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802.1 TSN over 802.11with updates from developments in 802.11be
IEEE 802.1 Plenary, November 2020
Dave Cavalcanti and Ganesh Venkatesan
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References to IEEE802.11 documents
▪ TSN Traffic stream classification over 802.11 (VLAN tag in TCLAS)
▪ Support for 802.1AS-2020 over 802.11 with Timing Measurement and Fine Timing Measurement protocols (IEEE Std. 802.11-2016)
▪ Support for Enhancements For Transit Links Within Bridged Networks (802.11ak features in pIEEE802.11 REVm D5.0)
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802.11 in an 802.1 TSN network
▪ Figure describing an end-to-end TSN network 802TSN Bridges, CNC, CUC, 802.11 AP with support for 802.11ak
CUC
CNC
End Device
End Device
End Device
End Device
TSN Bridge
Wireless TSN Access Point
Wireless TSN Domain
Wired TSN Domain
TSN features that can already operate over 802.11: 802.1AS time sync, Qbv, CB… 4.3.28.3.3 Infrastructure BSS with general links and Figure 4-15 in
IEEE P802.11 REVmd D5.0
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802.1AS Time Synchronization over 802.11
TSN Talker TSN Listener(Wi-Fi Client)
TSN Bridge802.11 Wireless TSN
Link
TSN-enabled Access Point
• A PLC’s control cycle can be synchronized with other PLCs/Sensors/Actuators over 802.11 links
• Time-Aware traffic shaping (e.g. 802.1Qbv) operate based on the same reference clock can be applied over 802.11 links
Synchronization across wired-wireless TSN
Ref: K. Stanton, Tutorial: The Time-Synchronization Standard from the AVB/TSN suite IEEE Std 802.1AS™-2011, IEEE 802 Plenary, July 2014
802.11 defined MAC specific support for 802.1AS
• Timing Measurement (TM) – 802.11-2012
• Fine Timing Measurement (FTM) – 802.11-2016
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802.11 modes for supporting 802.1AS802.1AS time synch over 802.11 TM 802.1AS time synch over 802.11 FTM
802.11 action frames are used to compute:
LinkDelay = [(t4-t1)-(t3-t2)]/2
NeighborRateRatio = (t1’-t1)/(t2’-t2)
TimeOffset = [(t2-t1)-(t4-t3)]/2
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Experiments with 802.1AS over 802.11 TM
CRB-A
NUC 1 NUC 2
CRB-B
I210 Controller
Ieee 1588
Timestamp AnalysisGM
I210 Controller
Ieee 1588
Timestamp
Analysis
I21
0 C
on
troller
IEEE 802.1AS
Intel WiFi 9560
IEEE1588
1 PPS Signal
I21
0 C
on
troller
IEEE 802.1AS
Intel WiFi 9560
IEEE1588
1 PPS Signal
AP STA
Apollo Lake
CRB
Apollo Lake
CRB
Gemini Lake
CRB
Gemini Lake
CRB
TGM TNodeD
T80211M T80211S
T80211S - T80211M
TNodeD- TGM
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Time-Aware Shaping (802.1Qbv) over 802.11A Time-aware (Qbv) scheduler defines when gates open/close to ensure time-sensitive frames are not interfered by other (Best-effort) traffic
STA 1
T T T T
T T T TT T T T
Shared medium
STA 2
Queues/Traffic ClassesAP
A Qbv schedule can operate on top of one of the 802.11 MAC (e.g. EDCA or 802.11ax Trigger based access modes)
The 802.11 network must execute the schedule and deliver frames with bounded latency
The 802.11 MAC access delay will impact achievable latency bounds and capacity/efficiency
A scheduled operation (e.g. based on 802.11ax triggered access) can provide more predictable latencies/higher efficiency
Further enhancements are being developed as part of 802.11be
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802.1Qbv over 802.11 (EDCA) test
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5ms 40ms 5ms
50 ms
GuardBest EffortPriority
Qb
vSc
hed
ule
Priority Traffic: 100 byte packet every 50 ms with background BE from 1Mbps to 100 Mbps and Qbv cycle time of 50 ms
4 Q
ue
ue
s
Test Setup for Qbv over 802.11ac/Wi-Fi 5
AP
Talker
Client
ListenerDUTs
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802.1Qbv Scheduling over 802.11ax
Schedule configuration: the CNC delivers a schedule to the 802.11ax AP (supporting TSN)
The AP uses the trigger-based mode to deliver the data according to the worst-case latency and reliability
Simulation Assumptions:
20 MHz channel, SISO, 100 Bytes packets, Channel model E, STAs randomly distributed in a 50 m radio, latency-optimized scheduling strategy, managed network (no OBSS).
9
18
28
35
45
0
10
20
30
40
50
1 1.5 2 2.5 3
Ca
pa
city
for
a P
DR
=99
.99
9%
UL Latency Bound (msec)
Capacity vs. Latency bound (msec)for Target PDR = 99.999%
Low latency/high reliability and capacity tradeoffs can be achieved
TF
.
.
.
DL BA
UL PPDU
AIFS + CWSIFS SIFS
Pre
amb
le
Resource Unit (RU)
Trigger Frame
Downlink Block Ack
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802.1CB FRER over 802.11
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WTSN Talker WTSN ListenerChannel 9
Channel 157
Channel 9
Channel 157
Time-sensitive traffic flow: 20 frames (50 Bytes) per sec
Tx STA 1 Rx STA 2Channel 9 Channel 9
Interfering traffic on channel 9 (3 Mbps)
Upper layer
802. 11 MAC
802.11 PHY
Link/Channel1 Link/Channel 2
802. 11 MAC
802.11 PHY
802.1CB FRER
Sequence generation functionSequence recovery function
Frame replication
Frame elimination
switch A
switch B
Talker Listener
AP
Multiple l inks/Channels
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802.11be Key Enhancements320 MHz channels
4096-QAM16 spatial streams
Multi-link operationMulti-AP operation
Deterministic Low latency/TSN support
802.11be features supporting TSN
AP1 AP2 AP3
Multi-link device A (AP)
STA1 STA2
Multi-link device (STA)
Data
Data
Link 1 (Channel X, Band Y)
Link 2 (Channel L, Band M)
STA3
Enables redundancy at the 802.11 MACNew tools to avoid congestion delay
MLO (Multi-Link Operation)
SharingAP
Shared AP1
Shared AP2
Source: C. Cordeiro [1]
Multi-AP features
Different flavors of multi-AP solutions are being considered (MAC-driven and PHY-driven)
Extending coordination beyond a single BSS to provide more control over key performance metrics
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Enhanced Determinism in 802.11be
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• Wi-Fi 6 can achieve single-digit millisecond latency, but the worst-case latency may still vary under congestion
• With multi-link operation, multi-AP and 320 MHz channels in Wi-Fi 7, latency will be reduced even further
• However, to provide more predictable low latency (enhanced determinism), new protocol enhancements need to be defined LL
LL
VO
VO VI
VI BE
BE
Time-Aware Function
SME-MLME SAP
Pause/Resume EDCAFs
https://mentor.ieee.org/802.11/dcn/20/11-20-0418-03-00be-low-latency-service-in-802-11be.pptx
Potential features for deterministic low latency
▪ QoS provisioning model for low latency reliable traffic streams
▪ Define dedicated, low-latency (LL) and reliable access category
▪ Time-Aware (Qbv) scheduled access integrated in the MAC with protected service periods
▪ Limit TXOP duration across networks and packet preemption
13
Potential areas to extend 802.11-802.1 TSN collaboration ▪ Configuration and adaptation of time-aware (802.1Qbv) scheduling over
wireless/802.11
• Should 802.1Qbv be aware of wireless links (with variable capacity)?
• Mapping of Qbv schedule to 802.11 QoS/TSPEC and admission control (ongoing discussions in 11be)
▪ 802.1CB over 802.11be MLD
• the MLD enables frame duplication and elimination within the 802.11 MAC (part of 802.1CB functionality)
• How to leverage the 802.11be MLD for optimized FRER with 802.1CB and 802.11be?
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Next steps
▪ TSN support is part of the 802.11be PAR
• Basic functionalities are being defined in 802.11be R1 (MLD, low latency/QoS features being discussed)
• 802.11be Draft 0.1 available
• Additional TSN support features will be discussed in R2 (starting soon)
• Opportunities to enhance TSN support (redundancy, preemption, …) and coordination with 802.1 TSN specifications
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