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).

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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

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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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