivity issue is usually circumvented by multi-AP coordination
   mechanisms.  In the context of multi-AP coordination, and assuming
   TDMA-based communication, a well-organised schedule can prevent
   collisions [FERN2019].  Therefore, for this specific type of
   scenario, the main issue is to handle handovers in a timely and
   accurate manner that can provide deterministic guarantees.  However,
   as the number of nodes in the shop floor increases, the connectivity
   problem becomes more complex.

   It is therefore relevant to also explore the possibility of a
   "decentralised" approach to factory communication, considering both
   mobile and static nodes.  In this case, and from a topology
   perspective, wireless industrial services are expected to be provided
   in both ad-hoc and infrastructure modes.  Within the ad-hoc
   communication domains, there is control-based traffic integrated with
   sensing (critical, non-critical), with real-time traffic as well as
   time-triggered traffic.  Each node is responsible for managing its
   access to the medium, requiring a cooperative protocol approach.

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5.2.3.  Requirements Considerations

   Based on the former recommendations, the following list of
   requirements is identified for wireless determinism and reliability
   and availability:

   *  A wider variety of traffic profiles MUST be supported, thus
      increasing the management complexity.

   *  Devices communicating via ad-hoc mode MUST integrate a
      collaborative communication approach, e.g., relaying, cluster-
      based scheduling approach.

   *  Low mobility MUST be supported (e.g., up to 2 m/s within a BSS).

   *  Multi-AP coordination MUST still be integrated.

   *  Frequent handover MUST be supported, ideally with a make-before-
      break approach.

   *  Neighbor detection and coverage problem detection MUST be
      implemented in ad-hoc nodes.

   We list next some key specific communication requirements:

   *  Latency: 20-40ms [ROBOTS1].

   *  Packet payload: small (e.g., 50 bytes) and variable bit rate
      [ROBOTS1].

5.3.  Autonomous Airborne Services

   ### Description

   Over the last decade several services have emerged that rely on the
   autonomous (full or partial) operation of airborne systems.  Examples
   of such systems are: logistics drones; swarm of drones (e.g. for
   surveillance); urban air mobility [UAM18]; single-pilot operation of
   commercial aircraft [BBN8436].

   Such autonomous airborne systems rely on advances in communications,
   navigation, and air traffic management to mitigate the significant
   workload of autonomous operations, namely through collaborative air-
   ground decision making.  Such decision making processes rely on an
   expanded role for ground operators, including tactical (re-routing)
   and emergency flight phases, and higher levels of decision support
   including real-time system monitoring.

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   Such a collaborative air-ground decision-making process is only
   possible with the support of a reliable wireless network capable of
   supporting the required data exchange (of different traffic types)
   within significant constraints in terms of delay and error avoidance.

5.3.1.  Recommendations related to wireless determinism and reliability

   Irrespective of the type of application (logistics, surveillance,
   urban air mobility, single pilot operation), an autonomous airborne
   system can be modelled as a multi-agent system in which agents need
   to use a wireless network to communicate reliably with each other
   and, possibly, with a control entity.  The nature and position of
   such agents will vary from application to application.  For example,
   all agents may be collocated in the same or different aircraft.

   A powerful and reliable wireless network plays an important role in
   meeting the challenges of autonomous airborne systems, such as
   coordination and collaboration strategies, control mechanisms and
   mission planning algorithms.  Therefore, wireless technologies will
   play a central role in creating the required network system,
   including air-to-air communications (single or multi-hop), but also
   air-to-ground communications.

   Air-to-air communications allow all airborne agents to establish
   efficient communications, enabling the reception of error-pruned data
   exchanged within the required timeframes.  For example, in a swarm,
   drones can communicate with each other either directly or indirectly
   by establishing multi-hop communication paths with other drones.

   In air-to-ground communications, airborne agents communicate with a
   control centre, such as a ground station, to receive real-time
   updated information (e.g. mission-related).  Air-to-ground
   communications are usually direct.

   Air-to-air and air-to-ground communications are combined by a
   communication architecture, which can be of different types.  In
   small autonomous systems (single drones used for logistics), a
   central control station is used with enough power to communicate with
   the drone.  In autonomous systems with a large number of agents, a
   decentralised approach should be used.

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5.3.2.  Requirements Considerations

   When analysing the main characteristics of wireless communication
   architectures, the requirements of high coverage and maintaining
   connectivity should be given first priority.  The former plays an
   important role in gathering the information needed to operate the
   autonomous system, while maintaining connectivity ensures real-time
   communication within the system.

   However, autonomous systems may operate in unfamiliar environments,
   with unpredictable threats and obstacles in time and space.
   Therefore, such systems should rely on wireless technology with high
   levels of reliability and availability.  For example, wireless
   technology that can keep two neighbouring agents connected even if
   their direct link falls below the required minimum signal-to-noise
   ratio (SNR) or receive signal strength indicator (RSSI) range.  At a
   system level, wireless network technologies, such as routing, should
   be able to cognitively respond to changes in the environment to adapt
   the communication system to ensure the required coverage and
   connectivity levels.

   In this sense, it is necessary to study routing protocols capable of
   ensuring the desired level of reliability and availability of the
   overall system.  This means that the wireless routing function should
   fulfil a number of requirements, including:

   *  Suitable for dynamic topologies.

   *  Scalable with the number of networked agents.

   *  Ensure low values of packet delays (KPI depends upon the specific
      application).

   *  Ensure high values of packet delivery (KPI depends upon the
      specific application).

   *  Ensure fast recovery in the presence of interrupted
      communications.

   *  Ensure low cost in terms of the utilization of network resources
      (e.g. network queues, transmission opportunities).

   *  Ensure high robustness to link failure.

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6.  Security Considerations

   This document describes industrial services communication
   requirements for the integration of reliable Wi-Fi technologies.  The
   different services have security considerations which have been
   described in the respective sources [IEEERTA], [NICT], [IIC],
   [AVNU2020], [ACIA].

7.  IANA Considerations

   This document has no IANA actions.

8.  Acknowledgments

   We thank the following former contributors: Matthias Kovatsch.

   The research leading to these results received funding in 2021 from
   the joint fortiss GmbH and Huawei project TSNWiFi (https://www.fortis
   s.org/en/research/projects/detail/tsnwifi(https://www.fortiss.org/en/
   research/projects/detail/tsnwifi)).

   The work of Carlos J.  Bernardos in this document has been partially
   supported by the Horizon Europe PREDICT-6G (Grant 101095890),
   DESIRE6G (Grant 101096466), Hexa-X-II (101095759) and UNICO I+D 6G-
   DATADRIVEN-04 project (TSI-063000-2021-132).

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

9.2.  Informative References

   [ACIA]     5G ACIA, ., "5G for Connected Industries and Automation",
              November 2019.

   [AVIONICS] Fischione, P.Park, P.Di Marco, J.Nah, and C., "Wireless
              Avionics Intra-Communications, A Survey of Benefits,
              Challenges, and Solutions, pp. 1-24", 2020.

   [AVNU2020] Bush, S., "Avnu Alliance White Paper Wireless TSN-
              Definitions, Use Cases & Standards Roadmap", 2020.

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   [BBN8436]  Pew, Deutsch, Stephen, and Richard W., "Single pilot
              commercial aircraft operation. BBN Report.", 2005.

   [DIETRICH2018]
              , & Fohler, G, Dietrich, S., May, G., von Hoyningen-Huene,
              J., Mueller, A., "Frame conversion schemes for cascaded
              wired/wireless communication networks of factory
              automation, Mobile Networks and Applications, 23(4),
              817-827", 2018.

   [FERN2019] Fernandez Ganzabal, Z., "Analysis of the Impact of
              Wireless Mobile Devices in Critical Industrial
              Applications", May 2019.

   [IEEERTA]  Meng, K., "IEEE 802.11 Real Time Applications TIG Report",
              2018.

   [IIC]      Linehan, M., "Time Sensitive Networks for Flexible
              Manufacturing Testbed Characterization and Mapping of
              Converged Traffic Types", 2020.

   [NENDICA]  Zein, Ed, N., "IEEE 802 Nendica Report, Flexible Factory
              IoT-Use Cases and Communication Requirements for Wired and
              Wireless Bridged Networks", 2020.

   [NICT]     NICT, "Wireless use cases and communication requirements
              in factories ( abridged edition ), Flex. Factories Proj",
              February 2018.

   [OPCFLC]   "OPC Foundation Field Level Communications (FLC)
              Initiative", September 2020,
              <https://opcfoundation.org/flc/>.

   [PARK2020] Park, Pangun, et al, ., "Wireless Avionics Intra-
              Communications, A Survey of Benefits, Challenges, and
              Solutions. IEEE Internet of Things Journal", 2020.

   [RFC8578]  Grossman, E., Ed., "Deterministic Networking Use Cases",
              RFC 8578, DOI 10.17487/RFC8578, May 2019,
              <https://www.rfc-editor.org/info/rfc8578>.

   [RFC9450]  Bernardos, CJ., Ed., Papadopoulos, G., Thubert, P., and F.
              Theoleyre, "Reliable and Available Wireless (RAW) Use
              Cases", RFC 9450, DOI 10.17487/RFC9450, August 2023,
              <https://www.rfc-editor.org/info/rfc9450>.

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   [ROBOTS1]  Hoebeke, J.Haxhibeqiri, E.A.Jarchlo, I.Moerman, and J.,
              "Flexible Wi-Fi Communication among Mobile Robots in
              Indoor Industrial Environments, Mob. Inf. Syst.", 2018.

   [UAM18]    Shamiyeh, Michael, Raoul Rothfeld, and Mirko Hornung, .,
              "A performance benchmark of recent personal air vehicle
              concepts for urban air mobility.  Proceedings of the 31st
              Congress of the International Council of the Aeronautical
              Sciences, Belo Horizonte, Brazil", 2018.

   [WAIC]     International Telecommunication Union, "Technical
              characteristics and operational objectives for wireless
              avionics intra-communications, Policy, vol. 2197, p. 58,".

Authors' Addresses

   Rute C. Sofia
   fortiss GmbH
   Guerickestr. 25
   80805 Munich
   Germany
   Email: sofia@fortiss.org

   Paulo Milheiro Mendes
   Airbus
   Willy-Messerschmitt Strasse 1
   81663 Munich
   Germany
   Email: paulo.mendes@airbus.com

   Carlos J. Bernardos (editor)
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   28911 Leganes, Madrid
   Spain
   Phone: +34 91624 6236
   Email: cjbc@it.uc3m.es
   URI:   http://www.it.uc3m.es/cjbc/

   Eve Schooler
   University of Oxford
   United States of America
   Email: eve.schooler@gmail.com
   URI:   http://www.eveschooler.com

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