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<front> <front>
<title abbrev='RAW Technologies'>Reliable and Available Wireless (RAW) Techno logies</title> <title abbrev='RAW Technologies'>Reliable and Available Wireless (RAW) Techno logies</title>
<seriesInfo name="RFC" value="9913"/>
<author initials='P' surname='Thubert' fullname='Pascal Thubert' role='editor '> <author initials='P' surname='Thubert' fullname='Pascal Thubert' role='editor '>
<!-- <organization abbrev='Cisco Systems'>Cisco Systems, Inc</organization > --> <organization>Independent</organization>
<address> <address>
<postal> <postal>
<city>Roquefort-les-Pins</city> <city>Roquefort-les-Pins</city>
<code>06330</code> <code>06330</code>
<country>France</country> <country>France</country>
</postal> </postal>
<email>pascal.thubert@gmail.com</email> <email>pascal.thubert@gmail.com</email>
</address> </address>
</author> </author>
<author initials='D' surname='Cavalcanti' fullname='Dave Cavalcanti'> <author initials='D' surname='Cavalcanti' fullname='Dave Cavalcanti'>
<organization abbrev='Intel'>Intel Corporation</organization> <organization abbrev='Intel'>Intel Corporation</organization>
<address> <address>
<postal> <postal>
<street>2111 NE 25th Ave </street> <street>2111 NE 25th Ave </street>
<city> Hillsboro, OR</city> <city> Hillsboro</city>
<region>OR</region>
<code>97124</code> <code>97124</code>
<country>USA</country> <country>United States of America</country>
</postal> </postal>
<phone>503 712 5566</phone> <phone>503 712 5566</phone>
<email>dave.cavalcanti@intel.com</email> <email>dave.cavalcanti@intel.com</email>
</address> </address>
</author> </author>
<author initials='X' surname='Vilajosana' fullname='Xavier Vilajosana'> <author initials='X' surname='Vilajosana' fullname='Xavier Vilajosana'>
<organization>Universitat Oberta de Catalunya</organization> <organization>Universitat Oberta de Catalunya</organization>
<address> <address>
<postal> <postal>
<street>156 Rambla Poblenou</street> <street>156 Rambla Poblenou</street>
skipping to change at line 79 skipping to change at line 77
<postal> <postal>
<street>Magyar tudosok korutja 11</street> <street>Magyar tudosok korutja 11</street>
<city> Budapest</city> <city> Budapest</city>
<code>1117</code> <code>1117</code>
<country>Hungary</country> <country>Hungary</country>
</postal> </postal>
<email>janos.farkas@ericsson.com</email> <email>janos.farkas@ericsson.com</email>
</address> </address>
</author> </author>
<date/> <date month="April" year="2026"/>
<area>Internet Area</area>
<workgroup>RAW</workgroup> <area>RTG</area>
<keyword>Draft</keyword> <workgroup>detnet</workgroup>
<keyword>example</keyword>
<abstract> <abstract>
<t> This document surveys the short and middle range radio technologies <t>This document surveys the short- and middle-range radio technologies
that are suitable to provide a Deterministic Networking / over which providing Deterministic Networking (DetNet), and more
Reliable and Available Wireless (RAW) service over, presents the specifically, Reliable and Available Wireless (RAW) service is suitable. I
characteristics that RAW may leverage, and explores the applicability t also
of the technologies to carry deterministic flows, as of its time of public presents the characteristics that RAW may leverage and explores the
ation. applicability of the technologies to carry deterministic flows, as of
The studied the time of publication. The studied technologies are Wi-Fi 6/7,
technologies are Wi-Fi 6/7, TimeSlotted Channel Hopping (TSCH), 3GPP Time-Slotted Channel Hopping (TSCH), 3GPP 5G, and L-band Digital
5G, and L-band Digital Aeronautical Communications System (LDACS). Aeronautical Communications System (LDACS).
</t> </t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section><name>Introduction</name> <section anchor="introduction">
<name>Introduction</name>
<t> <t>
Deterministic Networking (DetNet) <xref target="RFC8557"/> provides a capabil Deterministic Networking (DetNet) <xref target="RFC8557"/> provides a
ity to carry specified capability to carry specified unicast or multicast data flows for real-time
unicast or multicast data flows for real-time applications with extremely low applications with extremely low data loss rates and bounded latency within
data loss rates and bounded latency within a network a network domain. Techniques that might be used include
domain. Techniques that might be used include (1) reserving data-plane resou (1) reserving data plane resources for individual (or aggregated) DetNet
rces flows in some or all of the intermediate nodes along the path of the
for individual (or aggregated) DetNet flows in some or all of the flow,
intermediate nodes along the path of the flow, (2) providing explicit (2) providing explicit routes for DetNet flows that do not immediately
routes for DetNet flows that do not immediately change with the change with the network topology, and
network topology, and (3) distributing data from DetNet flow packets (3) distributing data from DetNet flow packets over time and/or space
over time and/or space (e.g., different frequencies, or non-Shared Risk Links (e.g., different frequencies or non-shared risk links) to ensure
) to ensure delivery of each packet in delivery of each packet in spite of the unavailability of a path.</t>
spite of the unavailability of a path. DetNet operates at the IP layer and t <t>DetNet operates at the IP layer and typically
ypically
delivers service over wired lower-layer technologies such as Time-Sensitive delivers service over wired lower-layer technologies such as Time-Sensitive
Networking (TSN) as defined by IEEE 802.1 and IEEE 802.3. Networking (TSN) as defined by IEEE 802.1 and IEEE 802.3.
</t> </t>
<t> <t>
The Reliable and Available Wireless (RAW) Architecture <xref target='I-D.ietf The Reliable and Available Wireless (RAW) architecture <xref
-raw-architecture'/> extends the DetNet Architecture <xref target="RFC8655"/> to target="RFC9912"/> extends the DetNet architecture <xref target="RFC8655"/>
adapt to the specific challenges of the wireless medium, in particular intermit to adapt to the specific challenges of the wireless medium, in particular,
tently lossy connectivity, by optimizing the use of diversity and multipathing. intermittently lossy connectivity, by optimizing the use of diversity and
<xref target='I-D.ietf-raw-architecture'/> defines the concepts of Reliability a multipathing. <xref target='RFC9912'/> defines the concepts of reliability
nd Availability that are used in this document. In turn, this document presents and availability that are used in this document. In turn, this document
wireless technologies with capabilities such as time synchronization and schedu presents wireless technologies with capabilities, such as time
ling of transmission, that would make RAW/DetNet operations possible over such m synchronization and scheduling of transmission, that would make RAW
edia. The technologies studied in this document were identified in the charter d operations possible over such media. The technologies studied in this
uring the RAW WG formation and inherited by DetNet document were identified in the charter during the RAW Working Group (WG) for
(when the WG picked up the work on RAW). mation and
inherited by DetNet (when the WG picked up the work on RAW).
</t> </t>
<t> <t>
Making wireless reliable and available is even more challenging than it is Making wireless reliable and available is even more challenging than it is
with wires, due to the numerous causes of radio transmission losses that add up with wires, due to the numerous causes of radio transmission losses that add up
to the congestion losses and the delays caused by overbooked shared resources . to the congestion losses and the delays caused by overbooked shared resources .
</t> </t>
<t> <t>
RAW, like DetNet, needs and leverages lower-layer capabilities such as time s RAW, like DetNet, needs and leverages lower-layer capabilities such as time
ynchronization and traffic shapers. To balance the adverse effects of the radio synchronization and traffic shapers. To balance the adverse effects of the
transmission losses, RAW leverages additional lower-layer capabilities, some of radio transmission losses, RAW leverages additional lower-layer
which may be specific or at least more typically applied to wireless. Such lower capabilities, some of which may be specific or at least more typically
-layer techniques include: applied to wireless. Such lower-layer techniques include:
</t> </t>
<ul> <ul>
<li> <li>per-hop retransmissions (also known as Automatic Repeat Request (ARQ)),</
per-hop retransmissions (aka Automatic Repeat Request or ARQ), li>
</li><li> <li>variation of the Modulation and Coding Scheme (MCS),</li>
variation of the modulation and coding scheme (MCS), <li>short-range broadcast,</li>
</li><li> <li>Multi-User - Multiple Input Multiple Output (MU-MIMO),</li>
short range broadcast, <li>constructive interference, and</li>
</li><li> <li>overhearing whereby multiple receivers are scheduled to receive the same
Multiple User - Multiple Input Multiple Output (MU-MIMO), transmission, which saves both energy on the sender and spectrum.
</li><li>
constructive interference, and
</li><li>
overhearing whereby multiple receivers are scheduled to receive the same tran
smission, which saves both energy on the sender and spectrum.
</li> </li>
</ul> </ul>
<t> <t>
These capabilities may be offered by the lower layer and may be controlled by RAW, separately or in combination. These capabilities may be offered by the lower layer and may be controlled by RAW, separately or in combination.
</t> </t>
<t> <t>
RAW defines a network-layer control loop that optimizes the use of links with RAW defines a network-layer control loop that optimizes the use of links
constrained spectrum and energy while maintaining the expected connectivity pro with constrained spectrum and energy while maintaining the expected
perties, typically reliability and latency. The control loop involves communicat connectivity properties, typically reliability and latency. The control
ion monitoring through Operations, Administration and Maintenance (OAM), path co loop involves communication monitoring through Operations, Administration,
ntrol through a Path computation Element (PCE) and a runtime distributed Path Se and Maintenance (OAM); path control through a Path Computation Element
lection Engine (PSE) and extended packet replication, elimination, and ordering (PCE) and a runtime distributed Path Selection Engine (PSE); and extended
functions (PREOF). Packet Replication, Elimination, and Ordering Functions (PREOF).
</t> </t>
<t> <t>
This document surveys the short and middle range radio technologies that are This document surveys the short- and middle-range radio technologies
suitable to provide a DetNet/RAW service over, over which providing a RAW service is suitable,
presents the characteristics that RAW may leverage, and explores the applicab presents the characteristics that RAW may leverage, and explores the applicab
ility of the technologies to carry deterministic flows. ility of
The studied technologies are Wi-Fi 6/7, TimeSlotted Channel Hopping (TSCH), 3 the technologies to carry deterministic flows. The studied technologies
GPP 5G, and L-band Digital Aeronautical Communications System (LDACS). are Wi-Fi 6/7, Time-Slotted Channel Hopping (TSCH), 3GPP 5G, and L-band
The purpose of this document is to support and enable work on the these (and Digital Aeronautical Communications System (LDACS). The purpose of this
possibly other similar compatible technologies) at the IETF specifically in the document is to support and enable work on the these (and possibly other
DetNet working group working on RAW. similar compatible technologies) at the IETF, specifically in the DetNet
Working Group working on RAW.
</t> </t>
<t> <t>
This document surveys existing networking technology and defines no protocol This document surveys existing networking technology; it does not define prot
behaviors or operational practices. ocol behaviors or operational practices.
The IETF specifications referenced herein each provide their own Security Con The IETF specifications referenced herein each provide their own security con
siderations, and lower layer technologies provide their own security at Layer-2; siderations, and lower-layer technologies provide their own security at Layer 2;
a security study of the technologies is explicitly not in scope. a security study of the technologies is explicitly not in scope.
</t> </t>
</section><!-- title="Introduction"--> </section>
<section anchor="terminology">
<name>Terminology</name>
<section><name>Terminology</name>
<t> <t>
This document uses the terminology and acronyms defined in Section 2 of <xref This document uses the terminology and acronyms defined in <xref
target="RFC8655"/> and Section 2 of <xref target='I-D.ietf-raw-architecture'/>. target="RFC8655" section="2"/> and <xref section="3" target='RFC9912'/>.
</t> </t>
</section><!-- Terminology --> </section>
<section anchor='detpak'><name>Towards Reliable and Available Wireless Networ ks</name> <section anchor='detpak'><name>Towards Reliable and Available Wireless Networ ks</name>
<section anchor='schre'><name>Scheduling for Reliability</name> <section anchor='schre'><name>Scheduling for Reliability</name>
<t> <t>
A packet network is reliable for critical (e.g., time-sensitive) packets A packet network is reliable for critical (e.g., time-sensitive) packets
when the undesirable statistical effects that affect the transmission of when the undesirable statistical effects that affect the transmission of
those packets, e.g., delay or loss, are eliminated. those packets (e.g., delay or loss) are eliminated.
</t> </t>
<t> <t>
The reliability of a Deterministic Network <xref target='RFC8655'/> The reliability of a deterministic network <xref target='RFC8655'/> often
often relies on precisely applying a tight schedule that controls the use relies on precisely applying a tight schedule that controls the use of
of time-shared resources such as CPUs and buffers, and maintains at all time-shared resources such as CPUs and buffers, and maintains at all times
time the amount of the critical packets within the available resources of the number of the critical packets within the available resources of the
the communication hardware (e.g.; buffers) and that of the transmission mediu communication hardware (e.g., buffers) and the transmission medium
m (e.g.; bandwidth, transmission slots). (e.g., bandwidth, transmission slots). The schedule can also be used to
The schedule can also be used to shape the flows by controlling the time of t shape the flows by controlling the time of transmission of the packets that
ransmission of the packets that compose the flow at every hop. compose the flow at every hop.
</t> </t>
<t> <t>
To achieve this, there must be a shared sense of time throughout the network. To achieve this, there must be a shared sense of time throughout the
The sense of time is usually provided by the lower layer and is not in network. The sense of time is usually provided by the lower layer and is
scope for RAW. As an example, the Precision Time Protocol, standardized as not in scope for RAW. As an example, the Precision Time Protocol (PTP),
IEEE 1588 and IEC 61588, has mapping through profiles to Ethernet, industrial standardized as IEEE 1588 and IEC 61588, has mapping through profiles to
and SmartGrid protocols, and Wi-Fi with IEEE Std 802.1AS. Ethernet, industrial and SmartGrid protocols, and Wi-Fi with IEEE Std
802.1AS.
</t> </t>
</section><!-- Towards Reliable and Available Networks --> </section>
<section anchor='divav'><name>Diversity for Availability</name> <section anchor='divav'><name>Diversity for Availability</name>
<t> <t>
Equipment (e.g., node) failure, for instance a broken switch or an access poi Equipment (e.g., node) failure can
nt rebooting, a broken be the cause of multiple packets being lost in a row before the
wire or radio adapter, or a fixed obstacle to the transmission, can flows are rerouted or the system recovers. Examples of equipment failure incl
be the cause of multiple packets lost in a row before the ude a broken switch, an access point rebooting, a broken
flows are rerouted or the system may recover. wire or radio adapter, or a fixed obstacle to the transmission.
</t> </t>
<t> <t>
This is not acceptable for critical applications such as related to safety. Equipment failure is not acceptable for critical applications such as those r elated to safety.
A typical process control loop will tolerate an occasional packet loss, but A typical process control loop will tolerate an occasional packet loss, but
a loss of several packets in a row will cause an emergency stop. a loss of several packets in a row will cause an emergency stop.
In an amusement ride (e.g., at Disneyland, Universal, or MGM Studios parks) In an amusement ride (e.g., at Disneyland, Universal Studios, or MGM Studios
a continuous loss of packet for a few 100ms may trigger an automatic parks),
a continuous loss of packets for a few 100 ms may trigger an automatic
interruption of the ride and cause the evacuation of the attraction floor to restart it. interruption of the ride and cause the evacuation of the attraction floor to restart it.
</t> </t>
<t> <t>
Network Availability is obtained by making the transmission resilient against Network availability is obtained by making the transmission resilient against
hardware failures and radio transmission losses due to uncontrolled events hardware failures and radio transmission losses due to uncontrolled events
such as co-channel interferers, multipath fading or moving obstacles. The such as co-channel interferers, multipath fading, or moving obstacles. The
best results are typically achieved by pseudo-randomly cumulating all forms best results are typically achieved by pseudorandomly cumulating all forms
of diversity, in the spatial domain with replication and elimination, in the of diversity -- in the spatial domain with replication and elimination, in th
e
time domain with ARQ and diverse scheduled transmissions, and in the time domain with ARQ and diverse scheduled transmissions, and in the
frequency domain with frequency hopping or channel hopping between frames. frequency domain with frequency hopping or channel hopping between frames.
</t> </t>
</section><!-- Diversity for Availability --> </section>
<section anchor='wessbenef'><name>Benefits of Scheduling</name>
<section anchor='wessbenef'>
<name>Benefits of Scheduling</name>
<t> <t>
Scheduling redundant transmissions of the critical packets on diverse paths Scheduling redundant transmissions of the critical packets on diverse paths
improves the resiliency against breakages and statistical transmission improves the resiliency against breakages and statistical transmission
loss, such as due to cosmic particles on wires, and interferences on loss, such as those due to cosmic particles on wires and interferences on
wireless. While transmission losses are orders of magnitude more frequent on wireless, wireless. While transmission losses are orders of magnitude more frequent on wireless,
redundancy and diversity are needed in all cases for life- and mission-critic al applications. redundancy and diversity are needed in all cases for life- and mission-critic al applications.
</t> </t>
<t> <t>
When required, the worst case time of delivery can be guaranteed as part of When required, the worst-case time of delivery can be guaranteed as part of
the end-to-end schedule, and the sense of time that must be shared the end-to-end schedule, and the sense of time that must be shared
throughout the network can be exposed to and leveraged by other applications. throughout the network can be exposed to and leveraged by other applications.
</t> </t>
<t> <t>
In addition, scheduling provides specific value over the wireless medium: In addition, scheduling provides specific value over the wireless medium:
</t> </t>
<ul> <ul>
<li> <li>
Scheduling allows a time-sharing operation, where every transmission is assig ned its own time/frequency resource. Sender and receiver are synchronized and sc heduled to talk on a given frequency resource at a given time and for a given du ration. This way, scheduling can avoid collisions between scheduled transmission s and enable a high ratio of critical traffic (think 60 or 70% of high priority traffic with ultra low loss) compared to statistical priority-based schemes. Scheduling allows a time-sharing operation, where every transmission is assig ned its own time/frequency resource. The sender and receiver are synchronized an d scheduled to talk on a given frequency resource at a given time and for a give n duration. This way, scheduling can avoid collisions between scheduled transmis sions and enable a high ratio of critical traffic (think 60% or 70% of high-prio rity traffic with ultra low loss) compared to statistical priority-based schemes .
</li> </li>
<li> <li>
Scheduling can be used as a technique for both time and frequency diversity ( Scheduling can be used as a technique for both time and frequency diversity
e.g., between transmission retries), allowing the next transmission to happen on (e.g., between transmission retries), allowing the next transmission to
a different frequency as programmed in both the sender and the receiver. happen on a different frequency as programmed in both the sender and the
This is useful to defeat co-channel interference from un-controlled receiver. This is useful to defeat co-channel interference from
transmitters as well as multipath fading. uncontrolled transmitters as well as multipath fading.
</li> </li>
<li> <li>
Transmissions can be also scheduled on multiple channels in parallel, Transmissions can be also scheduled on multiple channels in parallel,
which enables using the full available spectrum while avoiding the which enables the use of the full available spectrum while avoiding the
hidden terminal problem, e.g., when the next packet in a same flow interferes hidden terminal problem, e.g., when the next packet in a same flow interferes
on a same channel with the previous one that progressed a few hops farther. on a same channel with the previous one that progressed a few hops farther.
</li> </li>
<li> <li>
On the other hand, scheduling optimizes the bandwidth usage: compared to Scheduling optimizes the bandwidth usage. Compared to
classical Collision Avoidance techniques, there is no blank time related to classical collision avoidance techniques, there is no blank time related to
inter-frame space (IFS) and exponential back-off in scheduled operations. Interframe Space (IFS) and exponential back-off in scheduled operations.
A minimal Clear Channel Assessment may be needed to comply with the local A minimal clear channel assessment may be needed to comply with the local
regulations such as ETSI 300-328, but that will not detect a collision when regulations such as ETSI 300-328, but that will not detect a collision when
the senders are synchronized. the senders are synchronized.
</li> </li>
<li> <li>
Finally, scheduling plays a critical role to save energy. In IoT, energy is Scheduling plays a critical role in saving energy. In the Internet of Things
the foremost concern, and synchronizing sender and listener enables (IoT), energy is
the foremost concern, and synchronizing the sender and listener enables
always maintaining them in deep sleep when there is no scheduled always maintaining them in deep sleep when there is no scheduled
transmission. This avoids idle listening and long preambles and enables long transmission. This avoids idle listening and long preambles, and it enables l ong
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 years. battery-operated nodes to operate in a mesh topology for multiple years.
</li> </li>
</ul> </ul>
</section><!-- Benefits of Scheduling on Wireless --> </section>
</section>
</section><!-- Towards Reliable and Available Networks --> <section anchor="IEEE802.11">
<name>IEEE 802.11 Wireless Local Area Networks (WLAN)</name>
<section><name>IEEE 802.11</name> <t>In recent years, the evolution of the IEEE Std 802.11 standard
has taken a new direction, emphasizing improved reliability and reduced
<t> In the recent years, the evolution of the IEEE Std 802.11 standard latency in addition to minor improvements in speed, to enable new fields
has taken a new direction, emphasizing improved reliability and of application such as industrial IoT and Virtual Reality (VR).</t>
reduced latency in addition to minor improvements in speed, to enable <t>Leveraging IEEE Std 802.11, the Wi-Fi Alliance <xref target="WFA"/>
new fields of application such as Industrial IoT and Virtual Reality. delivered Wi-Fi 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-Fi is sensitive to frame loss, which can only be combated
with the maximum use of diversity in space, time, channel, and even
technology.</t>
</t> <t>In parallel, the Avnu Alliance <xref target="Avnu"/>, which focuses on
<t>Leveraging IEEE Std 802.11, the Wi-Fi Alliance <xref target="WFA"/> applications
delivered Wi-Fi 6, 7, and now 8 with more capabilities to schedule and deliver of TSN for real-time data, formed a workgroup to investigate TSN
frames in due time at fast rates. Still, as any radio technology, Wi-Fi is sensi capabilities over wireless, leveraging both 3GPP and IEEE Std 802.11
tive to frame loss, which can only be combated with the maximum use of diversity standards.</t>
, in space, time, channel, and even technology.
</t>
<t>
In parallel, the Avnu Alliance <xref target="Avnu"/>, which focuses on appl
ications of TSN for real time data, formed a workgroup for uses case with TSN ca
pabilities over wireless, leveraging both 3GPP and IEEE Std 802.11 standards.
</t> <t>To achieve the latter, the reliability must be handled at an upper
<t> layer that can select Wi-Fi and other wired or wireless technologies for
To achieve the latter, the reliability must be handled at an upper laye parallel transmissions. This is where RAW comes into play.</t>
r that can select Wi-Fi and other wired or wireless technologies for parallel tr <t>This section surveys the IEEE 802.11 features that are most relevant to
ansmissions. This is where RAW comes into play. RAW,
</t> noting that there are a great many more in the specification, some of
<t> which may also possibly be of interest for a RAW solution. For instance,
This section surveys 802.11 features that are most relevant to RAW, noting frame fragmentation reduces the impact of a very transient transmission
that there are a great many more in the specification, some of which possibly of loss, both on latency and energy consumption.</t>
interest as well for a RAW solution. For instance, frame fragmentation reduces
the impact of a very transient transmission loss, both on latency and energy co
nsumption.
</t>
<section><name>Provenance and Documents</name> <section>
<name>Provenance and Documents</name>
<t> <t>The IEEE 802 LAN/MAN Standards Committee (SC) develops and maintains
The IEEE 802 LAN/MAN Standards Committee (SC) develops and maintains networki networking standards and recommended practices for local, metropolitan, and
ng standards and recommended practices for local, metropolitan, and other area n other area networks using an open and accredited process, and it advocates
etworks, using an open and accredited process, and advocates them on a global ba them on a global basis. The most widely used standards are for Ethernet,
sis. The most widely used standards are for Ethernet, Bridging and Virtual Bridg Bridging and Virtual Bridged LAN, Wireless LAN, Wireless Personal Area Networ
ed LANs Wireless LAN, Wireless PAN, Wireless MAN, Wireless Coexistence, Media In k (PAN), Wireless MAN,
dependent Handover Services, and Wireless RAN. An individual Working Group provi Wireless Coexistence, Media Independent Handover Services, and Wireless
des the focus for each area. Radio Access Network (RAN). An individual working group provides the focus fo
</t> r each area.</t>
<t>
The IEEE 802.11 Wireless LAN (WLAN) standards define the underlyi
ng MAC and PHY layers for the Wi-Fi technology. While previous 802.11 generation
s, such as 802.11n and 802.11ac, have focused mainly on improving peak throughpu
t, more recent generations are also considering other performance vectors, such
as efficiency enhancements for dense environments in IEEEE Std 802.11ax <xref ta
rget='IEEE80211ax'/> (approved in 2021), throughput, latency, and reliability en
hancements in P802.11be <xref target='IEEE80211be'/> (approved in 2024).
</t>
<t>
IEEE Std 802.11-2012 includes support for TSN time synchronizatio
n based on IEEE 802.1AS over 802.11 Timing Measurement protocol. IEEE Std 802.11
-2016 additionally includes an extension to the 802.1AS operation over 802.11 fo
r Fine Timing Measurement (FTM), as well as the Stream Reservation Protocol (IEE
E 802.1Qat). 802.11 WLANs can also be part of a 802.1Q bridged networks with enh
ancements enabled by the 802.11ak amendment retrofitted in IEEE Std 802.11-2020.
Traffic classification based on 802.1Q VLAN tags is also supported in 802.11. O
ther 802.1 TSN capabilities such as 802.1Qbv and 802.1CB, which are media agnost
ic, can already operate over 802.11. The IEEE Std 802.11ax-2021 defines addition
al scheduling capabilities that can enhance the timeliness performance in the 80
2.11 MAC and achieve lower bounded latency. The IEEE 802.11be has introduced fea
tures to enhance the support for 802.1 TSN capabilities especially related to wo
rst-case latency, reliability and availability.
</t> <t>The IEEE 802.11 Wireless LAN (WLAN) standards define the
<t> underlying Medium Access Control (MAC) and Physical (PHY) layers for the
The IEEE 802.11 working group has been working in collaboration w Wi-Fi technology. While previous
ith the IEEE 802.1 working group for several years extending some 802.1 features 802.11 generations, such as 802.11n and 802.11ac, focused mainly
over 802.11. As with any wireless media, 802.11 imposes new constraints and res on improving peak throughput, more recent generations are also
trictions to TSN-grade QoS, and tradeoffs between latency and reliability guaran considering other performance vectors, such as efficiency enhancements
tees must be considered as well as managed deployment requirements. An overview for dense environments in IEEE Std 802.11ax <xref target='IEEE80211ax'/>
of 802.1 TSN capabilities and challenges for their extensions to 802.11 are disc (approved in 2021) and throughput, latency, and
ussed in <xref target='Cavalcanti_2019'/>. reliability enhancements in IEEE Std 802.11be <xref target='IEEE80211be'
</t> />
<t> (approved in 2024).</t>
Wi-Fi Alliance is the worldwide network of companies that drives glo <t>IEEE Std 802.11-2012 includes support for TSN time synchronization
bal Wi-Fi adoption and evolution through thought leadership, spectrum advocacy, based on IEEE 802.1AS over the 802.11 Timing Measurement
and industry-wide collaboration. The WFA work helps ensure that Wi-Fi devices an protocol. IEEE Std 802.11-2016 additionally includes an extension to
d networks provide users the interoperability, security, and reliability they ha the 802.1AS operation over 802.11 for Fine Timing Measurement (FTM),
ve come to expect. as well as the Stream Reservation Protocol (IEEE 802.1Qat). 802.11
</t> WLANs can also be part of 802.1Q bridged networks with enhancements
<t> enabled by the 802.11ak amendment retrofitted in IEEE Std
Avnu Alliance is also a global industry forum developing interoperabi 802.11-2020. Traffic classification based on 802.1Q VLAN tags is also
lity testing for TSN capable devices across multiple media including Ethernet, W supported in 802.11. Other 802.1 TSN capabilities such as 802.1Qbv and
i-Fi, and 5G. 802.1CB, which are media agnostic, can already operate over
</t> 802.11. The IEEE Std 802.11ax-2021 (which has been incorporated into
<t> IEEE Std 802.11-2024) defines additional scheduling capabilities that
The following <xref target='IEEE80211'/> specifications/certifica can enhance the timeliness performance in the 802.11 MAC and achieve
tions are relevant in the context of reliable and available wireless services an lower-bounded latency. IEEE 802.11be introduces features to enhance
d support for time-sensitive networking capabilities: the support for 802.1 TSN capabilities, especially those related to
</t><dl spacing='normal'> worst-case latency, reliability, and availability.</t>
<dt>Time Synchronization:</dt><dd> IEEE802.11-2016 with IEEE802.1AS; <t>The IEEE 802.11 Working Group has been working in collaboration
WFA TimeSync Certification.</dd> with the IEEE 802.1 Working Group for several years, extending some
<dt>Congestion Control:</dt><dd> IEEE Std 802.11-2016 Admission Cont 802.1 features over 802.11. As with any wireless media, 802.11 imposes
rol; WFA Admission Control.</dd> new constraints and restrictions to TSN-grade QoS, and trade-offs
<dt>Security:</dt><dd> WFA Wi-Fi Protected Access, WPA2 and WPA3.</d between latency and reliability guarantees must be considered as well
d> as managed deployment requirements. An overview of 802.1 TSN
<dt>Interoperating with IEEE802.1Q bridges:</dt><dd> IEEE Std 802.11 capabilities and challenges for their extensions to 802.11 are
-2020 incorporating 802.11ak.</dd> discussed in <xref target='Cavalcanti_2019'/>.</t>
<dt>Stream Reservation Protocol (part of <xref target='IEEE8021Qat'/ <t>The Wi-Fi Alliance is the worldwide network of companies that drives
>):</dt><dd> AIEEE802.11-2016</dd> global Wi-Fi adoption and evolution through thought leadership,
<dt>Scheduled channel access:</dt><dd> IEEE802.11ad Enhancements for spectrum advocacy, and industry-wide collaboration. The WFA work helps
very high throughput in the 60 GHz band <xref target='IEEE80211ad'/>.</dd> ensure that Wi-Fi devices and networks provide users the
<dt>802.11 Real-Time Applications:</dt><dd> Topic Interest Group (TI interoperability, security, and reliability they have come to expect.</t>
G) ReportDoc <xref target='IEEE_doc_11-18-2009-06'/>.</dd> <t>The Avnu Alliance is also a global industry forum developing
</dl><t> interoperability testing for TSN-capable devices across multiple
</t> media
including Ethernet, Wi-Fi, and 5G.</t>
<t>The following IEEE Std 802.11
specifications/certifications <xref target='IEEE80211'/> are relevant in
the context of reliable
and available wireless services and support for TSN capabilities:</t>
<ul spacing='normal'>
<li>Time synchronization: IEEE Std 802.11-2016 with IEEE Std 802.1AS; WFA Time
Sync Certification</li>
<li>Congestion control: IEEE Std 802.11-2016 Admission Control; WFA Admission
Control</li>
<li>Security: WFA Wi-Fi Protected Access, WPA2, and WPA3</li>
<li>Interoperating with IEEE 802.1Q bridges: IEEE Std 802.11-2020 incorporatin
g 802.11ak</li>
<li>Stream Reservation Protocol (part of <xref target='IEEE8021Qat'/>): IEEE80
2.11-2016</li>
<li>Scheduled channel access: IEEE 802.11ad enhancements for very high through
put in the 60 GHz band <xref target='IEEE80211ad'/></li>
<li>802.11 Real-Time Applications: Topic Interest Group (TIG) ReportDoc <xref
target='IEEE_doc_11-18-2009-06'/></li>
</ul>
<t> <t>In addition, major amendments being developed by the IEEE 802.11 Working
In addition, major amendments being developed by the IEEE802.11 Working Group include capabilities that can be used as the basis for providing
Group include capabilities that can be used as the basis for providing more reli more reliable and predictable wireless connectivity and support
able and predictable wireless connectivity and support time-sensitive applicatio time-sensitive applications:</t>
ns:
</t><dl spacing='normal'>
<dt>IEEE 802.11ax: Enhancements for High Efficiency (HE).</dt><dd
><xref target='IEEE80211ax'/></dd>
<dt>IEEE 802.11be Extreme High Throughput (EHT).</dt><dd><xref ta
rget='IEEE80211be'/></dd>
<dt>IEE 802.11ay Enhanced throughput for operation in license-exe
mpt bands above 45 GHz.</dt><dd> <xref target='IEEE80211ay'/></dd>
</dl><t>
</t>
<t>
The main 802.11ax, 802.11be, 802.11ad, and 802.11ay capabilities
and their relevance to RAW are discussed in the remainder of this section.
As P802.11bn is still in early stages of development, its
capabilities are not included in this document.
<ul spacing='normal'>
<li><xref target='IEEE80211ax'/>: Enhancements for High Efficiency (HE)</li>
<li><xref target='IEEE80211be'/>: Extreme High Throughput (EHT)</li>
<li><xref target='IEEE80211ay'/>: Enhanced throughput for operation in license
-exempt bands above 45 GHz</li>
</ul>
<t>The main 802.11ax, 802.11be, 802.11ad, and 802.11ay capabilities and
their relevance to RAW are discussed in the remainder of this section.
As P802.11bn is still in early stages of development, its capabilities
are not included in this document.
</t> </t>
</section> <!-- Provenance and Documents--> </section>
<section anchor="HE"><name>802.11ax High Efficiency (HE)</name> <section anchor="HE">
<section><name>General Characteristics</name> <name>802.11ax High Efficiency (HE)</name>
<t> <section>
The next generation Wi-Fi (Wi-Fi 6) is based on t
he IEEE802.11ax amendment <xref target='IEEE80211ax'/>, which includes specific
capabilities to increase efficiency, control and reduce latency. Some of these f
eatures include higher order 1024-QAM modulation, support for uplink multiple u
ser (MU) multiple input multiple output (MIMO), orthogonal frequency-division mu
ltiple access (OFDMA), trigger-based access and Target Wake time (TWT) for enhan
ced power savings. The OFDMA mode and trigger-based access enable the AP, after
reserving the channel using the clear channel assessment procedure for a given d
uration, to schedule multi-user transmissions, which is a key capability require
d to increase latency predictability and reliability for time-sensitive flows. 8
02.11ax can operate in up to 160 MHz channels and it includes support for operat
ion in the new 6 GHz band, which has been open to unlicensed use by the FCC and
other regulatory agencies worldwide.
</t>
<section><name>Multi-User OFDMA and Trigger-based Schedul
ed Access</name>
<t>
802.11ax introduced an OFDMA mode in whic
h multiple users can be scheduled across the frequency domain. In this mode, the
Access Point (AP) can initiate multi-user (MU) Uplink (UL) transmissions in the
same PHY Protocol Data Unit (PPDU) by sending a trigger frame. This centralized
scheduling capability gives the AP much more control of the channel in its Basi
c Service Set (BSS) and it can remove contention between associated stations for
uplink transmissions, therefore reducing the randomness caused by CSMA-based ac
cess between stations within the same BSS. The AP can also transmit simultaneous
ly to multiple users in the downlink direction by using a Downlink (DL) MU OFDMA
PPDU. In order to initiate a contention free Transmission Opportunity (TXOP) us
ing the OFDMA mode, the AP still follows the typical listen before talk procedur
e to acquire the medium, which ensures interoperability and compliance with unli
censed band access rules. However, 802.11ax also includes a multi-user Enhanced
Distributed Channel Access (MU-EDCA) capability, which allows the AP to get high
er channel access priority than other devices in its BSS.
</t>
</section> <!--Multi-User OFDMA and Trigger-based Schedul
ed Access -->
<section><name>Traffic Isolation via OFDMA Resour
ce Management and Resource Unit Allocation</name>
<t>
802.11ax relies on the notion of OFDMA Resource Unit (RU) to allocate <name>General Characteristics</name>
frequency chunks to different STAs over time. RUs provide a way to allow <t> The next generation Wi-Fi (Wi-Fi 6) is based on the IEEE802.11ax
for multiple stations to transmit simultaneously, starting and ending at amendment <xref target='IEEE80211ax'/>, which includes specific
the same time. The way this is achieved is via padding, where extra bits capabilities to increase efficiency and control and to reduce
are transmitted with the same power level. The current RU allocation latency. Some of these features include higher-order 1024-QAM
algorithms provide a way to achieve traffic isolation per station which modulation, support for uplink (UL) Multi-User - Multiple Input
while per se does not support time-aware scheduling, is a key aspect to Multiple Output (MU-MIMO), Orthogonal Frequency-Division Multiple
assist reliability, as it provides traffic isolation in a shared medium. Access (OFDMA), trigger-based access, and Target Wake Time (TWT) for
enhanced power savings. The OFDMA mode and trigger-based access enable
the Access Point (AP), after reserving the channel using the clear
channel assessment procedure for a given duration, to schedule
multi-user transmissions, which is a key capability required to
increase latency predictability and reliability for time-sensitive
flows. 802.11ax can operate in up to 160 MHz channels, and it includes
support for operation in the new 6 GHz band, which has been open to
unlicensed use by the Federal Communications Commission (FCC) and
other regulatory agencies worldwide.</t>
<section>
<name>Multi-User OFDMA and Trigger-Based Scheduled Access</name>
<t>802.11ax introduced an OFDMA mode in which multiple users can be
scheduled across the frequency domain. In this mode, the Access
Point (AP) can initiate multi-user UL transmissions in
the same PHY Protocol Data Unit (PPDU) by sending a trigger
frame. This centralized scheduling capability gives the AP much more
control of the channel in its Basic Service Set (BSS), and it can
remove contention between associated stations for UL
transmissions, therefore reducing the randomness caused by access base
d on Carrier
Sense Multiple Access (CSMA) between stations within
the same BSS. The AP can also transmit simultaneously to multiple
users in the downlink (DL) direction by using a DL MU OFDMA
PPDU. In order to initiate a contention-free Transmission
Opportunity (TXOP) using the OFDMA mode, the AP still follows the
typical listen-before-talk procedure to acquire the medium, which
ensures interoperability and compliance with unlicensed band access
rules. However, 802.11ax also includes a Multi-User Enhanced
Distributed Channel Access (MU-EDCA) capability, which allows the AP
to get higher channel access priority than other devices in its
BSS.</t>
</section>
</t> <section>
</section><!-- Traffic Isolation via OFDMA Resour <name>Traffic Isolation via OFDMA Resource Management and Resource Unit
ce Management and Resource Unit --> Allocation</name>
<section><name>Improved PHY Robustness</name> <t>802.11ax relies on the notion of an OFDMA Resource Unit (RU) to
<t> allocate frequency chunks to different stations over time. RUs provide
The 802.11ax PHY can operate with 0.8, 1. a
6 or 3.2 microsecond guard interval (GI). The larger GI options provide better p way to allow multiple stations to transmit simultaneously,
rotection against multipath, which is expected to be a challenge in industrial e starting and ending at the same time. The way this is achieved is
nvironments. The possibility to operate with smaller resource units (e.g. 2 MHz) via padding, where extra bits are transmitted with the same power
enabled by OFDMA also helps reduce noise power and improve SNR, leading to bett level. The current RU allocation algorithms provide a way to
er packet error rate (PER) performance. achieve traffic isolation per station. While this does not support
</t> time-aware scheduling per se, it is a key aspect to assist
<t> reliability, as it provides traffic isolation in a shared medium.
802.11ax supports beamforming as in 802.1 </t>
1ac, but introduces UL MU MIMO, which helps improve reliability. The UL MU MIMO </section>
capability is also enabled by the trigger based access operation in 802.11ax. <section>
</t> <name>Improved PHY Robustness</name>
</section> <!-- Improved PHY Robustness --> <t>The 802.11ax PHY can operate with a 0.8, 1.6, or 3.2 microsecond
<section><name>Support for 6GHz Band</name> Guard Interval (GI). The larger GI options provide better protection
<t> against multipath, which is expected to be a challenge in industrial
The 802.11ax specification <xref environments. The possibility of operating with smaller RUs
target='IEEE80211ax'/> includes support for operation in the 6 GHz band. Given t (e.g., 2 MHz) enabled by OFDMA also helps reduce noise power and
he amount of new spectrum available as well as the fact that no legacy 802.11 de improve Signal-to-Noise Ratio (SNR), leading to better Packet Error Rat
vice (prior 802.11ax) will be able to operate in this band, 802.11ax operation i e (PER) performance.</t>
n this new band can be even more efficient. <t>802.11ax supports beamforming as in 802.11ac but introduces UL
</t> MU-MIMO, which helps improve reliability. The UL MU-MIMO capability
</section> <!-- Support for 6GHz band --> is also enabled by the trigger-based access operation in 802.11ax.</t>
</section> <!-- General Characteristics--> </section>
<section><name>Support for 6 GHz Band</name>
<t>The 802.11ax specification <xref target='IEEE80211ax'/> includes
support for operation in the 6 GHz band. Given the amount of new
spectrum available, as well as the fact that no legacy 802.11 device
(prior 802.11ax) will be able to operate in this band, 802.11ax
operation in this new band can be even more efficient.</t>
</section>
</section>
<section><name>Applicability to Deterministic Flows</name> <section><name>Applicability to Deterministic Flows</name>
<t> <t>TSN capabilities, as defined by the IEEE 802.1 TSN standards,
TSN capabilities, as defined by the IEEE 802.1 TSN standa provide the underlying mechanism for supporting deterministic flo
rds, provide the underlying mechanism for supporting deterministic flows in a Lo ws in
cal Area Network (LAN). The 802.11 working group has incorporated support for ab a Local Area Network (LAN). The IEEE 802.11 Working Group has inc
solute time synchronization to extend the TSN 802.1AS protocol so that time-sens orporated
itive flow can experience precise time synchronization when operating over 802.1 support for absolute time synchronization to extend the TSN 802.1
1 links. As IEEE 802.11 and IEEE 802.1 TSN are both based on the IEEE 802 archit AS
ecture, 802.11 devices can directly implement some TSN capabilities without the protocol so that time-sensitive flows can experience precise time
need for a gateway/translation protocol. Basic features required for operation i synchronization when operating over 802.11 links. As IEEE 802.11
n a 802.1Q LAN are already enabled for 802.11. Some TSN capabilities, such as 80 and
2.1Qbv, can already operate over the existing 802.11 MAC SAP <xref target='Sudha IEEE 802.1 TSN are both based on the IEEE 802 architecture, 802.1
karan2021'/>. Implementation and experimental results of TSN capabilities (802.1 1
AS, 802.1Qbv, and 802.1CB) extended over standard Ethernet and Wi-Fi devices hav devices can directly implement some TSN capabilities without the
e also been described in <xref target='Fang_2021'/>. Nevertheless, the IEEE 802. need
11 MAC/PHY could be extended to improve the operation of IEEE 802.1 TSN features for a gateway/translation protocol. Basic features required for
and achieve better performance metrics <xref target='Cavalcanti1287'/>. operation in a 802.1Q LAN are already enabled for 802.11. Some TS
</t><t> N
TSN capabilities supported over 802.11 (which also extends to 80 capabilities, such as 802.1Qbv, can already operate over the exis
2.11ax), include: ting
</t> 802.11 MAC Service Access Point (SAP) <xref target='Sudhakaran202
<ol type='%d.'> 1'/>. Implementation and
<li> 802.1AS based Time Synchronization (other time synch experimental results of TSN capabilities (802.1AS, 802.1Qbv, and
ronization techniques may also be used) </li> 802.1CB) extended over standard Ethernet and Wi-Fi devices have a
<li> Interoperating with IEEE802.1Q bridges</li> lso
<li> Time-sensitive Traffic Stream Classification</li> been described in <xref target='Fang_2021'/>. Nevertheless, the I
</ol> EEE
<t> 802.11 MAC/PHY could be extended to improve the operation of IEEE
The existing 802.11 TSN capabilities listed above 802.1 TSN features and achieve better performance metrics <xref
, and the 802.11ax OFDMA and AP-controlled access within a BSS provide a new set target='Cavalcanti1287'/>.
of tools to better serve time-sensitive flows. However, it is important to unde </t>
rstand the tradeoffs and constraints associated with such capabilities, as well <t>TSN capabilities supported over 802.11 (which also extends to
as redundancy and diversity mechanisms that can be used to provide more predicta 802.11ax) include:</t>
ble and reliable performance. <ol type='1'>
</t> <li>802.1AS-based time synchronization (other time synchronizat
<section><name> 802.11 Managed Network Operation and Admission Co ion techniques may also be used) </li>
ntrol</name> <li>Interoperating with IEEE 802.1Q bridges</li>
<t> <li>Time-sensitive traffic stream classification</li>
Time-sensitive applications and TSN standards are expecte </ol>
d to operate in a managed network (e.g. industrial/enterprise network). This ena <t>The existing 802.11 TSN capabilities listed above, and the
bles to carefully manage and integrate the Wi-Fi operation with the overall TSN 802.11ax OFDMA and AP-controlled access within a BSS, provide a
management framework, as defined in the <xref target='IEEE802.1Qcc'/> specificat new set of tools to better serve time-sensitive
ion. flows. However, it is important to understand the trade-offs
</t> and constraints associated with such capabilities, as well as
<t> redundancy and diversity mechanisms that can be used to
Some of the random-access latency and interference from l provide more predictable and reliable performance.
egacy/unmanaged devices can be reduced under a centralized management mode as de
fined in <xref target='IEEE802.1Qcc'/>.
</t>
<t>
Existing traffic stream identification, configuration and
admission control procedures defined in <xref target='IEEE80211'/> QoS mechanis
m can be re-used. However, given the high degree of determinism required by many
time-sensitive applications, additional capabilities to manage interference and
legacy devices within tight time-constraints need to be explored.
</t>
</section> <!-- 802.11 Managed network operation and admission co
ntrol -->
<section><name>Scheduling for Bounded Latency and Diversity</name
>
<t>
As discussed earlier, the <xref target='IEEE80211ax'/> OF
DMA mode introduces the possibility of assigning different RUs (time/frequency r
esources) to users within a PPDU. Several RU sizes are defined in the specificat
ion (26, 52, 106, 242, 484, 996 subcarriers). In addition, the AP can also decid
e on MCS (Modulation and Coding Scheme) and grouping of users within a given OFM
DA PPDU. Such flexibility can be leveraged to support time-sensitive application
s with bounded latency, especially in a managed network where stations can be co
nfigured to operate under the control of the AP, in a controlled environment (wh
ich contains only devices operating on the unlicensed band installed by the faci
lity owner and where unexpected interference from other systems and/or radio acc
ess technologies only sporadically happens), or in a deployment where channel/li
nk redundancy is used to reduce the impact of unmanaged devices/interference.
</t> </t>
<t> <section><name>802.11 Managed Network Operation and Admission Con
When the network is lightly loaded, it is possible to ach trol</name>
ieve latencies under 1 msec when Wi-Fi is operated in contention-based (i.e., wi <t>Time-sensitive applications and TSN standards are expected
thout OFDMA) mode. It is also has been shown that it is possible to achieve 1 ms to operate in a managed network (e.g., an industrial/enterprise
ec latencies in controlled environment with higher efficiency when multi-user tr network). This enables careful management and integration of the
ansmissions are used (enabled by OFDMA operation) <xref target='Cavalcanti_2019 Wi-Fi operation with the overall TSN management framework, as
'/>. Obviously, there are latency, reliability and capacity tradeoffs to be cons defined in <xref target='IEEE802.1Qcc'/>.
idered. For instance, smaller RUs result in longer transmission durations, which
may impact the minimal latency that can be achieved, but the contention latency
and randomness elimination in an interference-free environment due to multi-use
r transmission is a major benefit of the OFDMA mode.
</t> </t>
<t> <t>Some of the random-access latency and interference from
The flexibility to dynamically assign RUs to each transmi legacy/unmanaged devices can be reduced under a centralized
ssion also enables the AP to provide frequency diversity, which can help increas management mode as defined in <xref target='IEEE802.1Qcc'/>.
e reliability.
</t> </t>
</section> <!--Scheduling for bounded latency and diversity--> <t>Existing traffic stream identification, configuration, and
</section> <!-- Applicability to deterministic flows --> admission control procedures defined in the QoS mechanism in <xre
</section><!-- 802.11ax High Efficiency (HE) --> f
target='IEEE80211'/> can be reused. However,
given the high degree of determinism required by many
time-sensitive applications, additional capabilities to manage
interference and legacy devices within tight time constraints
need to be explored.</t>
</section>
<section>
<name>Scheduling for Bounded Latency and Diversity</name>
<t>As discussed earlier, the OFDMA mode in <xref
target='IEEE80211ax'/> introduces the possibility of
assigning different RUs (time/frequency resources) to users
within a PPDU. Several RU sizes are defined in the
specification (26, 52, 106, 242, 484, and 996
subcarriers). In addition, the AP can also decide on a
Modulation and Coding Scheme (MCS) and grouping of users
within a given OFMDA PPDU. Such flexibility can be
leveraged to support time-sensitive applications with
bounded latency, especially:</t>
<ul>
<li>in a managed network where stations can be configured
to operate under the control of the AP,</li>
<li>in a controlled environment (which contains only
devices operating on the unlicensed band installed by the
facility owner and where unexpected interference from
other systems and/or radio access technologies only
sporadically happens), or</li>
<li>in a deployment where channel and link redundancy is
used to reduce the impact of unmanaged devices and
interference.</li>
</ul>
<t>When the network is lightly loaded, it is possible to achieve
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 possible to
achieve 1 ms latencies in a controlled environment with higher efficiency
when multi-user transmissions are used (enabled by OFDMA operation) <xref
target='Cavalcanti_2019'/>. Obviously, there are latency, reliability,
and capacity trade-offs to be considered. For instance, smaller RUs
result in longer transmission durations, which may impact the minimal
latency that can be achieved, but the contention latency and randomness
elimination in an interference-free environment due to multi-user
transmission is a major benefit of the OFDMA mode.</t>
<section anchor="EHT"><name>802.11be Extreme High Throughput (EHT)</name <t>The flexibility to dynamically assign RUs to each transmission also
> enables the AP to provide frequency diversity, which can help increase
reliability.</t>
</section>
</section>
</section>
<section anchor="EHT">
<name>802.11be Extreme High Throughput (EHT)</name>
<section><name>General Characteristics</name> <section><name>General Characteristics</name>
<t> <t><xref target='IEEE80211be'/> was the next
The <xref target='IEEE80211be'/> ammendment was major 802.11 amendment (after IEEE Std 802.11ax-2021) for
the next major 802.11 amendment (after IEEE Std 802.11ax-2021) for operation in operation in the 2.4, 5, and 6 GHz bands. 802.11be includ
the 2.4, 5 and 6 GHz bands. 802.11be includes new PHY and MAC features and it is es new
targeting extremely high throughput (at least 30 Gbps), as well as enhancements PHY and MAC features, and it is targeting extremely high
to worst case latency and jitter. It is also expected to improve the integratio throughput (at least 30 Gbps), as well as enhancements to
n with 802.1 TSN to support time-sensitive applications over Ethernet and Wirele worst-case latency and jitter. It is also expected to imp
ss LANs. rove
</t> the integration with 802.1 TSN to support time-sensitive
<t> applications over Ethernet and Wireless LANs.</t>
<t>The main features of 802.11be that are relevant to thi
s document include:</t>
<ol type='1'>
<li>320 MHz bandwidth and more efficient utilization of
non-contiguous spectrum</li>
<li>Multi-Link Operation (MLO)</li>
<li>QoS enhancements to reduce latency and increase rel
iability</li>
</ol>
</section>
<section>
<name>Applicability to Deterministic Flows</name>
<t>The 802.11 Real-Time Applications (RTA) Topic Intere
st
Group (TIG) provided detailed information on use cases,
issues, and potential solutions to improve support for
time-sensitive applications in 802.11. The RTA TIG repo
rt
<xref target='IEEE_doc_11-18-2009-06'/> was used as inp
ut to
the 802.11be project scope.</t>
The 802.11be main features relevant to th <t>Improvements for worst-case latency, jitter, and
is document include: reliability were the main topics identified in the RTA
</t><ol type='%d.'> report, which were motivated by applications in gaming,
<li> 320MHz bandwidth and more efficient industrial automation, robotics, etc. The RTA report al
utilization of non-contiguous spectrum. </li> so
<li> Multi-link operation. </li> highlighted the need to support additional TSN capabili
<li> QoS enhancements to reduce latency a ties,
nd increase reliability. </li> such as time-aware (802.1Qbv) shaping and packet replic
</ol><t> ation
</t> and elimination as defined in 802.1CB.
</section> <!-- General Characteristics-->
<section><name>Applicability to Deterministic Flows</name>
<t>
The 802.11 Real-Time Applications (RTA) Topic Int
erest Group (TIG) provided detailed information on use cases, issues and potenti
al solution directions to improve support for time-sensitive applications in 802
.11. The RTA TIG report <xref target='IEEE_doc_11-18-2009-06'/> was used as inpu
t to the 802.11be project scope.
</t>
<t>
Improvements for worst-case latency, jitter and r
eliability were the main topics identified in the RTA report, which were motivat
ed by applications in gaming, industrial automation, robotics, etc. The RTA repo
rt also highlighted the need to support additional TSN capabilities, such as tim
e-aware (802.1Qbv) shaping and packet replication and elimination as defined in
802.1CB.
</t>
<t>
IEEE Std 802.11be builds on and enhances 802.11ax
capabilities to improve worst case latency and jitter. Some of the enhancement
areas are discussed next.
</t>
<section><name>Enhanced Scheduled Operation for Bounded L
atency </name>
<t>
In addition to the throughput enhancement
s, 802.11be leverages the trigger-based scheduled operation enabled by 802.11ax
to provide efficient and more predictable medium access.
</t> </t>
<t> <t>IEEE Std 802.11be builds on and enhances 802.11ax
capabilities to improve worst case latency and
802.11be introduced QoS signaling jitter. Some of the enhancement areas are discussed
enhancements, such as an additional QoS characteristics element, that enables S next.</t>
TAs to provide detailed information about deterministic traffic stream to the AP
. This capability helps AP implementations to better support scheduling for dete
rministic flows.
</t>
</section> <!-- Enhanced scheduled operation for bounded
latency -->
<!--section><name>Multi-AP Coordination</name>
<t>
Multi-AP coordination is one of the main
new candidate features in 802.11be. It can provide benefits in throughput and ca
pacity and has the potential to address some of the issues that impact worst cas
e latency and reliability.
Multi-AP coordination is expected to addr
ess the contention due to overlapping Basic Service Sets (OBSS), which is one of
the main sources of random latency variations.
</t>
<t> Overall, multi-AP coordination algorithms consider three different phases:
setup (where APs handling overlapping BSSs are assigned roles in a manual
or automated way, e.g., coordinator and coordinated APs); coordination
(where APs establish links among themselves, e.g., from a coordinating AP
to coordinated APs; and then assign resources to served stations);
transmission (where the coordinating APs optimize the distribution of the
transmission opportunities).
</t>
<t>
Several multi-AP coordination approaches
have been discussed with different levels of complexities and benefits, but spec
ific coordination methods have not yet been defined. Out of the different
categories, MAC-driven examples include: coordinated OFDMA (Co-OFDMA);
Coordinated TDMA (Co-TDMA); HARQ; whereas PHY-driven examples include:
Coordinated Spatial Reuse (Co-SR) and Coordinated Beamforming (Co-BF).
</t> <section>
</section> Multi-AP coordination --> <name>Enhanced Scheduled Operation for Bounded Latency</n
ame>
<t>In addition to the throughput enhancements,
802.11be leverages the trigger-based scheduled
operation enabled by 802.11ax to provide efficien
t and
more predictable medium access.
</t>
<t>802.11be introduced QoS signaling enhancements,
such as an additional QoS characteristics element,
that enables stations to provide detailed information
about deterministic traffic stream to the AP. This
capability helps AP implementations to better support
scheduling for deterministic flows.</t>
</section>
<section><name>Multi-link operation</name> <section>
<t> <name>Multi-Link Operation</name>
802.11be introduces new features to impro <t>802.11be introduces new features to improve operation over
ve operation over multiple links and channels. By leveraging multiple links/chan multiple links and channels. By leveraging multiple links and channels,
nels, 802.11be can isolate time-sensitive traffic from network congestion, one o 802.11be can isolate time-sensitive traffic from network congestion,
f the main causes of large latency variations. In a managed 802.11be network, it one of the main causes of large latency variations. In a managed
should be possible to steer traffic to certain links/channels to isolate time-s 802.11be network, it should be possible to steer traffic to certain
ensitive traffic from other traffic and help achieve bounded latency. links and channels to isolate time-sensitive traffic from other traffic
The multi-link operation (MLO) is and help achieve bounded latency. The Multi-Link Operation (MLO) is
a major feature in the 802.11be amendment that can enhance latency and reliabil a major feature in the 802.11be amendment that can enhance latency
ity by enabling data frames to be duplicated across links. and reliability by enabling data frames to be duplicated across
</t> links.</t>
</section> <!--Multi-link operation--> </section>
</section> </section>
</section><!-- 802.11be Extreme High Throughput (EHT) --> </section>
<section><name>802.11ad and 802.11ay (mmWave operation)</name> <section>
<section><name>General Characteristics</name> <name>802.11ad and 802.11ay (mmWave Operation)</name>
<t> <section>
The IEEE 802.11ad amendment defines PHY and MAC c <name>General Characteristics</name>
apabilities to enable multi-Gbps throughput in the 60 GHz millimeter wave (mmWav <t>The IEEE 802.11ad amendment defines PHY and MAC
e) band. The standard addresses the adverse mmWave signal propagation characteri capabilities to enable multi-Gbps throughput in the 60
stics and provides directional communication capabilities that take advantage of GHz millimeter wave (mmWave) band. The standard
beamforming to cope with increased attenuation. An overview of the 802.11ad sta addresses the adverse mmWave signal propagation
ndard can be found in <xref target='Nitsche_2015'/>. characteristics and provides directional communication
</t> capabilities that take advantage of beamforming to
<t> cope with increased attenuation. An overview of the
The IEEE 802.11ay is currently developing enhance 802.11ad standard can be found in <xref
ments to the 802.11ad standard to enable the next generation mmWave operation ta target='Nitsche_2015'/>.</t>
rgeting 100 Gbps throughput. Some of the main enhancements in 802.11ay include M <t>The IEEE 802.11ay is currently developing enhancements to the
IMO, channel bonding, improved channel access and beamforming training. An overv 802.11ad standard to enable the next generation mmWave operation
iew of the 802.11ay capabilities can be found in <xref target='Ghasempour_2017'/ targeting 100 Gbps throughput. Some of the main enhancements in
>. 802.11ay include MIMO, channel bonding, improved channel access, and
</t> beamforming training. An overview of the 802.11ay capabilities can be
</section><!--General Characteristics --> found in <xref target='Ghasempour_2017'/>.</t>
<section><name>Applicability to deterministic flows</name> </section>
<t>
The high data rates achievable with 802.11ad and
802.11ay can significantly reduce latency down to microsecond levels. Limited in
terference from legacy and other unlicensed devices in 60 GHz is also a benefit.
However, directionality and short range typical in mmWave operation impose new
challenges such as the overhead required for beam training and blockage issues,
which impact both latency and reliability. Therefore, it is important to underst
and the use case and deployment conditions in order to properly apply and config
ure 802.11ad/ay networks for time sensitive applications.
</t>
<t>
The 802.11ad standard includes a scheduled access
mode in which the central controller, after contending and reserving the channe
l for a dedicated period, can allocate to stations contention-free service perio
ds. This scheduling capability is also available in 802.11ay, and it is one of t
he mechanisms that can be used to provide bounded latency to time-sensitive data
flows in interference-free scenarios. An analysis of the theoretical latency bo
unds that can be achieved with 802.11ad service periods is provided in <xref tar
get='Cavalcanti_2019'/>.
</t>
</section> <!-- Applicability to deterministic flows-->
</section><!-- 802.11ad and 802.11ay (mmWave operation) -->
</section><!-- title="IEEE 802.11" --> <section>
<name>Applicability to Deterministic Flows</name>
<t>The high-data rates achievable with 802.11ad and 802.11ay can
significantly reduce latency down to microsecond levels. Limited
interference from legacy and other unlicensed devices in 60 GHz is
also a benefit. However, the directionality and short range typical in
mmWave operation impose new challenges such as the overhead required
for beam training and blockage issues, which impact both latency and
reliability. Therefore, it is important to understand the use case and
deployment conditions in order to properly apply and configure
802.11ad/ay networks for time-sensitive applications.</t>
<t>The 802.11ad standard includes a scheduled access mode in which the
central controller, after contending and reserving the channel for a
dedicated period, can allocate to stations contention-free service
periods. This scheduling capability is also available in 802.11ay, and
it is one of the mechanisms that can be used to provide bounded
latency to time-sensitive data flows in interference-free
scenarios. An analysis of the theoretical latency bounds that can be
achieved with 802.11ad service periods is provided in <xref
target='Cavalcanti_2019'/>.
</t>
</section>
</section>
</section>
<section><name>IEEE 802.15.4 Timeslotted Channel Hopping </name> <section anchor="ieee-tsch">
<name>IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH)</name>
<t> IEEE Std 802.15.4 TSCH was the first IEEE radio specification aimed <t>IEEE Std 802.15.4 TSCH was the first IEEE radio specification aimed
directly at Industrial IoT applications, for use in directly at industrial IoT applications, for use in process control
Process Control loops and monitoring. It was used as a base for the maj loops and monitoring. It was used as a base for the major industrial
or wireless process control standards, Wireless Highway Addressable Remote
industrial wireless process control standards, Wireless HART and ISA100 Transducer Protocol (HART) and ISA100.11a.
.11a. </t>
</t><t> <t>While the MAC/PHY standards enable the relatively slow rates used in
While the MAC/PHY standards enable the relatively slow rates used in Pr process control (typically in the order of 4-5 per second), the
ocess technology is not suited for the faster periods used in
Control (typically in the order of 4-5 per second), the technology is n factory automation and motion control (1 to 10 ms).</t>
ot suited for the faster periods (1 to 10ms) used in Factory Automation and moti
on control.
</t>
<section><name>Provenance and Documents</name> <section>
<t> <name>Provenance and Documents</name>
The IEEE802.15.4 Task Group has been driving the development of low-power <t>The IEEE 802.15.4 Task Group has been driving the development of
low-cost radio technology. low-power, low-cost radio technology. The IEEE 802.15.4 Physical (PHY) layer
The IEEE802.15.4 physical layer has been designed to support demanding has
low-power scenarios targeting the use of unlicensed bands, both the 2.4 GHz been designed to support demanding low-power scenarios targeting the use of
and sub GHz Industrial, Scientific and Medical (ISM) bands. This has imposed unlicensed bands, both the 2.4 GHz and sub-GHz Industrial, Scientific and
requirements in terms of frame size, data rate and bandwidth to achieve Medical (ISM) bands. This has imposed requirements in terms of frame size,
reduced collision probability, reduced packet error rate, and acceptable data rate, and bandwidth to achieve reduced collision probability, reduced
range with limited transmission power. The PHY layer supports frames of up to packet error rate, and acceptable range with limited transmission
127 bytes. The Medium Access Control (MAC) sublayer overhead is in the order power. The PHY layer supports frames of up to 127 bytes. The Medium Access
of 10-20 bytes, leaving about 100 bytes to the upper layers. IEEE802.15.4 Control (MAC) sublayer overhead is in the order of 10-20 bytes, leaving
uses spread spectrum modulation such as the Direct Sequence Spread about 100 bytes to the upper layers. IEEE 802.15.4 uses spread spectrum
Spectrum (DSSS). modulation such as the Direct Sequence Spread Spectrum (DSSS).
</t> </t>
<t> <t>
The Timeslotted Channel Hopping (TSCH) mode was added to the 2015 revision of The Time-Slotted Channel Hopping (TSCH) mode was added to the 2015 revision o
the IEEE802.15.4 standard <xref target='IEEE802154'/>. TSCH is f
the IEEE 802.15.4 standard <xref target='IEEE802154'/>. TSCH is
targeted at the embedded and industrial world, where reliability, energy targeted at the embedded and industrial world, where reliability, energy
consumption and cost drive the application space. consumption, and cost drive the application space.
</t> </t>
<!-- TSN-like activities, past and present (introduce the likes of as OFDMA, URLLC and EHT) -->
<t> <t>
Time sensitive networking on low power constrained wireless networks, buildin Building on IEEE 802.15.4, TSN on low-power constrained wireless networks
g on IEEE802.15.4, has been partially addressed by ISA100.11a <xref target='ISA100.11a'/> and Wi
have been partially addressed by ISA100.11a <xref target='ISA100.11a'/> and relessHART
WirelessHART <xref target='WirelessHART'/>. Both technologies <xref target='WirelessHART'/>. Both technologies
involve a central controller that computes redundant paths for industrial involve a central controller that computes redundant paths for industrial
process control traffic over a TSCH mesh. Moreover, ISA100.11a introduces process control traffic over a TSCH mesh. Moreover, ISA100.11a introduces
IPv6 <xref target='RFC8200'/> capabilities with a Link-Local Address for the join process and a IPv6 capabilities <xref target='RFC8200'/> with a link-local address for the join process and a
global unicast address for later exchanges, but the IPv6 traffic typically global unicast address for later exchanges, but the IPv6 traffic typically
ends at a local application gateway and the full power of IPv6 for end-to-end ends at a local application gateway and the full power of IPv6 for end-to-end
communication is not enabled. communication is not enabled.
</t> </t>
<t> <t>
At the IETF, the 6TiSCH working group <xref target='TiSCH'/> has At the IETF, the 6TiSCH Working Group <xref target='TiSCH'/> has
enabled distributed routing and scheduling to exploit the deterministic enabled distributed routing and scheduling to exploit the deterministic
access capabilities provided by TSCH for IPv6. The group designed the essenti al access capabilities provided by TSCH for IPv6. The group designed the essenti al
mechanisms, the 6top layer and the Scheduling Functions (SFs), to enable mechanisms, the 6TiSCH Operation (6top) sublayer and the Scheduling Functions (SFs), to enable
the management plane operation while ensuring IPv6 is the management plane operation while ensuring IPv6 is
supported: supported.
</t> </t>
<ul> <ul>
<li> <li>The 6top Protocol (6P) is defined in <xref target='RFC8480'/> and
</li><li> provides a pairwise negotiation mechanism to the control plane operation.
The 6top Protocol (6P) defined in <xref target='RFC8480'/>. The protocol supports agreement on a schedule between neighbors, enabling
The 6P Protocol provides a pairwise negotiation mechanism to the control plan distributed scheduling.</li>
e operation. <li>6P goes hand in hand with an SF, the policy that decides how to
The protocol supports agreement on a schedule between neighbors, enabling maintain cells and trigger 6P transactions. The Minimal Scheduling Function
distributed scheduling. (MSF) <xref target='RFC9033'/> is the default SF defined by the 6TiSCH
</li><li>6P goes hand-in-hand with an SF, the policy that decides WG.</li>
how to maintain cells and trigger 6P transactions. The Minimal Scheduling <li>With these mechanisms, 6TiSCH can establish Layer 2 links between
Function (MSF) <xref target='RFC9033'/> is the default SF defined neighboring nodes and support best-effort traffic. The Routing Protocol for
by the 6TiSCH WG. Low-Power and Lossy Networks (RPL) <xref
</li><li>With these mechanisms 6TiSCH can establish layer 2 links between nei target='RFC6550'/> provides the routing structure, enabling the 6TiSCH
ghbouring nodes and devices to establish the links with well-connected neighbors, thus
support best effort traffic. RPL <xref target='RFC8480'/> provides the routin forming the acyclic network graphs.</li>
g structure,
enabling the 6TiSCH devices to establish the links with well connected neighb
ours and thus
forming the acyclic network graphs.
</li>
</ul> </ul>
<t> <t>
A Track at 6TiSCH is the application to wireless of the concept of a Recovery In 6TiSCH, a Track is the concept of a recovery graph in the RAW
Graph in architecture applied to wireless.
the RAW architecture. A Track can follow a simple sequence of relay nodes, or it can be structured
A Track can follow a simple sequence of relay nodes or can be structured as a as a
more complex Destination Oriented Directed Acyclic Graph (DODAG) to a unicast more complex Destination-Oriented Directed Acyclic Graph (DODAG) to a unicast
destination. Along a Track, 6TiSCH nodes reserve the resources to enable the destination. Along a Track, 6TiSCH nodes reserve the resources to enable the
efficient transmission of packets while aiming to optimize certain properties efficient transmission of packets while aiming to optimize certain properties
such as reliability and ensure small jitter or bounded latency. The Track such as reliability and ensure small jitter or bounded latency. The Track
structure enables Layer-2 forwarding schemes, reducing the overhead of taking structure enables Layer 2 forwarding schemes, reducing the overhead of making
routing decisions at the Layer-3. routing decisions at Layer 3.
</t> </t>
<!-- DetNet-like arching art (introduce the likes of ISA100.11a or WiHART) -->
<t> <t>
The 6TiSCH architecture <xref target='RFC9030'/> The 6TiSCH architecture <xref target='RFC9030'/>
identifies different models to schedule resources along so-called Tracks identifies different models to schedule resources along so-called Tracks
(see <xref target='Tracks'/>) exploiting the (see <xref target='Tracks'/>), exploiting the
TSCH schedule structure however the focus at 6TiSCH is on best effort traffic TSCH schedule structure; however, the focus in 6TiSCH is on best-effort traff
and the group was never chartered to produce standard work related to Tracks. ic,
and the group was never chartered to produce standards work related to Tracks
.
</t> </t>
<t> <t>
There are several works that can be used to complement the overview provided in this document. There are several works that can be used to complement the overview provided in this document.
For example <xref target='vilajosana21'/> provides a detailed description of For example, <xref target='vilajosana21'/> provides a detailed description of
the 6TiSCH protocols, the 6TiSCH protocols,
how they are linked together and how they are integrated with other standards how they are linked together, and how they are integrated with other standard
like RPL and 6Lo. s like RPL and 6Lo.
<!--
<xref target='morell13'/> introduces how label switching can be implemented i
n a TSCH network.
It proposes a policy to distribute labels in multihop network so as to enable
differential services
through the network paths. <xref target='dearmas16'/> presents an approach to
improve network reliability
at layer 3, considering and IEEE802.15.4 TSCH network and exploiting packet r
eplication and path diversity
for that aim.-->
</t> </t>
</section>
</section><!--Provenance and Documents-->
<section><name>General Characteristics</name> <section><name>General Characteristics</name>
<t> <t>
As a core technique in IEEE802.15.4, TSCH splits time in multiple time slots 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 perspective of when the send that repeat over time. Each device has its own perspective of when the send o
or receive and on which channel the transmission happens. This constitutes r receive occurs and
the device's Slotframe where the channel and destination of a transmission by on which channel the transmission happens. This constitutes
the device's slotframe, where the channel and destination of a transmission b
y
this device are a function of time. this device are a function of time.
The overall aggregation of all the Slotframes of all the devices constitutes The overall aggregation of all the slotframes of all the devices constitutes
a time/frequency matrix with at most one transmission in each cell of the a time/frequency matrix with at most one transmission in each cell of the
matrix (more in <xref target='slotFrames'/>). matrix (see more in <xref target='slotFrames'/>).
</t> </t>
<t> <t>
The IEEE 802.15.4 TSCH standard does not define any scheduling mechanism but The IEEE 802.15.4 TSCH standard does not define any scheduling mechanism
only provides the architecture that establishes a slotted structure that can but only provides the architecture that establishes a slotted structure
be that can be managed by a proper schedule. This schedule represents the
managed by a proper schedule. This schedule represents the possible communica possible communications of a node with its neighbors and is managed by a
tions of a node with its Scheduling Function such as the Minimal Scheduling Function (MSF) <xref
neighbors, and is managed by a Scheduling Function such as the Minimal target='RFC9033'/>. In MSF, each cell in the schedule is identified by its
Scheduling Function (MSF) <xref target='RFC9033'/>. In MSF, each cell in slotOffset and channelOffset coordinates. A cell's timeSlot offset
the schedule is identified by its slotoffset and channeloffset coordinates. A indicates its position in time, relative to the beginning of the
cell's timeslot offset indicates its position in time, relative to the slotframe. A cell's channel offset is an index that maps to a frequency at
beginning of the slotframe. A cell's channel offset is an index which maps to each iteration of the slotframe. Each packet exchanged between neighbors
a frequency at each iteration of the slotframe. Each packet exchanged between happens within one cell. The size of a cell is a timeSlot duration, between
neighbors happens within one cell. The size of a cell is a timeslot duration, 10 to 15 milliseconds. An Absolute Slot Number (ASN) indicates the number
between 10 to 15 milliseconds. An Absolute Slot Number (ASN) indicates of slots elapsed since the network started. It increments at every
the number of slots elapsed since the network started. It increments at every
slot. This is a 5-byte counter that can support networks running for more slot. This is a 5-byte counter that can support networks running for more
than 300 years without wrapping (assuming a 10-ms timeslot). Channel hopping than 300 years without wrapping (assuming a 10 ms timeSlot). Channel
provides increased reliability to multi-path fading and external hopping provides increased reliability to multipath fading and external
interference. It is handled by TSCH through a channel hopping sequence interference. It is handled by TSCH through a channel-hopping sequence
referred as macHopSeq in the IEEE802.15.4 specification. referred to as macHopSeq in the IEEE 802.15.4 specification.
</t> </t>
<t> <t>
<!-- bandwidth, beam forming-->
The Time-Frequency Division Multiple Access provided by TSCH enables the The Time-Frequency Division Multiple Access provided by TSCH enables the
orchestration of traffic flows, spreading them in time and frequency, orchestration of traffic flows, spreading them in time and frequency,
and hence enabling an efficient management of the bandwidth utilization. and hence enabling an efficient management of the bandwidth utilization.
Such efficient bandwidth utilization can be combined with OFDM modulations Such efficient bandwidth utilization can be combined with OFDM modulations
also supported by the IEEE802.15.4 standard <xref target='IEEE802154'/> also supported by the IEEE 802.15.4 standard <xref target='IEEE802154'/>
since the 2015 version. since the 2015 version.
</t> </t>
<t> <t>
<!-- spectrum --> 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 differ different coexisting technologies. Regulations such as the FCC, ETSI, and
ent coexisting technologies. ARIB impose duty cycle regulations to limit the use of the bands, but
Regulations such as FCC, ETSI and ARIB impose duty cycle regulations to limi interference may still constrain the probability of delivering a packet.
t the use of the bands but yet interference may constraint the probability to de Part of these reliability challenges are addressed at the MAC layer by
liver a packet. introducing redundancy and diversity, thanks to channel hopping,
Part of these reliability challenges are addressed at the MAC introducing re scheduling, and ARQ policies. Yet, the MAC layer operates with a 1-hop
dundancy and diversity, thanks to channel hopping, scheduling and ARQ policies. vision, being limited to local actions to mitigate underperforming links.
Yet, the MAC layer operates with a 1-hop vision, being limited to local acti
ons to mitigate underperforming links.
<!-- Pascal-> not sure if you want to mention here about the capability prov
ided by RAW to determine the best path regardless of the performance of a partic
ular link -->
</t> </t>
<section anchor='Tracks'><name>6TiSCH Tracks</name> <section anchor='Tracks'><name>6TiSCH Tracks</name>
<t> <t>
A Track in the 6TiSCH Architecture <xref target='RFC9030'/> In the 6TiSCH architecture <xref target="RFC9030"/>, a Track is the concept o
is the application to 6TiSCH networks of the concept of a protection path in f a DetNet
the <xref target='RFC8655'>"Detnet architecture"</xref>. architecture protection path applied to 6TiSCH networks. A Track can be
A Track can be structured as a Destination Oriented Directed Acyclic Graph structured as a Destination-Oriented Directed Acyclic Graph (DODAG) to a
(DODAG) to a destination for unicast traffic. destination for unicast traffic. Along a Track, 6TiSCH nodes reserve the
Along a Track, 6TiSCH nodes reserve the resources to enable the resources to enable the efficient transmission of packets while aiming to
efficient transmission of packets while aiming to optimize certain properties optimize certain properties such as reliability and ensure small jitter or
such as reliability and ensure small jitter or bounded latency. The Track bounded latency. The Track structure enables Layer 2 forwarding schemes,
structure enables Layer-2 forwarding schemes, reducing the overhead of taking reducing the overhead of making routing decisions at Layer 3.
routing decisions at the Layer-3.
</t> </t>
<t> <t>
Serial Tracks can be understood as the concatenation of cells or bundles Serial Tracks can be understood as the concatenation of cells or bundles
along a routing path from a source towards a destination. The serial Track along a routing path from a source towards a destination. The serial Track
concept is analogous to the circuit concept where resources are chained concept is analogous to the circuit concept where resources are chained
into a multi-hop topology, more in <xref target='fwd'/> on how that is used into a multi-hop topology; see more in <xref target='fwd'/> on how that is us ed
in the data plane to forward packets. in the data plane to forward packets.
</t> </t>
<t> <t>
Whereas scheduling ensures reliable delivery in bounded time along any Track, Whereas scheduling ensures reliable delivery in bounded time along any Track,
high availability requires the application of PREOF functions along a more high availability requires the application of PREOF functions along a more
complex DODAG Track structure. A DODAG has forking and joining nodes where complex DODAG Track structure. A DODAG has forking and joining nodes where
the concepts such as Replication and Elimination can be exploited. concepts like replication and elimination can be exploited.
Spatial redundancy increases the overall energy consumption in the network bu t Spatial redundancy increases the overall energy consumption in the network bu t
improves significantly the availability of the network as well as the packet significantly improves the availability of the network as well as the packet
delivery ratio. delivery ratio.
A Track may also branch off and rejoin, for the purpose of the so-called A Track may also branch off and rejoin, for the purpose of so-called
Packet Replication and Elimination (PRE), over non congruent branches. Packet Replication and Elimination (PRE), over non-congruent branches. PRE
PRE may be used to complement layer-2 ARQ and may be used to complement Layer 2 ARQ and receiver-end ordering to
receiver-end Ordering to complete/extend the PREOF functions. This enables complete/extend the PREOF functions. This enables meeting industrial
meeting industrial expectations of packet delivery within bounded delay expectations of packet delivery within bounded delay over a Track that
over a Track that includes wireless links, even when the Track includes wireless links, even when the Track extends beyond the 6TiSCH
extends beyond the network.
6TiSCH network.
</t> </t>
<t>The RAW Track described in the RAW Architecture <t>The RAW recovery graph described in the RAW architecture <xref target='RFC
<xref target='I-D.ietf-raw-architecture'/> inherits directly from that model. 9912'/>
RAW extends the graph beyond a DODAG as long as a given packet cannot loop inherits directly from that model. RAW extends the graph beyond a DODAG as
within the Track. long as a given packet cannot loop within the Track.</t>
</t> <figure anchor='fig4'><name>End-to-End Deterministic Track</name>
<figure anchor='fig4'><name>End-to-End deterministic Track</name> <artwork><![CDATA[
<artwork><![CDATA[
+-----+ +-----+
| IoT | | IoT |
| G/W | | G/W |
+-----+ +-----+
^ <---- Elimination ^ <---- Elimination
| | | |
Track branch | | Track branch | |
+-------+ +--------+ Subnet Backbone +-------+ +--------+ Subnet backbone
| | | |
+--|--+ +--|--+ +--|--+ +--|--+
| | | Backbone | | | Backbone | | | Backbone | | | Backbone
o | | | router | | | router o | | | router | | | router
+--/--+ +--|--+ +--/--+ +--|--+
o / o o---o----/ o o / o o---o----/ o
o o---o--/ o o o o o o o---o--/ o o o o o
o \ / o o LLN o o \ / o o LLN o
o v <---- Replication o v <---- Replication
o o
skipping to change at line 730 skipping to change at line 906
| | | |
+--|--+ +--|--+ +--|--+ +--|--+
| | | Backbone | | | Backbone | | | Backbone | | | Backbone
o | | | router | | | router o | | | router | | | router
+--/--+ +--|--+ +--/--+ +--|--+
o / o o---o----/ o o / o o---o----/ o
o o---o--/ o o o o o o o---o--/ o o o o o
o \ / o o LLN o o \ / o o LLN o
o v <---- Replication o v <---- Replication
o o
]]></artwork> ]]></artwork>
</figure> </figure>
<t>In the example above (see <xref target='fig4'/>), a Track is laid out <t>In <xref target='fig4'/>, a Track is laid out
from a field device in a 6TiSCH network to an IoT gateway that is located from a field device in a 6TiSCH network to an IoT gateway that is located
on a IEEE802.1 TSN backbone. on an IEEE 802.1 TSN backbone.
</t> </t>
<t> <t>
The Replication function in the field device sends a copy of each packet The Replication function in the field device sends a copy of each packet
over two different branches, and a PCE schedules each hop of both branches over two different branches, and a PCE schedules each hop of both branches
so that the two so that the two
copies arrive in due time at the gateway. In case of a loss on one branch, copies arrive in due time at the gateway. In case of a loss on one branch,
hopefully the other copy of the packet still makes it in due time. If two hopefully the other copy of the packet still makes it in due time. If two
copies make it to the IoT gateway, the Elimination function in the gateway copies make it to the IoT gateway, the Elimination function in the gateway
ignores the extra packet and presents only one copy to upper layers. ignores the extra packet and presents only one copy to upper layers.
</t> </t>
<t> <t>
At each 6TiSCH hop along the Track, the PCE may schedule more than one At each 6TiSCH hop along the Track, the PCE may schedule more than one
timeSlot for a packet, so as to support Layer-2 retries (ARQ). It is also timeSlot for a packet, so as to support Layer 2 retries (ARQ). It is also
possible that the field device only uses the second branch if sending over possible for the field device to only use the second branch if sending ove
r
the first branch fails. the first branch fails.
</t> </t>
<t> <t>
In current deployments, a TSCH Track does not necessarily support PRE but In current deployments, a TSCH Track does not necessarily support PRE but
is systematically multi-path. This means that a Track is scheduled so as is systematically multipath. This means that a Track is scheduled so as
to ensure that each hop has at least two forwarding solutions, and the to ensure that each hop has at least two forwarding solutions, and the
forwarding decision is to try the preferred one and use the other in forwarding decision is to try the preferred one and use the other in
case of Layer-2 transmission failure as detected by ARQ. case of Layer 2 transmission failure as detected by ARQ.
</t> </t>
<t>Methods to implement complex Tracks are described <t>Methods to implement complex Tracks are described
in <xref target='I-D.ietf-roll-dao-projection'/> and complemented by in <xref target='RFC9914'/> and complemented by
extensions to the RPL routing protocol in extensions to the RPL routing protocol in
<xref target='I-D.ietf-roll-nsa-extension'/> for best effort traffic, but a <xref target='I-D.ietf-roll-nsa-extension'/> for best-effort traffic, but a
centralized routing technique such as promoted in DetNet is still missing. centralized routing technique such as one promoted in DetNet is still missing
.
</t> </t>
<section anchor='Tschd'><name>Track Scheduling Protocol</name> <section anchor='Tschd'>
<t> <name>Track Scheduling Protocol</name>
Section "Schedule Management Mechanisms" of the 6TiSCH architecture <t>Section <xref section="4.4" sectionFormat="bare" target="RFC9030"/> of
describes 4 approaches to manage the TSCH schedule of the LLN nodes: the 6TiSCH architecture <xref target="RFC9030"/> describes four
Static Scheduling, neighbor-to-neighbor Scheduling, remote monitoring approaches to manage the TSCH schedule of the Low-Power and Lossy Network (
and scheduling management, and Hop-by-hop scheduling. LLN) nodes: static
The Track operation for DetNet corresponds to a remote monitoring and scheduling, neighbor-to-neighbor scheduling, remote monitoring and
scheduling management by a PCE. scheduling management, and hop-by-hop scheduling. The Track operation
for DetNet corresponds to a remote monitoring and scheduling management
by a PCE.
</t> </t>
</section> </section>
<section anchor='fwd'><name>Track Forwarding</name> <section anchor='fwd'><name>Track Forwarding</name>
<t> <t>In the 6TiSCH architecture <xref target='RFC9030'/>, forwarding is
By forwarding, the 6TiSCH Architecture <xref target='RFC9030'/> means the per-packet operation that allows a packet to be delivered to a next ho
the per-packet operation that allows delivering a packet to a next hop p
or an upper layer in this node. or an upper layer in a node. Forwarding is based on preexisting
Forwarding is based on pre-existing state that was installed as a state that was installed as a result of the routing computation of a
result of the routing computation of a Track by a PCE. Track by a PCE. The 6TiSCH architecture supports three different
The 6TiSCH architecture supports three different forwarding model, forwarding models: GMPLS Track Forwarding (TF), 6LoWPAN Fragment
G-MPLS Track Forwarding (TF), 6LoWPAN Fragment Forwarding (FF) and Forwarding (FF), and IPv6 Forwarding (6F), which is the classical IP
IPv6 Forwarding (6F) which is the classical IP operation operation <xref target='RFC9030'/>. The DetNet case relates to the
<xref target='RFC9030'/>. Track Forwarding operation under the control of a PCE.
The DetNet case relates to the Track Forwarding operation under the
control of a PCE.
</t> </t>
<t> <t>
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/Frequency resources called cells (see <xref target='slotFrames' />) Time and frequency resources called cells (see <xref target='slotFra mes'/>)
are allocated to enable the forwarding operation along the Track. are allocated to enable the forwarding operation along the Track.
In a Track cell, the normal operation of IEEE802.15.4 In a Track cell, the normal operation of IEEE 802.15.4
ARQ usually happens, though the ARQ usually happens, though the
acknowledgment may be omitted in some cases, for instance if there acknowledgment may be omitted in some cases, for instance, if there
is no scheduled cell for a retry. is no scheduled cell for a retry.
</t> </t>
<t>
Track Forwarding is the simplest and fastest. A bundle of cells set
to receive (RX-cells) is uniquely paired to a bundle of cells that
are set to transmit (TX-cells), representing a layer-2 forwarding
state that can be used regardless of the network layer protocol.
This model can effectively be seen as a Generalized Multi-protocol
Label Switching (G-MPLS) operation in that the information used to
switch a frame is not an explicit label, but rather related to other
properties of the way the packet was received, a particular cell in
the case of 6TiSCH.
As a result, as long as the TSCH MAC (and Layer-2 security) accepts
a frame, that frame can be switched regardless of the protocol,
whether this is an IPv6 packet, a 6LoWPAN fragment, or a frame from
an alternate protocol such as WirelessHART or ISA100.11a.
</t>
<t> <t>
A data frame that is forwarded along a Track normally has Track Forwarding is the simplest and fastest operation. A bundle of
a destination MAC address that is set to broadcast - cells set to receive
or a multicast address depending on MAC support. (RX-cells) is uniquely paired to a bundle of cells that are set to
This way, the MAC layer in the intermediate nodes accepts the transmit (TX-cells), representing a Layer 2 forwarding state that
incoming frame and 6top switches it without incurring a change in can be used regardless of the network-layer protocol. This model
the MAC header. In the case of IEEE802.15.4, this means effectively can effectively be seen as a Generalized Multiprotocol Label
broadcast, so that along the Track the short address for the Switching (GMPLS) operation in that the information used to
destination of the frame is set to 0xFFFF. switch a frame is not an explicit label but is rather related to
other properties about the way the packet was received (a particular
cell, in the case of 6TiSCH). As a result, as long as the TSCH
MAC (and Layer 2 security) accepts a frame, that frame can be
switched regardless of the protocol, whether this is an IPv6
packet, a 6LoWPAN fragment, or a frame from an alternate protocol
such as WirelessHART or ISA100.11a.
</t> </t>
<t> <t>
A Track is thus formed end-to-end as a succession of paired bundles, A data frame that is forwarded along a Track normally has a
a receive bundle from the previous hop and a transmit bundle to destination MAC address that is set to broadcast (or a multicast
the next hop along the Track, and a cell in such a bundle belongs to address, depending on MAC support). This way, the MAC layer in
at most one Track. the intermediate nodes accepts the incoming frame, and 6top
For a given iteration of the device schedule, the effective channel switches it without incurring a change in the MAC header. In the
of the cell is obtained by adding a pseudo-random number to the case of IEEE 802.15.4, this effectively means that the address is
channelOffset of the cell, which results in a rotation of the broadcast, so that the short address for the destination of the
frequency that used for transmission. frame is set to 0xFFFF along the Track.
The bundles may be computed so as to accommodate both variable rates </t>
and retransmissions, so they might not be fully used at a given <t>
iteration of the schedule. A Track is thus formed end to end as a succession of paired
The 6TiSCH architecture provides additional means to avoid waste of bundles: a receive bundle from the previous hop and a transmit
cells as well as overflows in the transmit bundle, as follows: bundle to the 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 effective channel of the cell is obtained by
adding a pseudorandom number to the channelOffset of the cell,
which results in a rotation of the frequency that was used for
transmission. The bundles may be computed so as to accommodate
both variable rates and retransmissions, so they might not be
fully used at a given iteration of the schedule. The 6TiSCH
architecture provides additional means to avoid waste of cells as
well as overflows in the transmit bundle, as described in the follow
ing paragraphs.
</t> </t>
<t> <t>
In 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. packets.
When all of the frame that were received for a given Track are When all of the frames that were received for a given Track are
effectively transmitted, any available TX-cell for that Track effectively transmitted, any available TX-cell for that Track
can be reused for upper layer traffic for which the next-hop router can be reused for upper-layer traffic for which the next-hop router
matches the next hop along the Track. In that case, the cell 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 that is being used is effectively a TX-cell from the Track, but the
short address for the destination is that of the next-hop router. short address for the destination is that of the next-hop router.
It results that a frame that is received in a RX-cell of a Track As 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 with a destination MAC address set to this node as opposed to
broadcast must be extracted from the Track and delivered to the broadcast must be extracted from the Track and delivered to the
upper layer (a frame with an unrecognized MAC address is dropped at upper layer (a frame with an unrecognized MAC address is dropped at
the lower MAC layer and thus is not received at the 6top sublayer). the lower MAC layer and thus is not received at the 6top sublayer).
</t> </t>
<t>On the other hand, it might happen that there are not enough <t>On the other hand, it might happen that there are not enough
TX-cells in the transmit bundle to accommodate the Track traffic, TX-cells in the transmit bundle to accommodate the Track traffic,
for instance if more retransmissions are needed than provisioned. for instance, if more retransmissions are needed than provisioned.
In that case, the frame can be placed for transmission in the In that case, the frame can be placed for transmission in the
bundle that is used for layer-3 traffic towards the next hop along bundle 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, the Track as long as it can be routed by the upper layer, that is,
typically, if the frame transports an IPv6 packet. The MAC address typically, if the frame transports an IPv6 packet. The MAC address
should be set to the next-hop MAC address to avoid confusion. should be set to the next-hop MAC address to avoid confusion.
It results that a frame that is received over a layer-3 bundle may As a result, a frame that is received over a Layer 3 bundle may
be in fact associated with a Track. In a classical IP link such as a n be in fact associated with a Track. In a classical IP link such as a n
Ethernet, off-Track traffic is typically in excess over reservation Ethernet, off-Track traffic is typically in excess over reservation
to be routed along the non-reserved path based on its QoS setting. to be routed along the non-reserved path based on its QoS setting.
But with 6TiSCH, since the use of the layer-3 bundle may be due to However, with 6TiSCH, since the use of the Layer 3 bundle may be due to
transmission failures, it makes sense for the receiver to recognize transmission failures, it makes sense for the receiver to recognize
a frame that should be re-Tracked, and to place it back on the a frame that should be re-Tracked and to place it back on the
appropriate bundle if possible. appropriate bundle if possible.
A frame should be re-Tracked if the Per-Hop-Behavior A frame should be re-Tracked if the per-hop-behavior
group indicated in the Differentiated Services Field in the group indicated in the Differentiated Services field in the
IPv6 header is set to Deterministic Forwarding, as discussed in IPv6 header is set to deterministic forwarding, as discussed in
<xref target='pmh'/>. <xref target='pmh'/>.
A frame is re-Tracked by scheduling it for transmission over the A frame is re-Tracked by scheduling it for transmission over the
transmit bundle associated with the Track, transmit bundle associated with the Track,
with the destination MAC address set to broadcast. with the destination MAC address set to broadcast.
</t> </t>
<section><name>OAM</name> <section>
<t> <name>OAM</name>
<t>"An Overview of Operations, Administration, and Maintenance (OAM)
<xref target='RFC7276'> "An Overview of Operations, Tools" <xref target='RFC7276'/> provides an
Administration, and Maintenance (OAM) Tools"</xref> provides an
overview of the existing tooling for OAM <xref target='RFC6291'/>. T racks are complex paths and new tooling overview of the existing tooling for OAM <xref target='RFC6291'/>. T racks are complex paths and new tooling
is necessary to manage them, with respect to load control, timing, is necessary to manage them, with respect to load control, timing,
and the Packet Replication and Elimination Functions (PREF). and the Packet Replication and Elimination Functions (PREF).
</t> </t>
<t> <t>
An example of such tooling can be found in the context of An example of such tooling can be found in the context of Bit Index
<xref target='RFC8279'>BIER</xref> and more specifically Explicit Replication (BIER)
<xref target='RFC9262'>BIER Traffic Engineering</xref> <xref target="RFC8279"/> and, more specifically, BIER Traffic
(BIER-TE). Engineering (BIER-TE) <xref target="RFC9262"/>.</t>
<!--
removed based on MB's review
<xref target='I-D.thubert-bier-replication-elimination'/>
leverages BIER-TE to control the process of PREF, and to provide
traceability of these operations, in the deterministic dataplane,
along a complex Track.
-->
<!--
For the 6TiSCH type of constrained environment,
<xref target='I-D.thubert-6lo-bier-dispatch'/> enables an efficient
encoding of the BIER bitmap within the 6LoRH framework.
-->
</t>
</section> </section>
</section> </section>
</section> <!-- 6TiSCH Tracks --> </section>
</section> <!-- General Characteristics --> </section>
<section><name>Applicability to Deterministic Flows</name> <section><name>Applicability to Deterministic Flows</name>
<t> <t>
<!-- expected capabilities for safety and automation, e.g., loops per second In the RAW context, low-power reliable networks should address
--> non-critical control scenarios such as Class 2 and monitoring scenarios
In the RAW context, low power reliable networks should address non-critical such as Class 4, as defined by <xref target='RFC5673'/>. As a low-power
control scenarios such as Class 2 and monitoring scenarios such as Class 4 technology targeting industrial scenarios, radio transducers provide
defined by the RFC5673 <xref target='RFC5673'/>. low data rates (typically between 50 kbps to 250 kbps) and robust
As a low power technology targeting industrial scenarios radio transducers p modulations to trade off performance for reliability. TSCH networks are
rovide organized in mesh topologies and connected to a backbone. Latency in the
low data rates (typically between 50kbps to 250kbps) and robust modulations mesh network is mainly influenced by propagation aspects such as
to trade-off performance to reliability. TSCH networks are organized in mesh interference. ARQ methods and redundancy techniques such as replication
topologies and connected to a backbone. Latency in the mesh network is and elimination should be studied to provide the needed performance to
mainly influenced by propagation aspects such as interference. address deterministic scenarios.
ARQ methods and redundancy techniques such as replication and elimination
should be studied to provide the needed performance to address deterministic
scenarios.
</t> </t>
<t> <t>
Nodes in a TSCH network are tightly synchronized. This enables building the Nodes in a TSCH network are tightly synchronized. This enables building
slotted structure and ensures efficient utilization of resources thanks to the slotted structure and ensures efficient utilization of resources
proper scheduling policies. Scheduling is key to orchestrate the resources thanks to proper scheduling policies. Scheduling is key to orchestrate the
that different nodes in a Track or a path are using. Slotframes can be resources that different nodes in a Track or a path are using. Slotframes
split in resource blocks reserving the needed capacity to certain flows. can be split in resource blocks, reserving the needed capacity to certain
Periodic and bursty traffic can be handled independently in the schedule, flows. Periodic and bursty traffic can be handled independently in the
using active and reactive policies and taking advantage of overprovisioned schedule, using active and reactive policies and taking advantage of
cells. Along a Track <xref target='Tracks'/>, resource blocks overprovisioned cells. Along a Track (see <xref target='Tracks'/>), resource
can be chained so nodes in previous hops transmit their data before the n blocks can be chained so nodes in previous hops transmit their data before
ext the next packet comes. This provides a tight control of latency along a
packet comes. Track. Collision loss is avoided for best-effort traffic by
This provides a tight control to latency along a Track. Collision loss is overprovisioning resources, giving time to the management plane of the
avoided for best effort traffic by overprovisioning resources, giving time network to dedicate more resources if needed.</t>
to the management plane of the network to dedicate more resources if needed. <section anchor='detnet'><name>Centralized Path Computation</name>
<!--
-time synchronization
- scheduling capabilities, discuss such things as Resource Units, time slot
s or resource blocks.
Can we reserve periodic resources vs. ask each time, what precision can w
e get in latency control.
- diversity scenarios, what's available,
- gap analysis, e.g. discuss multihop, or what's missing how to do PREOF fe
atures.
-->
</t>
<section anchor='detnet'><name>Centralized Path Computation</name>
<t> <t>
When considering end-to-end communication over TSCH, a 6TiSCH device usually When considering end-to-end communication over TSCH, a 6TiSCH device
does usually does not place a request for bandwidth between itself and another
not place a request for bandwidth between itself and another device in the ne device in the network. Rather, an Operation Control System (OCS) invoked
twork. through a Human/Machine Interface (HMI) provides the traffic specification
Rather, an Operation Control System (OCS) invoked through a Human/Machine Int (in particular, in terms of latency, reliability, and the end nodes) to a
erface PCE. With this, the PCE computes a Track between the end nodes and
(HMI) provides the Traffic Specification, in particular in terms of latency provisions every hop in the Track with per-flow state that describes the
and reliability, and the end nodes, to a PCE. per-hop operation for a given packet, the corresponding timeSlots, and the
With this, the PCE computes a Track between the end nodes and provisions ever flow identification to recognize which packet is placed in which Track,
y sort out duplicates, etc. An example of an OCS and HMI is depicted in
hop in the Track with per-flow state that describes the per-hop operation for <xref target='NorthSouth'/>.
a
given packet, the corresponding timeSlots, and the flow identification to
recognize which packet is placed in which Track, sort out duplicates, etc.
An example of Operational Control System and HMI
is depicted in <xref target='NorthSouth'/>.
</t> </t>
<t> <t>
For a static configuration that serves a certain purpose for a long period of 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 shot with a full time, it is expected that a node will be provisioned in one shot with a full
schedule, which incorporates the aggregation of its behavior for multiple schedule, which incorporates the aggregation of its behavior for multiple
Tracks. The 6TiSCH Architecture expects that the programing of the schedule Tracks. The 6TiSCH architecture expects that the programming of the schedule
is done over the Constrained Application Protocol (CoAP) such as discussed in is done over the Constrained Application Protocol (CoAP) as discussed in <xre
<xref target='I-D.ietf-6tisch-coap'>"6TiSCH f target='I-D.ietf-6tisch-coap'/>.
Resource Management and Interaction using CoAP"</xref>.
</t> </t>
<t> <t>
But an Hybrid mode may be required as well whereby a single Track is added, However, a Hybrid mode may be required as well, whereby a single Track is add
modified, or removed, for instance if it appears that a Track does not ed,
perform as expected. modified, or removed (for instance, if it appears that a Track does not
For that case, the expectation is that a protocol that flows along a Track perform as expected).
(to be), in a fashion similar to classical Traffic Engineering (TE) For that case, the
<xref target='CCAMP'/>, may be used to update the state in the devices. expectation is that a protocol that flows along a Track, in a
In general, that flow was not designed and it is expected that DetNet will de fashion similar to classical Traffic Engineering (TE) <xref target="CCAMP"/>,
termine the appropriate may be
used to update the state in the devices.
In general, that flow was not designed, and it is expected that DetNet will d
etermine the appropriate
end-to-end protocols to be used in that case. end-to-end protocols to be used in that case.
</t> </t>
<figure align='center' anchor='NorthSouth'>
<t keepWithNext='true'>Stream Management Entity</t><figure align='center' anchor
='NorthSouth'>
<name>Architectural Layers</name> <name>Architectural Layers</name>
<artwork align='left'><![CDATA[ <artwork align='left'><![CDATA[
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 \
Device- - 6TiSCH Device- - 6TiSCH
\ 6TiSCH 6TiSCH 6TiSCH 6TiSCH / Device \ 6TiSCH 6TiSCH 6TiSCH 6TiSCH / Device
----Device------Device------Device------Device-- ----Device------Device------Device------Device--
]]></artwork>
]]></artwork>
</figure> </figure>
<section anchor='pmh'><name>Packet Marking and Handling</name> <section anchor='pmh'><name>Packet Marking and Handling</name>
<t> <t>
Section "Packet Marking and Handling" of <xref target='RFC9030' section="4.7.1"/> describes the packet tagging and
<xref target='RFC9030'/> describes the packet tagging and
marking that is expected in 6TiSCH networks. marking that is expected in 6TiSCH networks.
</t> </t>
<section anchor='pmhft'><name>Tagging Packets for Flow Identification</name> <section anchor='pmhft'><name>Tagging Packets for Flow Identification</name>
<t> <t>
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.
</t> </t>
<t> <t>
It results that the tagging that is used for a DetNet flow outside the As a result, the tagging that is used for a DetNet flow outside the
6TiSCH Low Power Lossy Network (LLN) must be swapped into 6TiSCH formats and 6TiSCH Low-Power and Lossy Network (LLN) must be swapped into 6TiSCH formats
back as the packet and back as the packet
enters and then leaves the 6TiSCH network. enters and then leaves the 6TiSCH network.
</t> </t>
</section> </section>
<section anchor='pmhrre'><name>Replication, Retries and Elimination</name> <section anchor='pmhrre'><name>Replication, Retries, and Elimination</name>
<t> <t>
The 6TiSCH Architecture <xref target='RFC9030'/> leverages PREOF over The 6TiSCH architecture <xref target='RFC9030'/> leverages PREOF over
several alternate paths in a network to provide several alternate paths in a network to provide redundancy and parallel
redundancy and parallel transmissions to bound the end-to-end delay. transmissions to bound the end-to-end delay. Considering the scenario
Considering the scenario shown in <xref target='fig_ladder'/>, shown in <xref target='fig_ladder'/>, many different paths are possible
many different paths are possible for S to reach R. for S to reach R. A simple way to benefit from this topology could be
A simple way to benefit from this topology could be to use the to use the two independent paths via nodes A, C, E and via B, D, F, but m
two independent paths via nodes A, C, E and via B, D, F. ore complex paths are possible as well.
But more complex paths are possible as well.
</t> </t>
<figure anchor='fig_ladder' align='center'><name>A Typical Ladder Shape wi th Two Parallel Paths Toward the Destination</name> <figure anchor='fig_ladder' align='center'><name>A Typical Ladder Shape wi th Two Parallel Paths Toward the Destination</name>
<artwork align='center'><![CDATA[ <artwork align='center'><![CDATA[
(A) (C) (E) (A) (C) (E)
source (S) (R) (destination) source (S) (R) (destination)
(B) (D) (F) (B) (D) (F)
]]></artwork>
]]></artwork>
</figure> </figure>
<t> <t>By employing a packet replication function, each node forwards a copy
By employing a Packet Replication function, each node forwards of each data packet over two different branches. For instance, in <xref
a copy of each data packet over two different branches. target='fig_replication'/>, the source node S transmits the data packet to
For instance, in <xref target='fig_replication'/>, the source node S nodes A and B, in two different timeSlots within the same TSCH slotframe.
transmits the data packet to nodes A and B, in two different In the figure below, S transmits the same data packet twice: once to its
timeslots within the same TSCH slotframe. Destination Parent (DP) (A) and once to its Alternate Parent (AP) (B).
</t> </t>
<figure anchor='fig_replication' align='center'><name>Packet Replication : S transmits twice the same data packet, to its Destination Parent (DP) (A) and to its Alternate Parent (AP) (B).</name> <figure anchor='fig_replication' align='center'><name>Packet Replication </name>
<artwork align='center'><![CDATA[ <artwork align='center'><![CDATA[
===> (A) => (C) => (E) === ===> (A) => (C) => (E) ===
// \\// \\// \\ // \\// \\// \\
source (S) //\\ //\\ (R) (destination) source (S) //\\ //\\ (R) (destination)
\\ // \\ // \\ // \\ // \\ // \\ //
===> (B) => (D) => (F) === ===> (B) => (D) => (F) ===
]]></artwork>
</figure>
<t></t>
<t>By employing a packet elimination function once it receives the
first copy of a data packet, a node discards the subsequent copies.
Because the first copy that reaches a node is the one that matters, it
is the only copy that will be forwarded upward.</t>
]]></artwork> <t>Considering that the wireless medium is broadcast by nature, any
</figure> neighbor of a transmitter may overhear a transmission. By employing the
promiscuous overhearing function, nodes will have multiple opportunities
<t> to receive a given data packet. For instance, in <xref
By employing Packet Elimination function once a node receives the target='fig_replication'/>, when the source node S transmits the data
first copy of a data packet, it discards the subsequent copies. packet to node A, node B may overhear the transmission.
Because the first copy that reaches a node is the
one that matters, it is the only copy that will be
forwarded upward.
</t>
<t>
Considering that the wireless medium is broadcast by nature, any
neighbor of
a transmitter may overhear a transmission.
By employing the Promiscuous Overhearing function, nodes will hav
e multiple
opportunities to receive a given data packet.
For instance, in <xref target='fig_replication'/>, when the sourc
e node S
transmits the data packet to node A, node B may overhear this tra
nsmission.
</t> </t>
<t> <t>
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 tagged in Track but has no position about how the sequence numbers would be tagged in
the packet. the packet.
</t> </t>
<t> <t>
As it goes, 6TiSCH expects that timeSlots corresponding to copies As it goes, 6TiSCH expects that timeSlots corresponding to copies of
of a same packet along a Track are correlated by configuration, and does not the same packet along a Track are correlated by configuration, so
need to process the sequence numbers. processing the sequence numbers is not needed.
</t> </t>
<t> <t>
The semantics of the configuration must enable correlated timeSlots to be The semantics of the configuration must enable correlated timeSlots to be
grouped for transmit (and respectively receive) with 'OR' relations, grouped for transmit (and receive, respectively) with 'OR' relations,
and then an 'AND' relation must be configurable between groups. and then an 'AND' relation must be configurable between groups.
The semantics is that if the transmit (and respectively receive) operation The semantics are such that if the transmit (and receive, respectively) opera
succeeded in one timeSlot in an 'OR' group, then all the other timeslots in tion
succeeded in one timeSlot in an 'OR' group, then all the other timeSlots in
the group are ignored. the group are ignored.
Now, if there are at least two groups, the 'AND' relation between the groups Now, if there are at least two groups, the 'AND' relation between the groups
indicates that one operation must succeed in each of the groups. Further deta ils indicates that one operation must succeed in each of the groups. Further deta ils
can be found in the 6TiSCH Architecture document <xref target='RFC9030'/>. can be found in the 6TiSCH architecture document <xref target='RFC9030'/>.
</t> </t>
</section> </section>
</section> </section>
<section anchor='topo'><name>Topology and Capabilities</name> <section anchor='topo'><name>Topology and Capabilities</name>
<t>6TiSCH nodes are usually IoT devices, characterized by very limited amount <t>6TiSCH nodes are usually IoT devices, characterized by a very limited amou nt
of memory, just enough buffers to store one or a few IPv6 packets, and of memory, just enough buffers to store one or a few IPv6 packets, and
limited bandwidth between peers. It results that a node will maintain only a limited bandwidth between peers. As a result, a node will maintain only a
small number of peering information, and will not be able to store many small amount of peering information and will not be able to store many
packets waiting to be forwarded. Peers can be identified through MAC or IPv6 packets waiting to be forwarded. Peers can be identified through MAC or IPv6
addresses. addresses.
</t> </t>
<t> <t>
Neighbors can be discovered over the radio using mechanism such as Enhanced B Neighbors can be discovered over the radio using mechanisms such as enhanced
eacons, beacons,
but, though the neighbor information is available in the 6TiSCH interface but although the neighbor information is available in the 6TiSCH interface
data model, 6TiSCH does not describe a protocol to pro-actively push the data model, 6TiSCH does not describe a protocol to proactively push the
neighborhood information to a PCE. neighborhood information to a PCE.
This protocol should be described and should operate over CoAP. The protocol This protocol should be described and should operate over CoAP. The protocol
should be able to carry multiple metrics, in particular the same metrics as should be able to carry multiple metrics, in particular, the same metrics tha t are
used for RPL operations <xref target='RFC6551'/>. used for RPL operations <xref target='RFC6551'/>.
</t> </t>
<t> <t>
The energy that the device consumes in sleep, transmit and receive modes can The energy that the device consumes in sleep, transmit, and receive modes can
be evaluated and reported. So can the amount of energy that is stored in the be evaluated and reported, and so can the amount of energy that is stored in
device and the power that it can be scavenged from the environment. The PCE the
device and the power that can be scavenged from the environment. The PCE
should be able to compute Tracks that will implement policies on how the should be able to compute Tracks that will implement policies on how the
energy is consumed, for instance balance between nodes and ensure that the sp energy is consumed, for instance, policies that balance between nodes and ens
ent ure that the spent
energy does not exceeded the scavenged energy over a period of time. energy does not exceed the scavenged energy over a period of time.
</t> </t>
</section> </section>
<section anchor='schd'><name>Schedule Management by a PCE</name> <section anchor='schd'><name>Schedule Management by a PCE</name>
<t> <t>
6TiSCH supports a mixed model of centralized routes and distributed routes . 6TiSCH supports a mixed model of centralized routes and distributed routes .
Centralized routes can for example be computed by a entity such as a Centralized routes can, for example, be computed by an entity such as a
PCE <xref target='PCE'/>. PCE <xref target='PCE'/>.
Distributed routes are computed by <xref target='RFC6550'>RPL</xref>. Distributed routes are computed by RPL <xref target='RFC6550'/>.
</t> </t>
<t> <t>
Both methods may inject routes in the Routing Tables of the 6TiSCH routers . Both methods may inject routes in the routing tables of the 6TiSCH routers .
In either case, each route is associated with a 6TiSCH topology that can In either case, each route is associated with a 6TiSCH topology that can
be a RPL Instance topology or a Track. The 6TiSCH topology is be a RPL Instance topology or a Track. The 6TiSCH topology is
indexed by an Instance ID, in a format that reuses the RPLInstanceID as indexed by an Instance ID, in a format that reuses the RPLInstanceID as
defined in RPL. defined in RPL.
</t> </t>
<t> <t>
Both RPL and PCE rely on shared sources such as policies to define Global Both RPL and PCE rely on shared sources such as policies to define Global
and Local RPLInstanceIDs that can be used by either method. It is possible and Local RPLInstanceIDs that can be used by either method. It is possible
for centralized and distributed routing to share a same topology. for centralized and distributed routing to share the same topology.
Generally they will operate in different slotFrames, and centralized Generally, they will operate in different slotframes, and centralized
routes will be used for scheduled traffic and will have precedence over routes will be used for scheduled traffic and will have precedence over
distributed routes in case of conflict between the slotFrames. distributed routes in case of conflict between the slotframes.
</t> </t>
</section> <!--anchor="schd" title="Schedule Management by a PCE"--> </section>
<section anchor='slotFrames'><name>SlotFrames and Priorities</name> <section anchor='slotFrames'><name>Slotframes and Priorities</name>
<t> <t>
IEEE802.15.4 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. and frequencies in cells of transmission of equal duration.
In order to describe that formatting of time and frequencies, the In order to describe that formatting of time and frequencies, the
6TiSCH architecture defines a global concept that is called a Channel 6TiSCH 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 an 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) for period of the network scheduling operation (indexed by slotOffsets) for
that CDU matrix. that CDU matrix.
</t> </t>
<t> <t>
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 pseudo-random 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.
</t> </t>
<t> <t>
The size of a cell is a timeSlot duration, and The size of a cell is a timeSlot duration, and
values of 10 to 15 milliseconds are typical in 802.15.4 TSCH to values of 10 to 15 milliseconds are typical in 802.15.4 TSCH to
accommodate for the transmission of a frame and an acknowledgement, accommodate for the transmission of a frame and an acknowledgement,
including the security validation on the receive side which may take including the security validation on the receive side, which may take
up to a few milliseconds on some device architecture. The matrix up to a few milliseconds on some device architectures. The matrix
represents the overall utilisation of the spectrum over time by a represents the overall utilization of the spectrum over time by a
scheduled network operation. scheduled network operation.
</t> </t>
<t> <t>
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 conflict . traffic. The PCE has precedence in the allocation in case of a conflict .
Multiple schedules may coexist, in which Multiple schedules may coexist, in which
case the schedule adds a dimension to the matrix and the dimensions are case the schedule adds a dimension to the matrix, and the dimensions ar e
ordered by priority. ordered by priority.
</t> </t>
<t>A slotFrame is the base object that a PCE needs to manipulate
to program a schedule into one device. The slotFrame is a device <t>A slotframe is the base object that a PCE needs to manipulate to
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. schedule from the CDU matrix onto one device. Elaboration on that
Elaboration on that concept can be found in section "SlotFrames and concept can be found in <xref target="RFC9030" section="4.3.5"
Priorities" of <xref target='RFC9030'/>, and figures 17 and 18 of sectionFormat="of"/>, and Figures 17 and 18 of <xref
<xref target='RFC9030'/> illustrate that projection. target="RFC9030"/> illustrate that projection.
</t> </t>
</section> </section>
</section> </section>
</section>
</section>
</section><!-- Applicability to deterministic flows --> <section anchor="fiveg">
<name>5G</name>
</section> <!-- IEEE 802.15.4 TimeSlotted Channel Hopping-->
<section><name>5G</name>
<t> <t>5G technology enables deterministic communication. Based on the
5G technology enables deterministic communication. Based on the centralized centralized admission control and the scheduling of the wireless
admission control and the scheduling of the wireless resources, licensed or resources, licensed or unlicensed, Quality of Service (QoS) such as latency
unlicensed, quality of service such as latency and reliability can be and
guaranteed. 5G contains several features to achieve ultra-reliable and low reliability can be guaranteed. 5G contains several features to achieve
latency performance, e.g., support for different OFDM numerologies and ultra-reliable and low-latency performance (e.g., support for different
slot-durations, as well as fast processing capabilities and redundancy OFDM numerologies and slot durations), as well as fast processing
techniques that lead to achievable latency numbers of below 1ms with capabilities and redundancy techniques that lead to achievable latency
99.999% or higher confidence. numbers of below 1 ms with 99.999% or higher confidence.
</t> </t>
<t> <t>
5G also includes features to support Industrial IoT use cases, e.g., via the 5G also includes features to support industrial IoT use cases, e.g., via the
integration of 5G with TSN. This includes 5G capabilities for each TSN integration of 5G with TSN. This includes 5G capabilities for each TSN
component, latency, resource management, time synchronization, and component, latency, resource management, time synchronization, and
reliability. Furthermore, 5G support for TSN can be leveraged when 5G is used reliability. Furthermore, 5G support for TSN can be leveraged when 5G is used
as subnet technology for DetNet, in combination with or instead of TSN, which as the subnet technology for DetNet, in combination with or instead of TSN, w hich
is the primary subnet for DetNet. In addition, the support for integration is the primary subnet for DetNet. In addition, the support for integration
with TSN reliability was added to 5G by making DetNet reliability also with TSN reliability was added to 5G by making DetNet reliability also
applicable, due to the commonalities between TSN and DetNet reliability. applicable, due to the commonalities between TSN and DetNet reliability.
Moreover, providing IP service is native to 5G and 3GPP Release 18 adds direc t Moreover, providing IP service is native to 5G, and 3GPP Release 18 adds dire ct
support for DetNet to 5G. support for DetNet to 5G.
</t> </t>
<t> <t>
Overall, 5G provides scheduled wireless segments with high reliability and Overall, 5G provides scheduled wireless segments with high reliability and
availability. In addition, 5G includes capabilities for integration to IP availability. In addition, 5G includes capabilities for integration to IP
networks. This makes 5G a suitable technology to apply RAW upon. networks. This makes 5G a suitable technology upon which to apply RAW.
</t> </t>
<section><name>Provenance and Documents</name> <section><name>Provenance and Documents</name>
<t> <t>
The 3rd Generation Partnership Project (3GPP) incorporates many companies The 3rd Generation Partnership Project (3GPP) incorporates many companies
whose business is related to cellular network operation as well as network whose business is related to cellular network operation as well as network
equipment and device manufacturing. All generations of 3GPP technologies equipment and device manufacturing. All generations of 3GPP technologies
provide scheduled wireless segments, primarily in licensed spectrum which is provide scheduled wireless segments, primarily in licensed spectrum, which is
beneficial for reliability and availability. beneficial for reliability and availability.
</t> </t>
<t> <t>
In 2016, the 3GPP started to design New Radio (NR) technology belonging to In 2016, the 3GPP started to design New Radio (NR) technology belonging to
the fifth generation (5G) of cellular networks. NR has been designed from the fifth generation (5G) of cellular networks. NR has been designed from
the beginning to not only address enhanced Mobile Broadband (eMBB) services the beginning to not only address enhanced Mobile Broadband (eMBB) services
for consumer devices such as smart phones or tablets but is also tailored for consumer devices such as smart phones or tablets, but it is also
for future Internet of Things (IoT) communication and connected tailored for future IoT communication and connected
cyber-physical systems. In addition to eMBB, requirement categories have cyber-physical systems. In addition to eMBB, requirement categories have
been defined on Massive Machine-Type Communication (M-MTC) for a large been defined on Massive Machine-Type Communication (M-MTC) for a large
number of connected devices/sensors, and Ultra-Reliable Low-Latency number of connected devices/sensors and on Ultra-Reliable Low-Latency
Communication (URLLC) for connected control systems and critical Communications (URLLC) for connected control systems and critical
communication as illustrated in <xref target='fig-5g-triangle'/>. It is communication as illustrated in <xref target='fig-5g-triangle'/>. It is the
the URLLC capabilities that make 5G a great candidate for reliable URLLC capabilities that make 5G a great candidate for reliable low-latency
low-latency communication. With these three corner stones, NR is a complete communication. With these three cornerstones, NR is a complete solution
solution supporting the connectivity needs of consumers, enterprises, and supporting the connectivity needs of consumers, enterprises, and the public
public sector for both wide area and local area, e.g. indoor deployments. sector for both wide-area and local-area (e.g., indoor) deployments. A
A general overview of NR can be found in <xref target='TS38300'/>. general overview of NR can be found in <xref target='TS38300'/>.
</t> </t>
<figure anchor='fig-5g-triangle'><name>5G Application Areas</name> <figure anchor='fig-5g-triangle'><name>5G Application Areas</name>
<artwork align="center"><![CDATA[ <artwork align="center"><![CDATA[
enhanced enhanced
Mobile Broadband Mobile Broadband
^ ^
/ \ / \
/ \ / \
/ \ / \
skipping to change at line 1307 skipping to change at line 1437
+-----------------+ +-----------------+
Massive Ultra-Reliable Massive Ultra-Reliable
Machine-Type Low-Latency Machine-Type Low-Latency
Communication Communication Communication Communication
]]></artwork> ]]></artwork>
</figure> </figure>
<t> <t>
As a result of releasing the first NR specification in 2018 (Release 15), it As a result of releasing the first NR specification in 2018 (Release 15), it
has been proven by many companies that NR is a URLLC-capable technology and has been proven by many companies that NR is a URLLC-capable technology and
can deliver data packets at 10^-5 packet error rate within 1ms latency can deliver data packets at 10<sup>-5</sup> packet error rate within a 1 ms l atency
budget <xref target='TR37910'/>. Those evaluations were consolidated and budget <xref target='TR37910'/>. Those evaluations were consolidated and
forwarded to ITU to be included in the <xref target='IMT2020'/> work. forwarded to ITU to be included in the work on <xref target='IMT2020'/>.
</t> </t>
<t> <t>
In order to understand communication requirements for automation in vertical In order to understand communication requirements for automation in vertical
domains, 3GPP studied different use cases <xref target='TR22804'/> and domains, 3GPP studied different use cases <xref target='TR22804'/> and
released technical specification with reliability, availability and latency released a technical specification with reliability, availability, and latenc y
demands for a variety of applications <xref target='TS22104'/>. demands for a variety of applications <xref target='TS22104'/>.
</t> </t>
<t> <t>
As an evolution of NR, multiple studies have been conducted in scope of 3GPP As an evolution of NR, multiple studies that focus on radio aspects have been
Release 16 including the following two, focusing on radio aspects: conducted in scope of 3GPP
</t><ol type='%d.'> Release 16, including the following two:
<li> Study on physical layer enhancements for NR ultra-reliable and low
latency communication (URLLC) <xref target='TR38824'/>.</li>
<li> Study on NR industrial Internet of Things (I-IoT)
<xref target='TR38825'/>.</li>
</ol><t>
</t> </t>
<ol type='1'>
<li>"Study on physical layer enhancements for NR ultra-reliable and low
latency case (URLLC)" <xref target='TR38824'/></li>
<li>"Study on NR industrial Internet of Things (IoT)" <xref
target='TR38825'/></li>
</ol>
<t> <t>
Resulting of these studies, further enhancements to NR have been standardized As a result of these studies, further enhancements to NR have been standardiz
in 3GPP Release 16, hence, available in <xref target='TS38300'/>, and ed
in 3GPP Release 16 and are available in <xref target='TS38300'/> and
continued in 3GPP Release 17 standardization (according to <xref target='RP21 0854'/>). continued in 3GPP Release 17 standardization (according to <xref target='RP21 0854'/>).
</t> </t>
<t> <t>
In addition, several enhancements have been done on system architecture level In addition, several enhancements have been made on the system architecture l
which are reflected in System architecture for the 5G System (5GS) evel,
which are reflected in "System architecture for the 5G System (5GS)"
<xref target='TS23501'/>. <xref target='TS23501'/>.
These enhancements include multiple features in support of Time-Sensitive These enhancements include multiple features in support of Time-Sensitive
Communications (TSC) by Release 16 and Release 17. Further improvements are Communications (TSC) by Release 16 and Release 17. Further improvements, such
provided in Release 18, e.g., support for DetNet <xref target='TR2370046'/>. as support for DetNet <xref target='TR2370046'/>, are
provided in Release 18.
</t> </t>
<t> <t>
The adoption and the use of 5G is facilitated by multiple organizations. For The adoption and the use of 5G is facilitated by multiple organizations. For
instance, the 5G Alliance for Connected Industries and Automation (5G-ACIA) instance, the 5G Alliance for Connected Industries and Automation (5G-ACIA)
brings together widely varying 5G stakeholders including Information and brings together widely varying 5G stakeholders including Information and
Communication Technology (ICT) players and Operational Technology (OT) Communication Technology (ICT) players and Operational Technology (OT)
companies, e.g.: industrial automation enterprises, machine builders, and companies (e.g., industrial automation enterprises, machine builders, and
end users. Another example is the 5G Automotive Association (5GAA), which end users). Another example is the 5G Automotive Association (5GAA), which
bridges ICT and automotive technology companies to develop end-to-end bridges ICT and automotive technology companies to develop end-to-end
solutions for future mobility and transportation services. solutions for future mobility and transportation services.
</t> </t>
</section><!-- Provenance and Documents --> </section>
<section><name>General Characteristics</name> <section><name>General Characteristics</name>
<t> <t>
The 5G Radio Access Network (5G RAN) with its NR interface includes several The 5G Radio Access Network (5G RAN) with its NR interface includes several
features to achieve Quality of Service (QoS), such as a guaranteeably features to achieve Quality of Service (QoS), such as a guaranteeably
low latency or tolerable packet error rates for selected data flows. low latency or tolerable packet error rates for selected data flows.
Determinism is achieved by centralized admission control and scheduling of Determinism is achieved by centralized admission control and scheduling of
the wireless frequency resources, which are typically licensed frequency the wireless frequency resources, which are typically licensed frequency
bands assigned to a network operator. bands assigned to a network operator.
</t> </t>
<t> <t>
NR enables short transmission slots in a radio subframe, which benefits NR enables short transmission slots in a radio subframe, which benefits
low-latency applications. NR also introduces mini-slots, where prioritized low-latency applications. NR also introduces mini-slots, where prioritized
transmissions can be started without waiting for slot boundaries, further transmissions can be started without waiting for slot boundaries, further
reducing latency. As part of giving priority and faster radio access to reducing latency. As part of giving priority and faster radio access to
URLLC traffic, NR introduces preemption where URLLC data transmission can URLLC traffic, NR introduces preemption, where URLLC data transmission can
preempt ongoing non-URLLC transmissions. Additionally, NR applies very fast preempt ongoing non-URLLC transmissions. Additionally, NR applies very fast
processing, enabling retransmissions even within short latency bounds. processing, enabling retransmissions even within short latency bounds.
</t> </t>
<t> <t>
NR defines extra-robust transmission modes for increased reliability both NR defines extra-robust transmission modes for increased reliability for both
for data and control radio channels. Reliability is further improved by data and control radio channels. Reliability is further improved by
various techniques, such as multi-antenna transmission, the use of multiple various techniques, such as multi-antenna transmission, the use of multiple
frequency carriers in parallel and packet duplication over independent radio frequency carriers in parallel, and packet duplication over independent radio
links. NR also provides full mobility support, which is an important links. NR also provides full mobility support, which is an important
reliability aspect not only for devices that are moving, but also for reliability aspect not only for devices that are moving, but also for
devices located in a changing environment. devices located in a changing environment.
</t> </t>
<t> <t>
Network slicing is seen as one of the key features for 5G, allowing vertical Network slicing is seen as one of the key features for 5G, allowing
industries to take advantage of 5G networks and services. Network slicing is vertical industries to take advantage of 5G networks and services. Network
about transforming a Public Land Mobile Network (PLMN) from a single network slicing is about transforming a Public Land Mobile Network (PLMN) from a
to a network where logical partitions are created, with appropriate network single network to a network where logical partitions are created, with
isolation, resources, optimized topology and specific configuration to serve appropriate network isolation, resources, optimized topology, and specific
various service requirements. An operator can configure and manage the configurations to serve various service requirements. An operator can
mobile network to support various types of services enabled by 5G, for configure and manage the mobile network to support various types of
example eMBB and URLLC, depending on the different customers’ needs. services enabled by 5G (e.g., eMBB and URLLC), depending on the different
needs of customers.
</t> </t>
<t> <t>
Exposure of capabilities of 5G Systems to the network or applications Exposure of capabilities of 5G systems to the network or applications
outside the 3GPP domain have been added to Release 16 outside the 3GPP domain have been added to Release 16
<xref target='TS23501'/>. Via exposure interfaces, applications can access <xref target='TS23501'/>. Applications can access
5G capabilities, e.g., communication service monitoring and network 5G capabilities like communication service monitoring and network
maintenance. maintenance via exposure interfaces.
</t> </t>
<t> <t>
For several generations of mobile networks, 3GPP has considered how the For several generations of mobile networks, 3GPP has considered how the
communication system should work on a global scale with billions of users, communication system should work on a global scale with billions of users,
taking into account resilience aspects, privacy regulation, protection of taking into account resilience aspects, privacy regulation, protection of
data, encryption, access and core network security, as well as interconnect. data, encryption, access and core network security, as well as interconnect.
Security requirements evolve as demands on trustworthiness increase. For Security requirements evolve as demands on trustworthiness increase. For
example, this has led to the introduction of enhanced privacy protection example, this has led to the introduction of enhanced privacy protection
features in 5G. 5G also employs strong security algorithms, encryption of features in 5G. 5G also employs strong security algorithms, encryption of
traffic, protection of signaling and protection of interfaces. traffic, protection of signaling, and protection of interfaces.
</t> </t>
<t> <t>
One particular strength of mobile networks is the authentication, based on One particular strength of mobile networks is the authentication, based on
well-proven algorithms and tightly coupled with a global identity management well-proven algorithms and tightly coupled with a global identity management
infrastructure. Since 3G, there is also mutual authentication, allowing the infrastructure. Since 3G, there is also mutual authentication, allowing the
network to authenticate the device and the device to authenticate the network to authenticate the device and the device to authenticate the
network. Another strength is secure solutions for storage and distribution network. Another strength is secure solutions for storage and distribution
of keys fulfilling regulatory requirements and allowing international of keys, fulfilling regulatory requirements and allowing international
roaming. When connecting to 5G, the user meets the entire communication roaming. When connecting to 5G, the user meets the entire communication
system, where security is the result of standardization, product security, system, where security is the result of standardization, product security,
deployment, operations and management as well as incident handling deployment, operations, and management as well as incident-handling
capabilities. The mobile networks approach the entirety in a rather capabilities. The mobile networks approach the entirety in a rather
coordinated fashion which is beneficial for security. coordinated fashion, which is beneficial for security.
</t> </t>
</section><!-- General Characteristics --> </section>
<section><name>Deployment and Spectrum</name> <section><name>Deployment and Spectrum</name>
<t> <t>
The 5G system allows deployment in a vast spectrum range, addressing The 5G system allows deployment in a vast spectrum range, addressing
use-cases in both wide-area as well as local networks. Furthermore, 5G can use cases in both wide-area and local-area networks. Furthermore, 5G can
be configured for public and non-public access. be configured for public and non-public access.
</t> </t>
<t> <t>
When it comes to spectrum, NR allows combining the merits of many frequency When it comes to spectrum, NR allows combining the merits of many frequency
bands, such as the high bandwidths in millimeter Waves (mmW) for extreme bands, such as the high bandwidths in millimeter waves (mmWaves) for extreme
capacity locally, as well as the broad coverage when using mid- and low capacity locally and the broad coverage when using mid- and
frequency bands to address wide-area scenarios. URLLC is achievable in all low-frequency bands to address wide-area scenarios. URLLC is achievable in
these bands. Spectrum can be either licensed, which means that the license all these bands. Spectrum can be either licensed, which means that the
holder is the only authorized user of that spectrum range, or unlicensed, license holder is the only authorized user of that spectrum range, or
which means that anyone who wants to use the spectrum can do so. unlicensed, which means that anyone who wants to use the spectrum can do
so.
</t> </t>
<t> <t>
A prerequisite for critical communication is performance predictability, A prerequisite for critical communication is performance predictability,
which can be achieved by the full control of the access to the spectrum, which can be achieved by full control of access to the spectrum,
which 5G provides. Licensed spectrum guarantees control over spectrum usage which 5G provides. Licensed spectrum guarantees control over spectrum usage
by the system, making it a preferable option for critical communication. by the system, making it a preferable option for critical communication.
However, unlicensed spectrum can provide an additional resource for scaling However, unlicensed spectrum can provide an additional resource for scaling
non-critical communications. While NR is initially developed for usage of non-critical communications. While NR was initially developed for usage of
licensed spectrum, the functionality to access also unlicensed spectrum was licensed spectrum, the functionality to also access unlicensed spectrum was
introduced in 3GPP Release 16. Moreover, URLLC features are enhanced in introduced in 3GPP Release 16. Moreover, URLLC features are enhanced in
Release 17 <xref target='RP210854'/> to be better applicable to unlicensed Release 17 <xref target='RP210854'/> to be better applicable to unlicensed
spectrum. spectrum.
</t> </t>
<t> <t>
Licensed spectrum dedicated to mobile communications has been allocated to Licensed spectrum dedicated to mobile communications has been allocated to
mobile service providers, i.e. issued as longer-term licenses by national mobile service providers, i.e., issued as longer-term licenses by national
administrations around the world. These licenses have often been associated administrations around the world. These licenses have often been
with coverage requirements and issued across whole countries, or in large associated with coverage requirements and issued across whole countries or
regions. Besides this, configured as a non-public network (NPN) deployment, large regions. Besides this, configured as a non-public network (NPN)
5G can provide network services also to a non-operator defined organization deployment, 5G can also provide network services to a non-operator defined
and its premises such as a factory deployment. By this isolation, quality of organization and its premises such as a factory deployment. With this
service requirements, as well as security requirements can be achieved. An isolation, QoS requirements as well as security requirements can be
integration with a public network, if required, is also possible. The achieved. An integration with a public network, if required, is also
non-public (local) network can thus be interconnected with a public network, possible. The non-public (local) network can thus be interconnected with a
allowing devices to roam between the networks. public network, allowing devices to roam between the networks.
</t> </t>
<t> <t>
In an alternative model, some countries are now in the process of allocating In an alternative model, some countries are now in the process of allocating
parts of the 5G spectrum for local use to industries. These non-service parts of the 5G spectrum for local use to industries. These non-service
providers then have a choice of applying for a local license themselves and providers then have the choice to apply for a local license themselves and
operating their own network or cooperating with a public network operator or operate their own network or to cooperate with a public network operator or
service provider. service provider.
</t> </t>
</section><!-- Deployment and Spectrum --> </section>
<section><name>Applicability to Deterministic Flows</name> <section><name>Applicability to Deterministic Flows</name>
<section><name>System Architecture</name> <section><name>System Architecture</name>
<t> <t>
The 5G system <xref target='TS23501'/> consists of the User Equipment (UE) The 5G system <xref target='TS23501'/> consists of the User Equipment (UE)
at the terminal side, and the Radio Access Network (RAN) with the gNB as at the terminal side, the Radio Access Network (RAN) with the gNodeB (gNB) as
radio base station node, as well as the Core Network (CN), which is connected radio base station node, and the Core Network (CN), which is connected
to the external Data Network (DN). The core network is based on a service-bas to the external Data Network (DN). The CN is based on a service-based
ed architecture with the following central functions: Access and Mobility Manage
architecture with the central functions: Access and Mobility Management ment
Function (AMF), Session Management Function (SMF) and User Plane Function (UP Function (AMF), Session Management Function (SMF), and User Plane Function (U
F) PF)
as illustrated in <xref target='fig-5g-arch'/>. "(Note that this document onl as illustrated in <xref target='fig-5g-arch'/>. (Note that this document only
y explains key functions; however, <xref target='fig-5g-arch'/> provides a more
explains key functions, however, <xref target='fig-5g-arch'/> provides a more detailed view, and <xref target='SYSTOVER5G'/> summarizes the functions and p
detailed view, and rovides the full
<xref target='SYSTOVER5G'/> summarizes the functions and provides the full definitions of the acronyms used in the figure.)
definition of acronyms used in the figure.)"
</t> </t>
<t>The gNB’s main responsibility is the radio resource management, including <t>The gNB's main responsibility is radio resource management, including
admission control and scheduling, mobility control and radio measurement admission control and scheduling, mobility control, and radio measurement
handling. The AMF handles the UE’s connection status and security, while the handling. The AMF handles the UE's connection status and security, while the
SMF controls the UE’s data sessions. The UPF handles the user plane traffic. SMF controls the UE's data sessions. The UPF handles the user plane traffic.
</t> </t>
<t>The SMF can instantiate various Packet Data Unit (PDU) sessions for the <t>The SMF can instantiate various Packet Data Unit (PDU) sessions for the
UE, each associated with a set of QoS flows, i.e., with different QoS UE, each associated with a set of QoS flows, i.e., with different QoS
profiles. Segregation of those sessions is also possible, e.g., resource profiles). Segregation of those sessions is also possible; for example, resou
isolation in the RAN and in the CN can be defined (slicing). rce
isolation in the RAN and CN can be defined (slicing).
</t> </t>
<figure anchor='fig-5g-arch'><name>5G System Architecture</name> <figure anchor='fig-5g-arch'><name>5G System Architecture</name>
<artwork align="center"><![CDATA[ <artwork align="center"><![CDATA[
+----+ +---+ +---+ +---+ +---+ +---+ +----+ +---+ +---+ +---+ +---+ +---+
|NSSF| |NEF| |NRF| |PCF| |UDM| |AF | |NSSF| |NEF| |NRF| |PCF| |UDM| |AF |
+--+-+ +-+-+ +-+-+ +-+-+ +-+-+ +-+-+ +--+-+ +-+-+ +-+-+ +-+-+ +-+-+ +-+-+
| | | | | | | | | | | |
Nnssf| Nnef| Nnrf| Npcf| Nudm| Naf| Nnssf| Nnef| Nnrf| Npcf| Nudm| Naf|
| | | | | | | | | | | |
skipping to change at line 1553 skipping to change at line 1684
/ | | / | |
+--+-+ +--+--+ +--+---+ +----+ +--+-+ +--+--+ +--+---+ +----+
| UE +---+(R)AN+--N3--+ UPF +--N6--+ DN | | UE +---+(R)AN+--N3--+ UPF +--N6--+ DN |
+----+ +-----+ ++----++ +----+ +----+ +-----+ ++----++ +----+
| | | |
+-N9-+ +-N9-+
]]></artwork> ]]></artwork>
</figure> </figure>
<t> <t>
To allow UE mobility across cells/gNBs, handover mechanisms are supported in To allow UE mobility across cells/gNBs, handover mechanisms are supported
NR. For an established connection, i.e., connected mode mobility, a gNB can in NR. For an established connection (i.e., connected mode mobility), a gNB
configure a UE to report measurements of received signal strength and can configure a UE to report measurements of received signal strength and
quality of its own and neighbouring cells, periodically or event-based. quality of its own and neighboring cells, periodically or based on events.
Based on these measurement reports, the gNB decides to handover a UE to Based on these measurement reports, the gNB decides to hand over a UE to
another target cell/gNB. Before triggering the handover, it is hand-shaked another target cell/gNB. Before triggering the handover, it is handshaked
with the target gNB based on network signalling. A handover command is then with the target gNB based on network signaling. A handover command is then
sent to the UE and the UE switches its connection to the target cell/gNB. sent to the UE, and the UE switches its connection to the target cell/gNB.
The Packet Data Convergence Protocol (PDCP) of the UE can be configured to The Packet Data Convergence Protocol (PDCP) of the UE can be configured to
avoid data loss in this procedure, i.e., handle retransmissions if needed. avoid data loss in this procedure, i.e., to handle retransmissions if
Data forwarding is possible between source and target gNB as well. To needed. Data forwarding is possible between source and target gNB as
improve the mobility performance further, i.e., to avoid connection failures, well. To improve the mobility performance further (i.e., to avoid connection
e.g., due to too-late handovers, the mechanism of conditional handover is failures due to too-late handovers), the mechanism of
introduced in Release 16 specifications. Therein a conditional handover conditional handover is introduced in Release 16 specifications. Therein, a
command, defining a triggering point, can be sent to the UE before UE enters conditional handover command, defining a triggering point, can be sent to
a handover situation. A further improvement that has been introduced in the UE before the UE enters a handover situation. A further improvement that
Release 16 is the Dual Active Protocol Stack (DAPS), where the UE maintains has been introduced in Release 16 is the Dual Active Protocol Stack (DAPS),
the connection to the source cell while connecting to the target cell. This where the UE maintains the connection to the source cell while connecting
way, potential interruptions in packet delivery can be avoided entirely. to the target cell. This way, potential interruptions in packet delivery
can be avoided entirely.
</t> </t>
</section><!-- System Architecture --> </section>
<section><name>Overview of The Radio Protocol Stack</name> <section><name>Overview of the Radio Protocol Stack</name>
<t> <t>
The protocol architecture for NR consists of the L1 Physical layer (PHY) and The protocol architecture for NR consists of the Layer 1 Physical (PHY) layer
as part of the L2, the sublayers of Medium Access Control (MAC), Radio Link and,
Control (RLC), Packet Data Convergence Protocol (PDCP), as well as the as part of Layer 2, the sublayers of Medium Access Control (MAC), Radio Link
Control (RLC), Packet Data Convergence Protocol (PDCP), and
Service Data Adaption Protocol (SDAP). Service Data Adaption Protocol (SDAP).
</t> </t>
<t> <t>
The PHY layer handles signal processing related actions, such as The PHY layer handles actions related to signal processing, such as
encoding/decoding of data and control bits, modulation, antenna precoding encoding/decoding of data and control bits, modulation, antenna precoding,
and mapping. and mapping.
</t> </t>
<t> <t>
The MAC sub-layer handles multiplexing and priority handling of logical The MAC sublayer handles multiplexing and priority handling of logical
channels (associated with QoS flows) to transport blocks for PHY channels (associated with QoS flows) to transport blocks for PHY
transmission, as well as scheduling information reporting and error transmission, as well as scheduling information reporting and error
correction through Hybrid Automated Repeat Request (HARQ). correction through Hybrid Automated Repeat Request (HARQ).
</t> </t>
<t> <t>
The RLC sublayer handles sequence numbering of higher layer packets, The RLC sublayer handles sequence numbering of higher-layer packets,
retransmissions through Automated Repeat Request (ARQ), if configured, as retransmissions through Automated Repeat Request (ARQ), if configured, as
well as segmentation and reassembly and duplicate detection. well as segmentation and reassembly and duplicate detection.
</t> </t>
<t> <t>
The PDCP sublayer consists of functionalities for ciphering/deciphering, The PDCP sublayer consists of functionalities for ciphering/deciphering,
integrity protection/verification, re-ordering and in-order delivery, integrity protection/verification, reordering and in-order delivery, and
duplication and duplicate handling for higher layer packets, and acts as the duplication and duplicate handling for higher-layer packets. This sublayer al
so acts as the
anchor protocol to support handovers. anchor protocol to support handovers.
</t> </t>
<t> <t>
The SDAP sublayer provides services to map QoS flows, as established by the The SDAP sublayer provides services to map QoS flows, as established by the
5G core network, to data radio bearers (associated with logical channels), 5G core network, to data radio bearers (associated with logical channels),
as used in the 5G RAN. as used in the 5G RAN.
</t> </t>
<t> <t>
Additionally, in RAN, the Radio Resource Control (RRC) protocol, handles the Additionally, in RAN, the Radio Resource Control (RRC) protocol handles the
access control and configuration signalling for the aforementioned protocol access control and configuration signaling for the aforementioned protocol
layers. RRC messages are considered L3 and thus transmitted also via those layers. RRC messages are considered Layer 3 and are thus also transmitted via
those
radio protocol layers. radio protocol layers.
</t> </t>
<t> <t>To provide low latency and high reliability for one transmission
To provide low latency and high reliability for one transmission link, i.e., link (i.e., to transport data or control signaling of one radio
to transport data (or control signaling) of one radio bearer via one carrier, bearer via one carrier), several features have been introduced on the
several features have been introduced on the user plane protocols for PHY user plane protocols for PHY and Layer 2, as explained below.
and L2, as explained in the following.
</t> </t>
</section><!-- Overview of Radio Protocol Stack --> </section>
<section><name>Radio (PHY)</name> <section><name>Radio (PHY)</name>
<t> <t>
NR is designed with native support of antenna arrays utilizing benefits from NR is designed with native support of antenna arrays utilizing benefits from
beamforming, transmissions over multiple MIMO layers and advanced receiver beamforming, transmissions over multiple MIMO layers, and advanced receiver
algorithms allowing effective interference cancellation. Those antenna algorithms allowing effective interference cancellation. Those antenna
techniques are the basis for high signal quality and effectiveness of techniques are the basis for high signal quality and the effectiveness of
spectral usage. Spatial diversity with up to 4 MIMO layers in UL and up to 8 spectral usage. Spatial diversity with up to four MIMO layers in UL and up to
eight
MIMO layers in DL is supported. Together with spatial-domain multiplexing, MIMO layers in DL is supported. Together with spatial-domain multiplexing,
antenna arrays can focus power in desired direction to form beams. NR antenna arrays can focus power in the desired direction to form beams. NR
supports beam management mechanisms to find the best suitable beam for UE supports beam management mechanisms to find the best suitable beam for UE
initially and when it is moving. In addition, gNBs can coordinate their initially and when it is moving. In addition, gNBs can coordinate their
respective DL and UL transmissions over the backhaul network keeping respective downlink (DL) and uplink (UL) transmissions over the backhaul netw ork, keeping
interference reasonably low, and even make transmissions or receptions from interference reasonably low, and even make transmissions or receptions from
multiple points (multi-TRP). Multi-TRP can be used for repetition of data multiple points (multi-TRP). Multi-TRP can be used for repetition of a data
packet in time, in frequency or over multiple MIMO layers which can improve packet in time, in frequency, or over multiple MIMO layers, which can improve
reliability even further. reliability even further.
</t> </t>
<t> <t>
Any downlink transmission to a UE starts from resource allocation signaling Any DL transmission to a UE starts from resource allocation signaling
over the Physical Downlink Control Channel (PDCCH). If it is successfully over the Physical Downlink Control Channel (PDCCH). If it is successfully
received, the UE will know about the scheduled transmission and may receive received, the UE will know about the scheduled transmission and may receive
data over the Physical Downlink Shared Channel (PDSCH). If retransmission is data over the Physical Downlink Shared Channel (PDSCH). If retransmission is
required according to the HARQ scheme, a signaling of negative required according to the HARQ scheme, a signaling of negative
acknowledgement (NACK) on the Physical Uplink Control Channel (PUCCH) is acknowledgement (NACK) on the Physical Uplink Control Channel (PUCCH) is
involved and PDCCH together with PDSCH transmissions (possibly with involved, and PDCCH together with PDSCH transmissions (possibly with
additional redundancy bits) are transmitted and soft-combined with additional redundancy bits) are transmitted and soft-combined with
previously received bits. Otherwise, if no valid control signaling for previously received bits. Otherwise, if no valid control signaling for
scheduling data is received, nothing is transmitted on PUCCH (discontinuous scheduling data is received, nothing is transmitted on PUCCH (discontinuous
transmission - DTX),and the base station upon detecting DTX will retransmit transmission (DTX)), and upon detecting DTX, the base station will retransmit
the initial data. the initial data.
</t> </t>
<t> <t>
An uplink transmission normally starts from a Scheduling Request (SR) – a An UL transmission normally starts from a Scheduling Request (SR), a
signaling message from the UE to the base station sent via PUCCH. signaling message from the UE to the base station sent via PUCCH.
Once the scheduler is informed about buffer data in UE, e.g., by SR, the UE Once the scheduler is informed about buffer data in the UE (e.g., by SR), the UE
transmits a data packet on the Physical Uplink Shared Channel (PUSCH). transmits a data packet on the Physical Uplink Shared Channel (PUSCH).
Pre-scheduling not relying on SR is also possible (see following section). Pre-scheduling, not relying on SR, is also possible (see <xref target="schedu ling_qos"/>).
</t> </t>
<t> <t>
Since transmission of data packets require 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 reliability. NR channels, there are several methods to maintain the needed reliability. NR
uses Low Density Parity Check (LDPC) codes for data channels, Polar codes uses Low Density Parity Check (LDPC) codes for data channels, polar codes
for PDCCH, as well as orthogonal sequences and Polar codes for PUCCH. For for PDCCH, as well as orthogonal sequences and polar codes for PUCCH. For
ultra-reliability of data channels, very robust (low spectral efficiency) ultra-reliability of data channels, very robust (low-spectral efficiency)
Modulation and Coding Scheme (MCS) tables are introduced containing very low Modulation and Coding Scheme (MCS) tables are introduced containing very low
(down to 1/20) LDPC code rates using BPSK or QPSK. Also, PDCCH and PUCCH (down to 1/20) LDPC code rates using Binary Phase-Shift Keying (BPSK) or Quad rature Phase-Shift Keying (QPSK). Also, PDCCH and PUCCH
channels support multiple code rates including very low ones for the channel channels support multiple code rates including very low ones for the channel
robustness. robustness.
</t> </t>
<t> <t>
A connected UE reports downlink (DL) quality to gNB by sending Channel State A connected UE reports DL quality to gNB by sending Channel State
Information (CSI) reports via PUCCH while uplink (UL) quality is measured Information (CSI) reports via PUCCH while UL quality is measured
directly at gNB. For both uplink and downlink, gNB selects the desired MCS directly at gNB. For both UL and DL, gNB selects the desired MCS
number and signals it to the UE by Downlink Control Information (DCI) via number and signals it to the UE by Downlink Control Information (DCI) via
PDCCH channel. For URLLC services, the UE can assist the gNB by advising PDCCH channel. For URLLC services, the UE can assist the gNB by advising
that MCS targeting 10^-5 Block Error Rate (BLER) are used. Robust link that MCS targeting a 10<sup>-5</sup> Block Error Rate (BLER) are used. Robust
adaptation algorithms can maintain the needed level of reliability link
adaptation algorithms can maintain the needed level of reliability,
considering a given latency bound. considering a given latency bound.
</t> </t>
<t> <t>
Low latency on the physical layer is provided by short transmission duration Low latency on the PHY layer is provided by short transmission duration,
which is possible by using high Subcarrier Spacing (SCS) and the allocation which is possible by using high Subcarrier Spacing (SCS) and the allocation
of only one or a few Orthogonal Frequency Division Multiplexing (OFDM) of only one or a few Orthogonal Frequency Division Multiplexing (OFDM)
symbols. For example, the shortest latency for the worst case in DL can be symbols. For example, the shortest latency for the worst case is
0.23ms and in UL can be 0.24ms according to (section 5.7.1 in 0.23 ms in DL and 0.24 ms in UL (according to Section 5.7.1 in
<xref target='TR37910'/>). Moreover, if the initial transmission has failed, <xref target='TR37910'/>). Moreover, if the initial transmission has failed,
HARQ feedback can quickly be provided and an HARQ retransmission is HARQ feedback can quickly be provided and an HARQ retransmission
scheduled. scheduled.
</t> </t>
<t> <t>
Dynamic multiplexing of data associated with different services is highly Dynamic multiplexing of data associated with different services is highly
desirable for efficient use of system resources and to maximize system desirable for efficient use of system resources and to maximize system
capacity. Assignment of resources for eMBB is usually done with regular capacity. Assignment of resources for eMBB is usually done with regular
(longer) transmission slots, which can lead to blocking of low latency (longer) transmission slots, which can lead to blocking of low-latency
services. To overcome the blocking, eMBB resources can be pre-empted and services. To overcome the blocking, eMBB resources can be preempted and
re-assigned to URLLC services. In this way, spectrally efficient assignments reassigned to URLLC services. In this way, spectrally efficient assignments
for eMBB can be ensured while providing flexibility required to ensure a for eMBB can be ensured while providing the flexibility required to ensure a
bounded latency for URLLC services. In downlink, the gNB can notify the eMBB bounded latency for URLLC services. In DL, the gNB can notify the eMBB
UE about pre-emption after it has happened, while in uplink there are two UE about preemption after it has happened, while in UL there are two
pre-emption mechanisms: special signaling to cancel eMBB transmission and preemption mechanisms: special signaling to cancel eMBB transmission and
URLLC dynamic power boost to suppress eMBB transmission. URLLC dynamic power boost to suppress eMBB transmission.
</t> </t>
</section><!-- Radio (PHY) --> </section>
<section><name>Scheduling and QoS (MAC)</name> <section anchor="scheduling_qos"><name>Scheduling and QoS (MAC)</name>
<t> <t>
One integral part of the 5G system is the Quality of Service (QoS) framework One integral part of the 5G system is the Quality of Service (QoS) framework
<xref target='TS23501'/>. QoS flows are setup by the 5G system for certain <xref target='TS23501'/>. QoS flows are set up by the 5G system for certain
IP or Ethernet packet flows, so that packets of each flow receive the same IP or Ethernet packet flows, so that packets of each flow receive the same
forwarding treatment, i.e., in scheduling and admission control. QoS flows forwarding treatment (i.e., in scheduling and admission control). For example
can for example be associated with different priority level, packet delay , QoS flows
budgets and tolerable packet error rates. Since radio resources are can be associated with different priority levels, packet delay
budgets, and tolerable packet error rates. Since radio resources are
centrally scheduled in NR, the admission control function can ensure that centrally scheduled in NR, the admission control function can ensure that
only those QoS flows are admitted for which QoS targets can be reached. only QoS flows for which QoS targets can be reached are admitted.
</t> </t>
<t> <t>
NR transmissions in both UL and DL are scheduled by the gNB NR transmissions in both UL and DL are scheduled by the gNB
<xref target='TS38300'/>. This ensures radio resource efficiency, fairness <xref target='TS38300'/>. This ensures radio resource efficiency and fairness
in resource usage of the users and enables differentiated treatment of the in resource usage of the users, and it enables differentiated treatment of th
e
data flows of the users according to the QoS targets of the flows. Those QoS data flows of the users according to the QoS targets of the flows. Those QoS
flows are handled as data radio bearers or logical channels in NR RAN flows are handled as data radio bearers or logical channels in NR RAN
scheduling. scheduling.
</t> </t>
<t> <t>
The gNB can dynamically assign DL and UL radio resources to users, The gNB can dynamically assign DL and UL radio resources to users,
indicating the resources as DL assignments or UL grants via control channel indicating the resources as DL assignments or UL grants via control channel
to the UE. Radio resources are defined as blocks of OFDM symbols in spectral to the UE. Radio resources are defined as blocks of OFDM symbols in spectral
domain and time domain. Different lengths are supported in time domain, domain and time domain. Different lengths are supported in time domain,
i.e., (multiple) slot or mini-slot lengths. Resources of multiple frequency (i.e., multiple slot or mini-slot lengths). Resources of multiple frequency
carriers can be aggregated and jointly scheduled to the UE. carriers can be aggregated and jointly scheduled to the UE.
</t> </t>
<t> <t>
Scheduling decisions are based, e.g., on channel quality measured on Scheduling decisions are based, e.g., on channel quality measured on
reference signals and reported by the UE (cf. periodical CSI reports for DL reference signals and reported by the UE (cf. periodical CSI reports
channel quality). The transmission reliability can be chosen in the for DL channel quality). The transmission reliability can be chosen
scheduling algorithm, i.e., by link adaptation where an appropriate in the scheduling algorithm, i.e., chosen by link adaptation where an
transmission format (e.g., robustness of modulation and coding scheme, appropriate transmission format (e.g., robustness of modulation and
controlled UL power) is selected for the radio channel condition of the UE. coding scheme, controlled UL power) is selected for the radio channel
condition of the UE.
Retransmissions, based on HARQ feedback, are also controlled by the Retransmissions, based on HARQ feedback, are also controlled by the
scheduler. The feedback transmission in HARQ loop introduces delays, but scheduler. The feedback transmission in HARQ loop introduces delays, but
there are methods to minimize it by using short transmission formats, there are methods to minimize it by using short transmission formats,
sub-slot feedback reporting and PUCCH carrier switching. If needed to sub-slot feedback reporting, and PUCCH carrier switching. If needed to
avoid HARQ round-trip time delays, repeated transmissions can be also avoid HARQ round-trip time delays, repeated transmissions can be also
scheduled beforehand, to the cost of reduced spectral efficiency. scheduled beforehand, to the cost of reduced spectral efficiency.
</t> </t>
<t> <t>
In dynamic DL scheduling, transmission can be initiated immediately In dynamic DL scheduling, transmission can be initiated immediately when DL
when DL data becomes available in the gNB. However, for dynamic UL data becomes available in the gNB. However, for dynamic UL scheduling, when
scheduling, when data becomes available but no UL resources are available data becomes available but no UL resources are available yet, the UE
yet, the UE indicates the need for UL resources to the gNB via a (single bit) indicates the need for UL resources to the gNB via a (single bit)
scheduling request message in the UL control channel. When thereupon UL scheduling request message in the UL control channel. When UL resources
resources are scheduled to the UE, the UE can transmit its data and may are scheduled, the UE can transmit its data and may include a buffer status
include a buffer status report, indicating the exact amount of data per report that indicates the exact amount of data per logical channel still
logical channel still left to be sent. More UL resources may be scheduled left to be sent. More UL resources may be scheduled accordingly. To avoid
accordingly. To avoid the latency introduced in the scheduling request loop, the latency introduced in the scheduling request loop, UL radio resources
UL radio resources can also be pre-scheduled. can also be pre-scheduled.
</t> </t>
<t> <t>
In particular for periodical traffic patterns, the pre-scheduling can rely In particular, for periodical traffic patterns, the pre-scheduling can rely
on the scheduling features DL Semi-Persistent Scheduling (SPS) and UL on the scheduling features DL Semi-Persistent Scheduling (SPS) and UL
Configured Grant (CG). With these features, periodically recurring resources Configured Grant (CG). With these features, periodically recurring resources
can be assigned in DL and UL. Multiple parallels of those configurations are can be assigned in DL and UL. Multiple parallels of those configurations are
supported, in order to serve multiple parallel traffic flows of the same UE. supported in order to serve multiple parallel traffic flows of the same UE.
</t> </t>
<t> <t>
To support QoS enforcement in the case of mixed traffic with different QoS To support QoS enforcement in the case of mixed traffic with different
requirements, several features have recently been introduced. This way, QoS requirements, several features have recently been introduced. These
e.g., different periodical critical QoS flows can be served together with features allow different periodical critical QoS flows to be served,
best effort transmissions, by the same UE. Among others, these features together with best-effort transmissions, by the same UE. These features
(partly Release 16) are: 1) UL logical channel transmission restrictions include the following:</t>
allowing to map logical channels of certain QoS only to intended UL
resources of a certain frequency carrier, slot-length, or CG configuration,
and 2) intra-UE pre-emption and multiplexing, allowing critical UL
transmissions to either pre-empt non-critical transmissions or being
multiplexed with non-critical transmissions keeping different reliability
targets.
</t>
<ul>
<li>UL logical channel transmission restrictions, allowing logical
channels of certain QoS to only be mapped to intended UL resources of a certai
n frequency
carrier, slot length, or CG configuration.</li>
<li>intra-UE preemption and multiplexing, allowing critical UL
transmissions to either preempt non-critical transmissions or be
multiplexed with non-critical transmissions keeping different reliability
targets.</li>
</ul>
<t> <t>
When multiple frequency carriers are aggregated, duplicate parallel When multiple frequency carriers are aggregated, duplicate parallel
transmissions can be employed (beside repeated transmissions on one transmissions can be employed (beside repeated transmissions on one
carrier). This is possible in the Carrier Aggregation (CA) architecture carrier). This is possible in the Carrier Aggregation (CA) architecture
where those carriers originate from the same gNB, or in the Dual where those carriers originate from the same gNB or in the Dual
Connectivity (DC) architecture where the carriers originate from different Connectivity (DC) architecture where the carriers originate from different
gNBs, i.e., the UE is connected to two gNBs in this case. In both cases, gNBs (i.e., the UE is connected to two gNBs in this case). In both cases,
transmission reliability is improved by this means of providing frequency transmission reliability is improved by this means of providing frequency
diversity. diversity.
</t> </t>
<t> <t>
In addition to licensed spectrum, a 5G system can also utilize unlicensed In addition to licensed spectrum, a 5G system can also utilize unlicensed
spectrum to offload non-critical traffic. This version of NR is called NR-U, spectrum to offload non-critical traffic. This version of NR, called NR-U, is
part of 3GPP Release 16. The central scheduling approach applies also for part of 3GPP Release 16. The central scheduling approach also applies for
unlicensed radio resources, but in addition also the mandatory channel unlicensed radio resources and the mandatory channel
access mechanisms for unlicensed spectrum, e.g., Listen Before Talk (LBT) access mechanisms for unlicensed spectrum (e.g., Listen Before Talk (LBT)
are supported in NR-U. This way, by using NR, operators have and can control is supported in NR-U). This way, by using NR, operators have and can control
access to both licensed and unlicensed frequency resources. access to both licensed and unlicensed frequency resources.
</t> </t>
</section><!-- Scheduling and QoS (MAC) --> </section>
<section><name>Time-Sensitive Communications (TSC)</name> <section><name>Time-Sensitive Communications (TSC)</name>
<t> <t>
Recent 3GPP releases have introduced various features to support multiple Recent 3GPP releases have introduced various features to support multiple
aspects of Time-Sensitive Communication (TSC), which includes Time-Sensitive aspects of Time-Sensitive Communication (TSC), which includes Time-Sensitive
Networking (TSN) and beyond as described in this section. Networking (TSN) and beyond, as described in this section.
</t> </t>
<t> <t>
The main objective of Time-Sensitive Networking (TSN) is to provide The main objective of TSN is to provide guaranteed data delivery within a
guaranteed data delivery within a guaranteed time window, i.e., bounded low guaranteed time window (i.e., bounded low latency). IEEE 802.1 TSN <xref
latency. IEEE 802.1 TSN <xref target='IEEE802.1TSN'/> is a set of open target='IEEE802.1TSN'/> is a set of open standards that provide features to
standards that provide features to enable deterministic communication on enable deterministic communication on standard IEEE 802.3 Ethernet <xref
standard IEEE 802.3 Ethernet <xref target='IEEE802.3'/>. TSN standards can target='IEEE802.3'/>. TSN standards can be seen as a toolbox for traffic
be seen as a toolbox for traffic shaping, resource management, time shaping, resource management, time synchronization, and reliability.
synchronization, and reliability.
</t> </t>
<t> <t>
A TSN stream is a data flow between one end station (Talker) to another end A TSN stream is a data flow between one end station (talker) to another end
station (Listener). In the centralized configuration model, TSN bridges are station (listener). In the centralized configuration model, TSN bridges are
configured by the Central Network Controller (CNC) configured by the Central Network Controller (CNC)
<xref target='IEEE802.1Qcc'/> to provide deterministic connectivity for the <xref target='IEEE802.1Qcc'/> to provide deterministic connectivity for the
TSN stream through the network. Time-based traffic shaping provided by TSN stream through the network. Time-based traffic shaping provided by
Scheduled Traffic <xref target='IEEE802.1Qbv'/> may be used to achieve scheduled traffic <xref target='IEEE802.1Qbv'/> may be used to achieve
bounded low latency. The TSN tool for time synchronization is the bounded low latency. The TSN tool for time synchronization is the
generalized Precision Time Protocol (gPTP) <xref target='IEEE802.1AS'/>), generalized Precision Time Protocol (gPTP) <xref target='IEEE802.1AS'/>,
which provides reliable time synchronization that can be used by end which 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
<xref target='IEEE802.1Qbv'/>. High availability, as a result of <xref target='IEEE802.1Qbv'/>). High availability, as a result of
ultra-reliability, is provided for data flows by the Frame Replication and ultra-reliability, is provided for data flows by the Frame Replication and
Elimination for Reliability (FRER) <xref target='IEEE802.1CB'/> mechanism. Elimination for Reliability (FRER) mechanism <xref target='IEEE802.1CB'/>.
</t> </t>
<t> <t>
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 the meet functions for the 5G System (5GS) to deliver TSN streams so that
their QoS requirements. A key aspect of the integration is the 5GS appears their QoS requirements are met. A key aspect of the integration is
from the rest of the network as a set of TSN bridges, in particular, one that, from the rest of the network, the 5GS appears as a set of TSN bridges (
virtual bridge per User Plane Function (UPF) on the user plane. The 5GS in
particular, one virtual bridge per User Plane Function (UPF) on the
user plane). The 5GS
includes TSN Translator (TT) functionality for the adaptation of the 5GS to includes TSN Translator (TT) functionality for the adaptation of the 5GS to
the TSN bridged network and for hiding the 5GS internal procedures. The 5GS the TSN bridged network and for hiding the 5GS internal procedures. The 5GS
provides the following components: provides the following components:
</t><ol type='%d.'> </t><ol type='1'>
<li>interface to TSN controller, as per <xref target='IEEE802.1Qcc'/> for <li>interface to TSN controller, as per <xref target='IEEE802.1Qcc'/> for
the fully centralized configuration model</li> the fully centralized configuration model</li>
<li>time synchronization via reception and transmission of gPTP PDUs <li>time synchronization via reception and transmission of gPTP PDUs
<xref target='IEEE802.1AS'/></li> <xref target='IEEE802.1AS'/></li>
<li>low latency, hence, can be integrated with Scheduled Traffic <li>low latency, which allows integration with scheduled traffic
<xref target='IEEE802.1Qbv'/></li> <xref target='IEEE802.1Qbv'/></li>
<li>reliability, hence, can be integrated with FRER <li>reliability, which allows integration with FRER
<xref target='IEEE802.1CB'/></li> <xref target='IEEE802.1CB'/></li>
</ol><t> </ol>
</t>
<t> <t>
3GPP Release 17 <xref target='TS23501'/> introduced enhancements to 3GPP Release 17 <xref target='TS23501'/> introduced enhancements to
generalize support for Time-Sensitive Communications (TSC) beyond TSN. generalize support for TSC beyond TSN. This includes IP communications to
This includes IP communications to provide time-sensitive service to, e.g., provide time-sensitive services (e.g., to Video, Imaging, and Audio for
Video, Imaging and Audio for Professional Applications (VIAPA). The system Professional Applications (VIAPA)). The system model of 5G
model of 5G acting as a “TSN bridge” in Release 16 has been reused to enable acting as a "TSN bridge" in Release 16 has been reused to enable the 5GS
the 5GS acting as a “TSC node” in a more generic sense (which includes TSN acting as a "TSC node" in a more generic sense (which includes TSN bridge
bridge and IP node). In the case of TSC that does not involve TSN, and IP node). In the case of TSC that does not involve TSN, requirements
requirements are given via exposure interface and the control plane provides are given via exposure interfaces, and the control plane provides the service
the service based on QoS and time synchronization requests from an based on QoS and time synchronization requests from an Application Function
Application Function (AF). (AF).
</t> </t>
<t> <t>
<xref target='fig-5g-tsn'/> shows an illustration of 5G-TSN integration <xref target='fig-5g-tsn'/> shows an illustration of 5G-TSN integration
where an industrial controller (Ind Ctrlr) is connected to industrial where an industrial controller (Ind Ctrlr) is connected to industrial
Input/Output devices (I/O dev) via 5G. The 5GS can directly transport Input/Output devices (I/O dev) via 5G. The 5GS can directly transport
Ethernet frames since Release 15, thus, end-to-end Ethernet connectivity is Ethernet frames since Release 15; thus, end-to-end Ethernet connectivity is
provided. The 5GS implements the required interfaces towards the TSN provided. The 5GS implements the required interfaces towards the TSN
controller functions such as the CNC, thus adapts to the settings of the TSN controller functions such as the CNC, thus adapting to the settings of the TS N
network. A 5G user plane virtual bridge interconnects TSN bridges or connects network. A 5G user plane virtual bridge interconnects TSN bridges or connects
end stations, e.g., I/O devices to the TSN network. TSN Translators (TTs), end stations (e.g., I/O devices to the TSN network). TTs,
i.e., the Device-Side TSN Translator (DS-TT) at the UE and the Network-Side i.e., the Device-Side TSN Translator (DS-TT) at the UE and the Network-Side
TSN Translator (NW-TT) at the UPF have a key role in the interconnection. TSN Translator (NW-TT) at the UPF, have a key role in the interconnection.
Note that the introduction of 5G brings flexibility in various aspects, e.g., Note that the introduction of 5G brings flexibility in various aspects, e.g.,
more flexible network topology because a wireless hop can replace several a more flexible network topology because a wireless hop can replace several
wireline hops thus significantly reduce the number of hops end-to-end. wireline hops, thus significantly reducing the number of hops end to end.
<xref target='TSN5G'/> dives more into the integration of 5G with TSN. <xref target='TSN5G'/> dives more into the integration of 5G with TSN.
</t> </t>
<figure anchor='fig-5g-tsn'><name>5G - TSN Integration</name> <figure anchor='fig-5g-tsn'><name>5G - TSN Integration</name>
<artwork align="center"><![CDATA[ <artwork align="center"><![CDATA[
+------------------------------+ +------------------------------+
| 5G System | | 5G System |
| +---+| | +---+|
| +-+ +-+ +-+ +-+ +-+ |TSN|| | +-+ +-+ +-+ +-+ +-+ |TSN||
| | | | | | | | | | | |AF |......+ | | | | | | | | | | | |AF |......+
skipping to change at line 1952 skipping to change at line 2085
|dev| |bridge| | . |TT| | | | | |TT| . | |bridge| |dev| |bridge| | . |TT| | | | | |TT| . | |bridge|
+---+ +------+ | . +--+--+ +---+ +---+--+ . | +------+ +---+ +------+ | . +--+--+ +---+ +---+--+ . | +------+
| +..........................+ | | +..........................+ |
+------------------------------+ +------------------------------+
<----------------- end-to-end Ethernet -------------------> <----------------- end-to-end Ethernet ------------------->
]]></artwork> ]]></artwork>
</figure> </figure>
<t> <t>
NR supports accurate reference time synchronization in 1us accuracy level. NR supports accurate reference time synchronization in 1 µs accuracy level.
Since NR is a scheduled system, an NR UE and a gNB are tightly synchronized Since NR is a scheduled system, an NR UE and a gNB are tightly synchronized
to their OFDM symbol structures. A 5G internal reference time can be to their OFDM symbol structures. A 5G internal reference time can be
provided to the UE via broadcast or unicast signaling, associating a known provided to the UE via broadcast or unicast signaling, associating a known
OFDM symbol to this reference clock. The 5G internal reference time can be OFDM symbol to this reference clock. The 5G internal reference time can be
shared within the 5G network, i.e., radio and core network components. shared within the 5G network (i.e., radio and core network components).
Release 16 has introduced interworking with gPTP for multiple time domains, Release 16 has introduced interworking with gPTP for multiple time domains,
where the 5GS acts as a virtual gPTP time-aware system and supports the where the 5GS acts as a virtual gPTP time-aware system and supports the
forwarding of gPTP time synchronization information between end stations and forwarding of gPTP time synchronization information between end stations
bridges through the 5G user plane TTs. These account for the residence time and bridges through the 5G user plane TTs. These account for the residence
of the 5GS in the time synchronization procedure. One special option is when time of the 5GS in the time synchronization procedure. One special option
the 5GS internal reference time is not only used within the 5GS, but also to is when the 5GS internal reference time is not only used within the 5GS,
the rest of the devices in the deployment, including connected TSN bridges but also to the rest of the devices in the deployment, including connected
and end stations. Release 17 includes further improvements, i.e., methods TSN bridges and end stations. Release 17 includes further improvements
for propagation delay compensation in RAN, further improving the accuracy (i.e., methods for propagation delay compensation in RAN), further
for time synchronization over-the-air, as well as the possibility for the improving the accuracy for time synchronization over the air, as well as
TSN grandmaster clock to reside on the UE side. More extensions and the possibility for the TSN grandmaster clock to reside on the UE side.
flexibility were added to the time synchronization service making it general More extensions and flexibility were added to the time synchronization
for TSC with additional support of other types of clocks and time service, making it general for TSC and providing additional support for
distribution such as boundary clock, transparent clock peer-to-peer, other types of clocks and time distribution such as boundary clocks and
transparent clock end-to-end, aside from the time-aware system used for TSN. transparent clocks (both peer-to-peer and end-to-end) aside from the
Additionally, it is possible to use internal access stratum signaling to time-aware system used for TSN. Additionally, it is possible to use
distribute timing (and not the usual (g)PTP messages), for which the required internal access stratum signaling to distribute timing (and not the usual
accuracy can be provided by the AF <xref target='TS23501'/>. The same time (g)PTP messages), for which the required accuracy can be provided by the AF
synchronization service is expected to be further extended and enhanced in <xref target='TS23501'/>. The same time synchronization service is expected
Release 18 to support Timing Resiliency (according to study item to be further extended and enhanced in Release 18 to support Timing
<xref target='SP211634'/>), where the 5G system can provide a back-up or Resiliency (according to study item <xref target='SP211634'/>), where the
alternative timing source for the failure of the local GNSS source (or other 5G system can provide a backup or alternative timing source for the failure
primary timing source) used by the vertical. of the local GNSS source (or other primary timing source) used by the
vertical.
</t> </t>
<t> <t>
<!-- IETF DetNet is the technology to support
IETF Deterministic Networking (DetNet) is the technology to support
time-sensitive communications at the IP layer. 3GPP Release 18 includes a
study <xref target='TR2370046'/> on whether and how to enable 3GPP support
for DetNet such that a mapping is provided between DetNet and 5G. The support
for DetNet is considered to be added via the TSC framework introduced for
Release 17. The study includes what information needs to be exposed by the
5G System and the translation of DetNet flow specification to 5G QoS
parameters. Note that TSN is the primary subnetwork technology for DetNet.
Thus, the DetNet over TSN work, e.g., <xref target='RFC9023'/>, can be
leveraged via the TSN support built in 5G. As the standards are ready for
such an approach, it is out of scope for the 3GPP Release 18 study item
<xref target='TR2370046'/>.
-->
IETF Deterministic Networking (DetNet) is the technology to support
time-sensitive communications at the IP layer. 3GPP Release 18 includes a time-sensitive communications at the IP layer. 3GPP Release 18 includes a
study <xref target='TR2370046'/> on interworking between 5G and DetNet. study <xref target='TR2370046'/> on interworking between 5G and DetNet.
Along the TSC framework introduced for Release 17, the 5GS acts as Along the TSC framework introduced for Release 17, the 5GS acts as
a DetNet node for the support of DetNet, see Figure 7.1-1 in a DetNet node for the support of DetNet; see Figure 7.1-1 in
<xref target='TR2370046'/>. <xref target='TR2370046'/>.
The study provides details on how the 5GS is exposed by the Time Sensitive The study provides details on how the 5GS is exposed by the Time Sensitive
Communication and Time Synchronization Function (TSCTSF) to the DetNet Communication and Time Synchronization Function (TSCTSF) to the DetNet
controller as a router on a per UPF controller as a router on a per-UPF granularity (similarly to the per-UPF
granularity (similarly to the per UPF Virtual TSN Bridge granularity Virtual TSN Bridge granularity shown in <xref target="fig-5g-tsn"/>). In parti
shown in Figure 11). In particular, it is listed what parameters are cular, it lists the parameters that are
provided by the TSCTSF to the DetNet controller. The study also provided by the TSCTSF to the DetNet controller. The study also
includes how the TSCTSF maps DetNet flow parameters to 5G QoS includes how the TSCTSF maps DetNet flow parameters to 5G QoS
parameters. Note that TSN is the primary subnetwork technology for DetNet. parameters. Note that TSN is the primary subnetwork technology for DetNet.
Thus, the DetNet over TSN work, e.g., <xref target='RFC9023'/>, can be Thus, the work on DetNet over TSN, e.g., <xref target='RFC9023'/>, can be
leveraged via the TSN support built in 5G. leveraged via the TSN support built in 5G.
</t> </t>
<t> <t>
Redundancy architectures were specified in order to provide reliability Redundancy architectures were specified in order to provide reliability
against any kind of failure on the radio link or nodes in the RAN and the against any kind of failure on the radio link or nodes in the RAN and the
core network. Redundant user plane paths can be provided based on the dual core network. Redundant user plane paths can be
connectivity architecture, where the UE sets up two PDU sessions towards the provided based on the dual connectivity architecture, where the UE
same data network, and the 5G system makes the paths of the two PDU sessions sets up two PDU sessions towards the same data network, and the 5G
independent as illustrated in <xref target='fig-5g-dual-ue'/>. There are two system makes the paths of the two PDU sessions independent as
PDU sessions involved in the solution: the first spans from the UE via gNB1 illustrated in <xref target='fig-5g-single-ue'/>. There are two
to UPF1, acting as the first PDU session anchor, while the second spans from PDU sessions involved in the solution:
the UE via gNB2 to UPF2, acting as second the PDU session anchor. The The first spans from the UE via gNB1 to UPF1, acting as the first PDU
independent paths may continue beyond the 3GPP network. Redundancy Handling session anchor, while
Functions (RHFs) are deployed outside of the 5GS, i.e., in Host A (the the second spans from the UE via gNB2 to UPF2, acting as second the
device) and in Host B (the network). RHF can implement replication and PDU session anchor.
elimination functions as per <xref target='IEEE802.1CB'/> or the
Packet Replication, Elimination, and Ordering Functions (PREOF) of IETF
Deterministic Networking (DetNet) <xref target='RFC8655'/>.
</t> </t>
<figure anchor='fig-5g-single-ue'><name>Reliability with Single UE</name> <t>The independent paths may continue beyond the 3GPP
network. 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
implement replication and elimination functions as per <xref
target='IEEE802.1CB'/> or the Packet Replication, Elimination, and
Ordering Functions (PREOF) of IETF DetNet
<xref target='RFC8655'/>.
</t>
<figure anchor='fig-5g-single-ue'>
<name>Reliability with Single UE</name>
<artwork align="center"><![CDATA[ <artwork align="center"><![CDATA[
+........+ +........+
. Device . +------+ +------+ +------+ . Device . +------+ +------+ +------+
. . + gNB1 +--N3--+ UPF1 |--N6--+ | . . + gNB1 +--N3--+ UPF1 |--N6--+ |
. ./+------+ +------+ | | . ./+------+ +------+ | |
. +----+ / | | . +----+ / | |
. | |/. | | . | |/. | |
. | UE + . | DN | . | UE + . | DN |
. | |\. | | . | |\. | |
. +----+ \ | | . +----+ \ | |
. .\+------+ +------+ | | . .\+------+ +------+ | |
+........+ + gNB2 +--N3--+ UPF2 |--N6--+ | +........+ + gNB2 +--N3--+ UPF2 |--N6--+ |
+------+ +------+ +------+ +------+ +------+ +------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t> <t>
An alternative solution is that multiple UEs per device are used for user An alternative solution is that multiple UEs per device are used for user
plane redundancy as illustrated in <xref target='fig-5g-dual-ue'/>. Each UE plane redundancy as illustrated in <xref target='fig-5g-dual-ue'/>. Each UE
sets up a PDU session. The 5GS ensures that those PDU sessions of the sets up a PDU session. The 5GS ensures that the PDU sessions of the
different UEs are handled independently internal to the 5GS. There is no different UEs are handled independently internal to the 5GS. There
single point of failure in this solution, which also includes RHF outside is no single point of failure in this solution, which also includes
of the 5G system, e.g., as per FRER or as PREOF specifications. RHF outside of the 5G system, e.g., as per FRER <xref target="IEEE802.1CB"/> o
r PREOF <xref target="RFC8655"/>
specifications.
</t> </t>
<figure anchor='fig-5g-dual-ue'><name>Reliability with Dual UE</name> <figure anchor='fig-5g-dual-ue'><name>Reliability with Dual UE</name>
<artwork align="center"><![CDATA[ <artwork align="center"><![CDATA[
+.........+ +.........+
. Device . . Device .
. . . .
. +----+ . +------+ +------+ +------+ . +----+ . +------+ +------+ +------+
. | UE +-----+ gNB1 +--N3--+ UPF1 |--N6--+ | . | UE +-----+ gNB1 +--N3--+ UPF1 |--N6--+ |
. +----+ . +------+ +------+ | | . +----+ . +------+ +------+ | |
skipping to change at line 2077 skipping to change at line 2202
. | UE +-----+ gNB1 +--N3--+ UPF1 |--N6--+ | . | UE +-----+ gNB1 +--N3--+ UPF1 |--N6--+ |
. +----+ . +------+ +------+ | | . +----+ . +------+ +------+ | |
. . | DN | . . | DN |
. +----+ . +------+ +------+ | | . +----+ . +------+ +------+ | |
. | UE +-----+ gNB2 +--N3--+ UPF2 |--N6--+ | . | UE +-----+ gNB2 +--N3--+ UPF2 |--N6--+ |
. +----+ . +------+ +------+ +------+ . +----+ . +------+ +------+ +------+
. . . .
+.........+ +.........+
]]></artwork> ]]></artwork>
</figure> </figure>
<t> <t>
Note that the abstraction provided by the RHF and the location of the RHF Note that the abstraction provided by the RHF and the location of the
being outside of the 5G system make 5G equally supporting integration for RHF outside of the 5G system allow 5G to support
reliability both with FRER of TSN and PREOF of DetNet as they both rely on integration for reliability with both TSN FRER <xref target="IEEE802.1CB"/> an
the same concept. d DetNet PREOF <xref target="RFC8655"/>,
as they both rely on the same concept.
</t> </t>
</section>
</section>
</section>
</section><!-- Time-Sensitive Networking (TSN) Integration) --> <section anchor="ldacs">
<name>L-Band Digital Aeronautical Communications System (LDACS)</name>
</section><!-- Applicability to Deterministic Flows --> <t>One of the main pillars of the modern Air Traffic Management (ATM)
system is the existence of a communication infrastructure that enables
efficient aircraft guidance and safe separation in all phases of
flight. Although current systems are technically mature, they suffer
from the VHF band's increasing saturation in high-density areas and the
limitations posed by analog radio. Therefore, aviation (globally and in the
European Union (EU) in particular) strives for a sustainable modernization
of the aeronautical communication infrastructure.</t>
</section> <!-- 5G --> <t>In the long term, ATM communication shall transition from analog VHF
voice and VHF Digital Link (VDL) Mode 2 communication to more spectrum-effici
ent digital data
communication. The European ATM Master Plan foresees this transition to be
realized for terrestrial communications by the development and
implementation of the L-band Digital Aeronautical Communications System
(LDACS).</t>
<section><name>L-band Digital Aeronautical Communications System</name> <t>LDACS has been designed with applications related to the safety and
regularity of the flight in mind. It has therefore been designed as a
deterministic wireless data link (as far as possible).</t>
<t> <t>It is a secure, scalable, and spectrum-efficient data link with embedded
One of the main pillars of the modern Air Traffic Management (ATM) system is the navigation capability; thus, it is the first truly integrated
existence of a communication infrastructure that enables efficient aircraft gui Communications, Navigation, and Surveillance (CNS) system recognized by the
dance and safe separation in all phases of flight. Although current systems are International Civil Aviation Organization (ICAO). During flight tests, the
technically mature, they are suffering from the VHF band’s increasing saturation LDACS capabilities have been successfully demonstrated. A viable rollout
in high-density areas and the limitations posed by analogue radio. Therefore, a scenario has been developed, which allows gradual introduction of LDACS with
viation globally and the European Union (EU) in particular, strives for a sustai immediate use and revenues. Finally, ICAO is developing LDACS standards to
nable modernization of the aeronautical communication infrastructure. pave the way for the future.</t>
</t><t>
In the long-term, ATM communication shall transition from analogue VHF voice and
VDL2 communication to more spectrum efficient digital data communication. The E
uropean ATM Master Plan foresees this transition to be realized for terrestrial
communications by the development and implementation of the L-band Digital Aeron
autical Communications System (LDACS).
</t>
<t>
LDACS has been designed with applications related to the safety and
regularity of the flight in mind. It has therefore been designed as
a deterministic wireless data link (as far as possible).
</t>
<t>
It is a secure, scalable and spectrum efficient data link with
embedded navigation capability and thus, is the first truly integrate
d
Communications, Navigation, and Surveillance (CNS) system recognized
by the International Civil Aviation Organization
(ICAO) During flight tests the LDACS
capabilities have been successfully demonstrated. A viable roll-out
scenario has been developed which allows gradual introduction of LDAC
S
with immediate use and revenues. Finally, ICAO is developing LDACS
standards to pave the way for the future.
</t>
<t>
LDACS shall enable IPv6 based air-ground communication related to the safety and <t>LDACS shall enable IPv6-based air-ground communication related to the
regularity of the flight. The particular challenge is that no new frequencies c safety and regularity of the flight. The particular challenge is that no
an be made available for terrestrial aeronautical communication. It was thus nec new frequencies can be made available for terrestrial aeronautical
essary to develop procedures to enable the operation of LDACS in parallel with o communication. It was thus necessary to develop procedures to enable the
ther services in the same frequency band, more in <xref target='RFC9372'/>. operation of LDACS in parallel with other services in the same frequency
</t> band; see <xref target='RFC9372'/> for more information.</t>
<section><name>Provenance and Documents</name>
<t> <section>
The development of LDACS has already made substantial progress in the <name>Provenance and Documents</name>
Single European Sky ATM Research (SESAR) framework, and is currently being cont <t>The development of LDACS has already made substantial progress in
inued in the follow-up program, SESAR2020 <xref target='RIH18'/>. A key objectiv the Single European Sky ATM Research (SESAR) framework, and it is
e of the SESAR activities is to develop, implement and validate a modern aeronau currently being continued in the follow-up program, SESAR2020 <xref
tical data link able to evolve with aviation needs over long-term. To this end, target='RIH18'/>. A key objective of the SESAR activities is to
an LDACS specification has been produced <xref target='GRA19'/> and is continuou develop, implement, and validate a modern aeronautical data link able to
sly updated; transmitter demonstrators were developed to test the spectrum compa evolve with aviation needs over the long term. To this end, an LDACS
tibility of LDACS with legacy systems operating in the L-band <xref target='SAJ1 specification has been produced <xref target='GRA19'/> and is
4'/>; and the overall system performance was analyzed by computer simulations, i continuously updated; transmitter demonstrators were developed to test
ndicating that LDACS can fulfill the identified requirements <xref target='GRA11 the spectrum compatibility of LDACS with legacy systems operating in
'/>. the L-band <xref target='SAJ14'/>, and the overall system performance
</t><t> was analyzed by computer simulations, indicating that LDACS can fulfill
LDACS standardization within the framework of the ICAO started in Dec the identified requirements <xref target='GRA11'/>.</t>
ember 2016. The ICAO standardization group has produced an initial Standards and
Recommended Practices (SARPs) document <xref target='ICAO18'/>. The SARPs docum <t>LDACS standardization within the framework of the ICAO started in
ent defines the general characteristics of LDACS. December 2016. The ICAO standardization group has produced an initial
</t><t> Standards and Recommended Practices (SARPs) document <xref
Up to now the LDACS standardization has been focused on the developme target='ICAO18'/>. The SARPs document defines the general
nt of the physical layer and the data link layer, only recently have higher laye characteristics of LDACS.</t>
rs come into the focus of the LDACS development activities. There is currently n
o "IPv6 over LDACS" specification; however, SESAR2020 has started the testing of <t>Up to now, the LDACS standardization has been focused on the
IPv6-based LDACS testbeds. The IPv6 architecture for the aeronautical telecommu development of the Physical (PHY) layer and the data link layer; only rec
nication network is called the Future Communications Infrastructure (FCI). FCI s ently
hall support quality of service, diversity, and mobility under the umbrella of t have higher layers come into the focus of the LDACS development
he "multi-link concept". This work is conducted by ICAO working group WG-I. activities. There is currently no "IPv6 over LDACS" specification;
</t><t> however, SESAR2020 has started the testing of IPv6-based LDACS
In addition to standardization activities several industrial LDACS pr testbeds. The IPv6 architecture for the aeronautical telecommunication
ototypes have been built. One set of LDACS prototypes has been evaluated in flig network is called the Future Communications Infrastructure (FCI). FCI
ht trials confirming the theoretical results predicting the system performance < shall support QoS, diversity, and mobility under the
xref target='GRA18'/><xref target='BEL22'/><xref target='GRA23'/> . umbrella of the "multi-link concept". This work is conducted by the ICAO
</t> WG-I Working Group.</t>
</section><!-- Provenance and Documents --> <t>In addition to standardization activities,
several industrial LDACS prototypes have been built. One set of LDACS
prototypes has been evaluated in flight trials, confirming the
theoretical results predicting the system performance <xref
target='GRA18'/> <xref target='BEL22'/> <xref target='GRA23'/>.</t>
</section>
<section><name>General Characteristics</name> <section><name>General Characteristics</name>
<t> <t>
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 them LDACS access network contains several ground stations, each of which
providing one LDACS radio cell. The LDACS air interface is a provides one LDACS radio cell. The LDACS air interface is a
cellular data link with a star-topology connecting aircraft to cellular data link with a star topology connecting aircraft to
ground-stations with a full duplex radio link. Each ground-station ground stations with a full duplex radio link. Each ground station
is the centralized instance controlling all air-ground communications is the centralized instance controlling all air-ground communications
within its radio cell. within its radio cell.
</t> </t>
<t> <t>
The user data rate of LDACS is 315 kbit/s to 1428 kbit/s on the forwa The user data rate of LDACS is 315 kbit/s to 1428 kbit/s on the
rd link, and 294 kbit/s to 1390 kbit/s on the reverse link, depending on coding forward link (FL) and 294 kbit/s to 1390 kbit/s on the reverse link (
and modulation. Due to strong interference from legacy systems in the L-band, th RL),
e most robust coding and modulation should be expected for initial deployment, i depending on coding and modulation. Due to strong interference from
.e., 315/294 kbit/s on the forward/reverse link, respectively. legacy systems in the L-band, the most robust coding and modulation
should be expected for initial deployment, i.e., 315 kbit/s on
the FL and 294 kbit/s on the RL.
</t> </t>
<t> <t>
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 Distance
Measuring Equipment), is extracted from the LDACS communication links Measuring Equipment (DME), 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 Alternative Position, Navigation, and Timing (APNT)
capability to supplement the existing on-board GNSS (Global Navigatio capability to supplement the existing on-board Global Navigation
n Satellite System (GNSS) without the need for additional bandwidth.
Satellite System) without the need for additional bandwidth.
Operationally, there will be no difference for pilots whether the Operationally, there will be no difference for pilots whether the
navigation data are provided by LDACS or DME. This capability was navigation data are provided by LDACS or DME. This capability was
flight tested and proven during the MICONAV flight trials in 2019 flight tested and proven during the MICONAV flight trials in 2019
<xref target="BAT19"/>. <xref target="BAT19"/>.
</t> </t>
<t> <t>
In previous works and during the MICONAV flight campaign in 2019, it In previous works and during the MICONAV flight campaign in 2019, it
was also shown, that LDACS can be used for surveillance capability. was also shown that LDACS can be used for surveillance capability.
Filip et al. <xref target="FIL19"/> shown passive radar capabilities Filip et al.&nbsp;<xref target="FIL19"/> have shown the passive radar
of LDACS and capabilities of LDACS, and
Automatic Dependence Surveillance – Contract (ADS-C) was demonstrated Automatic Dependence Surveillance - Contract (ADS-C) was demonstrated
via LDACS during the flight campaign 2019 <xref target="SCH19"/>. via LDACS during the flight campaign 2019 <xref target="SCH19"/>.
</t> </t>
<t> <t>
Since LDACS has been mainly designed for air traffic management commu Since LDACS has been mainly designed for air traffic management
nication it supports mutual entity authentication, integrity and confidentiality communication, it supports mutual entity authentication, integrity
capabilities of user data messages and some control channel protection capabili and confidentiality capabilities of user data messages, and some
ties <xref target="MAE18"/>, <xref target="MAE191"/>, <xref target="MAE192"/>, control channel protection capabilities <xref target="MAE18"/>
<xref target="MAE20"/>. <!--<xref target='MAE19'/>.--> <xref target="MAE191"/> <xref target="MAE192"/> <xref
target="MAE20"/>.
</t> </t>
<t> <t>
Overall this makes LDACS the world's first truly integrated CNS syste Overall, this makes LDACS the world's first truly integrated CNS syst
m em
and is the worldwide most mature, secure, terrestrial long-range CNS and is the most mature, secure, and terrestrial long-range CNS
technology for civil aviation. technology for civil aviation worldwide.
</t> </t>
</section>
</section><!-- General Characteristics -->
<section><name>Deployment and Spectrum</name> <section><name>Deployment and Spectrum</name>
<t> <t>
LDACS has its origin in merging parts of the B-VHF <xref target="BRA0 6"/>, B-AMC LDACS has its origin in merging parts of the B-VHF <xref target="BRA0 6"/>, B-AMC
<xref target="SCH08"/>, TIA-902 (P34) <xref target="HAI09"/>, and WiM <xref target="SCH08"/>, TIA-902 (P34) <xref target="HAI09"/>, and WiM
AX IEEE 802.16e technologies AX IEEE 802.16e
<xref target="EHA11"/>. In 2007 the spectrum for LDACS was allocated <xref target="EHA11"/> technologies. In 2007, the spectrum for LDACS
at the World was allocated at the World
Radio Conference (WRC). Radio Conference (WRC).
</t> </t>
<t> <t>
It was decided to allocate the spectrum next to Distance Measuring It was decided to allocate the spectrum next to Distance Measuring
Equipment (DME), resulting in an in-lay approach between the DME Equipment (DME), resulting in an in-lay approach between the DME
channels for LDAC <xref target="SCH14"/>. channels for LDAC <xref target="SCH14"/>.
</t> </t>
<t> <t>
LDACS is currently being standardized by ICAO and several roll-out LDACS is currently being standardized by ICAO and several rollout
strategies are discussed: strategies are discussed.
</t> </t>
<t> <t>
The LDACS data link provides enhanced capabilities to existing The LDACS data link provides enhanced capabilities to existing
Aeronautical communications infrastructure enabling them to better aeronautical communications infrastructures, enabling them to better
support user needs and new applications. The deployment scalability o f support user needs and new applications. The deployment scalability o f
LDACS allows its implementation to start in areas where most needed t LDACS allows its implementation to start in areas where it is most ne
o eded to
Improve immediately the performance of already fielded infrastructure immediately improve the performance of and already-fielded infrastruc
. ture.
Later the deployment is extended based on operational demand. Later, the deployment is extended based on operational demand.
An attractive scenario for upgrading the existing VHF communication An attractive scenario for upgrading the existing VHF communication
systems by adding an additional LDACS data link is described below. systems by adding an additional LDACS data link is described below.
</t> </t>
<t> <t>
When considering the current VDL Mode 2 infrastructure and user base, When considering the current VDL Mode 2 infrastructure and user base,
a very attractive win-win situation comes about, when the a very attractive win-win situation comes about when the
technological advantages of LDACS are combined with the existing VDL technological advantages of LDACS are combined with the existing VDL
mode 2 infrastructure. LDACS provides at least 50 time more capacity Mode 2 infrastructure. LDACS provides at least 50 times more capacity
than VDL Mode 2 and is a natural enhancement to the existing VDL Mode than VDL Mode 2 and is a natural enhancement to the existing VDL Mode
2 business model. The advantage of this approach is that the VDL Mode 2 business model. The advantage of this approach is that the VDL Mode
2 infrastructure can be fully reused. Beyond that, it opens the way 2 infrastructure can be fully reused. Beyond that, it opens the way
for further enhancements <xref target="ICAO19"/>. for further enhancements <xref target="ICAO19"/>.
</t> </t>
</section><!-- Deployment and Spectrum --> </section>
<section><name>Applicability to Deterministic Flows</name> <section><name>Applicability to Deterministic Flows</name>
<t> <t>
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 roll-out . messages are a key feature for its successful deployment and rollout.
</t> </t>
<section><name>System Architecture</name> <section><name>System Architecture</name>
<t> <t>
Up to 512 Aircraft Station (AS) communicate to an LDACS Ground Up to 512 Aircraft Stations (ASes) communicate to an LDACS Ground
Station (GS) in the Reverse Link (RL). GS communicate to an AS in Station (GS) in the reverse link (RL). A GS communicates to an AS
the Forward Link (FL). Via an Access-Router (AC-R) GSs connect in
the LDACS sub-network to the global Aeronautical the forward link (FL). Via an Access-Router (AC-R), GSs connect
the LDACS subnetwork to the global Aeronautical
Telecommunications Network (ATN) to which the corresponding Air Telecommunications Network (ATN) to which the corresponding Air
Traffic Services (ATS) and Aeronautical Operational Control (AOC) Traffic Services (ATS) and Aeronautical Operational Control (AOC)
end systems are attached. end systems are attached.
</t> </t>
</section><!-- System Architecture --> </section>
<section><name>Overview of the Radio Protocol Stack</name> <section>
<t> <name>Overview of the Radio Protocol Stack</name>
The protocol stack of LDACS is implemented in the AS and GS: It <t>The protocol stack of LDACS is implemented in the AS and GS; it
consists of the Physical Layer (PHY) 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 blocks above it. Four are placed in the data link layer (DLL) of
the the AS and GS:</t>
AS and GS: (1) Medium Access Layer (MAC), (2) Voice Interface (VI <ol>
), <li>Medium Access Layer (MAC),</li>
(3) Data Link Service (DLS), and (4) LDACS Management Entity (LME <li>Voice Interface (VI),</li>
). <li>Data Link Service (DLS), and</li>
The last entity resides within the Sub-Network Layer: Sub-Network <li>LDACS Management Entity (LME).</li>
Protocol (SNP). The LDACS network is externally connected to voi </ol>
ce <t>The last entity resides within the subnetwork layer: the
units, radio control units, and the ATN Network Layer. Subnetwork Protocol (SNP). The LDACS network is externally
connected to voice units, radio control units, and the ATN
network layer.
</t> </t>
<t> <t>
Communications between MAC and LME layer is split into four distinct Communications between the MAC and LME layers is split into four
control channels: distinct control channels:</t>
The Broadcast Control Channel (BCCH) where LDACS ground stations ann <ol>
ounce their specific LDACS cell, including physical parameters and cell identifi <li>the Broadcast Control Channel (BCCH), where LDACS ground station
cation; the Random Access Channel (RACH) where LDACS airborne radios can request s announce their specific LDACS cell,
access to an LDACS cell; the Common Control Channel (CCCH) where LDACS ground s including physical parameters and cell identification;</li>
tations allocate resources to aircraft radios, enabling the airborne side to tra <li>the Random Access Channel (RACH), where LDACS airborne radios ca
nsmit user payload; the Dedicated Control Channel (DCCH) where LDACS airborne ra n request
dios can request user data resources from the LDACS ground station so the airbor access to an LDACS cell;</li>
ne side can transmit user payload. <li>the Common Control Channel (CCCH), where
Communications between MAC and DLS layer is handled by the Data Chan LDACS ground stations allocate resources to aircraft radios,
nel (DCH) where user payload is handled. enabling the airborne side to transmit the user payload; and</li>
<li>the Dedicated Control Channel (DCCH), where LDACS airborne
radios can request user data resources from the LDACS ground
station so the airborne side can transmit the user payload.</li>
</ol>
<t>Communications between the MAC and DLS layers is handled by the Dat
a Channel (DCH) where the user payload is
handled.
</t> </t>
<t> <t>
<xref target="fig_LDACSprotocolstack"/> shows the protocol stack of LDACS as implemented in the AS <xref target="fig_LDACSprotocolstack"/> shows the protocol stack of LDACS as implemented in the AS
and GS. and GS.
</t> </t>
<figure title="LDACS protocol stack in AS and GS" anchor="fig_LDACSp <figure anchor="fig_LDACSprotocolstack">
rotocolstack"> <name>LDACS Protocol Stack in AS and GS</name>
<artwork> <artwork><![CDATA[
<![CDATA[
IPv6 Network Layer IPv6 Network Layer
| |
| |
+------------------+ +----+ +------------------+ +----+
| SNP |--| | Sub-Network | SNP |--| | Subnetwork
| | | | Layer | | | | Layer
+------------------+ | | +------------------+ | |
| | LME| | | LME|
+------------------+ | | +------------------+ | |
| DLS | | | Logical Link | DLS | | | Logical Link
| | | | Control Layer | | | | Control Layer
+------------------+ +----+ +------------------+ +----+
| | | |
DCH DCCH/CCCH DCH DCCH/CCCH
| RACH/BCCH | RACH/BCCH
skipping to change at line 2289 skipping to change at line 2475
+--------------------------+ +--------------------------+
| |
+--------------------------+ +--------------------------+
| PHY | Physical Layer | PHY | Physical Layer
+--------------------------+ +--------------------------+
| |
| |
((*)) ((*))
FL/RL radio channels FL/RL radio channels
separated by separated by
Frequency Division Duplex frequency division duplex
]]></artwork>
]]>
</artwork>
</figure> </figure>
</section><!-- Overview of The Radio Protocol Stack --> </section>
<section><name>Radio (PHY)</name> <section><name>Radio (PHY)</name>
<t> <t>
The physical layer provides the means to transfer data over the r The PHY layer provides the means to transfer data over the
adio radio channel. The LDACS ground station supports bidirectional
channel. The LDACS ground-station supports bi-directional links links to multiple aircraft under its control. The FL
to direction (which is ground to air) and the RL
multiple aircraft under its control. The forward link direction direction (which is air to ground) are separated by
(FL; frequency division duplex. FL and RL use a
ground-to-air) and the reverse link direction (RL; air-to-ground) 500 kHz channel each. The ground station transmits a
are continuous stream of OFDM symbols on the FL. In the RL, differen
separated by frequency division duplex. Forward link and reverse t aircrafts are separated in time and
link use a 500 kHz channel each. The ground-station transmits a frequency using a combination of Orthogonal Frequency-Division
continuous stream of OFDM symbols on the forward link. In the Multiple Access (OFDMA) and Time-Division Multiple-Access
reverse link different aircraft are separated in time and frequen (TDMA). Thus, aircraft transmit discontinuously on the RL with r
cy adio bursts sent in precisely defined transmission
using a combination of Orthogonal Frequency-Division Multiple-Acc opportunities allocated by the ground station. The most
ess important service on the PHY layer of LDACS is the PHY time
(OFDMA) and Time-Division Multiple-Access (TDMA). Aircraft thus framing service, which indicates that the PHY layer is ready to
transmit discontinuously on the reverse link with radio bursts se transmit in a given slot and indicates PHY layer framing and
nt timing to the MAC time framing service. LDACS does not support
in precisely defined transmission opportunities allocated by the
ground-station. The most important service on the PHY layer of L
DACS
is the PHY time framing service, which indicates that the PHY lay
er is
ready to transmit in a given slot and to indicate PHY layer frami
ng
and timing to the MAC time framing service. LDACS does not suppor
t
beam-forming or Multiple Input Multiple Output (MIMO). beam-forming or Multiple Input Multiple Output (MIMO).
</t> </t>
</section><!-- Radio (PHY) --> </section>
<section><name>Scheduling, Frame Structure and QoS (MAC)</name> <section><name>Scheduling, Frame Structure, and QoS (MAC)</name>
<t> <t>
The data-link layer provides the necessary protocols to facilitat The data link layer provides the necessary protocols to
e facilitate concurrent and reliable data transfer for multiple
concurrent and reliable data transfer for multiple users. The LD users. The LDACS data link layer is organized in two
ACS sublayers: the medium access sublayer and the logical link
data link layer is organized in two sub-layers: The medium access control sublayer. The medium access sublayer manages the
sub-layer and the logical link control sub-layer. The medium acc organization of transmission opportunities in slots of time and
ess frequency. The logical link control sublayer provides
sub-layer manages the organization of transmission opportunities acknowledged point-to-point logical channels between the
in aircraft and the ground station using an automatic repeat
slots of time and frequency. The logical link control sub-layer request protocol. LDACS also supports unacknowledged
provides acknowledged point-to-point logical channels between the point-to-point channels and ground-to-air broadcast.
aircraft and the ground-station using an automatic repeat request </t>
protocol. LDACS supports also unacknowledged point-to-point chan <t>Next, the frame
nels structure of LDACS is introduced, followed by
and ground-to-air broadcast. a more in-depth discussion of the LDACS medium access.
Before going more into depth about the LDACS medium access, the f
rame structure of LDACS is introduced:
</t> </t>
<t> <t>
The LDACS framing structure for FL and RL is based on Super-Frame s The LDACS framing structure for FL and RL is based on Super-Frame s
(SF) of 240 ms duration. Each SF corresponds to 2000 OFDM symbol s. (SF) of 240 ms duration. Each SF corresponds to 2000 OFDM symbol s.
The FL and RL SF boundaries are aligned in time (from the view of the The FL and RL SF boundaries are aligned in time (from the view of the
GS). GS).
</t> </t>
<t> <t>
In the FL, an SF contains a Broadcast Frame of duration 6.72 ms ( In the FL, an SF contains a broadcast frame with a duration of 6.
56 72 ms (56
OFDM symbols) for the Broadcast Control Channel (BCCH), and four OFDM symbols) for the Broadcast Control Channel (BCCH) and four
Multi-Frames (MF), each of duration 58.32 ms (486 OFDM symbols). Multi-Frames (MF), each with a duration of 58.32 ms (486 OFDM sym
</t> bols).
<t>
In the RL, each SF starts with a Random Access (RA) slot of lengt
h
6.72 ms with two opportunities for sending RL random access frame
s
for the Random Access Channel (RACH), followed by four MFs. Thes
e
MFs have the same fixed duration of 58.32 ms as in the FL, but a
different internal structure
</t> </t>
<t> <t>
<xref target="fig_LDACSframesuper"/> and <xref target="fig_LDACSf In the RL, each SF starts with a Random Access (RA) slot with a
ramesmulti"/> illustrate the LDACS frame structure. length of 6.72 ms with two opportunities for sending RL random
access frames for the Random Access Channel (RACH), followed by
four MFs. These MFs have the same fixed duration of 58.32 ms
as in the FL but a different internal structure.
</t> </t>
<t>Figures <xref target="fig_LDACSframesuper" format="counter"/>
and <xref target="fig_LDACSframesmulti" format="counter"/>
illustrate the LDACS frame structure. This fixed frame structure allo
ws for the reliable and dependable
transmission of data.</t>
<figure title="SF structure for LDACS" anchor="fig_LDACSframesuper"> <figure anchor="fig_LDACSframesuper">
<artwork> <name>SF Structure for LDACS</name>
<![CDATA[ <artwork><![CDATA[
^ ^
| +------+------------+------------+------------+------------+ | +------+------------+------------+------------+------------+
| FL | BCCH | MF | MF | MF | MF | | FL | BCCH | MF | MF | MF | MF |
F +------+------------+------------+------------+------------+ F +------+------------+------------+------------+------------+
r <---------------- Super-Frame (SF) - 240ms ----------------> r <---------------- Super-Frame (SF) - 240 ms --------------->
e e
q +------+------------+------------+------------+------------+ q +------+------------+------------+------------+------------+
u RL | RACH | MF | MF | MF | MF | u RL | RACH | MF | MF | MF | MF |
e +------+------------+------------+------------+------------+ e +------+------------+------------+------------+------------+
n <---------------- Super-Frame (SF) - 240ms ----------------> n <---------------- Super-Frame (SF) - 240 ms --------------->
c c
y y
| |
----------------------------- Time ------------------------------> ----------------------------- Time ------------------------------>
| |
]]> ]]></artwork>
</artwork>
</figure> </figure>
<figure title="MF Structure for LDACS" anchor="fig_LDACSframesmulti" <figure anchor="fig_LDACSframesmulti">
> <name>MF Structure for LDACS</name>
<artwork> <artwork><![CDATA[
<![CDATA[
^ ^
| +-------------+------+-------------+ | +-------------+------+-------------+
| FL | DCH | CCCH | DCH | | FL | DCH | CCCH | DCH |
F +-------------+------+-------------+ F +-------------+------+-------------+
r <---- Multi-Frame (MF) - 58.32ms --> r <--- Multi-Frame (MF) - 58.32 ms -->
e e
q +------+---------------------------+ q +------+---------------------------+
u RL | DCCH | DCH | u RL | DCCH | DCH |
e +------+---------------------------+ e +------+---------------------------+
n <---- Multi-Frame (MF) - 58.32ms --> n <--- Multi-Frame (MF) - 58.32 ms -->
c c
y y
| |
-------------------- Time ------------------> -------------------- Time ------------------>
| |
]]> ]]></artwork>
</artwork>
</figure> </figure>
<t> <t>
This fixed frame structure allows for a reliable and dependable Next, the LDACS medium
transmission of data. Next, the LDACS medium access layer is introduced.
access layer is introduced:
</t> </t>
<t> <t>
LDACS medium access is always under the control of the ground-station LDACS medium access is always under the control of the ground station
of a radio cell. Any medium access for the transmission of user data of a radio cell. Any medium access for the transmission of user data
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.
</t> </t>
<t> <t>
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. the ground station.
Resources can either be requested "on demand" or permanently
Resources can either be requested "on demand", or permanently allocat allocated by a LDACS ground station with a given class of service.
ed by a LDACS ground station, with a given class of service. On the FL, this is done locally in the ground station; on the
On the forward link, this is done RL, a dedicated contention-free control channel is
locally in the ground-station, on the reverse link a dedicated used (the Dedicated Control Channel (DCCH); roughly 83 bits every 60
contention-free control channel is used (Dedicated Control Channel ms). A resource allocation is always announced in the control
(DCCH); roughly 83 bit every 60 ms). A resource allocation is always channel of the FL (Common Control Channel (CCCH);
announced in the control channel of the forward link (Common Control variable sized). Due to the spacing of the RL control
Channel (CCCH); variable sized). Due to the spacing of the reverse channels of every 60 ms, a medium access delay in the same order of
link control channels of every 60 ms, a medium access delay in the magnitude is to be expected.
same order of magnitude is to be expected.
</t> </t>
<t> <t>
Resources can also be requested "permanently". The permanent Resources can also be requested "permanently". The permanent
resource request mechanism supports requesting recurring resources in 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 message always go first in seen as a big problem since safety-related messages always go first i
any case. Scheduling of reverse link resources is done in physical n
Protocol Data Units (PDU) of 112 bit (or larger if more aggressive any case. Scheduling of RL resources is done in physical
coding and modulation is used). Scheduling on the forward link is Protocol Data Units (PDU) of 112 bits (or larger if more aggressive
done Byte-wise since the forward link is transmitted continuously by coding and modulation is used). Scheduling on the FL is
the ground-station. done byte wise since the FL is transmitted continuously by
the ground station.
</t> </t>
<t> <t>
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 befor
before-break). Beyond this, FCI diversity shall e break). Beyond this, FCI diversity shall
be implemented by the multi-link concept. be implemented by the multi-link concept.
</t> </t>
</section><!-- Scheduling, Frame Structure and QoS (MAC) --> </section>
</section>
</section><!-- Applicability to deterministic flows --> </section>
</section><!-- title="L-band Digital Aeronautical Communications System" -->
<section><name>IANA Considerations</name> <section><name>IANA Considerations</name>
<t> <t>This document has no IANA actions.</t>
This specification does not require IANA action.
</t>
</section> </section>
<section anchor='sec'><name>Security Considerations</name> <section anchor='sec'><name>Security Considerations</name>
<t> <t>
Most RAW technologies integrate some authentication or encryption Most RAW technologies integrate some authentication or encryption
mechanisms that were defined outside the IETF. mechanisms that are defined outside the IETF. The IETF
The IETF specifications referenced herein each provide their own specifications referenced herein each provide their own security
Security Considerations, and the lower layer technologies used considerations, and the lower-layer technologies used provide their
provide their own security at Layer-2. own security at Layer 2.
</t> </t>
</section> </section>
<section><name>Contributors</name>
<t> This document aggregates articles from authors specialized in each
technologies. Beyond the main authors listed in the front page, the following
contributors proposed additional text and refinement that improved the
document.
</t><dl spacing='normal'>
<dt>Georgios Z. Papadopoulos:</dt><dd> Contribute
d to the TSCH section. </dd>
<dt>Nils Maeurer:</dt><dd> Contributed to the LDA
CS section. </dd>
<dt>Thomas Graeupl:</dt><dd> Contributed to the L
DACS section. </dd>
<dt>Torsten Dudda, Alexey Shapin, and Sara Sandbe
rg:</dt><dd> Contributed to the 5G section. </dd>
<dt>Rocco Di Taranto:</dt><dd> Contributed to the Wi-Fi section<
/dd>
<dt>Rute Sofia:</dt><dd> Contributed to the Introduction and Ter
minology sections</dd>
</dl><t>
</t>
</section>
<section><name>Acknowledgments</name>
<t>
Many thanks to the participants of the RAW WG where a lot of the
work discussed here happened, and Malcolm Smith for his review of the 802.11 sec
tion. Special thanks for post directorate and IESG reviewers, Roman Danyliw, Vic
toria Pritchard, Donald Eastlake, Mohamed Boucadair, Jiankang Yao, Shivan Kaul S
ahib, Mallory Knodel, Ron Bonica, Ketan Talaulikar, Eric Vyncke, and Carlos Jesu
s Bernardos Cano.
</t>
</section><!-- ack -->
</middle> </middle>
<back> <back>
<displayreference target="IEEE802154" to="IEEE Std 802.15.4"/> <displayreference target="I-D.ietf-6tisch-coap" to="CoAP-6TiSCH"/>
<displayreference target="IEEE80211" to="IEEE Std 802.11"/> <displayreference target="I-D.ietf-roll-nsa-extension" to="NSA-EXT"/>
<displayreference target="IEEE8021Qat" to="IEEE Std 802.1Qat"/> <displayreference target="IEEE802154" to="IEEE802.15.4"/>
<displayreference target="IEEE80211ad" to="IEEE Std 802.11ad"/> <displayreference target="IEEE80211" to="IEEE802.11"/>
<displayreference target="IEEE80211ax" to="IEEE Std 802.11ax"/> <displayreference target="IEEE8021Qat" to="IEEE802.1Qat"/>
<displayreference target="IEEE80211ay" to="IEEE Std 802.11ay"/> <displayreference target="IEEE80211ad" to="IEEE802.11ad"/>
<displayreference target="IEEE80211be" to="IEEE 802.11be"/> <displayreference target="IEEE80211ax" to="IEEE802.11ax"/>
<displayreference target="IEEE80211ay" to="IEEE802.11ay"/>
<displayreference target="IEEE80211be" to="IEEE802.11be"/>
<references><name>References</name>
<references><name>Normative References</name> <references><name>Normative References</name>
<xi:include href='http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.R <xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5673.x
FC.5673.xml'/> <!-- Industrial Routing Requirements in Low-Power and Lossy Netwo ml'/>
rks --> <xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8557.x
<xi:include href='http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.R ml'/>
FC.8557.xml'/> <xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8655.x
<!-- DetNet PS --> ml'/>
<xi:include href='http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.R
FC.8655.xml'/> <reference anchor="RFC9912" target="https://www.rfc-editor.org/info/rfc9912">
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<xi:include href='http://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference. <title>Reliable and Available Wireless (RAW) Architecture</title>
I-D.ietf-raw-architecture.xml'/> <author initials="P." surname="Thubert" fullname="Pascal Thubert" role="edit
or">
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<seriesInfo name="RFC" value="9912"/>
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<references><name>Informative References</name> <references><name>Informative References</name>
<xi:include href='http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.R <xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9030.x
FC.9030.xml'/> <!-- 6Tisch Archi --> ml'/>
<xi:include href='http://xml2rfc.tools.ietf.org/public/rfc/bibxml/referenc <xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8480.x
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<xi:include href='http://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC. <xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9372.x
9372.xml'/> ml'/>
<xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9033.x
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erence.RFC.8938.xml'/> detnet-dataplane --> <xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8200.x
ml'/>
<xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6550.x
ml'/>
<xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6551.x
ml'/>
<xi:include href='https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6291.x
ml'/>
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ml'/>
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e.RFC.6550.xml'/> <!-- RPL --> <front>
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</front>
<seriesInfo name="RFC" value="9914"/>
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erence.I-D.thubert-bier-replication-elimination.xml'/> --> r" role="editor">
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rence.I-D.thubert-6lo-bier-dispatch.xml'/ --> </author>
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er-ietf-mpls/"> -ietf-6tisch/'>
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skipping to change at line 2850 skipping to change at line 3015
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<title> <title>
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</back> </references>
</rfc> <section numbered="false"><name>Acknowledgments</name>
<t>Many thanks to the participants of the RAW WG, where a lot of the work
discussed in this document happened, and to <contact fullname="Malcolm Smith
"/> for his
review of the section on IEEE 802.11. Special thanks for post directorate an
d IESG
reviewers <contact fullname="Roman Danyliw"/>, <contact
fullname="Victoria Pritchard"/>, <contact fullname="Donald Eastlake"/>,
<contact fullname="Mohamed Boucadair"/>, <contact fullname="Jiankang
Yao"/>, <contact fullname="Shivan Kaul Sahib"/>, <contact
fullname="Mallory Knodel"/>, <contact fullname="Ron Bonica"/>, <contact
fullname="Ketan Talaulikar"/>, <contact fullname="Éric Vyncke"/>, and
<contact fullname="Carlos J. Bernardos"/>.
</t>
</section>
<!-- CONVERT WARNING: wide character found at character 2041 of the output --> <section numbered="false"><name>Contributors</name>
<t>This document aggregates articles from authors specialized in each
technology. Beyond the main authors listed on the front page, the following
contributors proposed additional text and refinements that improved the
document.</t>
<ul spacing="normal">
<li><t><contact fullname="Georgios Z. Papadopoulos"/> contributed to <xref
target="ieee-tsch"/> ("IEEE 802.15.4 Time-Slotted Channel Hopping
(TSCH)").</t></li>
<li><t><contact fullname="Nils Maeurer"/> and <contact fullname="Thomas
Graeupl"/> contributed to <xref target="ldacs"/> ("L-Band Digital
Aeronautical Communications System (LDACS)").</t></li>
<li><t><contact fullname="Torsten Dudda"/>, <contact fullname="Alexey
Shapin"/>, and <contact fullname="Sara Sandberg"/> contributed to <xref
target="fiveg"/> ("5G").</t></li>
<li><t><contact fullname="Rocco Di Taranto"/> contributed to <xref
target="IEEE802.11"/> ("IEEE 802.11").</t></li>
<li><t><contact fullname="Rute Sofia"/> contributed to <xref
target="introduction"/> ("Introduction") and <xref target="terminology"/>
("Terminology").</t></li>
</ul>
</section>
</back>
</rfc>
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