rfc9913v1.txt   rfc9913.txt 
Internet Engineering Task Force (IETF) P. Thubert, Ed. Internet Engineering Task Force (IETF) P. Thubert, Ed.
Request for Comments: 9913 Request for Comments: 9913 Independent
Category: Informational D. Cavalcanti Category: Informational D. Cavalcanti
ISSN: 2070-1721 Intel ISSN: 2070-1721 Intel
X. Vilajosana X. Vilajosana
Universitat Oberta de Catalunya Universitat Oberta de Catalunya
C. Schmitt C. Schmitt
Research Institute CODE, UniBw M Research Institute CODE, UniBw M
J. Farkas J. Farkas
Ericsson Ericsson
February 2026 February 2026
Reliable and Available Wireless (RAW) Technologies Reliable and Available Wireless (RAW) Technologies
Abstract Abstract
This document surveys the short- and middle-range radio technologies This document surveys the short- and middle-range radio technologies
over which providing a Deterministic Networking (DetNet) / Reliable over which providing Deterministic Networking (DetNet), and more
and Available Wireless (RAW) service is suitable, presents the specifically, Reliable and Available Wireless (RAW) service is
characteristics that RAW may leverage, and explores the applicability suitable. It also presents the characteristics that RAW may leverage
of the technologies to carry deterministic flows, as of the time of and explores the applicability of the technologies to carry
publication. The studied technologies are Wi-Fi 6/7, Time-Slotted deterministic flows, as of the time of publication. The studied
Channel Hopping (TSCH), 3GPP 5G, and L-band Digital Aeronautical technologies are Wi-Fi 6/7, Time-Slotted Channel Hopping (TSCH), 3GPP
Communications System (LDACS). 5G, and L-band Digital Aeronautical Communications System (LDACS).
Status of This Memo Status of This Memo
This document is not an Internet Standards Track specification; it is This document is not an Internet Standards Track specification; it is
published for informational purposes. published for informational purposes.
This document is a product of the Internet Engineering Task Force This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents Internet Engineering Steering Group (IESG). Not all documents
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in the Revised BSD License. in the Revised BSD License.
Table of Contents Table of Contents
1. Introduction 1. Introduction
2. Terminology 2. Terminology
3. Towards Reliable and Available Wireless Networks 3. Towards Reliable and Available Wireless Networks
3.1. Scheduling for Reliability 3.1. Scheduling for Reliability
3.2. Diversity for Availability 3.2. Diversity for Availability
3.3. Benefits of Scheduling 3.3. Benefits of Scheduling
4. IEEE 802.11 4. IEEE 802.11 Wireless Local Area Networks (WLAN)
4.1. Provenance and Documents 4.1. Provenance and Documents
4.2. 802.11ax High Efficiency (HE) 4.2. 802.11ax High Efficiency (HE)
4.2.1. General Characteristics 4.2.1. General Characteristics
4.2.2. Applicability to Deterministic Flows 4.2.2. Applicability to Deterministic Flows
4.3. 802.11be Extreme High Throughput (EHT) 4.3. 802.11be Extreme High Throughput (EHT)
4.3.1. General Characteristics 4.3.1. General Characteristics
4.3.2. Applicability to Deterministic Flows 4.3.2. Applicability to Deterministic Flows
4.4. 802.11ad and 802.11ay (mmWave Operation) 4.4. 802.11ad and 802.11ay (mmWave Operation)
4.4.1. General Characteristics 4.4.1. General Characteristics
4.4.2. Applicability to Deterministic Flows 4.4.2. Applicability to Deterministic Flows
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wired lower-layer technologies such as Time-Sensitive Networking wired lower-layer technologies such as Time-Sensitive Networking
(TSN) as defined by IEEE 802.1 and IEEE 802.3. (TSN) as defined by IEEE 802.1 and IEEE 802.3.
The Reliable and Available Wireless (RAW) architecture [RFC9912] The Reliable and Available Wireless (RAW) architecture [RFC9912]
extends the DetNet architecture [RFC8655] to adapt to the specific extends the DetNet architecture [RFC8655] to adapt to the specific
challenges of the wireless medium, in particular, intermittently challenges of the wireless medium, in particular, intermittently
lossy connectivity, by optimizing the use of diversity and lossy connectivity, by optimizing the use of diversity and
multipathing. [RFC9912] defines the concepts of reliability and multipathing. [RFC9912] defines the concepts of reliability and
availability that are used in this document. In turn, this document availability that are used in this document. In turn, this document
presents wireless technologies with capabilities, such as time presents wireless technologies with capabilities, such as time
synchronization and scheduling of transmission, that would make RAW/ synchronization and scheduling of transmission, that would make RAW
DetNet operations possible over such media. The technologies studied operations possible over such media. The technologies studied in
in this document were identified in the charter during the RAW this document were identified in the charter during the RAW Working
Working Group (WG) formation and inherited by DetNet (when the WG Group (WG) formation and inherited by DetNet (when the WG picked up
picked up the work on RAW). the work on RAW).
Making wireless reliable and available is even more challenging than Making wireless reliable and available is even more challenging than
it is with wires, due to the numerous causes of radio transmission it is with wires, due to the numerous causes of radio transmission
losses that add up to the congestion losses and the delays caused by losses that add up to the congestion losses and the delays caused by
overbooked shared resources. overbooked shared resources.
RAW, like DetNet, needs and leverages lower-layer capabilities such RAW, like DetNet, needs and leverages lower-layer capabilities such
as time synchronization and traffic shapers. To balance the adverse as time synchronization and traffic shapers. To balance the adverse
effects of the radio transmission losses, RAW leverages additional effects of the radio transmission losses, RAW leverages additional
lower-layer capabilities, some of which may be specific or at least lower-layer capabilities, some of which may be specific or at least
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RAW defines a network-layer control loop that optimizes the use of RAW defines a network-layer control loop that optimizes the use of
links with constrained spectrum and energy while maintaining the links with constrained spectrum and energy while maintaining the
expected connectivity properties, typically reliability and latency. expected connectivity properties, typically reliability and latency.
The control loop involves communication monitoring through The control loop involves communication monitoring through
Operations, Administration, and Maintenance (OAM); path control Operations, Administration, and Maintenance (OAM); path control
through a Path Computation Element (PCE) and a runtime distributed through a Path Computation Element (PCE) and a runtime distributed
Path Selection Engine (PSE); and extended Packet Replication, Path Selection Engine (PSE); and extended Packet Replication,
Elimination, and Ordering Functions (PREOF). Elimination, and Ordering Functions (PREOF).
This document surveys the short- and middle-range radio technologies This document surveys the short- and middle-range radio technologies
over which providing a DetNet/RAW service is suitable, presents the over which providing a RAW service is suitable, presents the
characteristics that RAW may leverage, and explores the applicability characteristics that RAW may leverage, and explores the applicability
of the technologies to carry deterministic flows. The studied of the technologies to carry deterministic flows. The studied
technologies are Wi-Fi 6/7, Time-Slotted Channel Hopping (TSCH), 3GPP technologies are Wi-Fi 6/7, Time-Slotted Channel Hopping (TSCH), 3GPP
5G, and L-band Digital Aeronautical Communications System (LDACS). 5G, and L-band Digital Aeronautical Communications System (LDACS).
The purpose of this document is to support and enable work on the The purpose of this document is to support and enable work on the
these (and possibly other similar compatible technologies) at the these (and possibly other similar compatible technologies) at the
IETF, specifically in the DetNet Working Group working on RAW. IETF, specifically in the DetNet Working Group working on RAW.
This document surveys existing networking technology; it does not This document surveys existing networking technology; it does not
define protocol behaviors or operational practices. The IETF define protocol behaviors or operational practices. The IETF
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* Scheduling plays a critical role in saving energy. In the * Scheduling plays a critical role in saving energy. In the
Internet of Things (IoT), energy is the foremost concern, and Internet of Things (IoT), energy is the foremost concern, and
synchronizing the sender and listener enables always maintaining synchronizing the sender and listener enables always maintaining
them in deep sleep when there is no scheduled transmission. This them in deep sleep when there is no scheduled transmission. This
avoids idle listening and long preambles, and it enables long avoids idle listening and long preambles, and it enables long
sleep periods between traffic and resynchronization, allowing sleep periods between traffic and resynchronization, allowing
battery-operated nodes to operate in a mesh topology for multiple battery-operated nodes to operate in a mesh topology for multiple
years. years.
4. IEEE 802.11 4. IEEE 802.11 Wireless Local Area Networks (WLAN)
In recent years, the evolution of the IEEE Std 802.11 standard has In recent years, the evolution of the IEEE Std 802.11 standard has
taken a new direction, emphasizing improved reliability and reduced taken a new direction, emphasizing improved reliability and reduced
latency in addition to minor improvements in speed, to enable new latency in addition to minor improvements in speed, to enable new
fields of application such as industrial IoT and Virtual Reality fields of application such as industrial IoT and Virtual Reality
(VR). (VR).
Leveraging IEEE Std 802.11, the Wi-Fi Alliance [WFA] delivered Wi-Fi Leveraging IEEE Std 802.11, the Wi-Fi Alliance [WFA] delivered Wi-Fi
6, 7, and now 8 with more capabilities to schedule and deliver frames 6, 7, and now 8 with more capabilities to schedule and deliver frames
in due time at fast rates. Still, as with any radio technology, Wi- in due time at fast rates. Still, as with any radio technology, Wi-
Fi is sensitive to frame loss, which can only be combated with the Fi is sensitive to frame loss, which can only be combated with the
maximum use of diversity in space, time, channel, and even maximum use of diversity in space, time, channel, and even
technology. technology.
In parallel, the Avnu Alliance [Avnu], which focuses on applications In parallel, the Avnu Alliance [Avnu], which focuses on applications
of TSN for real-time data, formed a workgroup for uses case with TSN of TSN for real-time data, formed a workgroup to investigate TSN
capabilities over wireless, leveraging both 3GPP and IEEE Std 802.11 capabilities over wireless, leveraging both 3GPP and IEEE Std 802.11
standards. standards.
To achieve the latter, the reliability must be handled at an upper To achieve the latter, the reliability must be handled at an upper
layer that can select Wi-Fi and other wired or wireless technologies layer that can select Wi-Fi and other wired or wireless technologies
for parallel transmissions. This is where RAW comes into play. for parallel transmissions. This is where RAW comes into play.
This section surveys the IEEE 802.11 features that are most relevant This section surveys the IEEE 802.11 features that are most relevant
to RAW, noting that there are a great many more in the specification, to RAW, noting that there are a great many more in the specification,
some of which may also possibly be of interest for a RAW solution. some of which may also possibly be of interest for a RAW solution.
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* Congestion control: IEEE Std 802.11-2016 Admission Control; WFA * Congestion control: IEEE Std 802.11-2016 Admission Control; WFA
Admission Control Admission Control
* Security: WFA Wi-Fi Protected Access, WPA2, and WPA3 * Security: WFA Wi-Fi Protected Access, WPA2, and WPA3
* Interoperating with IEEE 802.1Q bridges: IEEE Std 802.11-2020 * Interoperating with IEEE 802.1Q bridges: IEEE Std 802.11-2020
incorporating 802.11ak incorporating 802.11ak
* Stream Reservation Protocol (part of [IEEE802.1Qat]): * Stream Reservation Protocol (part of [IEEE802.1Qat]):
AIEEE802.11-2016 IEEE802.11-2016
* Scheduled channel access: IEEE 802.11ad enhancements for very high * Scheduled channel access: IEEE 802.11ad enhancements for very high
throughput in the 60 GHz band [IEEE802.11ad] throughput in the 60 GHz band [IEEE802.11ad]
* 802.11 Real-Time Applications: Topic Interest Group (TIG) * 802.11 Real-Time Applications: Topic Interest Group (TIG)
ReportDoc [IEEE_doc_11-18-2009-06] ReportDoc [IEEE_doc_11-18-2009-06]
In addition, major amendments being developed by the IEEE 802.11 In addition, major amendments being developed by the IEEE 802.11
Working Group include capabilities that can be used as the basis for Working Group include capabilities that can be used as the basis for
providing more reliable and predictable wireless connectivity and providing more reliable and predictable wireless connectivity and
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The main 802.11ax, 802.11be, 802.11ad, and 802.11ay capabilities and The main 802.11ax, 802.11be, 802.11ad, and 802.11ay capabilities and
their relevance to RAW are discussed in the remainder of this their relevance to RAW are discussed in the remainder of this
section. As P802.11bn is still in early stages of development, its section. As P802.11bn is still in early stages of development, its
capabilities are not included in this document. capabilities are not included in this document.
4.2. 802.11ax High Efficiency (HE) 4.2. 802.11ax High Efficiency (HE)
4.2.1. General Characteristics 4.2.1. General Characteristics
The next generation Wi-Fi (Wi-Fi 6) is based on the IEEE Std 802.11ax The next generation Wi-Fi (Wi-Fi 6) is based on the IEEE802.11ax
amendment [IEEE802.11ax], which includes specific capabilities to amendment [IEEE802.11ax], which includes specific capabilities to
increase efficiency, control and reduce latency. Some of these increase efficiency and control and to reduce latency. Some of these
features include higher-order 1024-QAM modulation, support for uplink features include higher-order 1024-QAM modulation, support for uplink
Multi-User - Multiple Input Multiple Output (MU-MIMO), Orthogonal (UL) Multi-User - Multiple Input Multiple Output (MU-MIMO),
Frequency-Division Multiple Access (OFDMA), trigger-based access, and Orthogonal Frequency-Division Multiple Access (OFDMA), trigger-based
Target Wake Time (TWT) for enhanced power savings. The OFDMA mode access, and Target Wake Time (TWT) for enhanced power savings. The
and trigger-based access enable the Access Point (AP), after OFDMA mode and trigger-based access enable the Access Point (AP),
reserving the channel using the clear channel assessment procedure after reserving the channel using the clear channel assessment
for a given duration, to schedule multi-user transmissions, which is procedure for a given duration, to schedule multi-user transmissions,
a key capability required to increase latency predictability and which is a key capability required to increase latency predictability
reliability for time-sensitive flows. 802.11ax can operate in up to and reliability for time-sensitive flows. 802.11ax can operate in up
160 MHz channels, and it includes support for operation in the new 6 to 160 MHz channels, and it includes support for operation in the new
GHz band, which has been open to unlicensed use by the Federal 6 GHz band, which has been open to unlicensed use by the Federal
Communications Commission (FCC) and other regulatory agencies Communications Commission (FCC) and other regulatory agencies
worldwide. worldwide.
4.2.1.1. Multi-User OFDMA and Trigger-Based Scheduled Access 4.2.1.1. Multi-User OFDMA and Trigger-Based Scheduled Access
802.11ax introduced an OFDMA mode in which multiple users can be 802.11ax introduced an OFDMA mode in which multiple users can be
scheduled across the frequency domain. In this mode, the Access scheduled across the frequency domain. In this mode, the Access
Point (AP) can initiate multi-user uplink (UL) transmissions in the Point (AP) can initiate multi-user UL transmissions in the same PHY
same PHY Protocol Data Unit (PPDU) by sending a trigger frame. This Protocol Data Unit (PPDU) by sending a trigger frame. This
centralized scheduling capability gives the AP much more control of centralized scheduling capability gives the AP much more control of
the channel in its Basic Service Set (BSS), and it can remove the channel in its Basic Service Set (BSS), and it can remove
contention between associated stations for uplink transmissions, contention between associated stations for UL transmissions,
therefore reducing the randomness caused by access based on Carrier therefore reducing the randomness caused by access based on Carrier
Sense Multiple Access (CSMA) between stations within the same BSS. Sense Multiple Access (CSMA) between stations within the same BSS.
The AP can also transmit simultaneously to multiple users in the The AP can also transmit simultaneously to multiple users in the
downlink direction by using a downlink (DL) MU OFDMA PPDU. In order downlink (DL) direction by using a DL MU OFDMA PPDU. In order to
to initiate a contention-free Transmission Opportunity (TXOP) using initiate a contention-free Transmission Opportunity (TXOP) using the
the OFDMA mode, the AP still follows the typical listen-before-talk OFDMA mode, the AP still follows the typical listen-before-talk
procedure to acquire the medium, which ensures interoperability and procedure to acquire the medium, which ensures interoperability and
compliance with unlicensed band access rules. However, 802.11ax also compliance with unlicensed band access rules. However, 802.11ax also
includes a Multi-User Enhanced Distributed Channel Access (MU-EDCA) includes a Multi-User Enhanced Distributed Channel Access (MU-EDCA)
capability, which allows the AP to get higher channel access priority capability, which allows the AP to get higher channel access priority
than other devices in its BSS. than other devices in its BSS.
4.2.1.2. Traffic Isolation via OFDMA Resource Management and Resource 4.2.1.2. Traffic Isolation via OFDMA Resource Management and Resource
Unit Allocation Unit Allocation
802.11ax relies on the notion of an OFDMA Resource Unit (RU) to 802.11ax relies on the notion of an OFDMA Resource Unit (RU) to
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the underlying mechanism for supporting deterministic flows in a the underlying mechanism for supporting deterministic flows in a
Local Area Network (LAN). The IEEE 802.11 Working Group has Local Area Network (LAN). The IEEE 802.11 Working Group has
incorporated support for absolute time synchronization to extend the incorporated support for absolute time synchronization to extend the
TSN 802.1AS protocol so that time-sensitive flows can experience TSN 802.1AS protocol so that time-sensitive flows can experience
precise time synchronization when operating over 802.11 links. As precise time synchronization when operating over 802.11 links. As
IEEE 802.11 and IEEE 802.1 TSN are both based on the IEEE 802 IEEE 802.11 and IEEE 802.1 TSN are both based on the IEEE 802
architecture, 802.11 devices can directly implement some TSN architecture, 802.11 devices can directly implement some TSN
capabilities without the need for a gateway/translation protocol. capabilities without the need for a gateway/translation protocol.
Basic features required for operation in a 802.1Q LAN are already Basic features required for operation in a 802.1Q LAN are already
enabled for 802.11. Some TSN capabilities, such as 802.1Qbv, can enabled for 802.11. Some TSN capabilities, such as 802.1Qbv, can
already operate over the existing 802.11 MAC SAP [Sudhakaran2021]. already operate over the existing 802.11 MAC Service Access Point
Implementation and experimental results of TSN capabilities (802.1AS, (SAP) [Sudhakaran2021]. Implementation and experimental results of
802.1Qbv, and 802.1CB) extended over standard Ethernet and Wi-Fi TSN capabilities (802.1AS, 802.1Qbv, and 802.1CB) extended over
devices have also been described in [Fang_2021]. Nevertheless, the standard Ethernet and Wi-Fi devices have also been described in
IEEE 802.11 MAC/PHY could be extended to improve the operation of [Fang_2021]. Nevertheless, the IEEE 802.11 MAC/PHY could be extended
IEEE 802.1 TSN features and achieve better performance metrics to improve the operation of IEEE 802.1 TSN features and achieve
[Cavalcanti1287]. better performance metrics [Cavalcanti1287].
TSN capabilities supported over 802.11 (which also extends to TSN capabilities supported over 802.11 (which also extends to
802.11ax) include: 802.11ax) include:
1. 802.1AS-based time synchronization (other time synchronization 1. 802.1AS-based time synchronization (other time synchronization
techniques may also be used) techniques may also be used)
2. Interoperating with IEEE 802.1Q bridges 2. Interoperating with IEEE 802.1Q bridges
3. Time-sensitive traffic stream classification 3. Time-sensitive traffic stream classification
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4.2.2.2. Scheduling for Bounded Latency and Diversity 4.2.2.2. Scheduling for Bounded Latency and Diversity
As discussed earlier, the OFDMA mode in [IEEE802.11ax] introduces the As discussed earlier, the OFDMA mode in [IEEE802.11ax] introduces the
possibility of assigning different RUs (time/frequency resources) to possibility of assigning different RUs (time/frequency resources) to
users within a PPDU. Several RU sizes are defined in the users within a PPDU. Several RU sizes are defined in the
specification (26, 52, 106, 242, 484, and 996 subcarriers). In specification (26, 52, 106, 242, 484, and 996 subcarriers). In
addition, the AP can also decide on a Modulation and Coding Scheme addition, the AP can also decide on a Modulation and Coding Scheme
(MCS) and grouping of users within a given OFMDA PPDU. Such (MCS) and grouping of users within a given OFMDA PPDU. Such
flexibility can be leveraged to support time-sensitive applications flexibility can be leveraged to support time-sensitive applications
with bounded latency, especially in a managed network where stations with bounded latency, especially:
can be configured to operate under the control of the AP, in a
controlled environment (which contains only devices operating on the * in a managed network where stations can be configured to operate
unlicensed band installed by the facility owner and where unexpected under the control of the AP,
interference from other systems and/or radio access technologies only
sporadically happens), or in a deployment where channel and link * in a controlled environment (which contains only devices operating
redundancy is used to reduce the impact of unmanaged devices and on the unlicensed band installed by the facility owner and where
interference. unexpected interference from other systems and/or radio access
technologies only sporadically happens), or
* in a deployment where channel and link redundancy is used to
reduce the impact of unmanaged devices and interference.
When the network is lightly loaded, it is possible to achieve When the network is lightly loaded, it is possible to achieve
latencies under 1 msec when Wi-Fi is operated in a contention-based latencies under 1 ms when Wi-Fi is operated in a contention-based
mode (i.e., without OFDMA). It also has been shown that it is mode (i.e., without OFDMA). It also has been shown that it is
possible to achieve 1 msec latencies in a controlled environment with possible to achieve 1 ms latencies in a controlled environment with
higher efficiency when multi-user transmissions are used (enabled by higher efficiency when multi-user transmissions are used (enabled by
OFDMA operation) [Cavalcanti_2019]. Obviously, there are latency, OFDMA operation) [Cavalcanti_2019]. Obviously, there are latency,
reliability, and capacity trade-offs to be considered. For instance, reliability, and capacity trade-offs to be considered. For instance,
smaller RUs result in longer transmission durations, which may impact smaller RUs result in longer transmission durations, which may impact
the minimal latency that can be achieved, but the contention latency the minimal latency that can be achieved, but the contention latency
and randomness elimination in an interference-free environment due to and randomness elimination in an interference-free environment due to
multi-user transmission is a major benefit of the OFDMA mode. multi-user transmission is a major benefit of the OFDMA mode.
The flexibility to dynamically assign RUs to each transmission also The flexibility to dynamically assign RUs to each transmission also
enables the AP to provide frequency diversity, which can help enables the AP to provide frequency diversity, which can help
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contiguous spectrum contiguous spectrum
2. Multi-Link Operation (MLO) 2. Multi-Link Operation (MLO)
3. QoS enhancements to reduce latency and increase reliability 3. QoS enhancements to reduce latency and increase reliability
4.3.2. Applicability to Deterministic Flows 4.3.2. Applicability to Deterministic Flows
The 802.11 Real-Time Applications (RTA) Topic Interest Group (TIG) The 802.11 Real-Time Applications (RTA) Topic Interest Group (TIG)
provided detailed information on use cases, issues, and potential provided detailed information on use cases, issues, and potential
solution directions to improve support for time-sensitive solutions to improve support for time-sensitive applications in
applications in 802.11. The RTA TIG report [IEEE_doc_11-18-2009-06] 802.11. The RTA TIG report [IEEE_doc_11-18-2009-06] was used as
was used as input to the 802.11be project scope. input to the 802.11be project scope.
Improvements for worst-case latency, jitter, and reliability were the Improvements for worst-case latency, jitter, and reliability were the
main topics identified in the RTA report, which were motivated by main topics identified in the RTA report, which were motivated by
applications in gaming, industrial automation, robotics, etc. The applications in gaming, industrial automation, robotics, etc. The
RTA report also highlighted the need to support additional TSN RTA report also highlighted the need to support additional TSN
capabilities, such as time-aware (802.1Qbv) shaping and packet capabilities, such as time-aware (802.1Qbv) shaping and packet
replication and elimination as defined in 802.1CB. replication and elimination as defined in 802.1CB.
IEEE Std 802.11be builds on and enhances 802.11ax capabilities to IEEE Std 802.11be builds on and enhances 802.11ax capabilities to
improve worst case latency and jitter. Some of the enhancement areas improve worst case latency and jitter. Some of the enhancement areas
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Remote Transducer Protocol (HART) and ISA100.11a. Remote Transducer Protocol (HART) and ISA100.11a.
While the MAC/PHY standards enable the relatively slow rates used in While the MAC/PHY standards enable the relatively slow rates used in
process control (typically in the order of 4-5 per second), the process control (typically in the order of 4-5 per second), the
technology is not suited for the faster periods used in factory technology is not suited for the faster periods used in factory
automation and motion control (1 to 10 ms). automation and motion control (1 to 10 ms).
5.1. Provenance and Documents 5.1. Provenance and Documents
The IEEE 802.15.4 Task Group has been driving the development of low- The IEEE 802.15.4 Task Group has been driving the development of low-
power, low-cost radio technology. The IEEE 802.15.4 physical layer power, low-cost radio technology. The IEEE 802.15.4 Physical (PHY)
has been designed to support demanding low-power scenarios targeting layer has been designed to support demanding low-power scenarios
the use of unlicensed bands, both the 2.4 GHz and sub-GHz Industrial, targeting the use of unlicensed bands, both the 2.4 GHz and sub-GHz
Scientific and Medical (ISM) bands. This has imposed requirements in Industrial, Scientific and Medical (ISM) bands. This has imposed
terms of frame size, data rate, and bandwidth to achieve reduced requirements in terms of frame size, data rate, and bandwidth to
collision probability, reduced packet error rate, and acceptable achieve reduced collision probability, reduced packet error rate, and
range with limited transmission power. The PHY layer supports frames acceptable range with limited transmission power. The PHY layer
of up to 127 bytes. The Medium Access Control (MAC) sublayer supports frames of up to 127 bytes. The Medium Access Control (MAC)
overhead is in the order of 10-20 bytes, leaving about 100 bytes to sublayer overhead is in the order of 10-20 bytes, leaving about 100
the upper layers. IEEE 802.15.4 uses spread spectrum modulation such bytes to the upper layers. IEEE 802.15.4 uses spread spectrum
as the Direct Sequence Spread Spectrum (DSSS). modulation such as the Direct Sequence Spread Spectrum (DSSS).
The Time-Slotted Channel Hopping (TSCH) mode was added to the 2015 The Time-Slotted Channel Hopping (TSCH) mode was added to the 2015
revision of the IEEE 802.15.4 standard [IEEE802.15.4]. TSCH is revision of the IEEE 802.15.4 standard [IEEE802.15.4]. TSCH is
targeted at the embedded and industrial world, where reliability, targeted at the embedded and industrial world, where reliability,
energy consumption, and cost drive the application space. energy consumption, and cost drive the application space.
Building on IEEE 802.15.4, TSN on low-power constrained wireless Building on IEEE 802.15.4, TSN on low-power constrained wireless
networks has been partially addressed by ISA100.11a [ISA100.11a] and networks has been partially addressed by ISA100.11a [ISA100.11a] and
WirelessHART [WirelessHART]. Both technologies involve a central WirelessHART [WirelessHART]. Both technologies involve a central
controller that computes redundant paths for industrial process controller that computes redundant paths for industrial process
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The protocol supports agreement on a schedule between neighbors, The protocol supports agreement on a schedule between neighbors,
enabling distributed scheduling. enabling distributed scheduling.
* 6P goes hand in hand with an SF, the policy that decides how to * 6P goes hand in hand with an SF, the policy that decides how to
maintain cells and trigger 6P transactions. The Minimal maintain cells and trigger 6P transactions. The Minimal
Scheduling Function (MSF) [RFC9033] is the default SF defined by Scheduling Function (MSF) [RFC9033] is the default SF defined by
the 6TiSCH WG. the 6TiSCH WG.
* With these mechanisms, 6TiSCH can establish Layer 2 links between * With these mechanisms, 6TiSCH can establish Layer 2 links between
neighboring nodes and support best-effort traffic. The Routing neighboring nodes and support best-effort traffic. The Routing
Protocol for Low-Power and Lossy Networks (RPL) [RFC8480] provides Protocol for Low-Power and Lossy Networks (RPL) [RFC6550] provides
the routing structure, enabling the 6TiSCH devices to establish the routing structure, enabling the 6TiSCH devices to establish
the links with well-connected neighbors, thus forming the acyclic the links with well-connected neighbors, thus forming the acyclic
network graphs. network graphs.
A Track at 6TiSCH is the application to wireless of the concept of a In 6TiSCH, a Track is the concept of a recovery graph in the RAW
recovery graph in the RAW architecture. A Track can follow a simple architecture applied to wireless. A Track can follow a simple
sequence of relay nodes, or it can be structured as a more complex sequence of relay nodes, or it can be structured as a more complex
Destination-Oriented Directed Acyclic Graph (DODAG) to a unicast Destination-Oriented Directed Acyclic Graph (DODAG) to a unicast
destination. Along a Track, 6TiSCH nodes reserve the resources to destination. Along a Track, 6TiSCH nodes reserve the resources to
enable the efficient transmission of packets while aiming to optimize enable the efficient transmission of packets while aiming to optimize
certain properties such as reliability and ensure small jitter or certain properties such as reliability and ensure small jitter or
bounded latency. The Track structure enables Layer 2 forwarding bounded latency. The Track structure enables Layer 2 forwarding
schemes, reducing the overhead of making routing decisions at Layer schemes, reducing the overhead of making routing decisions at Layer
3. 3.
The 6TiSCH architecture [RFC9030] identifies different models to The 6TiSCH architecture [RFC9030] identifies different models to
skipping to change at line 805 skipping to change at line 809
provided in this document. For example, [vilajosana21] provides a provided in this document. For example, [vilajosana21] provides a
detailed description of the 6TiSCH protocols, how they are linked detailed description of the 6TiSCH protocols, how they are linked
together, and how they are integrated with other standards like RPL together, and how they are integrated with other standards like RPL
and 6Lo. and 6Lo.
5.2. General Characteristics 5.2. General Characteristics
As a core technique in IEEE 802.15.4, TSCH splits time in multiple As a core technique in IEEE 802.15.4, TSCH splits time in multiple
time slots that repeat over time. Each device has its own time slots that repeat over time. Each device has its own
perspective of when the send or receive occurs and on which channel perspective of when the send or receive occurs and on which channel
the transmission happens. This constitutes the device's Slotframe, the transmission happens. This constitutes the device's slotframe,
where the channel and destination of a transmission by this device where the channel and destination of a transmission by this device
are a function of time. The overall aggregation of all the are a function of time. The overall aggregation of all the
Slotframes of all the devices constitutes a time/frequency matrix slotframes of all the devices constitutes a time/frequency matrix
with at most one transmission in each cell of the matrix (see more in with at most one transmission in each cell of the matrix (see more in
Section 5.3.1.4). Section 5.3.1.4).
The IEEE 802.15.4 TSCH standard does not define any scheduling The IEEE 802.15.4 TSCH standard does not define any scheduling
mechanism but only provides the architecture that establishes a mechanism but only provides the architecture that establishes a
slotted structure that can be managed by a proper schedule. This slotted structure that can be managed by a proper schedule. This
schedule represents the possible communications of a node with its schedule represents the possible communications of a node with its
neighbors and is managed by a Scheduling Function such as the Minimal neighbors and is managed by a Scheduling Function such as the Minimal
Scheduling Function (MSF) [RFC9033]. In MSF, each cell in the Scheduling Function (MSF) [RFC9033]. In MSF, each cell in the
schedule is identified by its slotoffset and channeloffset schedule is identified by its slotOffset and channelOffset
coordinates. A cell's timeslot offset indicates its position in coordinates. A cell's timeSlot offset indicates its position in
time, relative to the beginning of the slotframe. A cell's channel time, relative to the beginning of the slotframe. A cell's channel
offset is an index that maps to a frequency at each iteration of the offset is an index that maps to a frequency at each iteration of the
slotframe. Each packet exchanged between neighbors happens within slotframe. Each packet exchanged between neighbors happens within
one cell. The size of a cell is a timeslot duration, between 10 to one cell. The size of a cell is a timeSlot duration, between 10 to
15 milliseconds. An Absolute Slot Number (ASN) indicates the number 15 milliseconds. An Absolute Slot Number (ASN) indicates the number
of slots elapsed since the network started. It increments at every of slots elapsed since the network started. It increments at every
slot. This is a 5-byte counter that can support networks running for slot. This is a 5-byte counter that can support networks running for
more than 300 years without wrapping (assuming a 10 ms timeslot). more than 300 years without wrapping (assuming a 10 ms timeSlot).
Channel hopping provides increased reliability to multipath fading Channel hopping provides increased reliability to multipath fading
and external interference. It is handled by TSCH through a channel- and external interference. It is handled by TSCH through a channel-
hopping sequence referred to as macHopSeq in the IEEE 802.15.4 hopping sequence referred to as macHopSeq in the IEEE 802.15.4
specification. specification.
The Time-Frequency Division Multiple Access provided by TSCH enables The Time-Frequency Division Multiple Access provided by TSCH enables
the orchestration of traffic flows, spreading them in time and the orchestration of traffic flows, spreading them in time and
frequency, and hence enabling an efficient management of the frequency, and hence enabling an efficient management of the
bandwidth utilization. Such efficient bandwidth utilization can be bandwidth utilization. Such efficient bandwidth utilization can be
combined with OFDM modulations also supported by the IEEE 802.15.4 combined with OFDM modulations also supported by the IEEE 802.15.4
standard [IEEE802.15.4] since the 2015 version. standard [IEEE802.15.4] since the 2015 version.
TSCH networks operate in ISM bands in which the spectrum is shared by TSCH networks operate in ISM bands in which the spectrum is shared by
different coexisting technologies. Regulations such as the FCC, different coexisting technologies. Regulations such as the FCC,
ETSI, and ARIB impose duty cycle regulations to limit the use of the ETSI, and ARIB impose duty cycle regulations to limit the use of the
bands, but interference may still constrain the probability of bands, but interference may still constrain the probability of
delivering a packet. Part of these reliability challenges are delivering a packet. Part of these reliability challenges are
addressed at the MAC introducing redundancy and diversity, thanks to addressed at the MAC layer by introducing redundancy and diversity,
channel hopping, scheduling, and ARQ policies. Yet, the MAC layer thanks to channel hopping, scheduling, and ARQ policies. Yet, the
operates with a 1-hop vision, being limited to local actions to MAC layer operates with a 1-hop vision, being limited to local
mitigate underperforming links. actions to mitigate underperforming links.
5.2.1. 6TiSCH Tracks 5.2.1. 6TiSCH Tracks
A Track in the 6TiSCH architecture [RFC9030] is the application to In the 6TiSCH architecture [RFC9030], a Track is the concept of a
6TiSCH networks of the concept of a protection path in the DetNet DetNet architecture protection path applied to 6TiSCH networks. A
architecture [RFC8655]. A Track can be structured as a Destination- Track can be structured as a Destination-Oriented Directed Acyclic
Oriented Directed Acyclic Graph (DODAG) to a destination for unicast Graph (DODAG) to a destination for unicast traffic. Along a Track,
traffic. Along a Track, 6TiSCH nodes reserve the resources to enable 6TiSCH nodes reserve the resources to enable the efficient
the efficient transmission of packets while aiming to optimize transmission of packets while aiming to optimize certain properties
certain properties such as reliability and ensure small jitter or such as reliability and ensure small jitter or bounded latency. The
bounded latency. The Track structure enables Layer 2 forwarding Track structure enables Layer 2 forwarding schemes, reducing the
schemes, reducing the overhead of making routing decisions at Layer overhead of making routing decisions at Layer 3.
3.
Serial Tracks can be understood as the concatenation of cells or Serial Tracks can be understood as the concatenation of cells or
bundles along a routing path from a source towards a destination. bundles along a routing path from a source towards a destination.
The serial Track concept is analogous to the circuit concept where The serial Track concept is analogous to the circuit concept where
resources are chained into a multi-hop topology; see more in resources are chained into a multi-hop topology; see more in
Section 5.2.1.2 on how that is used in the data plane to forward Section 5.2.1.2 on how that is used in the data plane to forward
packets. packets.
Whereas scheduling ensures reliable delivery in bounded time along Whereas scheduling ensures reliable delivery in bounded time along
any Track, high availability requires the application of PREOF any Track, high availability requires the application of PREOF
skipping to change at line 885 skipping to change at line 888
overall energy consumption in the network but significantly improves overall energy consumption in the network but significantly improves
the availability of the network as well as the packet delivery ratio. the availability of the network as well as the packet delivery ratio.
A Track may also branch off and rejoin, for the purpose of so-called A Track may also branch off and rejoin, for the purpose of so-called
Packet Replication and Elimination (PRE), over non-congruent Packet Replication and Elimination (PRE), over non-congruent
branches. PRE may be used to complement Layer 2 ARQ and receiver-end branches. PRE may be used to complement Layer 2 ARQ and receiver-end
ordering to complete/extend the PREOF functions. This enables ordering to complete/extend the PREOF functions. This enables
meeting industrial expectations of packet delivery within bounded meeting industrial expectations of packet delivery within bounded
delay over a Track that includes wireless links, even when the Track delay over a Track that includes wireless links, even when the Track
extends beyond the 6TiSCH network. extends beyond the 6TiSCH network.
The RAW Track described in the RAW architecture [RFC9912] inherits The RAW recovery graph described in the RAW architecture [RFC9912]
directly from that model. RAW extends the graph beyond a DODAG as inherits directly from that model. RAW extends the graph beyond a
long as a given packet cannot loop within the Track. DODAG as long as a given packet cannot loop within the Track.
+-----+ +-----+
| IoT | | IoT |
| G/W | | G/W |
+-----+ +-----+
^ <---- Elimination ^ <---- Elimination
| | | |
Track branch | | Track branch | |
+-------+ +--------+ Subnet backbone +-------+ +--------+ Subnet backbone
| | | |
skipping to change at line 967 skipping to change at line 970
[RFC9030]. The DetNet case relates to the Track Forwarding operation [RFC9030]. The DetNet case relates to the Track Forwarding operation
under the control of a PCE. under the control of a PCE.
A Track is a unidirectional path between a source and a destination. A Track is a unidirectional path between a source and a destination.
Time and frequency resources called cells (see Section 5.3.1.4) are Time and frequency resources called cells (see Section 5.3.1.4) are
allocated to enable the forwarding operation along the Track. In a allocated to enable the forwarding operation along the Track. In a
Track cell, the normal operation of IEEE 802.15.4 ARQ usually Track cell, the normal operation of IEEE 802.15.4 ARQ usually
happens, though the acknowledgment may be omitted in some cases, for happens, though the acknowledgment may be omitted in some cases, for
instance, if there is no scheduled cell for a retry. instance, if there is no scheduled cell for a retry.
Track Forwarding is the simplest and fastest. A bundle of cells set Track Forwarding is the simplest and fastest operation. A bundle of
to receive (RX-cells) is uniquely paired to a bundle of cells that cells set to receive (RX-cells) is uniquely paired to a bundle of
are set to transmit (TX-cells), representing a Layer 2 forwarding cells that are set to transmit (TX-cells), representing a Layer 2
state that can be used regardless of the network-layer protocol. forwarding state that can be used regardless of the network-layer
This model can effectively be seen as a Generalized Multiprotocol protocol. This model can effectively be seen as a Generalized
Label Switching (GMPLS) operation in that the information used to Multiprotocol Label Switching (GMPLS) operation in that the
switch a frame is not an explicit label but is rather related to information used to switch a frame is not an explicit label but is
other properties about the way the packet was received (a particular rather related to other properties about the way the packet was
cell, in the case of 6TiSCH). As a result, as long as the TSCH MAC received (a particular cell, in the case of 6TiSCH). As a result, as
(and Layer 2 security) accepts a frame, that frame can be switched long as the TSCH MAC (and Layer 2 security) accepts a frame, that
regardless of the protocol, whether this is an IPv6 packet, a 6LoWPAN frame can be switched regardless of the protocol, whether this is an
fragment, or a frame from an alternate protocol such as WirelessHART IPv6 packet, a 6LoWPAN fragment, or a frame from an alternate
or ISA100.11a. protocol such as WirelessHART or ISA100.11a.
A data frame that is forwarded along a Track normally has a A data frame that is forwarded along a Track normally has a
destination MAC address that is set to broadcast (or a multicast destination MAC address that is set to broadcast (or a multicast
address, depending on MAC support). This way, the MAC layer in the address, depending on MAC support). This way, the MAC layer in the
intermediate nodes accepts the incoming frame, and 6top switches it intermediate nodes accepts the incoming frame, and 6top switches it
without incurring a change in the MAC header. In the case of IEEE without incurring a change in the MAC header. In the case of IEEE
802.15.4, this means effectively broadcast, so that the short address 802.15.4, this effectively means that the address is broadcast, so
for the destination of the frame is set to 0xFFFF along the Track. that the short address for the destination of the frame is set to
0xFFFF along the Track.
A Track is thus formed end to end as a succession of paired bundles: A Track is thus formed end to end as a succession of paired bundles:
a receive bundle from the previous hop and a transmit bundle to the a receive bundle from the previous hop and a transmit bundle to the
next hop along the Track. A cell in such a bundle belongs to one next hop along the Track. A cell in such a bundle belongs to one
Track at most. For a given iteration of the device schedule, the Track at most. For a given iteration of the device schedule, the
effective channel of the cell is obtained by adding a pseudorandom effective channel of the cell is obtained by adding a pseudorandom
number to the channelOffset of the cell, which results in a rotation number to the channelOffset of the cell, which results in a rotation
of the frequency that was used for transmission. The bundles may be of the frequency that was used for transmission. The bundles may be
computed so as to accommodate both variable rates and computed so as to accommodate both variable rates and
retransmissions, so they might not be fully used at a given iteration retransmissions, so they might not be fully used at a given iteration
skipping to change at line 1009 skipping to change at line 1013
to avoid waste of cells as well as overflows in the transmit bundle, to avoid waste of cells as well as overflows in the transmit bundle,
as described in the following paragraphs. as described in the following paragraphs.
On one hand, a TX-cell that is not needed for the current iteration On one hand, a TX-cell that is not needed for the current iteration
may be reused opportunistically on a per-hop basis for routed may be reused opportunistically on a per-hop basis for routed
packets. When all of the frames that were received for a given Track packets. When all of the frames that were received for a given Track
are effectively transmitted, any available TX-cell for that Track can are effectively transmitted, any available TX-cell for that Track can
be reused for upper-layer traffic for which the next-hop router be reused for upper-layer traffic for which the next-hop router
matches the next hop along the Track. In that case, the cell that is matches the next hop along the Track. In that case, the cell that is
being used is effectively a TX-cell from the Track, but the short being used is effectively a TX-cell from the Track, but the short
address for the destination is that of the next-hop router. It address for the destination is that of the next-hop router. As a
results that a frame that is received in an RX-cell of a Track with a result, a frame that is received in an RX-cell of a Track with a
destination MAC address set to this node as opposed to broadcast must destination MAC address set to this node as opposed to broadcast must
be extracted from the Track and delivered to the upper layer (a frame be extracted from the Track and delivered to the upper layer (a frame
with an unrecognized MAC address is dropped at the lower MAC layer with an unrecognized MAC address is dropped at the lower MAC layer
and thus is not received at the 6top sublayer). and thus is not received at the 6top sublayer).
On the other hand, it might happen that there are not enough TX-cells On the other hand, it might happen that there are not enough TX-cells
in the transmit bundle to accommodate the Track traffic, for in the transmit bundle to accommodate the Track traffic, for
instance, if more retransmissions are needed than provisioned. In instance, if more retransmissions are needed than provisioned. In
that case, the frame can be placed for transmission in the bundle that case, the frame can be placed for transmission in the bundle
that is used for Layer 3 traffic towards the next hop along the Track that is used for Layer 3 traffic towards the next hop along the Track
as long as it can be routed by the upper layer, that is, typically, as long as it can be routed by the upper layer, that is, typically,
if the frame transports an IPv6 packet. The MAC address should be if the frame transports an IPv6 packet. The MAC address should be
set to the next-hop MAC address to avoid confusion. It results that set to the next-hop MAC address to avoid confusion. As a result, a
a frame that is received over a Layer 3 bundle may be in fact frame that is received over a Layer 3 bundle may be in fact
associated with a Track. In a classical IP link such as an Ethernet, associated with a Track. In a classical IP link such as an Ethernet,
off-Track traffic is typically in excess over reservation to be off-Track traffic is typically in excess over reservation to be
routed along the non-reserved path based on its QoS setting. routed along the non-reserved path based on its QoS setting.
However, with 6TiSCH, since the use of the Layer 3 bundle may be due However, with 6TiSCH, since the use of the Layer 3 bundle may be due
to transmission failures, it makes sense for the receiver to to transmission failures, it makes sense for the receiver to
recognize a frame that should be re-Tracked and to place it back on recognize a frame that should be re-Tracked and to place it back on
the appropriate bundle if possible. A frame should be re-Tracked if the appropriate bundle if possible. A frame should be re-Tracked if
the per-hop-behavior group indicated in the Differentiated Services the per-hop-behavior group indicated in the Differentiated Services
field in the IPv6 header is set to deterministic forwarding, as field in the IPv6 header is set to deterministic forwarding, as
discussed in Section 5.3.1.1. A frame is re-Tracked by scheduling it discussed in Section 5.3.1.1. A frame is re-Tracked by scheduling it
skipping to change at line 1057 skipping to change at line 1061
Explicit Replication (BIER) [RFC8279] and, more specifically, BIER Explicit Replication (BIER) [RFC8279] and, more specifically, BIER
Traffic Engineering (BIER-TE) [RFC9262]. Traffic Engineering (BIER-TE) [RFC9262].
5.3. Applicability to Deterministic Flows 5.3. Applicability to Deterministic Flows
In the RAW context, low-power reliable networks should address non- In the RAW context, low-power reliable networks should address non-
critical control scenarios such as Class 2 and monitoring scenarios critical control scenarios such as Class 2 and monitoring scenarios
such as Class 4, as defined by [RFC5673]. As a low-power technology such as Class 4, as defined by [RFC5673]. As a low-power technology
targeting industrial scenarios, radio transducers provide low data targeting industrial scenarios, radio transducers provide low data
rates (typically between 50 kbps to 250 kbps) and robust modulations rates (typically between 50 kbps to 250 kbps) and robust modulations
to trade-off performance to reliability. TSCH networks are organized to trade off performance for reliability. TSCH networks are
in mesh topologies and connected to a backbone. Latency in the mesh organized in mesh topologies and connected to a backbone. Latency in
network is mainly influenced by propagation aspects such as the mesh network is mainly influenced by propagation aspects such as
interference. ARQ methods and redundancy techniques such as interference. ARQ methods and redundancy techniques such as
replication and elimination should be studied to provide the needed replication and elimination should be studied to provide the needed
performance to address deterministic scenarios. performance to address deterministic scenarios.
Nodes in a TSCH network are tightly synchronized. This enables Nodes in a TSCH network are tightly synchronized. This enables
building the slotted structure and ensures efficient utilization of building the slotted structure and ensures efficient utilization of
resources thanks to proper scheduling policies. Scheduling is key to resources thanks to proper scheduling policies. Scheduling is key to
orchestrate the resources that different nodes in a Track or a path orchestrate the resources that different nodes in a Track or a path
are using. Slotframes can be split in resource blocks, reserving the are using. Slotframes can be split in resource blocks, reserving the
needed capacity to certain flows. Periodic and bursty traffic can be needed capacity to certain flows. Periodic and bursty traffic can be
handled independently in the schedule, using active and reactive handled independently in the schedule, using active and reactive
policies and taking advantage of overprovisioned cells. Along a policies and taking advantage of overprovisioned cells. Along a
Track (see Section 5.2.1), resource blocks can be chained so nodes in Track (see Section 5.2.1), resource blocks can be chained so nodes in
previous hops transmit their data before the next packet comes. This previous hops transmit their data before the next packet comes. This
provides a tight control to latency along a Track. Collision loss is provides a tight control of latency along a Track. Collision loss is
avoided for best-effort traffic by overprovisioning resources, giving avoided for best-effort traffic by overprovisioning resources, giving
time to the management plane of the network to dedicate more time to the management plane of the network to dedicate more
resources if needed. resources if needed.
5.3.1. Centralized Path Computation 5.3.1. Centralized Path Computation
When considering end-to-end communication over TSCH, a 6TiSCH device When considering end-to-end communication over TSCH, a 6TiSCH device
usually does not place a request for bandwidth between itself and usually does not place a request for bandwidth between itself and
another device in the network. Rather, an Operation Control System another device in the network. Rather, an Operation Control System
(OCS) invoked through a Human-Machine Interface (HMI) provides the (OCS) invoked through a Human/Machine Interface (HMI) provides the
traffic specification, in particular, in terms of latency and traffic specification (in particular, in terms of latency,
reliability, and the end nodes, to a PCE. With this, the PCE reliability, and the end nodes) to a PCE. With this, the PCE
computes a Track between the end nodes and provisions every hop in computes a Track between the end nodes and provisions every hop in
the Track with per-flow state that describes the per-hop operation the Track with per-flow state that describes the per-hop operation
for a given packet, the corresponding timeSlots, and the flow for a given packet, the corresponding timeSlots, and the flow
identification to recognize which packet is placed in which Track, identification to recognize which packet is placed in which Track,
sort out duplicates, etc. An example of an OCS and HMI is depicted sort out duplicates, etc. An example of an OCS and HMI is depicted
in Figure 2. in Figure 2.
For a static configuration that serves a certain purpose for a long For a static configuration that serves a certain purpose for a long
period of time, it is expected that a node will be provisioned in one period of time, it is expected that a node will be provisioned in one
shot with a full schedule, which incorporates the aggregation of its shot with a full schedule, which incorporates the aggregation of its
behavior for multiple Tracks. The 6TiSCH architecture expects that behavior for multiple Tracks. The 6TiSCH architecture expects that
the programming of the schedule is done over the Constrained the programming of the schedule is done over the Constrained
Application Protocol (CoAP) as discussed in [CoAP-6TiSCH]. Application Protocol (CoAP) as discussed in [CoAP-6TiSCH].
However, a Hybrid mode may be required as well, whereby a single However, a Hybrid mode may be required as well, whereby a single
Track is added, modified, or removed (for instance, if it appears Track is added, modified, or removed (for instance, if it appears
that a Track does not perform as expected). For that case, the that a Track does not perform as expected). For that case, the
expectation is that a protocol that flows along a Track (to be), in a expectation is that a protocol that flows along a Track, in a fashion
fashion similar to classical Traffic Engineering (TE) [CCAMP], may be similar to classical Traffic Engineering (TE) [CCAMP], may be used to
used to update the state in the devices. In general, that flow was update the state in the devices. In general, that flow was not
not designed, and it is expected that DetNet will determine the designed, and it is expected that DetNet will determine the
appropriate end-to-end protocols to be used in that case. appropriate end-to-end protocols to be used in that case.
Stream Management Entity
Operational Control System and HMI Operational Control System and HMI
-+-+-+-+-+-+-+ Northbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+-+-+-+-+-+-+ Northbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
PCE PCE PCE PCE PCE PCE PCE PCE
-+-+-+-+-+-+-+ Southbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+-+-+-+-+-+-+ Southbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
--- 6TiSCH------6TiSCH------6TiSCH------6TiSCH-- --- 6TiSCH------6TiSCH------6TiSCH------6TiSCH--
6TiSCH / Device Device Device Device \ 6TiSCH / Device Device Device Device \
skipping to change at line 1138 skipping to change at line 1140
5.3.1.1. Packet Marking and Handling 5.3.1.1. Packet Marking and Handling
Section 4.7.1 of [RFC9030] describes the packet tagging and marking Section 4.7.1 of [RFC9030] describes the packet tagging and marking
that is expected in 6TiSCH networks. that is expected in 6TiSCH networks.
5.3.1.1.1. Tagging Packets for Flow Identification 5.3.1.1.1. Tagging Packets for Flow Identification
Packets that are routed by a PCE along a Track are tagged to uniquely Packets that are routed by a PCE along a Track are tagged to uniquely
identify the Track and associated transmit bundle of timeSlots. identify the Track and associated transmit bundle of timeSlots.
It results that the tagging that is used for a DetNet flow outside As a result, the tagging that is used for a DetNet flow outside the
the 6TiSCH Low-Power and Lossy Network (LLN) must be swapped into 6TiSCH Low-Power and Lossy Network (LLN) must be swapped into 6TiSCH
6TiSCH formats and back as the packet enters and then leaves the formats and back as the packet enters and then leaves the 6TiSCH
6TiSCH network. network.
5.3.1.1.2. Replication, Retries, and Elimination 5.3.1.1.2. Replication, Retries, and Elimination
The 6TiSCH architecture [RFC9030] leverages PREOF over several The 6TiSCH architecture [RFC9030] leverages PREOF over several
alternate paths in a network to provide redundancy and parallel alternate paths in a network to provide redundancy and parallel
transmissions to bound the end-to-end delay. Considering the transmissions to bound the end-to-end delay. Considering the
scenario shown in Figure 3, many different paths are possible for S scenario shown in Figure 3, many different paths are possible for S
to reach R. A simple way to benefit from this topology could be to to reach R. A simple way to benefit from this topology could be to
use the two independent paths via nodes A, C, E and via B, D, F, but use the two independent paths via nodes A, C, E and via B, D, F, but
more complex paths are possible as well. more complex paths are possible as well.
skipping to change at line 1165 skipping to change at line 1167
source (S) (R) (destination) source (S) (R) (destination)
(B) (D) (F) (B) (D) (F)
Figure 3: A Typical Ladder Shape with Two Parallel Paths Toward Figure 3: A Typical Ladder Shape with Two Parallel Paths Toward
the Destination the Destination
By employing a packet replication function, each node forwards a copy By employing a packet replication function, each node forwards a copy
of each data packet over two different branches. For instance, in of each data packet over two different branches. For instance, in
Figure 4, the source node S transmits the data packet to nodes A and Figure 4, the source node S transmits the data packet to nodes A and
B, in two different timeslots within the same TSCH slotframe. S B, in two different timeSlots within the same TSCH slotframe. In the
transmits twice the same data packet to its Destination Parent (DP) figure below, S transmits the same data packet twice: once to its
(A) and to its Alternate Parent (AP) (B). Destination Parent (DP) (A) and once to its Alternate Parent (AP)
(B).
===> (A) => (C) => (E) === ===> (A) => (C) => (E) ===
// \\// \\// \\ // \\// \\// \\
source (S) //\\ //\\ (R) (destination) source (S) //\\ //\\ (R) (destination)
\\ // \\ // \\ // \\ // \\ // \\ //
===> (B) => (D) => (F) === ===> (B) => (D) => (F) ===
Figure 4: Packet Replication Figure 4: Packet Replication
By employing a packet elimination function once it receives the first By employing a packet elimination function once it receives the first
skipping to change at line 1194 skipping to change at line 1197
the promiscuous overhearing function, nodes will have multiple the promiscuous overhearing function, nodes will have multiple
opportunities to receive a given data packet. For instance, in opportunities to receive a given data packet. For instance, in
Figure 4, when the source node S transmits the data packet to node A, Figure 4, when the source node S transmits the data packet to node A,
node B may overhear the transmission. node B may overhear the transmission.
6TiSCH expects elimination and replication of packets along a complex 6TiSCH expects elimination and replication of packets along a complex
Track but has no position about how the sequence numbers would be Track but has no position about how the sequence numbers would be
tagged in the packet. tagged in the packet.
As it goes, 6TiSCH expects that timeSlots corresponding to copies of As it goes, 6TiSCH expects that timeSlots corresponding to copies of
the same packet along a Track are correlated by configuration, and the same packet along a Track are correlated by configuration, so
does not need to process the sequence numbers. processing the sequence numbers is not needed.
The semantics of the configuration must enable correlated timeSlots The semantics of the configuration must enable correlated timeSlots
to be grouped for transmit (and receive, respectively) with 'OR' to be grouped for transmit (and receive, respectively) with 'OR'
relations, and then an 'AND' relation must be configurable between relations, and then an 'AND' relation must be configurable between
groups. The semantics are such that if the transmit (and receive, groups. The semantics are such that if the transmit (and receive,
respectively) operation succeeded in one timeSlot in an 'OR' group, respectively) operation succeeded in one timeSlot in an 'OR' group,
then all the other timeslots in the group are ignored. Now, if there then all the other timeSlots in the group are ignored. Now, if there
are at least two groups, the 'AND' relation between the groups are at least two groups, the 'AND' relation between the groups
indicates that one operation must succeed in each of the groups. indicates that one operation must succeed in each of the groups.
Further details can be found in the 6TiSCH architecture document Further details can be found in the 6TiSCH architecture document
[RFC9030]. [RFC9030].
5.3.1.2. Topology and Capabilities 5.3.1.2. Topology and Capabilities
6TiSCH nodes are usually IoT devices, characterized by a very limited 6TiSCH nodes are usually IoT devices, characterized by a very limited
amount of memory, just enough buffers to store one or a few IPv6 amount of memory, just enough buffers to store one or a few IPv6
packets, and limited bandwidth between peers. It results that a node packets, and limited bandwidth between peers. As a result, a node
will maintain only a small amount of peering information and will not will maintain only a small amount of peering information and will not
be able to store many packets waiting to be forwarded. Peers can be be able to store many packets waiting to be forwarded. Peers can be
identified through MAC or IPv6 addresses. identified through MAC or IPv6 addresses.
Neighbors can be discovered over the radio using mechanisms such as Neighbors can be discovered over the radio using mechanisms such as
enhanced beacons, but although the neighbor information is available enhanced beacons, but although the neighbor information is available
in the 6TiSCH interface data model, 6TiSCH does not describe a in the 6TiSCH interface data model, 6TiSCH does not describe a
protocol to proactively push the neighborhood information to a PCE. protocol to proactively push the neighborhood information to a PCE.
This protocol should be described and should operate over CoAP. The This protocol should be described and should operate over CoAP. The
protocol should be able to carry multiple metrics, in particular, the protocol should be able to carry multiple metrics, in particular, the
skipping to change at line 1249 skipping to change at line 1252
Both methods may inject routes in the routing tables of the 6TiSCH Both methods may inject routes in the routing tables of the 6TiSCH
routers. In either case, each route is associated with a 6TiSCH routers. In either case, each route is associated with a 6TiSCH
topology that can be a RPL Instance topology or a Track. The 6TiSCH topology that can be a RPL Instance topology or a Track. The 6TiSCH
topology is indexed by an Instance ID, in a format that reuses the topology is indexed by an Instance ID, in a format that reuses the
RPLInstanceID as defined in RPL. RPLInstanceID as defined in RPL.
Both RPL and PCE rely on shared sources such as policies to define Both RPL and PCE rely on shared sources such as policies to define
Global and Local RPLInstanceIDs that can be used by either method. Global and Local RPLInstanceIDs that can be used by either method.
It is possible for centralized and distributed routing to share the It is possible for centralized and distributed routing to share the
same topology. Generally, they will operate in different slotFrames, same topology. Generally, they will operate in different slotframes,
and centralized routes will be used for scheduled traffic and will and centralized routes will be used for scheduled traffic and will
have precedence over distributed routes in case of conflict between have precedence over distributed routes in case of conflict between
the slotFrames. the slotframes.
5.3.1.4. SlotFrames and Priorities 5.3.1.4. Slotframes and Priorities
IEEE 802.15.4 TSCH avoids contention on the medium by formatting time IEEE 802.15.4 TSCH avoids contention on the medium by formatting time
and frequencies in cells of transmission of equal duration. In order and frequencies in cells of transmission of equal duration. In order
to describe that formatting of time and frequencies, the 6TiSCH to describe that formatting of time and frequencies, the 6TiSCH
architecture defines a global concept that is called a Channel architecture defines a global concept that is called a Channel
Distribution and Usage (CDU) matrix; a CDU matrix is a matrix of Distribution and Usage (CDU) matrix; a CDU matrix is a matrix of
cells with a height equal to the number of available channels cells with a height equal to the number of available channels
(indexed by ChannelOffsets) and a width (in timeSlots) that is the (indexed by channelOffsets) and a width (in timeSlots) that is the
period of the network scheduling operation (indexed by slotOffsets) period of the network scheduling operation (indexed by slotOffsets)
for that CDU matrix. for that CDU matrix.
The CDU matrix is used by the PCE as the map of all the channel The CDU matrix is used by the PCE as the map of all the channel
utilization. This organization depends on the time in the future. utilization. This organization depends on the time in the future.
The frequency used by a cell in the matrix rotates in a pseudorandom The frequency used by a cell in the matrix rotates in a pseudorandom
fashion, from an initial position at an epoch time, as the CDU matrix fashion, from an initial position at an epoch time, as the CDU matrix
iterates over and over. iterates over and over.
The size of a cell is a timeSlot duration, and values of 10 to 15 The size of a cell is a timeSlot duration, and values of 10 to 15
skipping to change at line 1287 skipping to change at line 1290
overall utilization of the spectrum over time by a scheduled network overall utilization of the spectrum over time by a scheduled network
operation. operation.
A CDU matrix is computed by the PCE, but unallocated timeSlots may be A CDU matrix is computed by the PCE, but unallocated timeSlots may be
used opportunistically by the nodes for classical best-effort IP used opportunistically by the nodes for classical best-effort IP
traffic. The PCE has precedence in the allocation in case of a traffic. The PCE has precedence in the allocation in case of a
conflict. Multiple schedules may coexist, in which case the schedule conflict. Multiple schedules may coexist, in which case the schedule
adds a dimension to the matrix, and the dimensions are ordered by adds a dimension to the matrix, and the dimensions are ordered by
priority. priority.
A slotFrame is the base object that a PCE needs to manipulate to A slotframe is the base object that a PCE needs to manipulate to
program a schedule into one device. The slotFrame is a device program a schedule into one device. The slotframe is a device's
perspective of a transmission schedule; there can be more than one perspective of a transmission schedule; there can be more than one
with different priorities so in case of a contention the highest with different priorities so in case of a contention the highest
priority applies. In other words, a slotFrame is the projection of a priority applies. In other words, a slotframe is the projection of a
schedule from the CDU matrix onto one device. Elaboration on that schedule from the CDU matrix onto one device. Elaboration on that
concept can be found in section "SlotFrames and Priorities" of concept can be found in Section 4.3.5 of [RFC9030], and Figures 17
[RFC9030], and Figures 17 and 18 in [RFC9030] illustrate that and 18 of [RFC9030] illustrate that projection.
projection.
6. 5G 6. 5G
5G technology enables deterministic communication. Based on the 5G technology enables deterministic communication. Based on the
centralized admission control and the scheduling of the wireless centralized admission control and the scheduling of the wireless
resources, licensed or unlicensed, Quality of Service (QoS) such as resources, licensed or unlicensed, Quality of Service (QoS) such as
latency and reliability can be guaranteed. 5G contains several latency and reliability can be guaranteed. 5G contains several
features to achieve ultra-reliable and low-latency performance (e.g., features to achieve ultra-reliable and low-latency performance (e.g.,
support for different OFDM numerologies and slot durations), as well support for different OFDM numerologies and slot durations), as well
as fast processing capabilities and redundancy techniques that lead as fast processing capabilities and redundancy techniques that lead
skipping to change at line 1657 skipping to change at line 1659
NR is designed with native support of antenna arrays utilizing NR is designed with native support of antenna arrays utilizing
benefits from beamforming, transmissions over multiple MIMO layers, benefits from beamforming, transmissions over multiple MIMO layers,
and advanced receiver algorithms allowing effective interference and advanced receiver algorithms allowing effective interference
cancellation. Those antenna techniques are the basis for high signal cancellation. Those antenna techniques are the basis for high signal
quality and the effectiveness of spectral usage. Spatial diversity quality and the effectiveness of spectral usage. Spatial diversity
with up to four MIMO layers in UL and up to eight MIMO layers in DL with up to four MIMO layers in UL and up to eight MIMO layers in DL
is supported. Together with spatial-domain multiplexing, antenna is supported. Together with spatial-domain multiplexing, antenna
arrays can focus power in the desired direction to form beams. NR arrays can focus power in the desired direction to form beams. NR
supports beam management mechanisms to find the best suitable beam supports beam management mechanisms to find the best suitable beam
for UE initially and when it is moving. In addition, gNBs can for UE initially and when it is moving. In addition, gNBs can
coordinate their respective DL and UL transmissions over the backhaul coordinate their respective downlink (DL) and uplink (UL)
network, keeping interference reasonably low, and even make transmissions over the backhaul network, keeping interference
transmissions or receptions from multiple points (multi-TRP). Multi- reasonably low, and even make transmissions or receptions from
TRP can be used for repetition of a data packet in time, in multiple points (multi-TRP). Multi-TRP can be used for repetition of
frequency, or over multiple MIMO layers, which can improve a data packet in time, in frequency, or over multiple MIMO layers,
reliability even further. which can improve reliability even further.
Any downlink transmission to a UE starts from resource allocation Any DL transmission to a UE starts from resource allocation signaling
signaling over the Physical Downlink Control Channel (PDCCH). If it over the Physical Downlink Control Channel (PDCCH). If it is
is successfully received, the UE will know about the scheduled successfully received, the UE will know about the scheduled
transmission and may receive data over the Physical Downlink Shared transmission and may receive data over the Physical Downlink Shared
Channel (PDSCH). If retransmission is required according to the HARQ Channel (PDSCH). If retransmission is required according to the HARQ
scheme, a signaling of negative acknowledgement (NACK) on the scheme, a signaling of negative acknowledgement (NACK) on the
Physical Uplink Control Channel (PUCCH) is involved, and PDCCH Physical Uplink Control Channel (PUCCH) is involved, and PDCCH
together with PDSCH transmissions (possibly with additional together with PDSCH transmissions (possibly with additional
redundancy bits) are transmitted and soft-combined with previously redundancy bits) are transmitted and soft-combined with previously
received bits. Otherwise, if no valid control signaling for received bits. Otherwise, if no valid control signaling for
scheduling data is received, nothing is transmitted on PUCCH scheduling data is received, nothing is transmitted on PUCCH
(discontinuous transmission (DTX)), and upon detecting DTX, the base (discontinuous transmission (DTX)), and upon detecting DTX, the base
station will retransmit the initial data. station will retransmit the initial data.
An uplink transmission normally starts from a Scheduling Request An UL transmission normally starts from a Scheduling Request (SR), a
(SR), a signaling message from the UE to the base station sent via signaling message from the UE to the base station sent via PUCCH.
PUCCH. Once the scheduler is informed about buffer data in the UE Once the scheduler is informed about buffer data in the UE (e.g., by
(e.g., by SR), the UE transmits a data packet on the Physical Uplink SR), the UE transmits a data packet on the Physical Uplink Shared
Shared Channel (PUSCH). Pre-scheduling, not relying on SR, is also Channel (PUSCH). Pre-scheduling, not relying on SR, is also possible
possible (see Section 6.4.4). (see Section 6.4.4).
Since transmission of data packets requires usage of control and data Since transmission of data packets requires usage of control and data
channels, there are several methods to maintain the needed channels, there are several methods to maintain the needed
reliability. NR uses Low Density Parity Check (LDPC) codes for data reliability. NR uses Low Density Parity Check (LDPC) codes for data
channels, polar codes for PDCCH, as well as orthogonal sequences and channels, polar codes for PDCCH, as well as orthogonal sequences and
polar codes for PUCCH. For ultra-reliability of data channels, very polar codes for PUCCH. For ultra-reliability of data channels, very
robust (low-spectral efficiency) Modulation and Coding Scheme (MCS) robust (low-spectral efficiency) Modulation and Coding Scheme (MCS)
tables are introduced containing very low (down to 1/20) LDPC code tables are introduced containing very low (down to 1/20) LDPC code
rates using BPSK or QPSK. Also, PDCCH and PUCCH channels support rates using Binary Phase-Shift Keying (BPSK) or Quadrature Phase-
multiple code rates including very low ones for the channel Shift Keying (QPSK). Also, PDCCH and PUCCH channels support multiple
robustness. code rates including very low ones for the channel robustness.
A connected UE reports downlink (DL) quality to gNB by sending A connected UE reports DL quality to gNB by sending Channel State
Channel State Information (CSI) reports via PUCCH while uplink (UL) Information (CSI) reports via PUCCH while UL quality is measured
quality is measured directly at gNB. For both uplink and downlink, directly at gNB. For both UL and DL, gNB selects the desired MCS
gNB selects the desired MCS number and signals it to the UE by number and signals it to the UE by Downlink Control Information (DCI)
Downlink Control Information (DCI) via PDCCH channel. For URLLC via PDCCH channel. For URLLC services, the UE can assist the gNB by
services, the UE can assist the gNB by advising that MCS targeting a advising that MCS targeting a 10^-5 Block Error Rate (BLER) are used.
10^-5 Block Error Rate (BLER) are used. Robust link adaptation Robust link adaptation algorithms can maintain the needed level of
algorithms can maintain the needed level of reliability, considering reliability, considering a given latency bound.
a given latency bound.
Low latency on the physical layer is provided by short transmission Low latency on the PHY layer is provided by short transmission
duration, which is possible by using high Subcarrier Spacing (SCS) duration, which is possible by using high Subcarrier Spacing (SCS)
and the allocation of only one or a few Orthogonal Frequency Division and the allocation of only one or a few Orthogonal Frequency Division
Multiplexing (OFDM) symbols. For example, the shortest latency for Multiplexing (OFDM) symbols. For example, the shortest latency for
the worst case is 0.23 ms in DL and 0.24 ms in UL (according to the worst case is 0.23 ms in DL and 0.24 ms in UL (according to
Section 5.7.1 in [TR37910]). Moreover, if the initial transmission Section 5.7.1 in [TR37910]). Moreover, if the initial transmission
has failed, HARQ feedback can quickly be provided and an HARQ has failed, HARQ feedback can quickly be provided and an HARQ
retransmission scheduled. retransmission scheduled.
Dynamic multiplexing of data associated with different services is Dynamic multiplexing of data associated with different services is
highly desirable for efficient use of system resources and to highly desirable for efficient use of system resources and to
maximize system capacity. Assignment of resources for eMBB is maximize system capacity. Assignment of resources for eMBB is
usually done with regular (longer) transmission slots, which can lead usually done with regular (longer) transmission slots, which can lead
to blocking of low-latency services. To overcome the blocking, eMBB to blocking of low-latency services. To overcome the blocking, eMBB
resources can be preempted and reassigned to URLLC services. In this resources can be preempted and reassigned to URLLC services. In this
way, spectrally efficient assignments for eMBB can be ensured while way, spectrally efficient assignments for eMBB can be ensured while
providing the flexibility required to ensure a bounded latency for providing the flexibility required to ensure a bounded latency for
URLLC services. In downlink, the gNB can notify the eMBB UE about URLLC services. In DL, the gNB can notify the eMBB UE about
preemption after it has happened, while in uplink there are two preemption after it has happened, while in UL there are two
preemption mechanisms: special signaling to cancel eMBB transmission preemption mechanisms: special signaling to cancel eMBB transmission
and URLLC dynamic power boost to suppress eMBB transmission. and URLLC dynamic power boost to suppress eMBB transmission.
6.4.4. Scheduling and QoS (MAC) 6.4.4. Scheduling and QoS (MAC)
One integral part of the 5G system is the Quality of Service (QoS) One integral part of the 5G system is the Quality of Service (QoS)
framework [TS23501]. QoS flows are set up by the 5G system for framework [TS23501]. QoS flows are set up by the 5G system for
certain IP or Ethernet packet flows, so that packets of each flow certain IP or Ethernet packet flows, so that packets of each flow
receive the same forwarding treatment (i.e., in scheduling and receive the same forwarding treatment (i.e., in scheduling and
admission control). For example, QoS flows can be associated with admission control). For example, QoS flows can be associated with
skipping to change at line 1774 skipping to change at line 1775
short transmission formats, sub-slot feedback reporting, and PUCCH short transmission formats, sub-slot feedback reporting, and PUCCH
carrier switching. If needed to avoid HARQ round-trip time delays, carrier switching. If needed to avoid HARQ round-trip time delays,
repeated transmissions can be also scheduled beforehand, to the cost repeated transmissions can be also scheduled beforehand, to the cost
of reduced spectral efficiency. of reduced spectral efficiency.
In dynamic DL scheduling, transmission can be initiated immediately In dynamic DL scheduling, transmission can be initiated immediately
when DL data becomes available in the gNB. However, for dynamic UL when DL data becomes available in the gNB. However, for dynamic UL
scheduling, when data becomes available but no UL resources are scheduling, when data becomes available but no UL resources are
available yet, the UE indicates the need for UL resources to the gNB available yet, the UE indicates the need for UL resources to the gNB
via a (single bit) scheduling request message in the UL control via a (single bit) scheduling request message in the UL control
channel. When thereupon UL resources are scheduled to the UE, the UE channel. When UL resources are scheduled, the UE can transmit its
can transmit its data and may include a buffer status report that data and may include a buffer status report that indicates the exact
indicates the exact amount of data per logical channel still left to amount of data per logical channel still left to be sent. More UL
be sent. More UL resources may be scheduled accordingly. To avoid resources may be scheduled accordingly. To avoid the latency
the latency introduced in the scheduling request loop, UL radio introduced in the scheduling request loop, UL radio resources can
resources can also be pre-scheduled. also be pre-scheduled.
In particular, for periodical traffic patterns, the pre-scheduling In particular, for periodical traffic patterns, the pre-scheduling
can rely on the scheduling features DL Semi-Persistent Scheduling can rely on the scheduling features DL Semi-Persistent Scheduling
(SPS) and UL Configured Grant (CG). With these features, (SPS) and UL Configured Grant (CG). With these features,
periodically recurring resources can be assigned in DL and UL. periodically recurring resources can be assigned in DL and UL.
Multiple parallels of those configurations are supported in order to Multiple parallels of those configurations are supported in order to
serve multiple parallel traffic flows of the same UE. serve multiple parallel traffic flows of the same UE.
To support QoS enforcement in the case of mixed traffic with To support QoS enforcement in the case of mixed traffic with
different QoS requirements, several features have recently been different QoS requirements, several features have recently been
introduced. This way, e.g., different periodical critical QoS flows introduced. These features allow different periodical critical QoS
can be served, together with best-effort transmissions by the same flows to be served, together with best-effort transmissions, by the
UE. These features (partly Release 16) include the following: same UE. These features include the following:
* UL logical channel transmission restrictions, allowing logical * UL logical channel transmission restrictions, allowing logical
channels of certain QoS to only be mapped to intended UL resources channels of certain QoS to only be mapped to intended UL resources
of a certain frequency carrier, slot length, or CG configuration. of a certain frequency carrier, slot length, or CG configuration.
* intra-UE preemption and multiplexing, allowing critical UL * intra-UE preemption and multiplexing, allowing critical UL
transmissions to either preempt non-critical transmissions or be transmissions to either preempt non-critical transmissions or be
multiplexed with non-critical transmissions keeping different multiplexed with non-critical transmissions keeping different
reliability targets. reliability targets.
skipping to change at line 1851 skipping to change at line 1852
by scheduled traffic [IEEE802.1Qbv] may be used to achieve bounded by scheduled traffic [IEEE802.1Qbv] may be used to achieve bounded
low latency. The TSN tool for time synchronization is the low latency. The TSN tool for time synchronization is the
generalized Precision Time Protocol (gPTP) [IEEE802.1AS], which generalized Precision Time Protocol (gPTP) [IEEE802.1AS], which
provides reliable time synchronization that can be used by end provides reliable time synchronization that can be used by end
stations and by other TSN tools (e.g., scheduled traffic stations and by other TSN tools (e.g., scheduled traffic
[IEEE802.1Qbv]). High availability, as a result of ultra- [IEEE802.1Qbv]). High availability, as a result of ultra-
reliability, is provided for data flows by the Frame Replication and reliability, is provided for data flows by the Frame Replication and
Elimination for Reliability (FRER) mechanism [IEEE802.1CB]. Elimination for Reliability (FRER) mechanism [IEEE802.1CB].
3GPP Release 16 includes integration of 5G with TSN, i.e., specifies 3GPP Release 16 includes integration of 5G with TSN, i.e., specifies
functions for the 5G System (5GS) to deliver TSN streams such that functions for the 5G System (5GS) to deliver TSN streams so that
the meet their QoS requirements. A key aspect of the integration is their QoS requirements are met. A key aspect of the integration is
the 5GS appears from the rest of the network as a set of TSN bridges, that, from the rest of the network, the 5GS appears as a set of TSN
in particular, one virtual bridge per User Plane Function (UPF) on bridges (in particular, one virtual bridge per User Plane Function
the user plane. The 5GS includes TSN Translator (TT) functionality (UPF) on the user plane). The 5GS includes TSN Translator (TT)
for the adaptation of the 5GS to the TSN bridged network and for functionality for the adaptation of the 5GS to the TSN bridged
hiding the 5GS internal procedures. The 5GS provides the following network and for hiding the 5GS internal procedures. The 5GS provides
components: the following components:
1. interface to TSN controller, as per [IEEE802.1Qcc] for the fully 1. interface to TSN controller, as per [IEEE802.1Qcc] for the fully
centralized configuration model centralized configuration model
2. time synchronization via reception and transmission of gPTP PDUs 2. time synchronization via reception and transmission of gPTP PDUs
[IEEE802.1AS] [IEEE802.1AS]
3. low latency, hence, can be integrated with scheduled traffic 3. low latency, which allows integration with scheduled traffic
[IEEE802.1Qbv] [IEEE802.1Qbv]
4. reliability, hence, can be integrated with FRER [IEEE802.1CB] 4. reliability, which allows integration with FRER [IEEE802.1CB]
3GPP Release 17 [TS23501] introduced enhancements to generalize 3GPP Release 17 [TS23501] introduced enhancements to generalize
support for TSC beyond TSN. This includes IP communications to support for TSC beyond TSN. This includes IP communications to
provide time-sensitive services (e.g., to Video, Imaging, and Audio provide time-sensitive services (e.g., to Video, Imaging, and Audio
for Professional Applications (VIAPA)). The system model of 5G for Professional Applications (VIAPA)). The system model of 5G
acting as a "TSN bridge" in Release 16 has been reused to enable the acting as a "TSN bridge" in Release 16 has been reused to enable the
5GS acting as a "TSC node" in a more generic sense (which includes 5GS acting as a "TSC node" in a more generic sense (which includes
TSN bridge and IP node). In the case of TSC that does not involve TSN bridge and IP node). In the case of TSC that does not involve
TSN, requirements are given via exposure interfaces, and the control TSN, requirements are given via exposure interfaces, and the control
plane provides the service based on QoS and time synchronization plane provides the service based on QoS and time synchronization
skipping to change at line 1933 skipping to change at line 1934
|I/O+--+ TSN +------+DS|UE+---+RAN+-+UPF|NW+------+ TSN +----+ |I/O+--+ TSN +------+DS|UE+---+RAN+-+UPF|NW+------+ TSN +----+
|dev| |bridge| | . |TT| | | | | |TT| . | |bridge| |dev| |bridge| | . |TT| | | | | |TT| . | |bridge|
+---+ +------+ | . +--+--+ +---+ +---+--+ . | +------+ +---+ +------+ | . +--+--+ +---+ +---+--+ . | +------+
| +..........................+ | | +..........................+ |
+------------------------------+ +------------------------------+
<----------------- end-to-end Ethernet -------------------> <----------------- end-to-end Ethernet ------------------->
Figure 7: 5G - TSN Integration Figure 7: 5G - TSN Integration
NR supports accurate reference time synchronization in 1us accuracy NR supports accurate reference time synchronization in 1 µs accuracy
level. Since NR is a scheduled system, an NR UE and a gNB are level. Since NR is a scheduled system, an NR UE and a gNB are
tightly synchronized to their OFDM symbol structures. A 5G internal tightly synchronized to their OFDM symbol structures. A 5G internal
reference time can be provided to the UE via broadcast or unicast reference time can be provided to the UE via broadcast or unicast
signaling, associating a known OFDM symbol to this reference clock. signaling, associating a known OFDM symbol to this reference clock.
The 5G internal reference time can be shared within the 5G network The 5G internal reference time can be shared within the 5G network
(i.e., radio and core network components). Release 16 has introduced (i.e., radio and core network components). Release 16 has introduced
interworking with gPTP for multiple time domains, where the 5GS acts interworking with gPTP for multiple time domains, where the 5GS acts
as a virtual gPTP time-aware system and supports the forwarding of as a virtual gPTP time-aware system and supports the forwarding of
gPTP time synchronization information between end stations and gPTP time synchronization information between end stations and
bridges through the 5G user plane TTs. These account for the bridges through the 5G user plane TTs. These account for the
residence time of the 5GS in the time synchronization procedure. One residence time of the 5GS in the time synchronization procedure. One
special option is when the 5GS internal reference time is not only special option is when the 5GS internal reference time is not only
used within the 5GS, but also to the rest of the devices in the used within the 5GS, but also to the rest of the devices in the
deployment, including connected TSN bridges and end stations. deployment, including connected TSN bridges and end stations.
Release 17 includes further improvements (i.e., methods for Release 17 includes further improvements (i.e., methods for
propagation delay compensation in RAN), further improving the propagation delay compensation in RAN), further improving the
accuracy for time synchronization over the air, as well as the accuracy for time synchronization over the air, as well as the
possibility for the TSN grandmaster clock to reside on the UE side. possibility for the TSN grandmaster clock to reside on the UE side.
More extensions and flexibility were added to the time More extensions and flexibility were added to the time
synchronization service, making it general for TSC, with additional synchronization service, making it general for TSC and providing
support of other types of clocks and time distribution such as additional support for other types of clocks and time distribution
boundary clock, transparent clock peer-to-peer, and transparent clock such as boundary clocks and transparent clocks (both peer-to-peer and
end-to-end, aside from the time-aware system used for TSN. end-to-end) aside from the time-aware system used for TSN.
Additionally, it is possible to use internal access stratum signaling Additionally, it is possible to use internal access stratum signaling
to distribute timing (and not the usual (g)PTP messages), for which to distribute timing (and not the usual (g)PTP messages), for which
the required accuracy can be provided by the AF [TS23501]. The same the required accuracy can be provided by the AF [TS23501]. The same
time synchronization service is expected to be further extended and time synchronization service is expected to be further extended and
enhanced in Release 18 to support Timing Resiliency (according to enhanced in Release 18 to support Timing Resiliency (according to
study item [SP211634]), where the 5G system can provide a backup or study item [SP211634]), where the 5G system can provide a backup or
alternative timing source for the failure of the local GNSS source alternative timing source for the failure of the local GNSS source
(or other primary timing source) used by the vertical. (or other primary timing source) used by the vertical.
IETF DetNet is the technology to support time-sensitive IETF DetNet is the technology to support time-sensitive
communications at the IP layer. 3GPP Release 18 includes a study communications at the IP layer. 3GPP Release 18 includes a study
[TR2370046] on interworking between 5G and DetNet. Along the TSC [TR2370046] on interworking between 5G and DetNet. Along the TSC
framework introduced for Release 17, the 5GS acts as a DetNet node framework introduced for Release 17, the 5GS acts as a DetNet node
for the support of DetNet; see Figure 7.1-1 in [TR2370046]. The for the support of DetNet; see Figure 7.1-1 in [TR2370046]. The
study provides details on how the 5GS is exposed by the Time study provides details on how the 5GS is exposed by the Time
Sensitive Communication and Time Synchronization Function (TSCTSF) to Sensitive Communication and Time Synchronization Function (TSCTSF) to
the DetNet controller as a router on a per-UPF granularity (similar the DetNet controller as a router on a per-UPF granularity (similarly
to the per-UPF Virtual TSN Bridge granularity shown in Figure 11). to the per-UPF Virtual TSN Bridge granularity shown in Figure 7). In
In particular, it lists the parameters that are provided by the particular, it lists the parameters that are provided by the TSCTSF
TSCTSF to the DetNet controller. The study also includes how the to the DetNet controller. The study also includes how the TSCTSF
TSCTSF maps DetNet flow parameters to 5G QoS parameters. Note that maps DetNet flow parameters to 5G QoS parameters. Note that TSN is
TSN is the primary subnetwork technology for DetNet. Thus, the work the primary subnetwork technology for DetNet. Thus, the work on
on DetNet over TSN, e.g., [RFC9023], can be leveraged via the TSN DetNet over TSN, e.g., [RFC9023], can be leveraged via the TSN
support built in 5G. support built in 5G.
Redundancy architectures were specified in order to provide Redundancy architectures were specified in order to provide
reliability against any kind of failure on the radio link or nodes in reliability against any kind of failure on the radio link or nodes in
the RAN and the core network. Redundant user plane paths can be the RAN and the core network. Redundant user plane paths can be
provided based on the dual connectivity architecture, where the UE provided based on the dual connectivity architecture, where the UE
sets up two PDU sessions towards the same data network, and the 5G sets up two PDU sessions towards the same data network, and the 5G
system makes the paths of the two PDU sessions independent as system makes the paths of the two PDU sessions independent as
illustrated in Figure 9. There are two PDU sessions involved in the illustrated in Figure 8. There are two PDU sessions involved in the
solution: The first spans from the UE via gNB1 to UPF1, acting as the solution: The first spans from the UE via gNB1 to UPF1, acting as the
first PDU session anchor, while the second spans from the UE via gNB2 first PDU session anchor, while the second spans from the UE via gNB2
to UPF2, acting as second the PDU session anchor. to UPF2, acting as second the PDU session anchor.
The independent paths may continue beyond the 3GPP network. The independent paths may continue beyond the 3GPP network.
Redundancy Handling Functions (RHFs) are deployed outside of the 5GS, Redundancy Handling Functions (RHFs) are deployed outside of the 5GS,
i.e., in Host A (the device) and in Host B (the network). RHF can i.e., in Host A (the device) and in Host B (the network). RHF can
implement replication and elimination functions as per [IEEE802.1CB] implement replication and elimination functions as per [IEEE802.1CB]
or the Packet Replication, Elimination, and Ordering Functions or the Packet Replication, Elimination, and Ordering Functions
(PREOF) of IETF DetNet [RFC8655]. (PREOF) of IETF DetNet [RFC8655].
skipping to change at line 2020 skipping to change at line 2021
+........+ + gNB2 +--N3--+ UPF2 |--N6--+ | +........+ + gNB2 +--N3--+ UPF2 |--N6--+ |
+------+ +------+ +------+ +------+ +------+ +------+
Figure 8: Reliability with Single UE Figure 8: Reliability with Single UE
An alternative solution is that multiple UEs per device are used for An alternative solution is that multiple UEs per device are used for
user plane redundancy as illustrated in Figure 9. Each UE sets up a user plane redundancy as illustrated in Figure 9. Each UE sets up a
PDU session. The 5GS ensures that the PDU sessions of the different PDU session. The 5GS ensures that the PDU sessions of the different
UEs are handled independently internal to the 5GS. There is no UEs are handled independently internal to the 5GS. There is no
single point of failure in this solution, which also includes RHF single point of failure in this solution, which also includes RHF
outside of the 5G system, e.g., as per the FRER or PREOF outside of the 5G system, e.g., as per FRER [IEEE802.1CB] or PREOF
specifications. [RFC8655] specifications.
+.........+ +.........+
. Device . . Device .
. . . .
. +----+ . +------+ +------+ +------+ . +----+ . +------+ +------+ +------+
. | UE +-----+ gNB1 +--N3--+ UPF1 |--N6--+ | . | UE +-----+ gNB1 +--N3--+ UPF1 |--N6--+ |
. +----+ . +------+ +------+ | | . +----+ . +------+ +------+ | |
. . | DN | . . | DN |
. +----+ . +------+ +------+ | | . +----+ . +------+ +------+ | |
. | UE +-----+ gNB2 +--N3--+ UPF2 |--N6--+ | . | UE +-----+ gNB2 +--N3--+ UPF2 |--N6--+ |
. +----+ . +------+ +------+ +------+ . +----+ . +------+ +------+ +------+
. . . .
+.........+ +.........+
Figure 9: Reliability with Dual UE Figure 9: Reliability with Dual UE
Note that the abstraction provided by the RHF and the location of the Note that the abstraction provided by the RHF and the location of the
RHF being outside of the 5G system make 5G equally supporting RHF outside of the 5G system allow 5G to support integration for
integration for reliability with both FRER of TSN and PREOF of reliability with both TSN FRER [IEEE802.1CB] and DetNet PREOF
DetNet, as they both rely on the same concept. [RFC8655], as they both rely on the same concept.
7. L-Band Digital Aeronautical Communications System (LDACS) 7. L-Band Digital Aeronautical Communications System (LDACS)
One of the main pillars of the modern Air Traffic Management (ATM) One of the main pillars of the modern Air Traffic Management (ATM)
system is the existence of a communication infrastructure that system is the existence of a communication infrastructure that
enables efficient aircraft guidance and safe separation in all phases enables efficient aircraft guidance and safe separation in all phases
of flight. Although current systems are technically mature, they of flight. Although current systems are technically mature, they
suffer from the VHF band's increasing saturation in high-density suffer from the VHF band's increasing saturation in high-density
areas and the limitations posed by analog radio. Therefore, aviation areas and the limitations posed by analog radio. Therefore, aviation
(globally and in the European Union (EU) in particular) strives for a (globally and in the European Union (EU) in particular) strives for a
sustainable modernization of the aeronautical communication sustainable modernization of the aeronautical communication
infrastructure. infrastructure.
In the long term, ATM communication shall transition from analog VHF In the long term, ATM communication shall transition from analog VHF
voice and VDL Mode 2 communication to more spectrum-efficient digital voice and VHF Digital Link (VDL) Mode 2 communication to more
data communication. The European ATM Master Plan foresees this spectrum-efficient digital data communication. The European ATM
transition to be realized for terrestrial communications by the Master Plan foresees this transition to be realized for terrestrial
development and implementation of the L-band Digital Aeronautical communications by the development and implementation of the L-band
Communications System (LDACS). Digital Aeronautical Communications System (LDACS).
LDACS has been designed with applications related to the safety and LDACS has been designed with applications related to the safety and
regularity of the flight in mind. It has therefore been designed as regularity of the flight in mind. It has therefore been designed as
a deterministic wireless data link (as far as possible). a deterministic wireless data link (as far as possible).
It is a secure, scalable, and spectrum-efficient data link with It is a secure, scalable, and spectrum-efficient data link with
embedded navigation capability; thus, it is the first truly embedded navigation capability; thus, it is the first truly
integrated Communications, Navigation, and Surveillance (CNS) system integrated Communications, Navigation, and Surveillance (CNS) system
recognized by the International Civil Aviation Organization (ICAO). recognized by the International Civil Aviation Organization (ICAO).
During flight tests, the LDACS capabilities have been successfully During flight tests, the LDACS capabilities have been successfully
skipping to change at line 2106 skipping to change at line 2107
simulations, indicating that LDACS can fulfill the identified simulations, indicating that LDACS can fulfill the identified
requirements [GRA11]. requirements [GRA11].
LDACS standardization within the framework of the ICAO started in LDACS standardization within the framework of the ICAO started in
December 2016. The ICAO standardization group has produced an December 2016. The ICAO standardization group has produced an
initial Standards and Recommended Practices (SARPs) document initial Standards and Recommended Practices (SARPs) document
[ICAO18]. The SARPs document defines the general characteristics of [ICAO18]. The SARPs document defines the general characteristics of
LDACS. LDACS.
Up to now, the LDACS standardization has been focused on the Up to now, the LDACS standardization has been focused on the
development of the physical layer and the data link layer; only development of the Physical (PHY) layer and the data link layer; only
recently have higher layers come into the focus of the LDACS recently have higher layers come into the focus of the LDACS
development activities. There is currently no "IPv6 over LDACS" development activities. There is currently no "IPv6 over LDACS"
specification; however, SESAR2020 has started the testing of specification; however, SESAR2020 has started the testing of
IPv6-based LDACS testbeds. The IPv6 architecture for the IPv6-based LDACS testbeds. The IPv6 architecture for the
aeronautical telecommunication network is called the Future aeronautical telecommunication network is called the Future
Communications Infrastructure (FCI). FCI shall support QoS, Communications Infrastructure (FCI). FCI shall support QoS,
diversity, and mobility under the umbrella of the "multi-link diversity, and mobility under the umbrella of the "multi-link
concept". This work is conducted by the ICAO WG-I Working Group. concept". This work is conducted by the ICAO WG-I Working Group.
In addition to standardization activities, several industrial LDACS In addition to standardization activities, several industrial LDACS
skipping to change at line 2133 skipping to change at line 2134
LDACS will become one of several wireless access networks connecting LDACS will become one of several wireless access networks connecting
aircraft to the Aeronautical Telecommunications Network (ATN). The aircraft to the Aeronautical Telecommunications Network (ATN). The
LDACS access network contains several ground stations, each of which LDACS access network contains several ground stations, each of which
provides one LDACS radio cell. The LDACS air interface is a cellular provides one LDACS radio cell. The LDACS air interface is a cellular
data link with a star topology connecting aircraft to ground stations data link with a star topology connecting aircraft to ground stations
with a full duplex radio link. Each ground station is the with a full duplex radio link. Each ground station is the
centralized instance controlling all air-ground communications within centralized instance controlling all air-ground communications within
its radio cell. its radio cell.
The user data rate of LDACS is 315 kbit/s to 1428 kbit/s on the The user data rate of LDACS is 315 kbit/s to 1428 kbit/s on the
forward link and 294 kbit/s to 1390 kbit/s on the reverse link, forward link (FL) and 294 kbit/s to 1390 kbit/s on the reverse link
depending on coding and modulation. Due to strong interference from (RL), depending on coding and modulation. Due to strong interference
legacy systems in the L-band, the most robust coding and modulation from legacy systems in the L-band, the most robust coding and
should be expected for initial deployment, i.e., 315 kbit/s on the modulation should be expected for initial deployment, i.e., 315 kbit/
forward link and 294 kbit/s on the reverse link. s on the FL and 294 kbit/s on the RL.
In addition to the communications capability, LDACS also offers a In addition to the communications capability, LDACS also offers a
navigation capability. Ranging data, similar to DME (Distance navigation capability. Ranging data, similar to DME (Distance
Measuring Equipment), is extracted from the LDACS communication links Measuring Equipment), is extracted from the LDACS communication links
between aircraft and LDACS ground stations. This results in LDACS between aircraft and LDACS ground stations. This results in LDACS
providing an APNT (Alternative Position, Navigation and Timing) providing an APNT (Alternative Position, Navigation and Timing)
capability to supplement the existing on-board GNSS (Global capability to supplement the existing on-board GNSS (Global
Navigation Satellite System) without the need for additional Navigation Satellite System) without the need for additional
bandwidth. Operationally, there will be no difference for pilots bandwidth. Operationally, there will be no difference for pilots
whether the navigation data are provided by LDACS or DME. This whether the navigation data are provided by LDACS or DME. This
skipping to change at line 2211 skipping to change at line 2212
As LDACS is a ground-based digital communications system for flight As LDACS is a ground-based digital communications system for flight
guidance and communications related to safety and regularity of guidance and communications related to safety and regularity of
flight, time-bounded deterministic arrival times for safety critical flight, time-bounded deterministic arrival times for safety critical
messages are a key feature for its successful deployment and rollout. messages are a key feature for its successful deployment and rollout.
7.4.1. System Architecture 7.4.1. System Architecture
Up to 512 Aircraft Stations (ASes) communicate to an LDACS Ground Up to 512 Aircraft Stations (ASes) communicate to an LDACS Ground
Station (GS) in the reverse link (RL). A GS communicates to an AS in Station (GS) in the reverse link (RL). A GS communicates to an AS in
the Forward Link (FL). Via an Access-Router (AC-R), GSs connect the the forward link (FL). Via an Access-Router (AC-R), GSs connect the
LDACS subnetwork to the global Aeronautical Telecommunications LDACS subnetwork to the global Aeronautical Telecommunications
Network (ATN) to which the corresponding Air Traffic Services (ATS) Network (ATN) to which the corresponding Air Traffic Services (ATS)
and Aeronautical Operational Control (AOC) end systems are attached. and Aeronautical Operational Control (AOC) end systems are attached.
7.4.2. Overview of the Radio Protocol Stack 7.4.2. Overview of the Radio Protocol Stack
The protocol stack of LDACS is implemented in the AS and GS; it The protocol stack of LDACS is implemented in the AS and GS; it
consists of the physical (PHY) layer with five major functional consists of the Physical (PHY) layer with five major functional
blocks above it. Four are placed in the data link layer (DLL) of the blocks above it. Four are placed in the data link layer (DLL) of the
AS and GS: AS and GS:
1. Medium Access Layer (MAC), 1. Medium Access Layer (MAC),
2. Voice Interface (VI), 2. Voice Interface (VI),
3. Data Link Service (DLS), and 3. Data Link Service (DLS), and
4. LDACS Management Entity (LME). 4. LDACS Management Entity (LME).
skipping to change at line 2294 skipping to change at line 2295
| |
((*)) ((*))
FL/RL radio channels FL/RL radio channels
separated by separated by
frequency division duplex frequency division duplex
Figure 10: LDACS Protocol Stack in AS and GS Figure 10: LDACS Protocol Stack in AS and GS
7.4.3. Radio (PHY) 7.4.3. Radio (PHY)
The physical layer provides the means to transfer data over the radio The PHY layer provides the means to transfer data over the radio
channel. The LDACS ground station supports bidirectional links to channel. The LDACS ground station supports bidirectional links to
multiple aircraft under its control. The forward link direction multiple aircraft under its control. The FL direction (which is
(which is ground to air) and the reverse link direction (which is air ground to air) and the RL direction (which is air to ground) are
to ground) are separated by frequency division duplex. Forward link separated by frequency division duplex. FL and RL use a 500 kHz
and reverse link use a 500 kHz channel each. The ground station channel each. The ground station transmits a continuous stream of
transmits a continuous stream of OFDM symbols on the forward link. OFDM symbols on the FL. In the RL, different aircrafts are separated
In the reverse link, different aircrafts are separated in time and in time and frequency using a combination of Orthogonal Frequency-
frequency using a combination of Orthogonal Frequency-Division Division Multiple Access (OFDMA) and Time-Division Multiple-Access
Multiple Access (OFDMA) and Time-Division Multiple-Access (TDMA). (TDMA). Thus, aircraft transmit discontinuously on the RL with radio
Thus, aircraft transmit discontinuously on the reverse link with bursts sent in precisely defined transmission opportunities allocated
radio bursts sent in precisely defined transmission opportunities by the ground station. The most important service on the PHY layer
allocated by the ground station. The most important service on the of LDACS is the PHY time framing service, which indicates that the
PHY layer of LDACS is the PHY time framing service, which indicates PHY layer is ready to transmit in a given slot and indicates PHY
that the PHY layer is ready to transmit in a given slot and indicates layer framing and timing to the MAC time framing service. LDACS does
PHY layer framing and timing to the MAC time framing service. LDACS not support beam-forming or Multiple Input Multiple Output (MIMO).
does not support beam-forming or Multiple Input Multiple Output
(MIMO).
7.4.4. Scheduling, Frame Structure, and QoS (MAC) 7.4.4. Scheduling, Frame Structure, and QoS (MAC)
The data link layer provides the necessary protocols to facilitate The data link layer provides the necessary protocols to facilitate
concurrent and reliable data transfer for multiple users. The LDACS concurrent and reliable data transfer for multiple users. The LDACS
data link layer is organized in two sublayers: the medium access data link layer is organized in two sublayers: the medium access
sublayer and the logical link control sublayer. The medium access sublayer and the logical link control sublayer. The medium access
sublayer manages the organization of transmission opportunities in sublayer manages the organization of transmission opportunities in
slots of time and frequency. The logical link control sublayer slots of time and frequency. The logical link control sublayer
provides acknowledged point-to-point logical channels between the provides acknowledged point-to-point logical channels between the
skipping to change at line 2399 skipping to change at line 2398
has to be requested with a resource request message stating the has to be requested with a resource request message stating the
requested amount of resources and class of service. The ground requested amount of resources and class of service. The ground
station performs resource scheduling on the basis of these requests station performs resource scheduling on the basis of these requests
and grants resources with resource allocation messages. Resource and grants resources with resource allocation messages. Resource
request and allocation messages are exchanged over dedicated request and allocation messages are exchanged over dedicated
contention-free control channels. contention-free control channels.
LDACS has two mechanisms to request resources from the scheduler in LDACS has two mechanisms to request resources from the scheduler in
the ground station. Resources can either be requested "on demand" or the ground station. Resources can either be requested "on demand" or
permanently allocated by a LDACS ground station with a given class of permanently allocated by a LDACS ground station with a given class of
service. On the forward link, this is done locally in the ground service. On the FL, this is done locally in the ground station; on
station; on the reverse link, a dedicated contention-free control the RL, a dedicated contention-free control channel is used (the
channel is used (the Dedicated Control Channel (DCCH); roughly 83 Dedicated Control Channel (DCCH); roughly 83 bits every 60 ms). A
bits every 60 ms). A resource allocation is always announced in the resource allocation is always announced in the control channel of the
control channel of the forward link (Common Control Channel (CCCH); FL (Common Control Channel (CCCH); variable sized). Due to the
variable sized). Due to the spacing of the reverse link control spacing of the RL control channels of every 60 ms, a medium access
channels of every 60 ms, a medium access delay in the same order of delay in the same order of magnitude is to be expected.
magnitude is to be expected.
Resources can also be requested "permanently". The permanent Resources can also be requested "permanently". The permanent
resource request mechanism supports requesting recurring resources at resource request mechanism supports requesting recurring resources at
given time intervals. A permanent resource request has to be given time intervals. A permanent resource request has to be
canceled by the user (or by the ground station, which is always in canceled by the user (or by the ground station, which is always in
control). User data transmissions over LDACS are therefore always control). User data transmissions over LDACS are therefore always
scheduled by the ground station, while control data uses statically scheduled by the ground station, while control data uses statically
(i.e., at net entry) allocated recurring resources (DCCH and CCCH). (i.e., at net entry) allocated recurring resources (DCCH and CCCH).
The current specification documents specify no scheduling algorithm. The current specification documents specify no scheduling algorithm.
However, performance evaluations so far have used strict priority However, performance evaluations so far have used strict priority
scheduling and round robin for equal priorities for simplicity. In scheduling and round robin for equal priorities for simplicity. In
the current prototype implementations, LDACS classes of service are the current prototype implementations, LDACS classes of service are
thus realized as priorities of medium access and not as flows. Note thus realized as priorities of medium access and not as flows. Note
that this can starve out low-priority flows. However, this is not that this can starve out low-priority flows. However, this is not
seen as a big problem since safety-related messages always go first seen as a big problem since safety-related messages always go first
in any case. Scheduling of reverse link resources is done in in any case. Scheduling of RL resources is done in physical Protocol
physical Protocol Data Units (PDU) of 112 bits (or larger if more Data Units (PDU) of 112 bits (or larger if more aggressive coding and
aggressive coding and modulation is used). Scheduling on the forward modulation is used). Scheduling on the FL is done byte wise since
link is done byte wise since the forward link is transmitted the FL is transmitted continuously by the ground station.
continuously by the ground station.
In order to support diversity, LDACS supports handovers to other In order to support diversity, LDACS supports handovers to other
ground stations on different channels. Handovers may be initiated by ground stations on different channels. Handovers may be initiated by
the aircraft (break before make) or by the ground station (make the aircraft (break before make) or by the ground station (make
before break). Beyond this, FCI diversity shall be implemented by before break). Beyond this, FCI diversity shall be implemented by
the multi-link concept. the multi-link concept.
8. IANA Considerations 8. IANA Considerations
This document has no IANA actions. This document has no IANA actions.
skipping to change at line 2565 skipping to change at line 2562
coap-03>. coap-03>.
[IEEE802.15.4] [IEEE802.15.4]
IEEE, "IEEE Standard for Low-Rate Wireless Networks", IEEE IEEE, "IEEE Standard for Low-Rate Wireless Networks", IEEE
Std 802.15.4-2015, DOI 10.1109/IEEESTD.2016.7460875, Std 802.15.4-2015, DOI 10.1109/IEEESTD.2016.7460875,
<https://doi.org/10.1109/IEEESTD.2016.7460875>. <https://doi.org/10.1109/IEEESTD.2016.7460875>.
[IEEE802.11] [IEEE802.11]
IEEE, "IEEE Standard for Information Technology -- IEEE, "IEEE Standard for Information Technology --
Telecommunications and Information Exchange between Telecommunications and Information Exchange between
Systems - Local and Metropolitan Area Networks -- Specific Systems Local and Metropolitan Area Networks -- Specific
Requirements - Part 11: Wireless LAN Medium Access Control Requirements Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) Specifications", IEEE (MAC) and Physical Layer (PHY) Specifications", IEEE
Std 802.11-2020, DOI 10.1109/IEEESTD.2021.9363693, 2020, Std 802.11-2024, DOI 10.1109/IEEESTD.2025.10979691, 2024,
<https://ieeexplore.ieee.org/document/9363693>. <https://ieeexplore.ieee.org/document/10979691>.
[IEEE802.11ax] [IEEE802.11ax]
IEEE, "IEEE Standard for Information Technology -- IEEE, "IEEE Standard for Information Technology --
Telecommunications and Information Exchange between Telecommunications and Information Exchange between
Systems Local and Metropolitan Area Networks -- Specific Systems Local and Metropolitan Area Networks -- Specific
Requirements Part 11: Wireless LAN Medium Access Control Requirements Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) Specifications Amendment 1: (MAC) and Physical Layer (PHY) Specifications Amendment 1:
Enhancements for High-Efficiency WLAN", IEEE Std 802.11ax- Enhancements for High-Efficiency WLAN", IEEE Std 802.11ax-
2021, DOI 10.1109/IEEESTD.2021.9442429, 2021, 2021, DOI 10.1109/IEEESTD.2021.9442429, 2021,
<https://ieeexplore.ieee.org/document/9442429>. <https://ieeexplore.ieee.org/document/9442429>.
skipping to change at line 2841 skipping to change at line 2838
[IEEE802.1Qcc] [IEEE802.1Qcc]
IEEE, "IEEE Standard for Local and metropolitan area IEEE, "IEEE Standard for Local and metropolitan area
networks -- Bridges and Bridged Networks -- Amendment 31: networks -- Bridges and Bridged Networks -- Amendment 31:
Stream Reservation Protocol (SRP) Enhancements and Stream Reservation Protocol (SRP) Enhancements and
Performance Improvements", IEEE Std 802.1Qcc-2018, Performance Improvements", IEEE Std 802.1Qcc-2018,
DOI 10.1109/IEEESTD.2018.8514112, DOI 10.1109/IEEESTD.2018.8514112,
<https://ieeexplore.ieee.org/document/8514112>. <https://ieeexplore.ieee.org/document/8514112>.
[IEEE802.3] [IEEE802.3]
IEEE, "IEEE Standard for Ethernet", IEEE Std 802.3-2018, IEEE, "IEEE Standard for Ethernet", IEEE Std 802.3-2022,
DOI 10.1109/IEEESTD.2018.8457469, DOI 10.1109/IEEESTD.2022.9844436,
<https://ieeexplore.ieee.org/document/8457469>. <https://ieeexplore.ieee.org/document/9844436>.
[TSN5G] 5G-ACIA, "Integration of 5G with Time-Sensitive Networking [TSN5G] 5G-ACIA, "Integration of 5G with Time-Sensitive Networking
for Industrial Communications", 5G-ACIA White Paper, for Industrial Communications", 5G-ACIA White Paper,
<https://5g-acia.org/whitepapers/integration-of-5g-with- <https://5g-acia.org/whitepapers/integration-of-5g-with-
time-sensitive-networking-for-industrial-communications>. time-sensitive-networking-for-industrial-communications>.
[MAE18] Maeurer, N. and A. Bilzhause, "A Cybersecurity [MAE18] Maeurer, N. and A. Bilzhause, "A Cybersecurity
Architecture for the L-band Digital Aeronautical Architecture for the L-band Digital Aeronautical
Communications System (LDACS)", 2018 IEEE/AIAA 37th Communications System (LDACS)", 2018 IEEE/AIAA 37th
Digital Avionics Systems Conference (DASC), pp. 1-10, Digital Avionics Systems Conference (DASC), pp. 1-10,
skipping to change at line 2982 skipping to change at line 2979
Mallory Knodel, Ron Bonica, Ketan Talaulikar, Éric Vyncke, and Carlos Mallory Knodel, Ron Bonica, Ketan Talaulikar, Éric Vyncke, and Carlos
J. Bernardos. J. Bernardos.
Contributors Contributors
This document aggregates articles from authors specialized in each This document aggregates articles from authors specialized in each
technology. Beyond the main authors listed on the front page, the technology. Beyond the main authors listed on the front page, the
following contributors proposed additional text and refinements that following contributors proposed additional text and refinements that
improved the document. improved the document.
* Georgios Z. Papadopoulos contributed to the TSCH section. * Georgios Z. Papadopoulos contributed to Section 5 ("IEEE 802.15.4
Time-Slotted Channel Hopping (TSCH)").
* Nils Maeurer and Thomas Graeupl contributed to the LDACS section. * Nils Maeurer and Thomas Graeupl contributed to Section 7 ("L-Band
Digital Aeronautical Communications System (LDACS)").
* Torsten Dudda, Alexey Shapin, and Sara Sandberg contributed to the * Torsten Dudda, Alexey Shapin, and Sara Sandberg contributed to
5G section. Section 6 ("5G").
* Rocco Di Taranto contributed to the Wi-Fi section. * Rocco Di Taranto contributed to Section 4 ("IEEE 802.11").
* Rute Sofia contributed to the Introduction and Terminology * Rute Sofia contributed to Section 1 ("Introduction") and Section 2
sections. ("Terminology").
Authors' Addresses Authors' Addresses
Pascal Thubert (editor) Pascal Thubert (editor)
Independent
06330 Roquefort-les-Pins 06330 Roquefort-les-Pins
France France
Email: pascal.thubert@gmail.com Email: pascal.thubert@gmail.com
Dave Cavalcanti Dave Cavalcanti
Intel Corporation Intel Corporation
2111 NE 25th Ave 2111 NE 25th Ave
Hillsboro, OR 97124 Hillsboro, OR 97124
United States of America United States of America
Phone: 503 712 5566 Phone: 503 712 5566
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