GMBH
Introduction to Time-Sensitive-Networking (TSN)
TSN Basics
Content GMBH
• What is TSN?
• Why do we need/want TSN?
• How does TSN work?
• TSN and OPC-UA
• Migration paths towards TSN/OPC-UA
• Why are FPGAs/SoCs the best choice for TSN?
• An implementation of TSN on an FPGA/SoC
• Summary
What is TSN? GMBH
Overview
• Extensions to normal Ethernet
• Synchronization
• Prioritization
• Determinism and Bounded Latency
• High Availability
• Process Network and Office Network combined
• Basically what the Real Time Ethernet Solutions
(e.g. Profinet, EtherCAT, …) do today, but in a
open standardized manner
• Set of IEEE 802.1 Standards
Why do we need/want TSN? GMBH
History of OT Communication
• We want to end the war on field communication!
• After over 40 years! Generation 3 (>Gbit/s)
Time Sensitive Networking
Generation 2 (~100Mbit/s)
Real Time Ethernet
Generation 1 (~10Mbit/s)
Fieldbuses
Generation 0 (Kbit/s)
Serial Communication
RS-232, RS-485, Profibus, Modbus, CanOpen, Profinet, Ethernet Powerlink, TSN according to IEEE 802.1 &
Descrete IO Connections DeviceNet, ControlNet, Data EtherNet/IP, EtherCAT, OPC-UA
... Highway, Sercos I/II Sercos III
... ...
Proprietary Technologies Open Standards
1970 1980 1990 2000 2010 2020
Why do we need/want TSN? GMBH
History of OT Communication
• Industrial Ethernet took over traditional
Fieldbuses in 2018 and is growing!
• The trend to Ethernet (as base for TSN) is there
* *
* Source: HMS Industrial Networks. Annual study of the industrial network market 2018
Why do we need/want TSN? GMBH
Drivers for TSN
• Open Standards for Communication
• Not driven by one large company
• Unlike e.g. Profinet (Siemens), EtherCAT (Beckhoff)…
• Vendor independence
• Easy migration path from existing networks
• Interoperability is a key driver for TSN
• ONE Network for everything
• Best effort and critical data over one network
• Vertical integration from the cloud to the
processing
Why do we need/want TSN? GMBH
TSN for automation
• Will be THE Ethernet based field bus of the future
• Enabler for Industry 4.0 and IIOT
• Vertical Integration with TSN from the cloud to the
factory floor possible
• Sensor-, actor- and control-equipment vendors
don’t need to create a version of their products
for each field bus
• One fits all
• Cheaper
Why do we need/want TSN? GMBH
TSN for automation
• Customers don’t need to choose a specific field
bus
• Better interoperability
• Multi source
• Competition between equipment vendors
• Cheaper
• No gateways needed
• Reduced complexity
Why do we need/want TSN? GMBH
TSN for automotive
• Will be the onboard bus of the future
• Enabler for autonomous cars
• Automotive Ethernet will replace the old CAN bus
• High bandwidth, low latency, high availability and
determinism are key requirements which are all
addressed by TSN
• Combined Advanced Driver Assistance Systems
(ADAS) with Infotainment and “normal” Car control
over one Network thanks to TSN
• Cleaner and cheaper cabling
Why do we need/want TSN? GMBH
TSN for utilities
• Some of the key features are already there
• E.g. Synchronization, Network redundancy
• Especially bounded latency and the possibility to
mix a “process bus” with a “station bus” in a
standardized manner by still fulfilling all
requirements are drivers for the utilities industry
to converge to TSN in the future.
How does TSN work? GMBH
Overview
• There is NOT ONE TSN standard
• A set of IEEE 802.1 standards which together form
TSN
• OSI Layer 2 functionalities
• Common-sense what the minimum set of
functionalities is to call it TSN is:
• Ethernet (Transport medium)
• Time Synchronization
• Traffic Classification (Priority Handling)
• Scheduled Traffic (Cycles and Time Slots)
How does TSN work? GMBH
Priority Handling
• IEEE 802.1Q
• VLAN (QoS)
• Distinguish between high priority, reserved and
best effort traffic classes (and even more)
• Know which traffic is important and has hard real-
time requirements, which traffic might have soft
real-time requirements and which traffic is just best
effort traffic
• It is the base for everything else in TSN
• Most of the other standards are Amendments to
IEEE802.1Q (e.g. Qbv, Qch, Qav etc.)
How does TSN work? GMBH
Synchronization
• IEEE 802.1AS (or also IEEE 1588)
• Time Synchronization
• Common time in every TSN node
• Which is the base for all other mechanisms in TSN
• Precision Time Protocol allows phase and
frequency synchronization over Ethernet
• Sub microsecond accuracy
• Widely used already (IEEE 1588)
• Every node (e.g. also Switches) must support PTP
• Boundary Clocks (multiport, switches, routers)
• Ordinary Clock (end nodes)
How does TSN work? GMBH
Scheduling
• IEEE 802.1Qbv
• Cycles and Time Slots
• Based on the synchronized time, the transmission
is divided into cycles and time slots
• Defines when a frame is allowed to be sent
depending on the traffic class
• Reserved time slots
• Guaranteed time slot to send a frame
• Best effort traffic will not block the network for real-
time traffic
• Can change order of frames (between traffic
classes)
How does TSN work? GMBH
Scheduling
• Hold a list with entries which traffic class is
allowed to send and for how long
• Repeated every cycle (cycle start can also be
defined)
• Multiple traffic classes can be active at the same
time
• Frames shall not exceed the end of a phase of a
specific traffic class
• Check if a frame can be sent before phase end
• A phase can span over multiple entries (this has to be
taken account for in the end of phase calculation)
How does TSN work? GMBH
Scheduling
• Exclusive access
• Only one traffic class per time
• Frames must end before the end of a phase
• Guard Bands might be required
High Priority Cyclic Phase Cyclic Phase
Medium Priority Reserved Phase Reserved Phase
Low Priority Best Effort Phas e Best Effort Phas e
Cycle
Cycle
N+1
N
How does TSN work? GMBH
Scheduling
• Overlapping access
• Frames must end before the end of a phase
• Priority scheduling during overlap
High Priority Cyclic Phase Cyclic Phase
Medium Priority Reserved Phase Reserved Phase
Low Priority Best Effort Phas e Best Effort Phas e
Cycle
Cycle
N+1
N
How does TSN work? GMBH
Scheduling
• Multicycle access
• Frames must end before the end of a cycle
• Priority scheduling during overlap
• Multiple phases of same class per cycle
High Priority Cyclic Phase Cyclic Phase Cyclic Phase Cyclic Phase
Medium Priority Reserved Phase Reserved Phase Reserved Phase Reserved Phase
Low Priority Best Effort Phas e Best Effort Phas e
Cycle
Cycle
N+1
N
How does TSN work? GMBH
Preemption
• IEEE 802.3br & IEEE 802.1Qbu
• Interrupting/preempting frames
• High priority frames can interrupt low priority
frames
• Low priority frame is stopped the high priority
frame sent and the low priority frame resumed
• A low priority frame can be split into multiple
fragments
• Only one frame can be preempted at the time
• Used when multiple traffic classes can be active
at the same time or no scheduling is done
How does TSN work? GMBH
Preemption
• Special Preamble an Start of Frame Delimiter
(SFD) and modified CRC to detect preemptable
and preempted frames
• Frame counter as part of Preamble & SFD
• Modified CRC per fragment (added)
• Minimal Ethernet frame size is preserved
• Min 64byte fragments (60bytes plus MCRC), max
wait delay of high priority frames
• Frames <124 can not be preempted
• Splitting done at sender, assembly of preempted
frames at receiver
• Will change the order of frames
How does TSN work? GMBH
Preemption
• Example, two traffic classes, simultaneous
sending
Frame 3
Frame 2 Frame 3
High Priority Queue Frame 1 Frame 2 Frame 3 Frame 4
Frame 6
Low Priority Queue Frame 5 Frame 6
Mux Frame Output Frame 5 (1P) Frame 1 Frame 2 Frame 3 Frame 5 (1F) Frame 4 Frame 5 (2F) Frame 6 (1P)
64 bytes
64 bytes
64 bytes
64 bytes
64 bytes
64 bytes
64 bytes
64 bytes
>=
>=
>=
>=
>=
>=
How does TSN work? GMBH
Cyclic Forwarding
• IEEE 802.1Qch
• Deterministic forwarding
• The delay depends on number of hops
• Each hop stores the frames received in one cycle
and forwards it in the next cycle
• Maximum delay of each communication path can
be easily calculated for real-time frames
• Cyclic Forwarding normally not done for best
effort traffic
• Frames will come as bursts in the next cycle
• Can change order of frames between different
traffic classes
How does TSN work? GMBH
Cyclic Forwarding
Received Frames
• Non TSN node sends
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
mixed traffic
Cycle
Cycle
Cycle
Cycle
N+1
N+2
N+3
N
• Cyclic Forwarding
Transmitted Frames Node 1
combined with Cyclic
Phase
Cyclic
Phase
Cyclic
Phase
Cyclic
Phase
Res Res Res Res
Scheduling High Priority
Medium Priority
Phase
Best Effort
Phase
1 5
Phase
2 6
Best Effort
Phase
12 13
Phase
9 10
Best Effort
Phase
15 16
Phase
17 19
Best Effort
Phase
Low Priority 3 4 7 8 11 14 18 22
• Best effort
forwarded when
Cycle
Cycle
Cycle
Cycle
N+1
N+2
N+3
N
possible (no
Transmitted Frames Node 2
Cyclic For- Cyclic
Phase
Cyclic
Phase
Cyclic
Phase
Cyclic
Phase
Res Res Res Res
warding)
High Priority Phase Phase
1 5
Phase
12 13
Phase
Best Effort Best Effort Best Effort Best Effort
Medium Priority Phase Phase
2 6
Phase
9 10
Phase
Low Priority 3 4 7 8 11 14 18
Cycle
Cycle
Cycle
Cycle
N+1
N+2
N+3
N
How does TSN work? GMBH
Traffic Shaping
• IEEE 802.1Qav
• Credit Based Shaper
• Two functionalities in one
• Avoid bursts of frames of the same traffic class or
stream
• Change priorities between different traffic classes or
streams
• Per stream or traffic class
• Can change order of frames
• Between different traffic classes
• Between different streams
How does TSN work? GMBH
Traffic Shaping
• Algorithm
• Decrement credit during sending (depending on
frame length)
• Increment credit when sending has to wait
• Allow sending only when credit is >=0
• Max and Min credit values for maximum wait time
and maximum burst lengths
• When credit >0 and not waiting to send set credit
to 0
• Increment and Decrement can be chosen
How does TSN work? GMBH
Traffic Shaping
Frame 3
Frame 2 Frame 3 Frame 5
Priority Queue 1 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5
Frame 8
Frame 7 Frame 8 Frame 1 0
Priority Queue 2 Frame 6 Frame 7 Frame 8 Frame 9 Frame 1 0
Priority Credit 1
Priority Credit 2
Frame Output Frame 1 Frame 6 Frame 2 Frame 7 Frame 3 Frame 8 Frame 9 Frame 4 Frame 5 Frame 1 0
How does TSN work? GMBH
Filtering and Policing
• IEEE 802.1Qci
• Filtering and Policing of incoming frames
• Protection against excess bandwidth usage, burst
sizes as well as against faulty or malicious
endpoints
• Fault isolation to one segment and not the whole
network
• Filter frames on ingress port based on:
• Arrival times
• Rates
• Bandwidth
How does TSN work? GMBH
Network Redundancy
• IEEE 802.1CB
• Network Redundancy
• Seamless redundancy (zero loss)
• Duplicating frames on sending to multiple paths
• Duplicate rejection on reception (take first)
• Redundancy Tagging of Frames
• Can be HSR or PRP according to IEC 62439-3 or
the scheme defined in IEEE 802.1CB which is
basically the same as HSR
How does TSN work? GMBH
Path Control and Reservation
• IEEE 802.1Qcc (& IEEE 802.1Qca)
• Stream definition, Scheduling and Bandwidth
configuration
• A scheme to configure streams in TSN nodes and
their characteristics:
• Time Slots
• Bandwidth
• Max frame sizes
• Priorities
• Talkers and Listeners say what they want
• Centralized or Decentralized configuration
How does TSN work? GMBH
Configuration and Supervision
• NETCONF/RESTCONF&YANG vs SNMP&MIB vs
OPC-UA vs LLDP
• Configuration and supervision of the TSN nodes
• Multiple schemes are currently present in the TSN
implementations
• Not 100% clear which scheme will win
• Probably NETCONF/RESTCONF&YANG for the
Network Infrastructure
• Probably OPC-UA for End Nodes (since it is there?)
• Big topic in the testbeds and standardization
How does TSN work? GMBH
And now?
• All of those TSN standards combine to a very
powerful toolset
• All standards can be combined as required
• It really depends on the application which standards
you require
• Which standards are mandatory?
• Profiles are in standardization phase to define which
are mandatory and optional for different industries
(e.g. automation (IEEE/IEC60802), automotive, …)
TSN and OPC-UA GMBH
TSN and Application Layers
• TSN handles only OSI Layer 2
• Unlike Profinet, EtherCAT etc. which define also the
communication and transport level with object
modeling and machine-machine communication
• Existing Real Time Protocols have migration
paths to use TSN as lower layer together with the
existing “proprietary” higher layer
• Profinet over TSN
• Sercos over TSN
• EtherCAT with TSN
• EtherNet/IP over TSN
• etc.
TSN and OPC-UA GMBH
Overview
• There is an Open Standard alternative
• Open Platform Communications Unified
Architecture (OPC-UA)
• Will replace in the future the “proprietary” higher
layers of the existing Real Time Ethernet protocols
• Close collaboration between the TSN working
group and the OPC foundation
• Together the build a complete field bus solution,
with TSN as the lower level and OPC-UA as the
higher level
TSN and OPC-UA GMBH
Overview
• OPC-UA defines two main things Application
• Transport mechanisms OPC-UA
• Data modeling
Transport
Ethernet TSN
• Two main communication schemes
• Client/Server 1:1 (Configuration in TSN)
• Publisher/Subscriber 1:N (Data Streams in TSN)
• Work in progress
• Most functionalities are already there
• Extensions coming bit by bit
• Many open source implementations of OPC-UA
• In ANSI C, C++, Java, .NET, etc.
Migration path towards TSN GMBH
Overview
• Commitments of the big companies behind the
existing Real Time Ethernet solutions to migrate
to TSN and OPC-UA (@TSNA conference)
1. Gateways between existing Real Time Ethernet
solutions and OPC-UA over TSN (partly done)
2. Replace the lower layer of the existing Real Time
Ethernet solutions with TSN (partly done)
3. Replace the higher layers of the existing Real Time
ethernet solutions with OPC-UA (in progress)
• The way is open for TSN/OPC-UA field
installations!
Migration path towards TSN GMBH
Interoperability Testing
• Priority number one is interoperability!
• The whole ecosystem will only be successful when
interoperability is guaranteed
• Several TSN (and OPC/UA) Testbeds to test
interoperability
• IIC TSN Testbed (link)
• LNI 4.0 TSN Testbed (link)
• Huawei TSN Testbed (link)
• UNH-IOL TSN Test Infrastructure (link)
• Etc.
Why are FPGAs/SoCs the best
GMBH
choice for TSN?
Overview
• Some of the TSN standards are still in draft state
or work in progress and there are more
standards/functionalities to come
• ASICs only for a small set of finished standards (e.g.
802.1AS, 802.1Qbv)
• FPGA Solutions can easily adapt to standard
changes and can be extended with upcoming
standards/functionalities
Why are FPGAs/SoCs the best
GMBH
choice for TSN?
Overview
• Real Time Data talkers and listener with very
short cycle times (e.g. 15.625us, 31.25us, 62.5us)
can be challenging in Software
• Real Time Data Talkers and Listeners in software will
generate high CPU load and/or require powerful
CPUs (expensive)
• Real Time Data Talkers and Listeners can be
implemented directly in the FPGA, allowing minimal
cycle times and CPU offloading (cheaper)
Why are FPGAs/SoCs the best
GMBH
choice for TSN?
Overview
• System on Chips (SoCs) (CPU and FPGA in one
chip) are especially suited for the combination of
TSN with OPC-UA
• TSN part runs in the FPGA
• Hard real-time requirements
• Configuration and OPC-UA runs on the CPU
• Soft real-time requirements
• Offloading of some functionalities from the CPU to
the FPGA possible, due to tight coupling of FPGA
and CPU (high bandwidth, low latency and DMA
data transfer over AXI)
How can a TSN switched End-node be
GMBH
implemented using FPGA technology?
Overview
• A switched End-node has normally 2.5 ports
• 2 forwarding ports
• Either for daisy chaining, redundancy or trunk ports
• 1 uplink port
• Show how a switched End-node was developed
in a modular manner supporting:
• Switching, Priority Handling, Synchronization,
Scheduling, Preemption, Cyclic Forwarding, Credit
Based Shaping, Redundancy and Filtering
How can a TSN switched End-node be
GMBH
implemented using FPGA technology?
Design
Application
OPC UA
Transport
(UDP, TCP, IP)
CPU
Data Data
RT RT
Source Talker
MAC Listener
Sink
(Sensor) (Drive)
ITF IN ITF OUT
Priority Priority
Handler Handler
and and
Arbiter Mux
Priority Priority
ITF PTP Preemption Handler Handler Preemption PTP ITF
Filter Filter
IN RX Merge and and Merge RX IN
Cycle Tag Cycle Tag
2.5 Port Switch
PHY with Redundancy PHY
(HSR/PRP/FRER)
Scheduler Scheduler
ITF PTP Preemption Priority Priority Preemption PTP ITF
and and
OUT TX Split Queues Queues Split TX OUT
Cycle Check Cycle Check
Credit PTP Credit
Schaper BC Schaper
Clock
How can a TSN switched End-node be
GMBH
implemented using FPGA technology?
Design Advantages
• This approach has several advantages:
• Step by step adding features reduced complexity
• Clean separation of features
• Features can be added and left away as needed
• Clean interfaces between modules
• Can be easily changed to an End-node (1 port)
• Future proof for new standards/features
• Also for more ports
• Can be used as TSN solution with any MAC/CPU
• Can run also as pure FPGA solution
• Talker and Listeners in the FPGA
How can a TSN switched End-node be
GMBH
implemented using FPGA technology?
Design Disadvantage
• But:
• To keep the design simple and to have no
requirements on external RAM (DDR3/DDR4…) all
FIFOs and Buffers are implemented with Block-RAM
• The size of the FIFOs depends on the Cycle duration
and Link Speed (10/100/1000Mbit/s) since in worst
case a frame has to be buffered for a whole Cycle and
the Link Speed defines the maximum number of
frames (bytes/s)
• For Cycle durations over 1ms and a Link Speed of >=1G
it might be better to use external RAM
• If the Cycle duration, Link Speed, Maximum Bandwidth
usage and even the Schedule is known at synthesis
time, buffers can be reduced quite a bit
Summary GMBH
TSN
• Set of IEEE 802.1 standards
• Open standards
• Not driven by one big company
• Defines extensions to Ethernet
• Synchronization
• Determinism and Bounded Latency
• High Availability
• Allows vertical integration
• Real-time data and best-effort data over the same
communication media
Summary GMBH
Future of real-time Ethernet
• TSN/OPC-UA will be the field communication of
the future
• In automation, automotive, utilities etc.
• Open (and open source OPC-UA)
• Migration plans from existing Real Time Ethernet
solutions towards TSN/OPC-UA
• TSN/OPC-UA is a living ecosystem which will
constantly extended
• Many prototypes do already exist!
Summary GMBH
FPGA and TSN
• FPGAs and SoCs are currently the devices of
choice to implement TSN/OPC-UA
• TSN and OPC-UA are work in progress and will be
changed and extended
• FPGAs allow offloading of Tasks from the CPU to
the FPGA
• Short cycles and Talkers and Listeners in the FPGA
• TSN solutions can be designed in a modular level
• Only instantiate what will be needed depending on
the application
GMBH
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