https://www.onera.fr/sites/default/files/323/Slides-TSN-Training-public.pdf
EDEN Project
TSN Training
Marc Boyer (ONERA)
Pierre Julien Chaine (AD&S)
2 Element of contexts
3 Per topic overview
4 Bibliography
EDEN / TSN Training
TSN is not a technology
TSN is the name of a IEEE task group of the IEEE 802.1 Working Group
TSN : Time-Sensitive Networking
Documents : Naming : 802.1Q, 802.1ad, and 802.1Qat...
From one up to even four letters after 802.1
Uppercase : standards
Lower-case : amendments
-REV : revision (more extensive changes to the existing text than can be
undertaken in an amendment)
Document Access :
Working documents : need to be member (≈)
Published standard :
≈ free after 6 months : IEEE Standards runs a Get IEEE802 program that
allows anyone to download the standards for free, 6 months after publication.
Or buy it
2/29EDEN / TSN Training Boyer, Chaine September 25th, 2020
Ethernet frame
Some numbers
Bouding delays
Element of contexts
Ethernet frame(s)
Address : 6 Bytes / 48 bits
EtherType : size (if ≤ 1500) or encapsulated protocol
802.1Q Header : Tag protocol identier (TPID) = 0x8100
Priority code point (PCP) : 3 bits / 0-7
Drop eligible indicator (DEI) : 1 bit
VLAN identier (VID) : 12-bits
0x000 : no VLAN / 0xFFF : forbidden / 4,094 VLANs
Payload : 60-1500 Bytes
CRC/FCS : the frame check sequence (FCS) is a four-octet cyclic
redundancy check (CRC)
IFG/IPG : Inter Frame Gap aka Inter Packet Gap
3/29EDEN / TSN Training Boyer, Chaine September 25th, 2020
Some magnitude numbers : eciency
Bit rate is of importance, but which part is really usable ?
Eciency = payload
medium use
Ethernet eciency (units in bytes) :
Overhead : 8+6+6+4+2+4+12= 42
Minimal payload : 42
Ethernet packet + IFG : 84 Bytes  1542 Bytes
≈ 1, 2%,
= 50%,
≈ 97%
Encapsulation :
IP overhead : 20
UDP overhead : 16
4/29EDEN / TSN Training Boyer, Chaine September 25th, 2020
Some magnitude numbers : transmission time
Link speed 1B 64B 143B 1542B
10Mbit/s 0.8µs 51.2µs 114µs 1.23ms
100Mbit/s 80ns 5.12µs 11.4µs 0.123 ms
1Gbit/s 8ns 0.512µs 1.14µs 12.3 µs
10Gbit/s 0.8ns 51.2ns 0.114µs 1.23 µs
Table  Emission times
Light speed
30 cm/ns
1.5m in 51 ns
Signal speed
Common value
≈ 60% light
speed [1, N.6]
5/29EDEN / TSN Training Boyer, Chaine September 25th, 2020
Flow specication and network performances
average vs. maximal value
value distribution
ow common characteristics
throughput : stability
burst : delay
example : number of vehicles on a
road, per year, per day, between
5pm and 7 pm...
the token bucket
throughput r, burst b
on any observation interval of
duration d, the data amount is less
b + d · r (1)
6/29EDEN / TSN Training Boyer, Chaine September 25th, 2020
The problem of cyclic dependencies
The waiting time of R in queue 1 depends on
the ow characteristics of R (known) and of G' that depends on
the ow characteristics of G (known) and of B' that depends on
the ow characteristics of B (known) and of R' that depends on
the waiting time of R in queue 1...
7/29EDEN / TSN Training Boyer, Chaine September 25th, 2020
Time synchronization
Ultra reliability
Bounded low latency
Per topic overview
The TSN promise
Figure  TSN Overview, J. Farkas [2]
8/29EDEN / TSN Training Boyer, Chaine September 25th, 2020
802.1AS Time synchronization
802.1AS, based on IEEE 1588 (aka PTP) previous version in 2011, WG
2016-2019, updated in 2020 (802.1AS-Rev is now 802.1AS)
notion of Grand Master (GM) : clock source
a better 802.1AS, in particular
redundancy : on paths and GMs
but not all kind of faults
not considering instability of the Grandmaster Clock, such as time glitches,
excess jitter, or wander... [16, 7.2.4.3], c 2020 IEEE.
elect the best GM
measure node-to-node delay (regular exchanges)
GM sends it clock, slaves correct local clock
warning : don't forget synchronization messages in the network design
9/29EDEN / TSN Training Boyer, Chaine September 25th, 2020
Measuring propagation delay
Objective : compute d
Hypotheses :
t ideal physical time
c(t) clock on initiator at
time t
c(t) ≈ (1 + )t + o
 clock drift on initiator
o clock oset
c0(t) ≈ (1 + 0)t + o0
2D = (c(t4) − c
(t3)) − (c(t1) − c
= d + d
+ (t4 − t1) + 
(d − d
+ t1 − t4)
D ≈
d + d0
≈ d
t1 Pdelay_Req
EDEN / TSN Training Boyer, Chaine September 25th, 2020
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 frame
if (P,V)=no ([1,  8.6.2 Ingress ltering])
Denes the subset of ports where the frame could be forwarded ([1,  8.6.3
Frame ltering])
Then does the same checking as at ingress for all potential output ports ([1,
 8.6.4 Egress ltering])
802.1Qci : Per-Stream Filtering and Policing  PSFP
actions done at reception (before
queuing, after VLAN checking)
per stream identication !
set the trac class (IPV  internal
priority 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
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
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)
Explicit path control
Based on existing protocols
Latency sources
Store and forward =⇒ (transmission + propagation) per hop
Queuing delay depends on trac load : no simple time & space partitioning (same
pb in AFDX)
TSN oers mechanisms to guarantee performances by
limiting amount of interference
taking interference into account when computing QoS
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 : denition related to QoS, global overview of QoS-related
Ex : The purpose of this Clause 6 is to serve as a guide to the reader to
understand the model for Quality of 4 Service (QoS) provision in IEEE Std
802.1Q-2018. [5,  6] c 2019 IEEE
2 QoS in end-systems, rewall, NAT, etc
This standard species procedures and managed objects for Quality of Service
(QoS) features specied in 19 IEEE Std 802.1Q, such as (...) in a network
system which is not a bridge. [5,  1.1] c 2019 IEEE
Static priority
Basic behavior
Trac class #7 (≈ queue) has the higher priority
can create starvation of lower priority levels
partialy solved by 802.1Qci (Per-stream ltering and policing)
partialy solved by 802.1Qbu + 802.3br
802.1Qaz : Bandwidth Sharing (SP/WRR, SP/DRR...  pre-TSN)
Enhanced Transmission Selection for
Bandwidth Sharing Between Trac
Classes (aka ETS)
802.1Qaz, 2011 (pre-TSN)
Simple hierarchical scheduling : Static
priority + Round-Robin-like
Introduced for data centers
Bandwidth Sharing is
WRR cited in the standard
DRR used in Linux
not able to nd choice of Cisco,
Network calculus models exist
[6, 7, 8, 9], but not comparison with
other mechanisms TSN not done
802.1Qav : Credit-Based Shaped (CBS)
Forwarding and Queuing Enhancements for
Time-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, and
decreases when the queue transmits
It limits the associated queue to throuput s
Its shapes/spreads/smoothes the output
Designed to
avoid starvation
limit jitter
Network calculus models exist [10, 11]
802.1Qaz + 802.1Qav : ETS+CBS
802.1Qbv : Time Aware Shaper  TAS
Enhancements for Scheduled Trac
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 a
Integration with GCL : update of credit
evolution rules
End-to-end TT schedule requires
global build of local schedules
synchronisation of local clocks (eg.
802.1Qch : Cyclic Queuing and Forwarding  CQF
Not a new mechanism : based on 802.1Qci (Filtering) and 802.1Qbv (Time
Aware 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)
802.1Qcr : Asynchronous Trac Shaping  ATS
Still in Draft version (19 May 2020  802.1Qcr, Draft 2.3)
Queue waiting create jitter
ATS introduces delay to absorb the jitter
computes a Eligibility Time per frame
a local value (no global synchronisation)
token-bucket parameters
use some share variables between ATS schedulers
head of queue can not be selected before this Eligibility Time
ATS : implementation and equivalent model
Complexity relies in computattion of Eligibility Time
Computed in order to be equivalent to group reshaping (token bucket) with
aggregate queuing
A major theoretical breakthrough
reshaping comes for free
avoid cyclic dependency problem
A few technical attention points
latency performances done on equivalent model
no proof of equivalence up to now
requiring upstream information
802.3br & 802.1Qbu : Preemption
Two classes of queues : express and
An express frame ready for
transmission can fragment a
preemptable frame being transmited
A frame of size ≤ 143B can not be
reduced the non-preemption cost by
a factor of ≈ 10
a two levels only system
preemption has overhead (12 B +
12B IFG + 8B preamble)
SMD : Start mPacket Delimiter
SMD-Sx : SMD Start x ∈ [0, 1, 2, 3]
SMD-Cx : SMD Continuation
x ∈ [0, 1, 2, 3]
QoS mechanisms in a bridge
802.1Qat : Stream Reservation Protocol  SRP
AVB group, Published in 2010, included in 802.1Q-2018
SRP utilizes three signaling protocols
MMRP : Talker registrations
MVRP : declare membership in a VLAN where a Stream is being sourced
MSRP : 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 Listeners
Listener : The end station that is the destination, receiver, or consumer of a
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., with
in [12,  35.2.2.8.2] c 2010 IEEE
MAC Address : 48 bits
Unique ID : 16 bits, used to distinguish among multiple streams sourced by the
same System
Trac Specication (TSpec)
MaxFrameSize : maximum frame, excluding any overhead
MaxIntervalFrames maximum number of frames that the Talker may transmit in
one class measurement interval (34.4)
802.1Qcc : Stream Reservation Protocol (SRP) Enhancements and Performa
not only an SRP improvement, but also
 46 Time-Sensitive Networking (TSN) conguration
3 conguration models
Fully distributed model
Centralized network/distributed user model
Fully centralized model [13,  46.1.3.2]
User/network conguration information
details on interface between application on network
The YANG model(s)
MIB encode a local congurations
YANG oer a global view
comes from IETF (RFC 6020, 7950)
data modelling language, like XML, JSON
TSN group denes YANG modules specic to TSN
≈ one YANG module per addenda
git repository : https://github.com/YangModels/yang
[1] IEEE Standard for Local and Metropolitan Area Networks  Bridges and
Bridged Networks,
IEEE Standard IEEE n
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 networksBridges and
Bridged NetworksAmendment 28 : Per-Stream Filtering and Policing,
Standard IEEE n
802.1Qci (2017).
[4] IEEE Draft Standard for Local and metropolitan area networks  Frame
Replication and Elimination for Reliability,
Rapport Technique IEEE n
802.1CB (September 2017).
[5] IEEE Standard for Local and metropolitan area networks  Quality of
Service Provision by Network Systems  Draft 1.1,
802.1DC/D1.1 (2019).
[6] A. Soni, X. Li, J.-L. Scharbarg et C. Fraboul,
WCTT analysis of avionics Switched Ethernet Network with WRR
Dans Proc. of the 26th International Conference on Real-Time Networks
and Systems (RTNS), pp. 213222. ACM (2018).
[7] M. Boyer, G. Stea et W. Mangoua Sofack,
Decit Round Robin with Network Calculus,
Dans Proc. of the 6th International Conference on Performance
Evaluation Methodologies and Tools (ValueTools 2012), Cargese, France
(October, 912 2012).
[8] M. Boyer, N. Navet, M. Fumey, J. Migge et L. Havet,
Combining static priority and weighted round-robin like packet scheduling
in AFDX for incremental certication and mixed-criticality support,
Dans Proc. of the 5th European Conference for Aeronautics and Space
Sciences  Real Time Avionics and Networks Session (EUCASS 2013),
Munich, Germany (July 1st5th 2013).
[9] A. Soni, X. Li, J.-L. Scharbarg et C. Fraboul,
Integrating Oset in Worst Case Delay Analysis of Switched Ethernet
Network With Decit Round Robbin,
Dans Proc. of 23rd IEEE International Conference on Emerging
Technologies and Factory Automation (ETFA), vol. 1, pp. 353359. IEEE
[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 Trac of Additional Stream
Reservation Class in Ethernet-AVB Network,
MDPI Sensors, 18 (11) (2018).
[12] Virtual Bridged Local Area Networks Amendment 14 : Stream Reservation
Protocol (SRP),
IEEE 802.1Qat (2010).
[13] IEEE Standard for Local and metropolitan area networks Bridges and
Bridged Networks  Amendment 31 : Stream Reservation Protocol (SRP)
Enhancements and Performance Improvements,
802.1Qcc (2018).
[14] MEF,
Subscriber Ethernet Service Attributes,
Rapport Technique MEF Forum n
MEF 10.4 (2018).
[15] Frame Replication and Elimination for Reliability  Amendment :
Extended Stream identication functions  Draft D0.7,
P802.1CBdb/D0.7 (2020).
[16] Local and metropolitan area networks - Timing and Synchronization for
Time-Sensitive Applications in Bridged Local Area Network,
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 Sensitive
Dans Proceedings of the 24th International Conference on Real-Time
Networks and Systems (RTNS'16), RTNS'16, pp. 183192, New York,
NY, USA, Association for Computing Machinery (2016).