Internet DRAFT - draft-sofia-raw-industrialreq
draft-sofia-raw-industrialreq
Reliable and Available Wireless Working Group R.C. Sofia
Internet-Draft fortiss GmbH
Intended status: Informational M. Kovatsch
Expires: 8 September 2021 Huawei Technologies
P. Mendes
Airbus
7 March 2021
Requirements for Reliable Wireless Industrial Services
draft-sofia-raw-industrialreq-00
Abstract
This document provides an overview on communication requirements for
handling reliable wireless services within the context of industrial
environments. The goal of the draft is to bring awareness to
communication requirements of current and future wireless industrial
services; how can they co-exist with wired infrastructures; key
drivers for reliable wireless integration; relevant communication
requirements to take into consideration; current and future
challenges derived from the use of wireless.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the mailing list
(raw@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/raw/.
Source for this draft and an issue tracker can be found at
https://github.com/rute19104/draft-raw-requirements.
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 4 September 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction
2. Conventions used in this document
3. Definitions
4. Wireless Industrial Services Today
4.1. Equipment and Process Control Services
4.2. Quality Supervision Services
4.3. Factory Resource Management Services
4.4. Display Services
4.5. Human Safety Services
4.6. Mobile Robotics Services
4.7. Power Grid Control
4.8. Wireless Avionics Intra-communication
5. Additional Reliable Wireless Industrial Services
5.1. AR/VR Services within Flexible Factories
5.1.1. Description
5.1.2. Wireless Integration Recommendations
5.1.3. Requirements Considerations
5.2. Decentralized Shop-floor Communication Services
5.2.1. Description
5.2.2. Wireless Integration Recommendations
5.2.3. Requirements Considerations
5.3. Autonomous Airborne Services
5.3.1. Wireless Integration Recommendations
5.3.2. Requirements Considerations
6. Security Considerations
7. IANA Considerations
8. Acknowledgments
9. References
9.1. Normative References
9.2. Informative References
Authors' Addresses
1. Introduction
Within industrial environments, short-range wireless standards, such
as IEEE 802.11ax, are gaining prominence as there exists an
increasing need for flexibility in terms of infrastructure layout, of
processes support. Wireless, and specifically Wireless Fidelity (Wi-
Fi), is now reaching a maturity point where the available
transmission rates become highly competitive in comparison to wired
environments, thus increasing flexibility, providing a lower cost and
higher availability in scenarios requiring, for instance, mobility
support. There are, nonetheless, barriers to the integration of
wireless in industrial environments. Firstly, being wireless a
shared medium, it experiences challenges such as interference and
signal strength variability depending on its surroundings. These
features raise issues concerning critical services availability,
resilience, and security support. Secondly, wireless relies on
probabilistic Quality of Service (QoS) and therefore requires tuning
to be able to support time-sensitive traffic with bounded latency,
low jitter, zero congestion loss. However, the recent advancements
of OFDMA-based wireless in the context of IEEE 802.11 standards such
as 802.11ax and 802.11be bring in interesting features in the context
of supporting critical industrial applications, e.g., a higher degree
of flexibility in terms of resource management; frequency allocation
aspects that can provide better traffic isolation, or even mechanisms
that can assist a tighter time synchronization across wireless
environments, thus providing the means to better support traffic in
converged networks. Still, being able to address the communication
challenges that exist in industrial domains require a better
understanding of communication requirements that the existing and
future industrial applications may attain. Hence, the focus of this
draft is on discussing industrial application requirements, currently
and for the future and how to best support time-sensitive
applications and services within industrial converged networks. For
that purpose, the draft debates on wireless industrial services
collected from related normative and informational references on the
industrial domain; debates on key drivers for the integration of
wireless; debates on specific wireless mechanisms that may assist
such integration and challenges thereof; and elaborates on specific
requirements to observe both for current wireless services as well as
for 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 (aka bounded latency), concerns the end-to-end
transmission delay between a transmitter and a receiver, when a
traffic flow is triggered by an application. By definition,
latency corresponds to the time interval between sending the first
packet of a flow from a source to a destination, until the instant
of reception of the last packet of that flow.
* Periodicity stands for whether or not the data transmission is
executed in a periodic fashion and whenever possible, the specific
periodicity per unit of time has been specified.
* "Transmit data size" corresponds to the data payload in bytes.
* Tolerance to packet loss is presented as "0" (zero congestion
loss); tolerant (the application has tolerance to packet loss).
Packet loss occurs when packets fail to reach a specific
destination on a network. Packet loss is usually measured as a
percentage of packets loss in regards to the overall packets sent.
In the context of deterministic networking and in particular, of
Time-sensitive Networking (TSN), a packet is lost when it is not
received within a specific deadline.
* "Time sync" refers to the need to ensure IEEE 1588
synchronization.
* "Node density" provides (wherever available) a glimpse into the
number of end-nodes per 20mx20m.
4. Wireless Industrial Services Today
This section describes industrial applications where IEEE 802.11 is
already being applied, derived from an analysis of related work.
Industrial wireless services focused on the strengthening of
industrial manufacturing environments have been intensively
documented via the IEEE Nendica group [NENDICA], the Internet
Industrial Consortium [IIC], the OPC FLC working group [OPCFLC]. The
IEEE Nendica 2020 report [NENDICA] comprises several end-to-end use-
cases and a technical analysis of the identified features and
functions supported via wireless/wired deterministic environments.
Based on surveys to industry, the report provides a first
characterization of wireless services in factories (Wi-Fi 5),
characterizing 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
concerning the support of 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, summarizing the problem statement (main 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 aggregates the different services
in 3 classes (A,B,C) and provides communication requirements for each
class categorized 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 latency
bound); time synchronization needs (in the order of micro/
milliseconds); throughput needs (high, moderate, low). The report
concludes with guidelines concerning implementation aspects, e.g.,
traffic classification aspects and new capabilities to support real-
time applications.
The Avnu Alliance provides a white paper describing steps for the
integration of TSN over WiFi [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 being complementary to wired within
connected cabines, i.e., in regards to the wiring harness within
vehicles (cars, airplanes, trains), which are currently expensive and
which require a complex onboarding. Wireless can assist in lowering
the costs, if it can be adapted to the critical latency, safety
requirements and regulations. Such cases would require 100
micosecond level cycles, according to Avnu. The 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 debated in the
context of 5G ACIA [ACIA], NICT [NICT], and IETF Deterministic
Networking [RFC8578]. These sources provide an overview on user
stories, and debate on the challenges brought by the integration of
wireless. However, communication requirements are not presented in a
systematic way. Lastly, the IETF RAW working group has an active
draft which provides an initial overview on the challenges of
wireless industrial use-cases [IETFRAW-USECASES].
Derived from the analysis of the aforementioned sources, this section
provides a description of categories of applications, and respective
communication requirements. The following categories of applications
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 selected communication requirements and which are presented for
each category of applications have been extracted from the different
available related work. The parameters are: bounded latency;
periodicity; transmit data size; tolerance to packet loss; time
synchronization needs; node density characterization.
4.1. Equipment and Process Control Services
This category of industrial wireless services refers to the data
exchange required to send, for instance, commands to mobile robots/
vehicles, production equipment, and also to receive status
information. Reasons for wireless integration concern: flexibility
of deployment, reconfigurability, mobility, maintenance cost
reduction.
In this category, examples of applications and respective
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.
- 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[micro]s.
* Mobile robotics
- Bounded latency: 50 -10 ms.
* AR/VR, remote HMI
- Bounded latency: 10 - 1 ms.
- Time synchronization: ~1 [micro]s.
- Time synchronization: 10-1[micro]s.
* Machine, production line controls
- Bounded latency: 10 - 1 ms.
4.2. Quality Supervision Services
Quality supervision comprises industrial services that collect and
assess information related to products and states of machines during
production. Reasons for wireless integration concern: flexibility of
deployment, maintenance cost reduction.
Examples of applications in this category, and their communication
requirements are:
* Inline inspection
- Bounded latency: bellow 10ms.
- Time synchronization: 10-1[micro]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[micro]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[micro]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 capturing information about whether production is
proceeding under proper environmental conditions, and whether staff
and devices contributing to productivity enhancement are being
managed appropriately. Reasons for wireless integration concern:
flexibility of deployment, reconfigurability, maintenance cost
reduction.
Services debated in this context are:
* Machine monitoring
- Bounded latency: 100ms-10s.
- Periodic.
- Time synchronization: 10-1[micro]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.
- 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 targets workers, allowing them to receive
requested support information. It also targets managers in regards
to monitoring of production status and processes. Reasons for
wireless integration are: scalability, flexibility of deployment,
mobility support. 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.
- Tolerance to packet loss: yes.
- Node density: 1-30.
4.5. Human Safety Services
Refers to industrial wireless services that concern collecting data
to infer about potential dangers 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 to consider 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.
4.7. Power Grid Control
Power grid control concerns services that support communication links
for predictive maintenance and to isolate faults on high voltage
lines, transformers, reactors, etc. Reasons to integrate wireless
concern: wire replacement maintenance cost reduction.
* 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 replacing cabling. Within the context of avionics
[AVIONICS], _Wireless Avionics Intra-communication (WAIC)_ systems
[WAIC] are expected to significantly benefit from determinist
communications, given their higher criticality. For instance, flight
control systems, integrating a large number of endpoints (sensors and
actuators), require high reliability and bounded latency to assist in
estimating and controlling the state of the aircraft. Real-time data
needs to be delivered with strict deadlines for most control systems.
The WAIC standardization process is still ongoing, without a clear
indication about the frequencies that would be reserved for such
systems, although the frequency band 4.2 GHz to 4.4 GHz is the one
that currently seems most popular. Nevertheless, independently of
the allocated frequency bands, the determinisc guarantees required by
WAIC services may be achieved by means of the integration of
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.
In terms of potential KPIs, specific communication requirements can
be identified:
* 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].
As an example of current standards that may support the deterministic
requirements of WAIC system, we can point to 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 may be supported by 802.11ax capability of dividing 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 can be achieved by
assigning more than one RU to the same station, for instance (an
aspect that is not covered by IEEE 802.11ax but already under
discussion for IEEE 802.11be). Through the central scheduling of the
RUs contention overhead can be avoided, which increases efficiency in
scenarios of dense deployments as is the case of WAIC applications.
In this context, OFDMA and the concept of spatial reuse is relevant,
to assist large-scale simultaneous transmission, while at the same
time preventing collision and interference, and guaranteeing 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)
decentralized shop-floor communication and iii) wireless cabin intra-
communications. Based on these examples, wireless integration
recommendations are debated and a list of specific requirements is
provided.
5.1. AR/VR Services within Flexible Factories
5.1.1. Description
While Video is today integrated both into industrial automation
systems, and also used with the shop-floor to assist the worker, the
integration of AR/VR in the shop-floor in industrial environments is
still in the beginning. It is, however, being applied within the
electric industry as a way to improve productivity and safety of
workers, also overlaying real-time metadata over equipment under
maintenance or operation.
In this context, it is important to ensure that the AR/AV traffic
does not interfere with the critical traffic of the production
system, i.e., performance characteristics like latency and jitter for
the critical traffic shall be independent from disturbances.
Moreover, it is also important to provide the AR/VR application with
low latency, also in the verge of mobility.
5.1.2. Wireless Integration Recommendations
The support of AR/AV in the context of remote maintenance
environments is bound to increase within industrial environments,
given the relevancy in terms of remote maintenance and equipment
operations. It is also relevant to consider its use within the
context of worker safety and it can be foreseen that AV-based remote
maintenance will, in the future, be supported via mobile devices
carried by workers on the go. Wireless is therefore a key
communication asset for this type of applications. In terms of
traffic in a converged network, AR/AV is a bandwidth intensive real-
time service. It therefore requires specific handling (other than
Best Effort, BE). Moreover, the AR/AV traffic flows must not create
disturbance when transmitted via wireless. Hence, traffic isolation
is an important aspect to ensure for this type of traffic profile.
A third aspect to address in the future concerns the fact that there
will most likely be the need to support multiple AR/AV streams from
different end-users within a single Wireless Local Area Network
(WLAN), thus increasing the need for traffic isolation. A fourth
aspect concerns the fact that VR systems, if not adequately support,
result in VR sickness. Specific network and non-network requirements
have already been identified by IEEE 802, MPEG, 3GPP. Such
requirements contemplate, for instance, support of higher frame
rates, reducing the motion-to-photon latency, higher data
transmission rates, low jitter, etc.
5.1.3. Requirements Considerations
In such applications, to ensure minimum interference, a few aspects
need to be ensured:
* The AR/AV traffic needs to be isolated in order to prevent
interference, i.e., it SHOULD have a specific CoS assigned
(downlink and uplink).
* Between wireless devices (stations) and AP, there is the need to
ensure that the AR/AV traffic is handled in a way that does not
hinder critical traffic.
* Low mobility SHOULD be supported.
* Multiple user support SHOULD be provided.
* VR sickness MUST be prevented [IEEERTA].
* A tight integration of the AR/VR systems with production systems
SHOULD be address in way compatible with the deterministic wired
infrastructure. For instance, Audio Video Bridging (AVB) in the
wired TSN infrastructure. Specifically, AVB is usually blocked by
the time-aware shaper, and impacted by: TAS, CBS, FIFO and FPNS
(fixed priority non-preemptive scheduling).
* A software-based mechanism on the AP SHOULD support an adequate
mapping of CoS to the wireless QoS (e.g., EDCA UPs).
* MAC layer contention MUST be mitigated for all wireless stations
within the area (within the range of the same AP or not).
Specific communication requirements:
* Latency: 3-10ms [IEEERTA].
* Bandwidth, 0.1-2Gbps [IEEERTA].
* Data payload, over 4Kbytes [IEEERTA].
5.2. Decentralized 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.
Wireless is, for instance, a key driver for scenarios involving
mobile vehicles [NICT]. NICT also describes already production
environments, in particular environments with elevated temperatures,
where wireless communication is used to support safety of workers and
to remotely monitor production status. Such environments comprise
different applications (e.g., safety of workers, 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 debated in the cost of self-organizing
production lines [DIETRICH2018]. Therefore, the notion 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. Wireless Integration Recommendations
Prior related work debates on centralized communication architectures
(infrastructure mode), and for this case, the issue of connectivity
is usually circumvented via multiple AP coordination mechanisms.
Within the context of multi-AP coordination and assuming TDMA-based
communication, a well-organized schedule can prevent collisions
[FERN2019]. Hence, for this specific type of scenario, the main
issue concerns handling handovers in a timely and precise way,
capable of providing deterministic guarantees. However, with an
increase on the number of nodes on a shop-floor, connectivity issues
become more complex.
Therefore, it is relevant to explore also the possibility of a
"decentralized" approach to shop-floor communication, considering
both mobile and static nodes. In this case, and from a topology
perspective, wireless industrial services are expected to be provided
over both ad-hoc and infrastructure mode. Within the ad-hoc
communication areas, 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, thus requiring a cooperative protocol approach.
5.2.3. Requirements Considerations
In such environment, connectivity becomes more complex requiring
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: * 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 emerged that rely on the
autonomous (total or partial) operation of airborne systems.
Examples of such systems are: logistic drones; swarm of drones (e.g.
for surveillance); urban Air Mobility [UAM18]; single Pilot operation
of commercial aircrafts [BBN8436].
Such autonomous airborne systems rely on advances in communications,
navigation, and air traffic management to mitigate the significant
workload of autonomous operations, namely by means of air-ground
collaborative decision making. Such decision making processes rely
on expanding the role of ground operators, including tactical (re-
routing) and emergency flight phases, as well as higher levels of
decision support including systems monitoring in real-time.
Such air-ground collaborative decision making process can only be
possible with the support of a reliable wireless network able to
assist in the required data exchange (of different types of traffic)
within significant constraints in terms of delay and error avoidance.
5.3.1. Wireless Integration Recommendations
Independently of the type of application (logistics, surveillance,
urban air mobility, single pilot operation), an autonomous airborne
system can be models as a multi-agent system, in which agents need to
use a wireless network to communicate reliably between them and in
possible with a control entity. The nature and position of such
agentes differ from application to application. For instance, all
agents may be collocated in the same or different flying vehicles.
A high-performance and reliable wireless network has an important
role in meeting the challenges of autonomous airborne systems, such
as coordination and collaboration strategies, control mechanisms, and
mission planning algorithms. Hence, wireless technologies plan a
central role in the creation of the needed networking system,
including air-to-air communications (single or multi-hop) but air-to-
ground communications.
Air-to-air communications allow all airborne agents to establish
efficient communication, allowing the reception of error prune data
exchanged within the required time frames. For instance, in a swarm
drones can either communicate with each other directly, or indirectly
by constructing multi-hop communication paths with other drones.
In what concerns air-to-ground communications, airborne agents
communicate with a control center, such as a ground station, to
obtain real-time updated information (e.g. mission related). Air-to-
ground communication is usually direct communication.
The air-to-air and air-to-ground communications are combined through
a communication architecture, which can be of different types. In
small autonomous systems (single drones used for logistics), a
central control station is deployed with enough powerf to communicate
with the drone. In autonomous systems with a large number of agents,
a decentralized approach should be used.
5.3.2. Requirements Considerations
When analysing the major properties of wireless communication
architectures, the first priority should go to requirements of high
coverage and maintaining connectivity. The former plays an important
role in gathering the information needed for the operation of the
autonomous system, while maintaining connectivity ensures the real-
time communication within the system.
However, autonomous systems may operate in unknown environments, with
the unpredicted appearance of threats and obstacles in time and
space. Hence such systems should rely on wireless technology that
has a high level of reliability and availability. For instance,
wireless technology that is able to keep two neighbour agents
connected, even when their direct link drops below the required
minimum signal-to-noise ratio (SNR) or receive signal strength
indicators (RSSI) range. On a system level, wireless network
technologies, such as routing, should be able to react cognitively to
changes of the environment to adapt the communication system in order
to ensure the needed coverage and connectivity levels.
In this sense it is required the investigation of routing protocols
able to ensure the desirable level or reliability and availability of
complete system. This means that the wireless routing function
should fulfill a set 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.
6. Security Considerations
This document describes industrial application communication
requirements for the integration of reliable Wi-Fi technologies. The
different applications 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
The research leading to these results received funding from joint
fortiss GmbH and Huawei project TSNWiFi (https://www.fortiss.org/en/r
esearch/projects/detail/tsnwifi(https://www.fortiss.org/en/research/
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.
[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.
[IETFRAW-USECASES]
Bernardos, G.P.P.T.F.T.a.C., "RAW use cases," IETF draft -
RAW working group", 2020,
<https://datatracker.ietf.org/doc/draft-ietf-raw-use-
cases/>.
[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>.
[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
Matthias Kovatsch
Huawei Technologies
Riesstr. 25 C, 3.0G
80992 Munich
Germany
Email: ietf@kovatsch.net
Paulo Milheiro Mendes
Airbus
Willy-Messerschmitt Strasse 1
81663 Munich
Germany
Email: paulo.mendes@airbus.com
