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Keywords: determinism, availability, routing, path

Internet Engineering Task Force (IETF) CJ. Bernardos, Ed.
Request for Comments: 9450 UC3M
Category: Informational G. Papadopoulos
ISSN: 2070-1721 IMT Atlantique
P. Thubert
Cisco
F. Theoleyre
CNRS
August 2023
Reliable and Available Wireless (RAW) Use Cases
Abstract
The wireless medium presents significant specific challenges to
achieve properties similar to those of wired deterministic networks.
At the same time, a number of use cases cannot be solved with wires
and justify the extra effort of going wireless. This document
presents wireless use cases (such as aeronautical communications,
amusement parks, industrial applications, pro audio and video,
gaming, Unmanned Aerial Vehicle (UAV) and vehicle-to-vehicle (V2V)
control, edge robotics, and emergency vehicles), demanding reliable
and available behavior.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9450.
Copyright Notice
Copyright (c) 2023 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
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Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Aeronautical Communications
2.1. Problem Statement
2.2. Specifics
2.3. Challenges
2.4. The Need for Wireless
2.5. Requirements for RAW
2.5.1. Non-latency-critical Considerations
3. Amusement Parks
3.1. Use Case Description
3.2. Specifics
3.3. The Need for Wireless
3.4. Requirements for RAW
3.4.1. Non-latency-critical Considerations
4. Wireless for Industrial Applications
4.1. Use Case Description
4.2. Specifics
4.2.1. Control Loops
4.2.2. Monitoring and Diagnostics
4.3. The Need for Wireless
4.4. Requirements for RAW
4.4.1. Non-latency-critical Considerations
5. Professional Audio and Video
5.1. Use Case Description
5.2. Specifics
5.2.1. Uninterrupted Stream Playback
5.2.2. Synchronized Stream Playback
5.3. The Need for Wireless
5.4. Requirements for RAW
5.4.1. Non-latency-critical Considerations
6. Wireless Gaming
6.1. Use Case Description
6.2. Specifics
6.3. The Need for Wireless
6.4. Requirements for RAW
6.4.1. Non-latency-critical Considerations
7. Unmanned Aerial Vehicles and Vehicle-to-Vehicle Platooning and
Control
7.1. Use Case Description
7.2. Specifics
7.3. The Need for Wireless
7.4. Requirements for RAW
7.4.1. Non-latency-critical Considerations
8. Edge Robotics Control
8.1. Use Case Description
8.2. Specifics
8.3. The Need for Wireless
8.4. Requirements for RAW
8.4.1. Non-latency-critical Considerations
9. Instrumented Emergency Medical Vehicles
9.1. Use Case Description
9.2. Specifics
9.3. The Need for Wireless
9.4. Requirements for RAW
9.4.1. Non-latency-critical Considerations
10. Summary
11. IANA Considerations
12. Security Considerations
13. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
Based on time, resource reservation, and policy enforcement by
distributed shapers [RFC2475], Deterministic Networking (DetNet)
provides the capability to carry specified unicast or multicast data
streams for real-time applications with extremely low data loss rates
and bounded latency so as to support time-sensitive and mission-
critical applications on a converged enterprise infrastructure.
DetNet aims at eliminating packet loss for a committed bandwidth,
while ensuring a worst-case end-to-end latency, regardless of the
network conditions and across technologies. By leveraging lower
layer (Layer 2 (L2) and below) capabilities, Layer 3 (L3) can exploit
the use of a service layer, steering over multiple technologies and
using media independent signaling to provide high reliability,
precise time delivery, and rate enforcement. DetNet can be seen as a
set of new Quality of Service (QoS) guarantees of worst-case
delivery. IP networks become more deterministic when the effects of
statistical multiplexing (jitter and collision loss) are mostly
eliminated. This requires a tight control of the physical resources
to maintain the amount of traffic within the physical capabilities of
the underlying technology, e.g., by using time-shared resources
(bandwidth and buffers) per circuit, by shaping or scheduling the
packets at every hop, or by using a combination of these techniques.
Key attributes of DetNet include:
* time synchronization on all the nodes,
* multi-technology path with co-channel interference minimization,
* frame preemption and guard time mechanisms to ensure a worst-case
delay, and
* new traffic shapers, both within and at the edge, to protect the
network.
Wireless operates on a shared medium, and transmissions cannot be
guaranteed to be fully deterministic due to uncontrolled
interferences, including self-induced multipath fading. The term RAW
stands for "Reliable and Available Wireless" and refers to the
mechanisms aimed for providing high reliability and availability for
IP connectivity over a wireless medium. Making wireless reliable and
available is even more challenging than it is with wires, due to the
numerous causes of loss in transmission that add up to the congestion
losses and due to the delays caused by overbooked shared resources.
The wireless and wired media are fundamentally different at the
physical level. While the generic Problem Statement in [RFC8557] for
DetNet applies to the wired as well as the wireless medium, the
methods to achieve RAW necessarily differ from those used to support
Time-Sensitive Networking over wires, e.g., due to the wireless radio
channel specifics.
So far, open standards for DetNet have prevalently been focused on
wired media, with Audio Video Bridging (AVB) and Time-Sensitive
Networking (TSN) at the IEEE and DetNet [RFC8655] at the IETF.
However, wires cannot be used in several cases, including mobile or
rotating devices, rehabilitated industrial buildings, wearable or in-
body sensory devices, vehicle automation, and multiplayer gaming.
Purpose-built wireless technologies such as [ISA100], which
incorporates IPv6, were developed and deployed to cope with the lack
of open standards, but they yield a high cost in Operational
Expenditure (OPEX) and Capital Expenditure (CAPEX) and are limited to
very few industries, e.g., process control, concert instruments, or
racing.
This is now changing (as detailed in [RAW-TECHNOS]):
* IMT-2020 has recognized Ultra-Reliable Low Latency Communication
(URLLC) as a key functionality for the upcoming 5G.
* IEEE 802.11 has identified a set of real applications
[IEEE80211RTA], which may use the IEEE802.11 standards. They
typically emphasize strict end-to-end delay requirements.
* The IETF has produced an IPv6 stack for IEEE Std. 802.15.4 Time-
Slotted Channel Hopping (TSCH) and an architecture [RFC9030] that
enables RAW on a shared MAC.
Experiments have already been conducted with IEEE802.1 TSN over
IEEE802.11be [IEEE80211BE]. This mode enables time synchronization
and time-aware scheduling (trigger based access mode) to support TSN
flows.
This document extends the "Deterministic Networking Use Cases"
document [RFC8578] and describes several additional use cases that
require "reliable/predictable and available" flows over wireless
links and possibly complex multi-hop paths called "Tracks". This is
covered mainly by the "Wireless for Industrial Applications"
(Section 5 of [RFC8578]) use case, as the "Cellular Radio" (Section 6
of [RFC8578]) is mostly dedicated to the (wired) link part of a Radio
Access Network (RAN). Whereas, while the "Wireless for Industrial
Applications" use case certainly covers an area of interest for RAW,
it is limited to IPv6 over the TSCH mode of IEEE 802.15.4e (6TiSCH),
and thus, its scope is narrower than the use cases described next in
this document.
2. Aeronautical Communications
Aircraft are currently connected to Air-Traffic Control (ATC) and
Airline Operational Control (AOC) via voice and data communication
systems through all phases of a flight. Within the airport terminal,
connectivity is focused on high-bandwidth communications, whereas en
route it's focused on high reliability, robustness, and range.
2.1. Problem Statement
Up to 2020, civil air traffic had been growing constantly at a
compound rate of 5.8% per year [ACI19], and despite the severe impact
of the COVID-19 pandemic, air-traffic growth is expected to resume
very quickly in post-pandemic times [IAT20] [IAC20]. Thus, legacy
systems in Air-Traffic Management (ATM) are likely to reach their
capacity limits, and the need for new aeronautical communication
technologies becomes apparent. Especially problematic is the
saturation of VHF band in high density areas in Europe, the US, and
Asia [SESAR] [FAA20], calling for suitable new digital approaches
such as the Aeronautical Mobile Airport Communications System
(AeroMACS) for airport communications, SatCOM for remote domains, and
the L-band Digital Aeronautical Communication System (LDACS) as the
long-range terrestrial aeronautical communication system. Making the
frequency spectrum's usage a more efficient transition from analog
voice to digital data communication [PLA14] is necessary to cope with
the expected growth of civil aviation and its supporting
infrastructure. A promising candidate for long-range terrestrial
communications, already in the process of being standardized in the
International Civil Aviation Organization (ICAO), is LDACS [ICAO2022]
[RFC9372].
Note that the large scale of the planned Low Earth Orbit (LEO)
constellations of satellites can provide fast end-to-end latency
rates and high data-rates at a reasonable cost, but they also pose
challenges, such as frequent handovers, high interference, and a
diverse range of system users, which can create security issues since
both safety-critical and not safety-critical communications can take
place on the same system. Some studies suggest that LEO
constellations could be a complete solution for aeronautical
communications, but they do not offer solutions for the critical
issues mentioned earlier. Additionally, of the three communication
domains defined by ICAO, only passenger entertainment services can
currently be provided using these constellations. Safety-critical
aeronautical communications require reliability levels above 99.999%,
which is higher than that required for regular commercial data links.
Therefore, addressing the issues with LEO-based SatCOM is necessary
before these solutions can reliably support safety-critical data
transmission [Maurer2022].
2.2. Specifics
During the creation process of a new communication system, analog
voice is replaced by digital data communication. This sets a
paradigm shift from analog to digital wireless communications and
supports the related trend towards increased autonomous data
processing that the Future Communications Infrastructure (FCI) in
civil aviation must provide. The FCI is depicted in Figure 1:
Satellite
# #
# # #
# # #
# # #
# # #
# # #
# # #
# Satellite-based # #
# Communications # #
# SatCOM (#) # #
# # Aircraft
# # % %
# # % %
# # % Air-Air %
# # % Communications %
# # % LDACS A/A (%) %
# # % %
# Aircraft % % % % % % % % % % Aircraft
# | Air-Ground |
# | Communications |
# | LDACS A/G (|) |
# Communications in | |
# and around airports | |
# AeroMACS (-) | |
# | |
# Aircraft-------------+ | |
# | | |
# | | |
# Ground network | | Ground network |
SatCOM <---------------------> Airport <----------------------> LDACS
ground ground ground
transceiver transceiver transceiver
Figure 1: The Future Communication Infrastructure (FCI)
FCI includes:
* AeroMACS for airport and terminal maneuvering area domains,
* LDACS Air/Ground for terminal maneuvering area and en route
domains,
* LDACS Air/Ground for en route or oceanic, remote, and polar
regions, and
* SatCOM for oceanic, remote, and polar regions.
2.3. Challenges
This paradigm change brings a lot of new challenges:
* Efficiency: It is necessary to keep latency, time, and data
overhead of new aeronautical data links to a minimum.
* Modularity: Systems in avionics usually operate for up to 30
years. Thus, solutions must be modular, easily adaptable, and
updatable.
* Interoperability: All 192 members of the ICAO must be able to use
these solutions.
* Dynamicity: The communication infrastructure needs to accommodate
mobile devices (airplanes) that move extremely fast.
2.4. The Need for Wireless
In a high-mobility environment, such as aviation, the envisioned
solutions to provide worldwide coverage of data connections with in-
flight aircraft require a multi-system, multi-link, multi-hop
approach. Thus, air, ground, and space-based data links that provide
these technologies will have to operate seamlessly together to cope
with the increasing needs of data exchange between aircraft, air-
traffic controller, airport infrastructure, airlines, air network
service providers (ANSPs), and so forth. Wireless technologies have
to be used to tackle this enormous need for a worldwide digital
aeronautical data link infrastructure.
2.5. Requirements for RAW
Different safety levels need to be supported. All network traffic
handled by the Airborne Internet Protocol Suite (IPS) System are not
equal, and the QoS requirements of each network traffic flow must be
considered n order to avoid having to support QoS requirements at the
granularity of data flows. These flows are grouped into classes that
have similar requirements, following the Diffserv approach
[ARINC858P1]. These classes are referred to as Classes of Service
(CoS), and the flows within a class are treated uniformly from a QoS
perspective. Currently, there are at least eight different priority
levels (CoS) that can be assigned to packets. For example, a high-
priority message requiring low latency and high resiliency could be a
"WAKE" warning indicating two aircraft are dangerously close to each
other, while a less safety-critical message with low-to-medium
latency requirements could be the "WXGRAPH" service providing
graphical weather data.
Overhead needs to be kept to a minimum since aeronautical data links
provide comparatively small data rates on the order of kbit/s.
Policy needs to be supported when selecting data links. The focus of
RAW here should be on the selectors that are responsible for the
track a packet takes to reach its end destination. This would
minimize the amount of routing information that must travel inside
the network because of precomputed routing tables, with the selector
being responsible for choosing the most appropriate option according
to policy and safety.
2.5.1. Non-latency-critical Considerations
Achieving low latency is a requirement for aeronautics
communications, though the expected latency is not extremely low, and
what is important is to keep the overall latency bounded under a
certain threshold. Low latency in LDACS communications [RFC9372]
translates to a latency in the Forward Link (FL - Ground -> Air) of
30-90 ms and a latency in the Reverse Link (RL - Air -> Ground) of
60-120 ms. This use case is not latency critical from that view
point. On the other hand, given the controlled environment, end-to-
end mechanisms can be applied to guarantee bounded latency where
needed.
3. Amusement Parks
3.1. Use Case Description
The digitalization of amusement parks is expected to significantly
decrease the cost for maintaining the attractions. Such deployment
is a mix between multimedia (e.g., Virtual and Augmented Reality and
interactive video environments) and non-multimedia applications (e.g,
access control, industrial automation for a roller coaster).
Attractions may rely on a large set of sensors and actuators, which
react in real time. Typical applications comprise:
* Emergency: the safety of the operators and visitors has to be
preserved, and the attraction must be stopped appropriately when a
failure is detected.
* Video: augmented and virtual realities are integrated in the
attraction. Wearable mobile devices (e.g., glasses and virtual
reality headsets) need to offload one part of the processing
tasks.
* Real-time interactions: visitors may interact with an attraction,
like in a real-time video game. The visitors may virtually
interact with their environment, triggering actions in the real
world (through actuators) [KOB12].
* Geolocation: visitors are tracked with a personal wireless tag, so
that their user experience is improved. This requires special
care to ensure that visitors' privacy is not breached, and users
are anonymously tracked.
* Predictive maintenance: statistics are collected to predict the
future failures or to compute later more complex statistics about
the attraction's usage, the downtime, etc.
* Marketing: to improve the customer experience, owners may collect
a large amount of data to understand the behavior and the choices
of their clients.
3.2. Specifics
Amusement parks comprise a variable number of attractions, mostly
outdoor, over a large geographical area. The IT infrastructure is
typically multiscale:
* Local area: The sensors and actuators controlling the attractions
are colocated. Control loops trigger only local traffic, with a
small end-to-end delay, typically less than 10 ms, like classical
industrial systems [IEEE80211RTA].
* Wearable devices: Wearable mobile devices are free to move in the
park. They exchange traffic locally (identification,
personalization, multimedia) or globally (billing, child-
tracking).
* Edge computing: Computationally intensive applications offload
some tasks. Edge computing seems to be an efficient way to
implement real-time applications with offloading. Some non-time-
critical tasks may rather use the cloud (predictive maintenance,
marketing).
3.3. The Need for Wireless
Removing cables helps to easily change the configuration of the
attractions or upgrade parts of them at a lower cost. The attraction
can be designed modularly and can upgrade or insert novel modules
later on in the life cycle of the attraction. Novelty of attractions
tends to increase the attractiveness of an amusement park,
encouraging previous visitors to regularly visit the park.
Some parts of the attraction are mobile, like trucks of a roller-
coaster or robots. Since cables are prone to frequent failures in
this situation, wireless transmissions are recommended.
Wearable devices are extensively used for a user experience
personalization. They typically need to support wireless
transmissions. Personal tags may help to reduce the operating costs
[DISNEY15] and increase the number of charged services provided to
the audience (e.g., VIP tickets or interactivity). Some applications
rely on more sophisticated wearable devices, such as digital glasses
or Virtual Reality (VR) headsets for an immersive experience.
3.4. Requirements for RAW
The network infrastructure must support heterogeneous traffic, with
very different critical requirements. Thus, flow isolation must be
provided.
The transmissions must be scheduled appropriately, even in the
presence of mobile devices. While [RFC9030] already proposes an
architecture for synchronized, IEEE Std. 802.15.4 Time-Slotted
Channel Hopping (TSCH) networks, the industry requires a multi-
technology solution that is able to guarantee end-to-end requirements
across heterogeneous technologies with strict Service Level Agreement
(SLA) requirements.
Nowadays, long-range wireless transmissions are used mostly for best-
effort traffic. On the contrary, [IEEE802.1AS] is used for critical
flows using Ethernet devices. However, we need an IP-enabled
technology to interconnect large areas, independent of the Physical
(PHY) and Medium Access Control (MAC) layers.
It is expected that several different technologies (long vs. short
range) are deployed, which have to cohabit the same area. Thus, we
need to provide L3 mechanisms able to exploit multiple co-interfering
technologies (i.e., different radio technologies using overlapping
spectrum, and therefore, potentially interfering with each other).
It is worth noting that low-priority flows (e.g., predictive
maintenance, marketing) are delay tolerant; a few minutes or even
hours would be acceptable. While classical unscheduled wireless
networks already accommodate best-effort traffic, this would force
several colocated and subefficient deployments. Unused resources
could rather be used for low-priority flows. Indeed, allocated
resources are consuming energy in most scheduled networks, even if no
traffic is transmitted.
3.4.1. Non-latency-critical Considerations
While some of the applications in this use case involve control loops
(e.g., sensors and actuators) that require bounded latencies below 10
ms that can therefore be considered latency critical, there are other
applications as well that mostly demand reliability (e.g., safety-
related or maintenance).
4. Wireless for Industrial Applications
4.1. Use Case Description
A major use case for networking in industrial environments is the
control networks where periodic control loops operate between a
collection of sensors that measure a physical property (such as the
temperature of a fluid), a Programmable Logic Controller (PLC) that
decides on an action (such as "warm up the mix"), and actuators that
perform the required action (such as the injection of power in a
resistor).
4.2. Specifics
4.2.1. Control Loops
Process Control designates continuous processing operations, like
heating oil in a refinery or mixing up soda. Control loops in the
Process Control industry operate at a very low rate, typically four
times per second. Factory Automation, on the other hand, deals with
discrete goods, such as individual automobile parts, and requires
faster loops, to the rate of milliseconds. Motion control that
monitors dynamic activities may require even faster rates on the
order of and below the millisecond.
In all those cases, a packet must flow reliably between the sensor
and the PLC, be processed by the PLC, and be sent to the actuator
within the control loop period. In some particular use cases that
inherit from analog operations, jitter might also alter the operation
of the control loop. A rare packet loss is usually admissible, but
typically, a loss of multiple packets in a row will cause an
emergency halt of the production and incur a high cost for the
manufacturer.
Additional details and use cases related to industrial applications
and their RAW requirements can be found in [RAW-IND-REQS].
4.2.2. Monitoring and Diagnostics
A secondary use case deals with monitoring and diagnostics. This
data is essential to improve the performance of a production line,
e.g., by optimizing real-time processing or by maintenance windows
using Machine Learning predictions. For the lack of wireless
technologies, some specific industries such as Oil and Gas have been
using serial cables, literally by the millions, to perform their
process optimization over the previous decades. However, few
industries would afford the associated cost. One of the goals of the
Industrial Internet of Things is to provide the same benefits to all
industries, including SmartGrid, transportation, building,
commercial, and medical. This requires a cheap, available, and
scalable IP-based access technology.
Inside the factory, wires may already be available to operate the
control network. However, monitoring and diagnostics data are not
welcome in that network for several reasons. On the one hand, it is
rich and asynchronous, meaning that it may influence the
deterministic nature of the control operations and impact the
production. On the other hand, this information must be reported to
the operators over IP, which means the potential for a security
breach via the interconnection of the Operational Technology network
with the Internet Technology network and the potential of a rogue
access.
4.3. The Need for Wireless
Wires used on a robot arm are prone to breakage, after a few thousand
flexions, a lot faster than a power cable that is wider in diameter
and more resilient. In general, wired networking and mobile parts
are not a good match, mostly in the case of fast and recurrent
activities, as well as rotation.
When refurbishing older premises that were built before the Internet
age, power is usually available everywhere, but data is not. It is
often impractical, time consuming and expensive to deploy an Ethernet
fabric across walls and between buildings. Deploying a wire may take
months and cost tens of thousands of US Dollars.
Even when wiring exists, like in the case of an existing control
network, asynchronous IP packets, such as diagnostics, may not be
welcome for operational and security reasons. For those packets, the
option to create a parallel wireless network offers a credible
solution that can scale with the many sensors and actuators that
equip every robot, valve, and fan that are deployed on the factory
floor. It may also help detect and prevent a failure that could
impact the production, like the degradation (vibration) of a cooling
fan on the ceiling. IEEE Std. 802.15.4 TSCH [RFC7554] is a promising
technology for that purpose, mostly if the scheduled operations
enable the use of the same network by asynchronous and deterministic
flows in parallel.
4.4. Requirements for RAW
As stated by the "Deterministic Networking Problem Statement"
[RFC8557], a deterministic network is backwards compatible with
(capable of transporting) statistically multiplexed traffic while
preserving the properties of the accepted deterministic flows. While
the "6TiSCH Architecture" [RFC9030] serves that requirement, the work
at 6TiSCH was focused on best-effort IPv6 packet flows. RAW should
be able to lock so-called "hard cells" (i.e., scheduled cells
[6TiSCH-TERMS]) for use by a centralized scheduler and leverage time
and spatial diversity over a graph of end-to-end paths called a
"Track" that is based on those cells.
Over recent years, major industrial protocols have been migrating
towards Ethernet and IP. (For example, [ODVA] with EtherNet/IP [EIP]
and [PROFINET], where ODVA is the organization that supports network
technologies built on the Common Industrial Protocol (CIP) including
EtherNet/IP.) In order to unleash the full power of the IP hourglass
model, it should be possible to deploy any application over any
network that has the physical capacity to transport the industrial
flow, regardless of the MAC/PHY technology, wired, or wireless, and
across technologies. RAW mechanisms should be able to set up a Track
over a wireless access segment and a wired or wireless backbone to
report both sensor data and critical monitoring within a bounded
latency and should be able to maintain the high reliability of the
flows over time. It is also important to ensure that RAW solutions
are interoperable with existing wireless solutions in place and with
legacy equipment whose capabilities can be extended using
retrofitting. Maintainability, as a broader concept than
reliability, is also important in industrial scenarios [MAR19].
4.4.1. Non-latency-critical Considerations
Monitoring and diagnostics applications do not require latency-
critical communications but demand reliable and scalable
communications. On the other hand, process-control applications
involve control loops that require a bounded latency and, thus, are
latency critical. However, they can be managed end-to-end, and
therefore DetNet mechanisms can be applied in conjunction with RAW
mechanisms.
5. Professional Audio and Video
5.1. Use Case Description
Many devices support audio and video streaming [RFC9317] by employing
802.11 wireless LAN. Some of these applications require low latency
capability, for instance, when the application provides interactive
play or when the audio plays in real time -- meaning being live for
public addresses in train stations or in theme parks.
The professional audio and video industry (ProAV) includes:
* Virtual Reality / Augmented Reality (VR/AR)
* Production and post-production systems, such as CD and Blu-ray
disk mastering.
* Public address, media, and emergency systems at large venues
(e.g., airports, train stations, stadiums, and theme parks).
5.2. Specifics
5.2.1. Uninterrupted Stream Playback
Considering the uninterrupted audio or video stream, a potential
packet loss during the transmission of audio or video flows cannot be
tackled by re-trying the transmission, as it is done with file
transfer, because by the time the lost packet has been identified, it
is too late to proceed with packet re-transmission. Buffering might
be employed to provide a certain delay that will allow for one or
more re-transmissions. However, such an approach is not viable in
applications where delays are not acceptable.
5.2.2. Synchronized Stream Playback
In the context of ProAV over packet networks, latency is the time
between the transmitted signal over a stream and its reception.
Thus, for sound to remain synchronized to the movement in the video,
the latency of both the audio and video streams must be bounded and
consistent.
5.3. The Need for Wireless
Audio and video devices need the wireless communication to support
video streaming via IEEE 802.11 wireless LAN, for instance. Wireless
communications provide huge advantages in terms of simpler
deployments in many scenarios where the use of a wired alternative
would not be feasible. Similarly, in live events, mobility support
makes wireless communications the only viable approach.
Deployed announcement speakers, for instance, along the platforms of
the train stations, need the wireless communication to forward the
audio traffic in real time. Most train stations are already built,
and deploying novel cables for each novel service seems expensive.
5.4. Requirements for RAW
The network infrastructure needs to support heterogeneous types of
traffic (including QoS).
Content delivery must have bounded latency (to the lowest possible
latency).
The deployed network topology should allow for multipath. This will
enable for multiple streams to have different (and multiple) paths
(Tracks) through the network to support redundancy.
5.4.1. Non-latency-critical Considerations
For synchronized streaming, latency must be bounded. Therefore,
depending on the actual requirements, this can be considered as
"latency critical". However, the most critical requirement of this
use case is reliability, which can be achieved by the network
providing redundancy. Note that in many cases, wireless is only
present in the access where RAW mechanisms could be applied, but
other wired segments are also involved (like the Internet), and
therefore latency cannot be guaranteed.
6. Wireless Gaming
6.1. Use Case Description
The gaming industry includes [IEEE80211RTA] real-time mobile gaming,
wireless console gaming, wireless gaming controllers, and cloud
gaming. Note that they are not mutually exclusive (e.g., a console
can connect wirelessly to the Internet to play a cloud game). For
RAW, wireless console gaming is the most relevant one. We next
summarize the four:
* Real-time mobile gaming:
Real-time mobile gaming is very sensitive to network latency and
stability. The mobile game can connect multiple players together
in a single game session and exchange data messages between game
server and connected players. Real-time means the feedback should
present on-screen as users operate in-game. For good game
experience, the end-to-end latency plus game servers processing
time must be the same for all players and should not be noticeable
as the game is played. RAW technologies might help in keeping
latencies low on the wireless segments of the communication.
* Wireless console gaming:
While gamers may use a physical console, interactions with a
remote server may be required for online games. Most of the
gaming consoles today support Wi-Fi 5 but may benefit from a
scheduled access with Wi-Fi 6 in the future. Previous Wi-Fi
versions have an especially bad reputation among the gaming
community, the main reasons being high latency, lag spikes, and
jitter.
* Wireless Gaming controllers:
Most controllers are now wireless for the freedom of movement.
Controllers may interact with consoles or directly with the gaming
server in the cloud. A low and stable end-to-end latency is here
of predominant importance.
* Cloud Gaming:
Cloud gaming requires low-latency capability as the user commands
in a game session are sent back to the cloud server. Then, the
cloud server updates the game context depending on the received
commands, renders the picture/video to be displayed on the user
devices, and streams the picture/video content to the user
devices. User devices might very likely be connected wirelessly.
6.2. Specifics
While a lot of details can be found at [IEEE80211RTA], we next
summarize the main requirements in terms of latency, jitter, and
packet loss:
* Intra Basic Service Set (BSS) latency is less than 5 ms.
* Jitter variance is less than 2 ms.
* Packet loss is less than 0.1%.
6.3. The Need for Wireless
Gaming is evolving towards wireless, as players demand being able to
play anywhere, and the game requires a more immersive experience
including body movements. Besides, the industry is changing towards
playing from mobile phones, which are inherently connected via
wireless technologies. Wireless controllers are the rule in modern
gaming, with increasingly sophisticated interactions (e.g., haptic
feedback, augmented reality).
6.4. Requirements for RAW
Time-sensitive networking extensions:
Extensions, such as time-aware shaping and redundancy, can be
explored to address congestion and reliability problems present in
wireless networks. As an example, in haptics, it is very
important to minimize latency failures.
Priority tagging (Stream identification):
One basic requirement to provide better QoS for time-sensitive
traffic is the capability to identify and differentiate time-
sensitive packets from other (like best-effort) traffic.
Time-aware shaping:
This capability (defined in IEEE 802.1Qbv) consists of gates to
control the opening and closing of queues that share a common
egress port within an Ethernet switch. A scheduler defines the
times when each queue opens or closes, therefore, eliminating
congestion and ensuring that frames are delivered within the
expected latency bounds. Though, note that while this requirement
needs to be signaled by RAW mechanisms, it would actually be
served by the lower layer.
Dual/multiple link:
Due to the fact that competitions and interference are common and
hardly in control under wireless network, to improve the latency
stability, dual/multiple link proposal is brought up to address
this issue.
Admission Control:
Congestion is a major cause of high/variable latency, and it is
well known that if the traffic load exceeds the capability of the
link, QoS will be degraded. QoS degradation may be acceptable for
many applications today. However, emerging time-sensitive
applications are highly susceptible to increased latency and
jitter. To better control QoS, it is important to control access
to the network resources.
6.4.1. Non-latency-critical Considerations
Depending on the actual scenario, and on use of Internet to
interconnect different users, the communication requirements of this
use case might be considered as latency critical due to the need of
bounded latency. However, note that, in most of these scenarios,
part of the communication path is not wireless, and DetNet mechanisms
cannot be applied easily (e.g., when the public Internet is
involved), and therefore, reliability is the critical requirement.
7. Unmanned Aerial Vehicles and Vehicle-to-Vehicle Platooning and
Control
7.1. Use Case Description
Unmanned Aerial Vehicles (UAVs) are becoming very popular for many
different applications, including military and civil use cases. The
term "drone" is commonly used to refer to a UAV.
UAVs can be used to perform aerial surveillance activities, traffic
monitoring (i.e., the Spanish traffic control has recently introduced
a fleet of drones for quicker reactions upon traffic congestion
related events [DGT2021]), support of emergency situations, and even
transporting of small goods (e.g., medicine in rural areas). Note
that the surveillance and monitoring application would have to comply
with local regulations regarding location privacy of users.
Different considerations have to be applied when surveillance is
performed for traffic rules enforcement (e.g., generating fines), as
compared to when traffic load is being monitored.
Many types of vehicles, including UAVs but also others, such as cars,
can travel in platoons, driving together with shorter distances
between vehicles to increase efficiency. Platooning imposes certain
vehicle-to-vehicle considerations, most of these are applicable to
both UAVs and other vehicle types.
UAVs and other vehicles typically have various forms of wireless
connectivity:
* Cellular: for communication with the control center, remote
maneuvering, and monitoring of the drone;
* IEEE 802.11: for inter-drone communications (i.e., platooning) and
providing connectivity to other devices (i.e., acting as Access
Point).
Note that autonomous cars share many of the characteristics of the
aforementioned UAV case. Therefore, it is of interest for RAW.
7.2. Specifics
Some of the use cases and tasks involving UAVs require coordination
among UAVs. Others involve complex computing tasks that might not be
performed using the limited computing resources that a drone
typically has. These two aspects require continuous connectivity
with the control center and among UAVs.
Remote maneuvering of a drone might be performed over a cellular
network in some cases, but there are situations that need very low
latency and deterministic behavior of the connectivity. Examples
involve platooning of drones or sharing of computing resources among
drones (like a drone offloading some function to a neighboring
drone).
7.3. The Need for Wireless
UAVs cannot be connected through any type of wired media, so it is
obvious that wireless is needed.
7.4. Requirements for RAW
The network infrastructure is composed of the UAVs themselves,
requiring self-configuration capabilities.
Heterogeneous types of traffic need to be supported, from extremely
critical traffic types requiring ultra-low latency and high
resiliency to traffic requiring low-to-medium latency.
When a given service is decomposed into functions (which are hosted
at different UAVs and chained), each link connecting two given
functions would have a well-defined set of requirements (e.g.,
latency, bandwidth, and jitter) that must be met.
7.4.1. Non-latency-critical Considerations
Today's solutions keep the processing operations that are critical
local (i.e., they are not offloaded). Therefore, in this use case,
the critical requirement is reliability, and, only for some
platooning and inter-drone communications, latency is critical.
8. Edge Robotics Control
8.1. Use Case Description
The edge robotics scenario consists of several robots, deployed in a
given area (like a shopping mall) and inter-connected via an access
network to a network edge device or a data center. The robots are
connected to the edge so that complex computational activities are
not executed locally at the robots but offloaded to the edge. This
brings additional flexibility in the type of tasks that the robots
perform, reduces the costs of robot-manufacturing (due to their lower
complexity), and enables complex tasks involving coordination among
robots (that can be more easily performed if robots are centrally
controlled).
Simple examples of the use of multiple robots are cleaning, video
surveillance (note that this have to comply with local regulations
regarding user privacy at the application level), search and rescue
operations, and delivering of goods from warehouses to shops.
Multiple robots are simultaneously instructed to perform individual
tasks by moving the robotic intelligence from the robots to the
network's edge. That enables easy synchronization, scalable
solution, and on-demand option to create flexible fleet of robots.
Robots would have various forms of wireless connectivity:
* Cellular: as an additional communication link to the edge, though
primarily as backup, since ultra-low latency is needed.
* IEEE 802.11: for connection to the edge and also inter-robot
communications (i.e., for coordinated actions).
8.2. Specifics
Some of the use cases and tasks involving robots might benefit from
decomposition of a service into small functions that are distributed
and chained among robots and the edge. These require continuous
connectivity with the control center and among drones.
Robot control is an activity requiring very low latency (0.5-20 ms
[Groshev2021]) between the robot and the location where the control
intelligence resides (which might be the edge or another robot).
8.3. The Need for Wireless
Deploying robots in scenarios such as shopping malls for the
applications mentioned cannot be done via wired connectivity.
8.4. Requirements for RAW
The network infrastructure needs to support heterogeneous types of
traffic, from robot control to video streaming.
When a given service is decomposed into functions (which are hosted
at different UAVs and chained), each link connecting two given
functions would have a well-defined set of requirements (e.g.,
latency, bandwidth, and jitter) that must be met.
8.4.1. Non-latency-critical Considerations
This use case might combine multiple communication flows, with some
of them being latency critical (like those related to robot-control
tasks). Note that there are still many communication flows (like
some offloading tasks) that only demand reliability and availability.
9. Instrumented Emergency Medical Vehicles
9.1. Use Case Description
An instrumented ambulance would have one or multiple network segments
that are connected to end systems such as:
* vital signs sensors attached to the casualty in the ambulance to
relay medical data to hospital emergency room,
* a radio-navigation sensor to relay position data to various
destinations including dispatcher,
* voice communication for ambulance attendant (likely to consult
with ER doctor), and
* voice communication between driver and dispatcher.
The LAN needs to be routed through radio-WANs (a radio network in the
interior of a network, i.e., it is terminated by routers) to complete
the network linkage.
9.2. Specifics
What we have today is multiple communication systems to reach the
vehicle via:
* a dispatching system,
* a cellphone for the attendant,
* a special purpose telemetering system for medical data,
* etc.
This redundancy of systems does not contribute to availability.
Most of the scenarios involving the use of an instrumented ambulance
are composed of many different flows, each of them with slightly
different requirements in terms of reliability and latency.
Destinations might be either the ambulance itself (local traffic), a
near edge cloud, or the general Internet/cloud. Special care (at
application level) have to be paid to ensure that sensitive data is
not disclosed to unauthorized parties by properly securing traffic
and authenticating the communication ends.
9.3. The Need for Wireless
Local traffic between the first responders and ambulance staff and
the ambulance equipment cannot be done via wired connectivity as the
responders perform initial treatment outside of the ambulance. The
communications from the ambulance to external services must be
wireless as well.
9.4. Requirements for RAW
We can derive some pertinent requirements from this scenario:
* High availability of the internetwork is required. The exact
level of availability depends on the specific deployment scenario,
as not all emergency agencies share the same type of instrumented
emergency vehicles.
* The internetwork needs to operate in damaged state (e.g., during
an earthquake aftermath, heavy weather, a wildfire, etc.). In
addition to continuity of operations, rapid restore is a needed
characteristic.
* The radio-WAN has characteristics similar to the cellphone's --
the vehicle will travel from one radio coverage area to another,
thus requiring some hand-off approach.
9.4.1. Non-latency-critical Considerations
In this case, all applications identified do not require latency-
critical communication but do need high reliability and availability.
10. Summary
This document enumerates several use cases and applications that need
RAW technologies, focusing on the requirements from reliability,
availability, and latency. While some use cases are latency
critical, there are also several applications that are not latency
critical but do pose strict reliability and availability
requirements.
11. IANA Considerations
This document has no IANA actions.
12. Security Considerations
This document covers several representative applications and network
scenarios that are expected to make use of RAW technologies. Each of
the potential RAW use cases will have security considerations from
both the use-specific perspective and the RAW technology perspective.
[RFC9055] provides a comprehensive discussion of security
considerations in the context of DetNet, which are generally also
applicable to RAW.
13. Informative References
[6TiSCH-TERMS]
Palattella, MR., Ed., Thubert, P., Watteyne, T., and Q.
Wang, "Terms Used in IPv6 over the TSCH mode of IEEE
802.15.4e", Work in Progress, Internet-Draft, draft-ietf-
6tisch-terminology-10, 2 March 2018,
<https://datatracker.ietf.org/doc/html/draft-ietf-6tisch-
terminology-10>.
[ACI19] Airports Council International, "Annual World Airport
Traffic Report, 2019", 2019,
<https://store.aci.aero/product/annual-world-airport-
traffic-report-2019/>.
[ARINC858P1]
SAE International, "Internet Protocol Suite (IPS) for
Aeronautical Safety Services Part 1 Airborne IPS System
Technical Requirements", ARINC858P1, June 2021,
<https://www.sae.org/standards/content/arinc858p1/>.
[DGT2021] Menéndez, J., "Drones: asà es la vigilancia" [Drones: this
is surveillance], January 2021,
<https://revista.dgt.es/es/reportajes/2021/01ENERO/0126-
Como-funciona-un-operativo-con-drones.shtml>.
[DISNEY15] Kuang, C., "Disney's $1 Billion Bet on a Magical
Wristband", March 2015,
<https://www.wired.com/2015/03/disney-magicband/>.
[EIP] ODVA, "EtherNet/IP | ODVA Technologies | Industrial
Automation", <https://www.odva.org/technology-standards/
key-technologies/ethernet-ip/>.
[FAA20] U.S. Department of Transportation: Federal Aviation
Administration (FAA), "Next Generation Air Transportation
System (NextGen)", <https://www.faa.gov/nextgen/>.
[Groshev2021]
Groshev, M., Guimarães, C., de la Oliva, A., and R. Gazda,
"Dissecting the Impact of Information and Communication
Technologies on Digital Twins as a Service", IEEE Access,
Volume 9, DOI 10.1109/ACCESS.2021.3098109, July 2021,
<https://doi.org/10.1109/ACCESS.2021.3098109>.
[IAC20] Iacus, S., Natale, F., Santamaria, C., Spyratos, S., and
M. Vespe, "Estimating and projecting air passenger traffic
during the COVID-19 coronavirus outbreak and its socio-
economic impact", Safety Science, Volume 129,
DOI 10.1016/j.ssci.2020.104791, September 2020,
<https://doi.org/10.1016/j.ssci.2020.104791>.
[IAT20] IATA, "Economic Performance of the Airline Industry",
November 2020, <https://www.iata.org/en/iata-
repository/publications/economic-reports/airline-industry-
economic-performance---november-2020---report/>.
[ICAO2022] International Civil Aviation Organization (ICAO), "CHAPTER
13 L-Band Digital Aeronautical Communications System
(LDACS)", International Standards and Recommended
Practices, Annex 10 - Aeronautical Telecommunications,
Volume III, Communication Systems, 2022,
<https://www.ldacs.com/wp-content/uploads/2023/03/
WP06.AppA-DCIWG-6-LDACS_SARPs.pdf>.
[IEEE802.1AS]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks--Timing and Synchronization for Time-Sensitive
Applications", DOI 10.1109/IEEESTD.2020.9121845, IEEE
802.1AS-2020, June 2020,
<https://doi.org/10.1109/IEEESTD.2020.9121845>.
[IEEE80211BE]
Cavalcanti, D. and G. Venkatesan, "802.1 TSN over 802.11
with updates from developments in 802.11be", IEEE plenary
meeting, November 2020,
<https://www.ieee802.org/1/files/public/docs2020/new-
Cavalcanti-802-1TSN-over-802-11-1120-v02.pdf>.
[IEEE80211RTA]
IEEE standard for Information Technology, "IEEE 802.11
Real Time Applications TIG Report", November 2018.
[ISA100] ISA, "ISA100, Wireless Systems for Automation",
<https://www.isa.org/isa100/>.
[KOB12] Kober, J., Glisson, M., and M. Mistry, "Playing catch and
juggling with a humanoid robot",
DOI 10.1109/HUMANOIDS.2012.6651623, November 2012,
<https://doi.org/10.1109/HUMANOIDS.2012.6651623>.
[MAR19] Martinez, B., Cano, C., and X. Vilajosana, "A Square Peg
in a Round Hole: The Complex Path for Wireless in the
Manufacturing Industry", IEEE Communications Magazine,
Volume 57, Issue 4, DOI 10.1109/MCOM.2019.1800570, April
2019, <https://doi.org/10.1109/MCOM.2019.1800570>.
[Maurer2022]
Mäurer, N., Guggemos, T., Ewert, T., Gräupl, T., Schmitt,
C., and S. Grundner-Culemann, "Security in Digital
Aeronautical Communications A Comprehensive Gap Analysis",
International Journal of Critical Infrastructure
Protection, Volume 38, DOI 10.1016/j.ijcip.2022.100549,
September 2022,
<https://doi.org/10.1016/j.ijcip.2022.100549>.
[ODVA] ODVA, "ODVA | Industrial Automation | Technologies and
Standards", <https://www.odva.org/>.
[PLA14] Plass, S., Hermenier, R., Lücke, O., Gomez Depoorter, D.,
Tordjman, T., Chatterton, M., Amirfeiz, M., Scotti, S.,
Cheng, Y., Pillai, P., Gräupl, T., Durand, F., Murphy, K.,
Marriott, A., and A. Zaytsev, "Flight Trial Demonstration
of Seamless Aeronautical Networking", IEEE Communications
Magazine, Volume 52, Issue 5,
DOI 10.1109/MCOM.2014.6815902, May 2014,
<https://doi.org/10.1109/MCOM.2014.6815902>.
[PROFINET] PROFINET, "PROFINET Technology",
<https://us.profinet.com/technology/profinet/>.
[RAW-IND-REQS]
Sofia, R. C., Kovatsch, M., and P. Mendes, "Requirements
for Reliable Wireless Industrial Services", Work in
Progress, Internet-Draft, draft-ietf-raw-industrial-
requirements-00, 10 December 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-raw-
industrial-requirements-00>.
[RAW-TECHNOS]
Thubert, P., Ed., Cavalcanti, D., Vilajosana, X., Schmitt,
C., and J. Farkas, "Reliable and Available Wireless
Technologies", Work in Progress, Internet-Draft, draft-
ietf-raw-technologies-08, 10 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-raw-
technologies-08>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>.
[RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
Internet of Things (IoT): Problem Statement", RFC 7554,
DOI 10.17487/RFC7554, May 2015,
<https://www.rfc-editor.org/info/rfc7554>.
[RFC8557] Finn, N. and P. Thubert, "Deterministic Networking Problem
Statement", RFC 8557, DOI 10.17487/RFC8557, May 2019,
<https://www.rfc-editor.org/info/rfc8557>.
[RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases",
RFC 8578, DOI 10.17487/RFC8578, May 2019,
<https://www.rfc-editor.org/info/rfc8578>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[RFC9030] Thubert, P., Ed., "An Architecture for IPv6 over the Time-
Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)",
RFC 9030, DOI 10.17487/RFC9030, May 2021,
<https://www.rfc-editor.org/info/rfc9030>.
[RFC9055] Grossman, E., Ed., Mizrahi, T., and A. Hacker,
"Deterministic Networking (DetNet) Security
Considerations", RFC 9055, DOI 10.17487/RFC9055, June
2021, <https://www.rfc-editor.org/info/rfc9055>.
[RFC9317] Holland, J., Begen, A., and S. Dawkins, "Operational
Considerations for Streaming Media", RFC 9317,
DOI 10.17487/RFC9317, October 2022,
<https://www.rfc-editor.org/info/rfc9317>.
[RFC9372] Mäurer, N., Ed., Gräupl, T., Ed., and C. Schmitt, Ed.,
"L-Band Digital Aeronautical Communications System
(LDACS)", RFC 9372, DOI 10.17487/RFC9372, March 2023,
<https://www.rfc-editor.org/info/rfc9372>.
[SESAR] SESAR, "SESAR Joint Undertaking",
<https://www.sesarju.eu/>.
Acknowledgments
Nils Mäurer, Thomas Gräupl, and Corinna Schmitt have contributed
significantly to this document, providing input for the Aeronautical
communication section. Rex Buddenberg has also contributed to the
document, providing input to the "Instrumented Emergency Medical
Vehicles" section.
The authors would like to thank Toerless Eckert, Xavi Vilajosana
Guillen, Rute Sofia, Corinna Schmitt, Victoria Pritchard, John
Scudder, Joerg Ott, and Stewart Bryant for their valuable comments on
draft versions of this document.
The work of Carlos J. Bernardos in this document has been partially
supported by the Horizon Europe PREDICT-6G (Grant 101095890) and
UNICO I+D 6G-DATADRIVEN-04 project.
Authors' Addresses
Carlos J. Bernardos (editor)
Universidad Carlos III de Madrid
Av. Universidad, 30
28911 Madrid
Spain
Phone: +34 91624 6236
Email: cjbc@it.uc3m.es
URI: http://www.it.uc3m.es/cjbc/
Georgios Papadopoulos
IMT Atlantique
Office B00 - 114A
2 Rue de la Chataigneraie
35510 Cesson-Sevigne - Rennes
France
Phone: +33 299 12 70 04
Email: georgios.papadopoulos@imt-atlantique.fr
Pascal Thubert
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 MOUGINS - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Fabrice Theoleyre
CNRS
ICube Lab, Pole API
300 boulevard Sebastien Brant - CS 10413
67400 Illkirch
France
Phone: +33 368 85 45 33
Email: fabrice.theoleyre@cnrs.fr
URI: https://fabrice.theoleyre.cnrs.fr/