EDEN Projet TSN Training TSN for embedded systems

EDEN ProjectTSN Training

Marc Boyer (ONERA)

Pierre Julien Chaine (AD&S)

Outline

1 Introduction

2 Element of contexts

3 Per topic overview

4 Bibliography

EDEN / TSN Training

Introduction

TSN is not a technology

TSN is the name of a IEEE task group of the IEEE 802.1 Working GroupTSN : Time-Sensitive Networkinghttp://ieee802.org/1/pages/tsn.htmlhttps://1.ieee802.org/

Documents : Naming : 802.1Q, 802.1ad, and 802.1Qat...From one up to even four letters after 802.1

Uppercase : standardsLower-case : amendments-REV : revision (more extensive changes to the existing text than can beundertaken in an amendment)

Document Access :Working documents : need to be member (≈)Published standard :

≈ free after 6 months : �IEEE Standards runs a Get IEEE802 program thatallows anyone to download the standards for free, 6 months after publication.�Or buy it

2/29EDEN / TSN Training Boyer, Chaine September 25th, 2020

http://ieee802.org/1/pages/tsn.html

https://1.ieee802.org/

https://ieeexplore.ieee.org/browse/standards/get-program/page/

Outline

1 Introduction

2 Element of contextsEthernet frameSome numbersBouding delays


4 Bibliography

EDEN / TSN Training

Element of contexts

Ethernet frame

Ethernet frame(s)

Address : 6 Bytes / 48 bits

EtherType : size (if ≤ 1500) or encapsulated protocol

802.1Q Header : Tag protocol identi�er (TPID) = 0x8100Priority code point (PCP) : 3 bits / 0-7Drop eligible indicator (DEI) : 1 bitVLAN identi�er (VID) : 12-bits0x000 : no VLAN / 0xFFF : forbidden / 4,094 VLANs

Payload : 60-1500 Bytes

CRC/FCS : the frame check sequence (FCS) is a four-octet cyclicredundancy check (CRC)

IFG/IPG : Inter Frame Gap aka Inter Packet Gap


Outline

1 Introduction



4 Bibliography

EDEN / TSN Training

Element of contexts

Some numbers

Some magnitude numbers : e�ciency

E�ciencyBit rate is of importance, but which part is really usable ?E�ciency = payload

medium use

Ethernet e�ciency (units in bytes) :

Overhead : 8+6+6+4+2+4+12= 42

Minimal payload : 42

Ethernet packet + IFG : 84 Bytes � 1542 Bytes1

42+42≈ 1, 2%, 42

42+42= 50%, 1500

1500+42≈ 97%

Encapsulation :IP overhead : 20UDP overhead : 16


EDEN / TSN Training

Element of contexts

Some numbers

Some magnitude numbers : transmission time

Link speed 1B 64B 143B 1542B

10Mbit/s 0.8µs 51.2µs 114µs 1.23ms100Mbit/s 80ns 5.12µs 11.4µs 0.123 ms1Gbit/s 8ns 0.512µs 1.14µs 12.3 µs10Gbit/s 0.8ns 51.2ns 0.114µs 1.23 µs

Table � Emission times

Light speed30 cm/ns

1.5m in 51 nsSignal speedCommon value≈ 60% light

speed [1, �N.6]


Outline

1 Introduction



4 Bibliography

EDEN / TSN Training

Element of contexts

Bouding delays

Flow speci�cation and network performances

average vs. maximal valuevalue distribution

�ow common characteristicsthroughput : stabilityburst : delayexample : number of vehicles on aroad, per year, per day, between5pm and 7 pm...

the token bucketthroughput r, burst bon any observation interval ofduration d, the data amount is lessthan

b+ d · r (1)


EDEN / TSN Training

Element of contexts

Bouding delays

The problem of cyclic dependencies

The waiting time of R in queue 1 depends onthe �ow characteristics of R (known) and of G' that depends onthe �ow characteristics of G (known) and of B' that depends onthe �ow characteristics of B (known) and of R' that depends onthe waiting time of R in queue 1...


Outline

1 Introduction


3 Per topic overviewTime synchronizationUltra reliabilityBounded low latencyCon�guration

4 Bibliography

EDEN / TSN Training

Per topic overview

The TSN promise

Figure � TSN Overview, J. Farkas [2]


Outline

1 Introduction



4 Bibliography

EDEN / TSN Training

Per topic overview

Time synchronization

802.1AS Time synchronization

802.1AS, based on IEEE 1588 (aka PTP) previous version in 2011, WG2016-2019, updated in 2020 (802.1AS-Rev is now 802.1AS)

notion of Grand Master (GM) : clock source

a better 802.1AS, in particularredundancy : on paths and GMsbut not all kind of faultsnot considering �instability of the Grandmaster Clock, such as time glitches,excess jitter, or wander...� [16, 7.2.4.3], c©2020 IEEE.

principleselect the �best� GMmeasure node-to-node delay (regular exchanges)GM sends it clock, slaves correct local clock

warning : don't forget synchronization messages in the network design


EDEN / TSN Training

Per topic overview

Time synchronization

Measuring propagation delay

Objective : compute d

Hypotheses :t ideal physical timec(t) clock on initiator attime tc(t) ≈ (1 + ε)t+ o

ε clock drift on initiatoro clock o�set

c′(t) ≈ (1 + ε′)t+ o′

Computation

2D = (c(t4) − c′(t3)) − (c(t1) − c

′(t2))

= d+ d′+ ε(t4 − t1) + ε

′(d− d

′+ t1 − t4)

D ≈d+ d′

2≈ d

t1 Pdelay_Req

t2

t3

Pdelay_R

esp,c′ (t2)

t4

Pdelay_R

esp,c′ (t3)

d

d′


Outline

1 Introduction



4 Bibliography

EDEN / TSN Training

Per topic overview

Ultra reliability

VLAN (802.1Q pre-TSN)

Based on a Filtering Data Base (FDB, [1, � 8.8])

Associate to each (port,VID) a status yes/no

When a frame with VID V is received on port P and VID V, drop the frameif (P,V)=no ([1, � 8.6.2 Ingress �ltering])

De�nes the subset of ports where the frame could be forwarded ([1, � 8.6.3Frame �ltering])

Then does the same checking as at ingress for all potential output ports ([1,� 8.6.4 Egress �ltering])


EDEN / TSN Training

Per topic overview

Ultra reliability

802.1Qci : Per-Stream Filtering and Policing � PSFP

actions done at reception (beforequeuing, after VLAN checking)

per stream identi�cation !

set the tra�c class (IPV � internalpriority value)

can drop out of contract frames

also a local GCL

Omitted for copyright reasons.

Figure � PSPF architecture [3, Fig. 8-12],c©2017 IEEE


EDEN / TSN Training

Per topic overview

Ultra reliability

802.1CB : Frame Replication and Elimination for Reliability � FRER

Figure � FRER Illustration, [4, Fig. 7-1]

Frame duplication/replication

Elimination can be done inside the network

Can lead to out-of-order delivery


EDEN / TSN Training

Per topic overview

Ultra reliability

802.1Qca : IS-IS Path Control and Reservation � PCR

It's about routing

Automatic Ethernet routing :Spanning Tree (LAN)IS-IS Shortest Path Tree (ISP)

802.1QcaExplicit path controlBased on existing protocols


Outline

1 Introduction



4 Bibliography

EDEN / TSN Training

Per topic overview

Bounded low latency

Latency sources

Store and forward =⇒ (transmission + propagation) per hop

Queuing delay depends on tra�c load : no simple �time & space partitioning� (samepb in AFDX)

TSN o�ers mechanisms to guarantee performances by

limiting amount of interferencetaking interference into account when computing QoS


EDEN / TSN Training

Per topic overview

Bounded low latency

802.1DC : a global QoS overview

802.1DC is still in draft version (d1.1)

802-1DC is made of two materials :1 QoS guide : de�nition related to QoS, global overview of QoS-related

mechanismsEx : �The purpose of this Clause 6 is to serve as a guide to the reader tounderstand the model for Quality of 4 Service (QoS) provision in IEEE Std802.1Q-2018.� [5, � 6] c©2019 IEEE

2 QoS in end-systems, �rewall, NAT, etc�This standard speci�es procedures and managed objects for Quality of Service(QoS) features speci�ed in 19 IEEE Std 802.1Q, such as (...) in a networksystem which is not a bridge.� [5, � 1.1] c©2019 IEEE


EDEN / TSN Training

Per topic overview

Bounded low latency

Static priority

Basic behavior

Tra�c class #7 (≈ queue) has the higher priority

Limitscan create starvation of lower priority levelspartialy solved by 802.1Qci (Per-stream �ltering and policing)non-preemptionpartialy solved by 802.1Qbu + 802.3br


EDEN / TSN Training

Per topic overview

Bounded low latency

802.1Qaz : Bandwidth Sharing (SP/WRR, SP/DRR... � pre-TSN)

Enhanced Transmission Selection forBandwidth Sharing Between Tra�cClasses (aka ETS)

802.1Qaz, 2011 (pre-TSN)

Simple hierarchical scheduling : Staticpriority + Round-Robin-like

Introduced for data centers

Bandwidth Sharing isimplementation-de�ned

WRR cited in the standardDRR used in Linuxnot able to �nd choice of Cisco,Juniper...

Network calculus models exist[6, 7, 8, 9], but not comparison withother mechanisms TSN not done


EDEN / TSN Training

Per topic overview

Bounded low latency

802.1Qav : Credit-Based Shaped (CBS)

�Forwarding and Queuing Enhancements forTime-Sensitive Stream � FQTSS�

802.1Qaz, 2011 (AVB, pre-TSN)

CBS shaper is optionnal

Each CBS shaper has a �slope� s parameter(in bit/s)

A credit increases when the queue waits, anddecreases when the queue transmits

It limits the associated queue to throuput s

Its shapes/spreads/smoothes the output

Designed toavoid starvationlimit jitter

Network calculus models exist [10, 11]


EDEN / TSN Training

Per topic overview

Bounded low latency

802.1Qaz + 802.1Qav : ETS+CBS


EDEN / TSN Training

Per topic overview

Bounded low latency

802.1Qbv : Time Aware Shaper � TAS

�Enhancements for Scheduled Tra�c�

A gate is associated to each queue

The gate is either open or closed

A global cyclic schedule (Gate Control List �GCL), w.r.t local clock

Building schedule is out of standard

�Exclusive gating� ≈ one gate opened at atime

Integration with GCL : update of creditevolution rules

End-to-end TT schedule requiresglobal build of local schedulessynchronisation of local clocks (eg.802.1AS)


EDEN / TSN Training

Per topic overview

Bounded low latency

802.1Qch : Cyclic Queuing and Forwarding � CQF

Not a new �mechanism� : based on 802.1Qci (Filtering) and 802.1Qbv (TimeAware Shaper)

Divide time into time intervals of common length T

Frames received in one interval are forwarded in the next one

Global synchronisation =⇒ Low jitter (2T), simple delay computation (T ×nb of hops)


EDEN / TSN Training

Per topic overview

Bounded low latency

802.1Qcr : Asynchronous Tra�c Shaping � ATS

Still in Draft version (19 May 2020 � 802.1Qcr, Draft 2.3)

Queue waiting create jitter

ATS introduces delay to absorb the jittercomputes a �Eligibility Time� per frame

a local value (no global synchronisation)token-bucket parametersuse some share variables between ATS schedulers

head of queue can not be selected before this Eligibility Time


EDEN / TSN Training

Per topic overview

Bounded low latency

ATS : implementation and equivalent model

Complexity relies in computattion of �Eligibility Time�

Computed in order to be equivalent to group reshaping (token bucket) withaggregate queuing

A major theoretical breakthroughreshaping comes for freeavoid cyclic dependency problem

A few technical attention pointslatency performances done on equivalent modelno proof of equivalence up to nowrequiring upstream information


EDEN / TSN Training

Per topic overview

Bounded low latency

802.3br & 802.1Qbu : Preemption

Two classes of queues : express andpreemptable

An express frame ready fortransmission can fragment apreemptable frame being transmited

A frame of size ≤ 143B can not bepreemptedreduced the non-preemption cost bya factor of ≈ 10

Limitsa two levels only systempreemption has overhead (12 B +12B IFG + 8B preamble)

SMD : Start mPacket Delimiter

SMD-Sx : SMD Start x ∈ [0, 1, 2, 3]

SMD-Cx : SMD Continuationx ∈ [0, 1, 2, 3]


EDEN / TSN Training

Per topic overview

Bounded low latency

QoS mechanisms in a bridge


Outline

1 Introduction



4 Bibliography

EDEN / TSN Training

Per topic overview

Con�guration

802.1Qat : Stream Reservation Protocol � SRP

AVB group, Published in 2010, included in 802.1Q-2018

SRP utilizes three signaling protocols

MMRP : Talker registrationsMVRP : declare membership in a VLAN where a Stream is being sourcedMSRP : signaling protocol to reserve network resource

what is a stream ? [12][� 3]

Stream : A unidirectional �ow of data from a Talker to one or more ListenersListener : The end station that is the destination, receiver, or consumer of astream.Talker : The end station that is the source or producer of a stream.

stream characteristics

StreamID : �A 64-bit field that uniquely identifies a stream.�, within [12, � 35.2.2.8.2] c©2010 IEEE

MAC Address : 48 bitsUnique ID : 16 bits, used to distinguish among multiple streams sourced by thesame System

Tra�c Speci�cation (TSpec)MaxFrameSize : maximum frame, excluding any overheadMaxIntervalFrames maximum number of frames that the Talker may transmit inone �class measurement interval� (34.4)


EDEN / TSN Training

Per topic overview

Con�guration

802.1Qcc : Stream Reservation Protocol (SRP) Enhancements and Performance Improvements

not only an SRP improvement, but also

� 46 Time-Sensitive Networking (TSN) con�guration3 con�guration models

Fully distributed modelCentralized network/distributed user modelFully centralized model [13, � 46.1.3.2]

User/network con�guration informationdetails on interface between application on network


EDEN / TSN Training

Per topic overview

Con�guration

The YANG model(s)

MIB encode a local con�gurations

YANG o�er a global view

comes from IETF (RFC 6020, 7950)

data modelling language, like XML, JSON

TSN group de�nes YANG modules speci�c to TSN≈ one YANG module per addenda

git repository : https://github.com/YangModels/yang


https://github.com/YangModels/yang

Outline

1 Introduction



4 Bibliography

Bibliographie

[1] IEEE Standard for Local and Metropolitan Area Networks � Bridges andBridged Networks,IEEE Standard IEEE no 802.1Q (2018).

[2] J. Farkos,Standards from IEEE, IETF, 3GPP, and Beyond � ,Proc. of the TSN/A Conference 2019.

[3] IEEE Standard for Local and metropolitan area networks�Bridges andBridged Networks�Amendment 28 : Per-Stream Filtering and Policing ,Standard IEEE no 802.1Qci (2017).

[4] IEEE Draft Standard for Local and metropolitan area networks � FrameReplication and Elimination for Reliability ,Rapport Technique IEEE no 802.1CB (September 2017).

[5] IEEE Standard for Local and metropolitan area networks � Quality ofService Provision by Network Systems � Draft 1.1 ,IEEE Standard IEEE no 802.1DC/D1.1 (2019).

[6] A. Soni, X. Li, J.-L. Scharbarg et C. Fraboul,WCTT analysis of avionics Switched Ethernet Network with WRRScheduling.,Dans Proc. of the 26th International Conference on Real-Time Networksand Systems (RTNS), pp. 213�222. ACM (2018).

[7] M. Boyer, G. Stea et W. Mangoua Sofack,De�cit Round Robin with Network Calculus,Dans Proc. of the 6th International Conference on PerformanceEvaluation Methodologies and Tools (ValueTools 2012), Cargese, France(October, 9�12 2012).

[8] M. Boyer, N. Navet, M. Fumey, J. Migge et L. Havet,Combining static priority and weighted round-robin like packet schedulingin AFDX for incremental certi�cation and mixed-criticality support,Dans Proc. of the 5th European Conference for Aeronautics and SpaceSciences � Real Time Avionics and Networks Session (EUCASS 2013),Munich, Germany (July 1st�5th 2013).

[9] A. Soni, X. Li, J.-L. Scharbarg et C. Fraboul,Integrating O�set in Worst Case Delay Analysis of Switched EthernetNetwork With De�cit Round Robbin,Dans Proc. of 23rd IEEE International Conference on EmergingTechnologies and Factory Automation (ETFA), vol. 1, pp. 353�359. IEEE(2018).

[10] J. A. Ruiz de Azua et M. Boyer,Complete modelling of AVB in Network Calculus Framework,Dans Proc. of the 22nd Int. Conf. on Real-Time Networks and Systems(RTNS 2014), Versailles, France (October 8-10 2014).

[11] L. Zhao, F. He et E. Li,Improving Worst-Case Delay Analysis for Tra�c of Additional StreamReservation Class in Ethernet-AVB Network,MDPI Sensors, 18 (11) (2018).

[12] Virtual Bridged Local Area Networks Amendment 14 : Stream ReservationProtocol (SRP),Rapport Technique IEEE no IEEE 802.1Qat (2010).

[13] IEEE Standard for Local and metropolitan area networks� Bridges andBridged Networks � Amendment 31 : Stream Reservation Protocol (SRP)Enhancements and Performance Improvements,Standard IEEE no 802.1Qcc (2018).

[14] MEF,Subscriber Ethernet Service Attributes,Rapport Technique MEF Forum no MEF 10.4 (2018).

[15] Frame Replication and Elimination for Reliability � Amendment :Extended Stream identi�cation functions � Draft D0.7 ,Rapport Technique IEEE no P802.1CBdb/D0.7 (2020).

[16] Local and metropolitan area networks - Timing and Synchronization forTime-Sensitive Applications in Bridged Local Area Network,Rapport Technique IEEE no IEEE 802.1AS (2020).

[17] S. S. Craciunas, R. S. Oliver, M. Chmelík et W. Steiner,Scheduling Real-Time Communication in IEEE 802.1Qbv Time SensitiveNetworks,Dans Proceedings of the 24th International Conference on Real-TimeNetworks and Systems (RTNS'16), RTNS'16, pp. 183�192, New York,NY, USA, Association for Computing Machinery (2016).

EDEN Projet TSN Training TSN for embedded systems

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