Requirements for Reliable Wireless Industrial Services
draft-ietf-detnet-raw-industrial-req-00
| Document | Type | Active Internet-Draft (detnet WG) | |
|---|---|---|---|
| Authors | Rute C. Sofia , Paulo Mendes , Carlos J. Bernardos , Eve Schooler | ||
| Last updated | 2024-01-19 | ||
| Replaces | draft-ietf-raw-industrial-requirements | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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draft-ietf-detnet-raw-industrial-req-00
Deterministic Networking Working Group R.S. Sofia
Internet-Draft fortiss GmbH
Intended status: Informational P. Mendes
Expires: 21 July 2024 Airbus
CJ. Bernardos, Ed.
UC3M
E. Schooler
University of Oxford
18 January 2024
Requirements for Reliable Wireless Industrial Services
draft-ietf-detnet-raw-industrial-req-00
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.
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This Internet-Draft will expire on 21 July 2024.
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
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 . . . . . . . . . . . . . . . . 12
4.7. Power Grid Control . . . . . . . . . . . . . . . . . . . 13
4.8. Wireless Avionics Intra-communication . . . . . . . . . . 14
5. Additional Reliable Wireless Industrial Services . . . . . . 15
5.1. AR/VR Services within Flexible Factories . . . . . . . . 15
5.1.1. Description . . . . . . . . . . . . . . . . . . . . . 15
5.1.2. Wireless Integration Recommendations . . . . . . . . 16
5.1.3. Requirements Considerations . . . . . . . . . . . . . 16
5.2. Decentralised Shop-floor Communication Services . . . . . 17
5.2.1. Description . . . . . . . . . . . . . . . . . . . . . 17
5.2.2. Wireless Integration Recommendations . . . . . . . . 18
5.2.3. Requirements Considerations . . . . . . . . . . . . . 18
5.3. Autonomous Airborne Services . . . . . . . . . . . . . . 19
5.3.1. Wireless Integration Recommendations . . . . . . . . 19
5.3.2. Requirements Considerations . . . . . . . . . . . . . 20
6. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
9.1. Normative References . . . . . . . . . . . . . . . . . . 21
9.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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.
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Wireless, and in particular the latest evolution of Wireless Fidelity
(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. Wi-Fi brings
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
elaborates specific requirements to be considered for both current
wireless services and a subset of future industrial wireless
services.
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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 IEEE 802.11 is
already being used, derived from an analysis of related work.
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
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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
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].
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Derived from the analysis of the above sources, this section provides
a description of service categories and their communication
requirements. The following application categories 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.
In this category, examples of services and their communication
requirements are:
* Control of machines and robots.
- Bounded latency: below 10 ms.
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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).
* 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.
- Periodic.
- Transmit data size (bytes): 10-400 (small).
- Tolerance to packet loss: 0.
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- 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.
- Time synchronization: 10-1 "U+00B5" s.
* Machine, production line controls
- Bounded latency: 10 - 1 ms.
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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.
- Time synchronization: 10-1 "U+00B5"s.
- Transmit data size (bytes): 64-1M.
- Tolerance to packet loss: 0.
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- 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.
- Periodic, once per second.
* Facility control environment
- Bounded latency: 1s-50s.
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- 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)
- Bounded latency: 500ms.
- Sporadic, once per 100ms.
- Transmit data size (bytes): 10-6K.
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- 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.
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.
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- 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.
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.
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* 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.
* 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].
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* 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. We have specifically selected three different examples of
such use-cases: 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 wireless
integration 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.
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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. Wireless Integration Recommendations
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.
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
A number of issues need to be addressed in such applications to
ensure minimal interference:
* 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.
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* 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].
* 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.
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5.2.2. Wireless Integration Recommendations
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.
5.2.3. Requirements Considerations
In such an environment, connectivity becomes more complex and
requires additional support:
* 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.
Specific communication requirements that can be considered are:
* Latency: 20-40ms [ROBOTS1].
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* 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.
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. Wireless Integration Recommendations
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.
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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.
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.
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* 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.
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.fortiss.or
g/en/research/projects/detail/tsnwifi(https://www.fortiss.org/en/rese
arch/projects/detail/tsnwifi))
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.
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[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.
[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] Fernández 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>.
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[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>.
[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/
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Eve Schooler
University of Oxford
United States of America
Email: eve.schooler@gmail.com
URI: http://www.eveschooler.com
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