Time Sensitive Networks for Flexible
Manufacturing Testbed
Characterization and Mapping of Converged
Traffic Types
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Characterization and Mapping of Converged Traffic Types
Table of Contents
The IIC’s Time-Sensitive Networks for Flexible Manufacturing Testbed .................................. 4
TSN Overview ............................................................................................................................... 4
TSN Benefits ................................................................................................................................. 5
Overview of Traffic Types .............................................................................................................. 6
Vertical and Horizontal .................................................................................................................. 6

Traffic Type Characteristics .................................................................................................... 8
Traffic Type Descriptions ..................................................................................................... 11
Isochronous ................................................................................................................................ 11
Cyclic …………………………………………………………………………………………………………………………………………..12
Events......................................................................................................................................... 15
Events—Alarms and Operator Commands ...................................................................................... 16
Events—Control................................................................................................................................ 17
Configuration & Diagnostics ........................................................................................................ 17
Network Control ......................................................................................................................... 19
Best Effort................................................................................................................................... 20
Video 21
Audio/Voice ................................................................................................................................ 22
Traffic Type Characteristics Summary .......................................................................................... 23

Mapping Traffic Types ......................................................................................................... 24
Mapping Overview ...................................................................................................................... 24
Recommendation Types ................................................................................................................... 25
TSN Mechanisms .............................................................................................................................. 25
Mapped Device Types ...................................................................................................................... 30
Traffic Types Mappings................................................................................................................ 31
Mapping Traffic Type: Network Control ........................................................................................... 31
Mapping Traffic Type: Isochronous .................................................................................................. 32
Mapping Traffic Type: Cyclic............................................................................................................. 35
Mechanisms for Implementing Option Strict Priority: ................................................................ 37
Mechanisms for Implementing Option Scheduled Traffic: ......................................................... 38
Mapping Traffic Type: Events ........................................................................................................... 38
Traffic Type: Events—Control Events .......................................................................................... 38
Traffic Type: Events—Alarms and Operator Commands ............................................................ 39
Mapping Traffic Type: Configuration & Diagnostics ......................................................................... 40
Mapping Traffic Type: Best Effort..................................................................................................... 41
Mapping Traffic Types: Video & Audio ............................................................................................ 41
Mapping Summary ...................................................................................................................... 42

Summary ............................................................................................................................. 43
Authors and Legal Notice ..................................................................................................... 43

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FiguresFigure 1: Exclusive gating for Isochronous traffic. ...................................................................................... 35
Figure 2: Exclusive gating for Cyclic traffic. ................................................................................................. 37

TablesTable 1: Table: Set of IEEE TSN Enhancements ............................................................................................. 5
Table 2: Traffic Type Characteristic............................................................................................................. 11
Table 3:Traffic Type Characteristics - Isochronous ..................................................................................... 12
Table 4:Traffic Type Characteristics - Cyclic ................................................................................................ 14
Table 5: Traffic Type Characteristics – Events – Alarms and Operator commands .................................... 16
Table 6: Traffic Type Characteristics – Events - Control ............................................................................. 17
Table 7: Traffic Type Characteristics – Configuration & Diagnostics .......................................................... 18
Table 8: Traffic Type Characteristics – Network Control ............................................................................ 19
Table 9: Traffic Type Characteristics – Best Effort ...................................................................................... 20
Table 10: Traffic Type Characteristics - Video............................................................................................. 21
Table 11: Traffic Type Characteristics – Audio/Video ................................................................................. 22
Table 12: Summary of Traffic Type characterizations ................................................................................ 23
Table 13: Description of TSN Mechanisms ................................................................................................. 30
Table 14: Summary of Traffic Type Mappings ............................................................................................ 42

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This document describes application traffic types that are found in industrial and process control
systems and supported in the Industrial Internet Consortium’s Time Sensitive Networks for
Flexible Manufacturing testbed, including different types of critical control traffic and othertraffic that may be in a manufacturing network. The IEEE 802.1Q specification, Annex lists traffic
types as a means to structure network transmission priority and packet-drop preference. We
enhance those traffic types by adding types found in typical manufacturing Industrial Automation
and Control Systems (IACS), with a list of characteristics to describe them precisely. We thenrecommend IEEE 802.1 TSN mechanisms to support these traffic types in a converged network.

THE IIC’S TIME-SENSITIVE NETWORKS FOR FLEXIBLE MANUFACTURING TESTBEDThe Industrial Internet Consortium (IIC), with over 200 members, aims to deliver a trustworthy
Industrial Internet of Things (IIoT) in which the world’s systems and devices are securely
connected and controlled to deliver transformational outcomes. The IIC has three main areas ofactivity: engage IIoT communities (ecosystem), develop guidance with technology and security
architectures and drive innovation through testbeds. In 2015, the IIC Steering Committee
approved the establishment of the Time-Sensitive Networks for Flexible Manufacturing testbed
to display the value and readiness of time-sensitive networks to support real-time control andsynchronization of high-performance machines. It has over 25 participants from a range ofcompanies including chip vendors, IACS vendors, network infrastructure vendors, testing vendors
and certification organizations. The testbed liaises with a range of standard development
organizations including the IEEE, Avnu Alliance, OPC Foundation, IEC, ODVA, LNI4.0 and others.
By aligning adopters, technology providers and standards developers, the testbed accelerates
the adoption of this beneficial technology.

TSN OVERVIEW
Time-Sensitive Networking (TSN) enhances Ethernet (specifically IEEE 802.1 and 802.3), a
foundational piece of the “internet of things.” TSN adds a range of functions and capabilities toEthernet to make it more applicable to industrial applications that require more deterministic
characteristics than possible in previous Ethernet implementations. The table below summarizes
those enhancements.

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List of TSN Enhancements

Standard

Title
Forwarding and Queuing Enhancements for Time-Sensitive Streams
IEEE 802.1Qav
Incorporated in IEEE 802.1Q since 2009 clause 8.6.8.2 and Annex L.
Timing and Synchronization for Time-Sensitive Applications
IEEE 802.1AS-Rev
The -Rev version is in progress.
IEEE 802.1Qbu & IEEE Frame preemption
802.3br
Incorporated in IEEE 802.1Q since 2016 clause 6.7.2
Enhancements for Scheduled TrafficIEEE 802.1Qbv
Incorporated in IEEE 802.1Q since 2015 clauseStream Reservation Protocol (SRP) Enhancements and PerformanceIEEE 802.1Qcc
Improvements. Approved in 2018 and to be incorporated in October 2018
Per-Stream Filtering and Policing
IEEE 802.1Qci
Incorporated in IEEE 802.1Q since 2017 clause 8.6.5.1.2.
Frame Replication & Elimination for Reliability
IEEE 802.1CB
Approved in 2017
Table 1: Table: Set of IEEE TSN Enhancements

Automation and control systems comprise a large part of the estimated 50 billion things in IIoT,
and these systems require the various devices, including the network, to perform in a
deterministic way. The IIC’s TSN Testbed for Flexible Manufacturing applies TSN technology to a
manufacturing system to support the type of manufacturing application found in production
environments and to display its capabilities and value.

TSN BENEFITSTSN provides benefits to automation and control vendors as well as end customers, including:

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robust, reliable delivery of data,
guaranteed latency,
increased availability of network services for end-devices,
accessibility of data driving IIOT big-data analytics and machine-learning applications,
automated system configuration and management,
system composability to add sub-systems and functions to existing systems withsignificantly reduced testingeasy integration of innovations from open networks (more bandwidth, reliability andoptions) andability to converge applications and traffic on a single, open network.

The first section of this whitepaper describes the traffic types in an industrial environment thatconverge onto a single, open TSN network. The second section maps the defined traffic types tothe existing and recently updated Ethernet Quality of Service (QoS) mechanisms, such as TSN
traffic-shaping mechanisms.

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OVERVIEW OF TRAFFIC TYPES
Annex I.1 of the IEEE Standard for Local and metropolitan area networks: Bridges and Bridged
Networks (802.1Q) lists eight traffic types. Of those listed, in particular, network control, voice,video, critical applications, excellent effort and best effort have direct relevance to IACS, whileinternetwork control and background traffic generally do not.
We focus on the types of traffic flows that IACS use that are reliant on the QoS they receive fromthe network and how that may affect the QoS of other traffic types. The specific types are:

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Network Control, which includes Precision Time Protocol (PTP) traffic critical to the IACS
and the network’s ability to provide TSN services,
Excellent Effort, which includes IACS configuration and diagnostics traffic,
Voice (audio), which may be part of an IACS systems or used for Audio services provided
in the manufacturing zone,
Video, which may be part of an IACS systems or used for video services provided in the
manufacturing zone andBest Effort.

The following three new types that may be considered sub-types of Critical Application, but havespecific characteristics:Isochronous, where IACS devices need to exchange data synchronously at a defined
periodic rate,
Cyclic, where IACS devices exchange data at a defined rate, andEvents, where IACS devices create messages that need to be received and acted upon ina defined time period without loss.

VERTICAL AND HORIZONTALIn a discrete factory or process automation plant there are various traffic types with different
delivery requirements. Generally speaking, there is vertical communication between theautomation control devices and the plant-level systems and applications, e.g. Scada,Manufacturing Execution Systems (MES) and Human-Machine Interfaces (HMI), and horizontal
communication between the automation and control devices. Horizontal communication can be
broken down to controller-to-controller and controller-to-field-equipment (e.g. actuators,
sensors and drives), a.k.a. input and outputs (I/O). Historically various types of fieldbuses support
these diverse communication requirements and thereby segment the IACS traffic flows onto
separate networks. This significantly limits the type and volume of data available for IoT
applications.
Current, pre-TSN Ethernet (IEEE 802.1 and 802.3) QoS capabilities include traffic-shaping
mechanisms, bandwidth allocation, prioritization and queue management techniques, but lackthe ability to guarantee latency (the amount of time to transmit a packet in the network), jitter
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Ethernet is predominantly used for vertical communication, such as management, configuration,
backup, historical data, diagnostics, alarms and process graphics updates, usually taking place
between the controllers and the plant management and historian servers.
Horizontal communication is where real-time traffic types exist, either as controller-to-controller
communication or controller-to-field-equipment, and are often supported by specific industrial
Ethernet solutions (e.g. EtherNet/IP, Sercos, Powerlink, Profinet IO, Ethercat, CC-Link). Many ofthese worked around the precise QoS guarantees of pre-TSN Ethernet by including existing
standard QoS mechanisms of prioritization and queue management, or by proprietaryenhancements to Ethernet for synchronization and time-based bandwidth utilization.
Alternatively, real-time traffic types may use legacy fieldbuses (e.g. Profibus, Foundation
Fieldbus, DeviceNet, CAN, Interbus, etc.) in special local networks. The use of proprietaryenhanced, segmented Ethernet protocols or fieldbus technologies hinder access to and sharingof data in those networks as opposed to when standard Ethernet is used.
Vertical communication traffic types comprise communication between the controllers, the local
plant management servers and cloud services. It may include:
Alarms and events: the controllers, after processing data received from I/O field devices, reportbreaches of the process variable range (an event) or larger breach of such ranges (an alarm) to
the servers and thus to the operators of the plant,
Process graphics update information: the operators monitor the status of the process equipment
and current process values in the industrial process,Historian information: to observe the behavior of the process using various complex analysis
where process variables evolution over time must be taken into account,
Operator commands: the operators must be capable of intervening on the various processdevices,
Configuration: the files and commands used to configure the various automation and control
devices,Server backup: the application servers and critical devices in the plant usually backed up forrecovery purposes regularly, which can create bandwidth utilization peaks andDiagnostics: to perform maintenance and analysis of reported alarms and diagnostics on fieldequipment.
Horizontal communication comprises communication between IACS devices (such as controllers,
I/O equipment, drives, encoders and other field-level communication), including:
Isochronous: cyclic traffic streams from synchronized applications with very short cycle times anda low jitter requirement.
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Cyclic controller-controller: where controllers exchange variables as a part of shared applications.
There is more tolerance to jitter and frame loss than isochronous communication.
Cyclic controller-IO or controller-drive: where sensors and actuators exchange data with
controllers
Events: where IACS devices communicate change-of-state, alarms/warnings when thresholds are
exceeded or operator commands.

TRAFFIC TYPE CHARACTERISTICS
TSN lets information technology (IT) and operational technology (OT) applications share the same
physical network infrastructure without influencing the other by introducing a toolbox ofmechanisms, such as scheduled traffic (IEEE 802.1Qbv), to provide new levels of Data Delivery
Guarantees to Ethernet-based communication. The following application-centric communication
characteristics enable the identification of a small number of distinct traffic types that are shared
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Traffic Types Characteristics
Description

Characteristic
Data Transmission
Periodicity

Traffic types comprise data streams that can either be transmitted in acyclic/periodic (e.g. signal transmission) or acyclic/sporadic (e.g. event-driven)manner.

Typical period

For traffic types that transmit cyclic/periodic data streams, period denotes theplanned data transmission interval (often also called “cycle”) at the application
layer. The interval is provided as a typical range in orders of magnitude of time, i.e.
80% of the industrial applications in scope of the given traffic type are within theprovided range.
For the traffic types with acyclic/sporadic data transmission periodicity thischaracteristic does not apply.

Application Synchronized
to Network

Denotes whether an application producing a traffic type is synchronized to the
network time at the application layer. Applications that are synchronized to the
network time can align their sending behavior to mechanisms provided by the
network (e.g. scheduling) for reduced latency and jitter in the network
communication.
Available options are: yes or no.

Data Delivery Guarantee

Denotes the application’s delivery constraints of the network for unimpaired
operation. To guide the selection of appropriate Ethernet QoS mechanisms
including the enhancements from IEEE 802.1 TSN, the scope of this characteristic islimited to the application’s data transmission requirements. Any non-applicationrelated requirements and any impact from the application itself and the sending
and receiving device’s communication stack are out of scope. Three Data Delivery
Guarantees are defined:

Deadline: data delivery of each packet or set of packets in a stream isguaranteed to occur at all registered receivers at or before a specified
time (i.e. relative to the start of a communication cycle) and is applicable
only to traffic types with cyclic/periodic data transmission periodicity,

Latency: data delivery of each packet in a stream is guaranteed to occur at
all registered receivers within a predictable timespan starting when thepacket is transmitted by the sender and ending when the packet isreceived andBandwidth: data delivery of each packet in a stream is guaranteed tooccur at all registered receivers if the bandwidth utilization is within the
resources reserved by the sender.

For each option, a typical quantification shall be provided with the Data Delivery
Guarantee, i.e. 80% of the industrial applications in scope of the given traffic typeare within the provided quantification.
In the case that a packet cannot be delivered within the given latency or deadline
requirement, that packet may be considered as lost or discarded by theapplication.
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Characteristic
Tolerance to Interference

Traffic Types Characteristics
Description
Denotes the application’s tolerance of a certain amount of latency variation of thepacket’s transmission (i.e. jitter) for the traffic types with cyclic/periodic datatransmission periodicity.
In the case of a highly jitter-sensitive application, no jitter is expected and is to be
indicated with the jitter value of zero, meaning that this jitter must be negligible.
If the application can cope with jitter, the response is yes and the amount of jitteris specified in a range.
Other sources of jitter in application processing besides network transmission jitter
exist, e.g. stemming from local OS scheduling or time synchronization. These
additional sources of jitter commonly have effects beyond individual traffic types
and need to be considered separately.
For traffic types with none or bandwidth Data Delivery Guarantees the response isyes and jitter is not specified.

Tolerance to Loss

Denotes the application’s tolerance to a certain amount of consecutive packet loss
from an IACS device in network transmission. Industrial applications may consider apacket lost if not received within the Data Delivery Guarantee. In this case, aquantifiable number of tolerable lost packets shall be provided. Alternatively, theoption “yes” can be provided for applications that tolerate packet loss to theextent that basic redundancy protocols such as Spanning Tree suffice to recoverfrom potential network interruptions.
In the case of a highly loss-sensitive application, where no single packet may belost, “no (0 frames)” is the only available option.
Packet loss can occur from network congestion and network error. In the mappingof required features, both cases should be considered.
It should also be noted that the Transmission Control Protocol (TCP) provides aform of protection from data loss, but many of the Industrial applications consider
the packet lost sooner than this mechanism can respond.

Typical Application Data
Size

Denotes the size of application data (payload) to be transmitted in the Ethernet
frames. The size can be fixed (the data is always with the exact same size) or
variable (data size varies from packet to packet, but not exceeding the given
maximum size).
The application data size provides a typical range in orders of magnitude of bytes,
i.e. 80% of the industrial applications in scope of the given traffic type in theprovided range.
Where individual packet sizes widely fluctuate or cannot be determined at design
or configuration time, data volume estimates (e.g. required bandwidth) is
provided.

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Traffic Types Characteristics
Description

Characteristic
Criticality

Describes the criticality of the data for the operation of the critical parts of thesystem. Application criticality is used as a criterion to guide the selection of theappropriate QoS/TSN mechanisms and bandwidth reservations in case of
conflicting requirements.
The following categories of criticality are defined:

high: for traffic types used either by application or the network services
that are highly critical for the operation of the system. Data loss of thistraffic type may cause critical system malfunction and cannot be repeatedor retransmitted by the application,

medium: for traffic types used either by application or the network
services that are relevant but not continuously needed for the operationof the critical part of the system. Data loss of these traffic types may cause
degraded operation but not a system malfunction. Data loss can becompensated by repeating/retransmitting the same data and

low: for traffic types used either by application or the network services
that are not relevant for the operation of the critical part of the system.
Data loss can be compensated by repeating/retransmitting the same data.

Note that the criticality of the data is not to be confused with the traffic classpriority. Traffic class priority is one mechanism to address the criticality, but not
the only one. TSN provides additional mechanisms, such as frame preemption,scheduled traffic, to address the criticality of the traffic.
Table 2: Traffic Type Characteristic

NOTE: Solution-specific characteristics including any type of traffic-class prioritization,
coordination or dependencies (e.g. offsets between flows) among the traffic streams and types
are out-of-scope for the above.
NOTE: Application data streams may be based on 1:1 transmissions between the sender andreceiver or 1:many (a.k.a. multicast) between a sender and multiple receivers. It is not expectedthat the cardinality of application traffic (i.e. 1:1 or 1:many) has an immediate influence on the
QoS mechanisms (beyond stream configuration) and is therefore out-of-scope of thiswhitepaper.

TRAFFIC TYPE DESCRIPTIONSThis section describes the traffic types including a table of specific traffic type characteristics (asdescribed above) for each.

ISOCHRONOUS
For the isochronous traffic type, applications in each device are synchronized to a common time,
which is strictly monotonic and steadily increasing, without jumps or leaps. Devices
synchronously sample inputs and apply outputs by exchanging data at a defined periodic rate or
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cycle. When applied to motion applications, this rate can be fast, in some cases, under 100
microseconds. For tight control loops, transmission jitter must be minimal, with no interference
from other traffic. Messages need a guaranteed delivery time. If they arrive later than thisdeadline, they are ignored for that cycle or discarded, thus potentially affecting the control loop.
Message sizes are fixed at design time and remain constant for each cycle. Payload sizes are
typically under 100 bytes per device. This traffic type can be used for controller-to-controller,
controller-to-I/O-communication and device-to-device in synchronous exchanges.
Examples include:

time-synchronized applications where data must be produced and delivered consistently
and where packets are delivered with a bounded latency, in other words before or by thedeadline andapplications with implicit synchronization where devices act on reception of a frame andtherefore lack Tolerance to Interference and require very low jitter to produce an on-time
delivery (at a specific point in time).

An example is turbine control in a power generation hydro plant, drive to drive in a masterfollower application or a drive to an encoder.

Traffic Type Isochronous
Characteristic

Value

Notes

Periodicity

Cyclic/periodic

Typical Period< 2ms

Application synchronized to
network

Yes

Data Delivery Guarantee

Deadline

Usually within one data transmission period

Tolerance to Interference0

Least possible jitter is required

Tolerance to Loss

None

Seamless redundancy is required

Typical Application Data size

Fixed (30 ~ 100 bytes)

Criticality

High
Table 3:Traffic Type Characteristics - Isochronous

CYCLICThis traffic type involves cyclic/periodic communication between devices. The applications ineach device are not synchronized to a common time. Devices sample inputs and apply outputs
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cyclically, which may or may not be the same as the data transmission period. When applied toa client-server protocol (e.g. PROFINET IO), messages will be clustered while in a
publish/subscribe environment (e.g. EtherNet/IP) messages may be distributed over the cycle
time (e.g. from devices) or clustered together (e.g. controller to devices). For best control, thetime between a device sending a message and its reception should be minimized, withpredictable interruptions from other traffic. Messages need a defined maximum latency time.
Data message sizes are fixed at design time and remain constant for each cycle. This type can beused for controller-to-controller, controller to I/O and device-to-device communication.
Examples include:








input/output updates sent to/from actuators and sensors and a programmable logic
controller in a discrete manufacturing facility with request packet interval (RPI) times
usually measured in milliseconds and cycle times usually 3 to 4 times the RPI,
process graphic updates that need to be updated on a cyclic polling basis, with up to 1
second cycle times; the process controllers send this information to the servers of theplant; maximum frame size varies following each vendor but may reach the Ethernet
Maximum Transmission Unit (MTU) 1500 bytes,
historian information where process controllers create data traffic which is cyclic, but withan update rate or cycle time of around one second. Maximum frame size varies following
each vendor but may reach the Ethernet MTU andcyclic diagnostics where a diagnostic computer checks the functionality of a follower drive
in a master-follower application, i.e. by 1500 bytes (Ethernet MTU) each 4 ms.

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Traffic Type: Cyclic
Characteristic

Value

Periodicity

Cyclic/periodic

Typical Period

2 ~ 20ms

Application synchronized to
networkNo

Data Delivery Guarantee
Tolerance to Interference
Tolerance to Loss

Notes

Latency

Typically it is less than 90% of the period, e.g.
may be 100µs ~ 2ms.

<= latency

The jitter is constrained by the latency
requirement.

1 ~ 4 frames

Applications are designed to tolerate the loss of
one to 4 successive frames (1 ~ 4 periods).

Typical Application Data size

Fixed (50 ~ 1000 bytes)

Criticality

High
Table 4:Traffic Type Characteristics - Cyclic

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EVENTSIn a system when an input or output variable change occurs that requires attention, event
messages are generated. Events may be a change-of-state, operator commands, or an alarm or
warning that thresholds were exceeded. Depending upon the change, this might be a single
message, or a flurry of messages (domino effect).
The network must be able to handle a burst of messages without loss, up to a certain number ofmessages or bandwidth. After this period messages can be lost until the allowed bandwidth
quantity has been restored.
Examples include:

Alarms or Operator Commands that create traffic that may tolerate up to 2 seconds
latencies and are acyclic. Alarms are prone to flooding when issues arise in the systembeing controlled. Maximum frame size varies by application but may reach 1500 bytes.
Control Events create another type of event traffic that is acyclic and has a typical latency
requirement from 10 to 50 milliseconds. Maximum frame sizes vary but are usuallysmaller than the previous ones, reaching 100 ~ 200 bytes.
Human-machine interface cyclic data that is not critical enough or does not have direct
impact on the application may also be considered under this traffic type.

Due to the significantly different requirements, characteristics for “Alarms and Operator
Commands” and “Control” events will be separately described. While both application categories
send the data in non-periodic manner, some per-device and upper bound for the worst-casebandwidth usage shall be given by the application.

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EVENTS—ALARMS AND OPERATOR COMMANDS
Traffic Type: Events—Alarms and Operator commands
Characteristic

Value

Notes

Periodicity

Acyclic/sporadic

Typical Periodn.a.

Application synchronized to network No
Data Delivery Guarantee
Tolerance to Interference

Latency (~ 2s)<= latency

Jitter is not a concern as long as the latency
guarantees are maintained.

Yes

Alarm showers of up to 2000 alarms per second
should be guaranteed, after which some packet loss
is acceptable. The number is application dependent.

Tolerance to Loss

Typical Application data size

Variable (100 ~1500 bytes)

Criticality

MediumTable 5: Traffic Type Characteristics – Events – Alarms and Operator commands

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EVENTS—CONTROL
Traffic Type: Events - Control
Characteristic

Value

Notes

Periodicity

Acyclic/sporadic

Typical Periodn.a.

Application synchronized
to network

No

Data Delivery Guarantee

Latency (10ms ~ 50ms)

Tolerance to Interference
Tolerance to Loss<= latency

Jitter is not a concern as long as the latency
guarantees are maintained.

Yes

Applications are designed to tolerate the loss of someframes but may degrade system integrity.

Typical Application data
size

Variable (100 ~ 200
bytes)

Criticality

High
Table 6: Traffic Type Characteristics – Events - Control

CONFIGURATION & DIAGNOSTICS
The Configuration & Diagnostics traffic type is for the transport of configuration and diagnostic
data, such as device configuration and firmware downloads. This data is traditionally sent using
TCP/IP-based protocols that contain lost message recovery capabilities. This data is not time
critical, but it must eventually be delivered.
Examples include:






Configuration activities create traffic with maximum frame sizes up to the Ethernet MUT
in an acyclic manner. This traffic type may occasionally create peaks of bandwidth
utilization with a latency of up to 1 second.
Diagnostic activities to monitor equipment health that creates acyclic traffic type.
Process information from the application, such as order scheduling and production.
Network and system management and configuration (e.g. SNMP, RESTCONF/NETCONF,
firmware updates) protocol traffic are also considered part of this traffic type.

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Traffic Type: Configuration & Diagnostics
Characteristic

Value

Periodicity

Acyclic/sporadic

Typical Period

n.a.

Notes

Application synchronized to network No
Data Delivery Guarantee

Bandwidth

Additionally, the latency is in the range of 100ms

Tolerance to Interferencen.a.

Tolerance to LossYes

No seamless redundancy is required.

Typical Application Data size

VariableCan be large packets of 500 ~ 1500 bytes

Criticality

MediumTable 7: Traffic Type Characteristics – Configuration & Diagnostics

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NETWORK CONTROLThe network control traffic type contains network control messages. These messages are low involume but have critical delivery requirements. Many of the messages are cyclic, but not relative
to any TSN network cycle times.
Examples of network control include:

clock synchronization (e.g. PTP),
network redundancy (e.g. MSTP, RSTP) andtopology detection (e.g. LLDP).
Traffic Type: Network Control
Characteristic

Value

Notes

Periodicity

Cyclic/periodic

Typical Period

50ms ~ 1s

Application synchronized to
networkNo

Data Delivery Guarantee

Bandwidth

Typically 1 ~ 2 Mbps.

Yes

Transmission jitter should not exceed theperiod.

Yes

Excessive loss of network control frames canlead to loss of network functions (e.g. linkdown state or grand master fail-over).

Tolerance to Interference

Tolerance to Loss
Typical Application data size

Variable (50 ~ 500 bytes)

Criticality

High
Table 8: Traffic Type Characteristics – Network Control

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BEST EFFORTThe Best Effort traffic type is the default for the transport of any application data that does not
require a better service guarantee from the network than “as good as possible.” In other words,
best effort applications are not provided bandwidth or timing guarantees beyond a potential
generic bandwidth reservation for the entire best effort traffic in the network. Best effort traffic
follows may suffer from data loss when higher priority traffic uses does not leave sufficient
bandwidth.
Examples include:

Non-critical retrieval of telemetry data
Non automation and control application data.
Traffic Type: Best Effort
Characteristic

Value

Periodicity

Acyclic/sporadic

Typical Periodn.a.

Application synchronized to
networkNo

Data Delivery Guarantee

Notes

None

Typically networks are configured to provide
some bandwidth to best effort.

Tolerance to Interferencen.a.

Tolerance to Loss

Yes

Typical Application data size

Variable (30 ~ 1500 bytes)

Criticality

Low
Table 9: Traffic Type Characteristics – Best Effort

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VIDEO
Video traffic is the streaming of video data between endoints. IACS often include video systems,
but this traffic will be mapped to previous types such as Cyclic or potentially Isochronous data
depending on the criticality of the application. The characteristics below describe video forhuman consumption. Video streaming for human consumption tends to have lower performancerequirements and is reflected in the IEEE 802.1Q, where Video “traffic is characterized by lessthan 10 ms delay and, hence, maximum jitter (one-way transmission through the LAN
infrastructure of a single campus).”
Examples include:Video Surveillance traffic used to monitor production conditions visually but are not partof any control process.
Traffic Type VII: Video
Characteristics

Value

Periodicity

Cyclic/periodic

Typical Period

Frame Rate

Application synchronized to
networkNo

Data Delivery Guarantee
Tolerance to Interference

Bandwidth

Notes

Latency greater than 10ms may impact application
performance

n.a.
Yes

Loss of packets may lead to decreased quality, but
not necessarily application failure

Typical Application Data size

Variable

Large packets (1000 - 1500 bytes)

Criticality

Low

Tolerance to Loss

Table 10: Traffic Type Characteristics - Video

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AUDIO/VOICE
Audio traffic is the streaming of audio or voice traffic between end-points. As with video traffic,
IACS systems often include sound sensors and actuators, but such end-devices treat thestreaming data as cyclic or potentially isochronous data depending on the criticality of theapplication. Audio streaming for human consumption tends to have lower performancerequirements and is reflected in the IEEE 802.1Q where audio traffic is “characterized by less than
100 ms delay, or other applications with low latency as the primary QoS requirement.”
Traffic Type: Audio/Voice
Characteristic

Value

Periodicity

Cyclic/periodic

Typical Period

Sample Rate

Application synchronized to
network

No

Notes

Bandwidth

Data Delivery Guarantee
Tolerance to Interference

Latency greater than 40ms may impact application
performance

n.a.
Yes

Loss of packets may lead to decreased quality, but
not necessarily application failure.

Typical Application Data size

Variable

Large packets (1000 - 1500 bytes)

Criticality

Low

Tolerance to Loss

Table 11: Traffic Type Characteristics – Audio/Video

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TRAFFIC TYPE CHARACTERISTICS SUMMARY

TypicalPeriodSynchronized
to network

Data
Delivery
Guarantee

Tolerance to
Loss

TypicalApplication
data size(Bytes)Isochronous

Periodic

< 2ms

Yes

Deadline

0

None

Fixed: 30 ~
100

High

CyclicPeriodic

2 ~ 20ms

No

Latency<=latency

1~4
FramesFixed: 50 ~
1000

High

Events:Alarms &Operator
Commands

Sporadicn.a.

No

Latency<=latency

Yes

Variable:
100 ~ 1500

MediumEvents:ControlSporadicn.a.

No

Latency<=latency

Yes

Variable:
100 ~ 200

High

Network
Control

Periodic

50ms ~
1s

No

Bandwidth

Yes

Yes

Variable: 50
~ 500

High

Config &Diagnostics

Sporadicn.a.

No

Bandwidth

n.a.

Yes

Variable:
500 ~ 1500

MediumBest Effort

Sporadic

n.a.

No

None

n.a.

Yes

Variable: 30
~1500

Low

Video

Periodic

Frame
Rate

No

Latencyn.a.

Yes

Variable:1000 ~
1500

Low

Audio/Voice

Periodic

SampleRate

No

Latencyn.a.

Yes

Variable:1000 ~
1500

Low

Tolerance toInterference

Types

Periodicity

The table below summarizes the traffic types and their characteristics.

CriticalityTable 12: Summary of Traffic Type characterizations

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MAPPING TRAFFIC TYPES
We have so far identified and characterized different types of traffic that may be in a converged
industrial network. The remaining sections describe the enhanced set of IEEE 802 TSN/QoS
mechanisms and maps that are needed to support each of them. The purpose of this mapping is
to establish common application requirements so that customers and implementers haveconfidence their requirements will be met regardless of traffic type mix, topology or type of
network infrastructure used, so long as the mapped mechanisms are available in the network
infrastructure and end-devices. These mappings are not a “profile”, but are input to standards
organizations that may develop them. The configuration of these TSN mechanisms and networks
is generally out of scope of this document.
The goal of this paper is to describe a set of mappings that is intended to support all the traffic
types in a broad range of deployments. Different mappings for specific traffic types may
sufficiently support that traffic type in limited situations. They are not included.
Different TSN/QoS mechanisms may also affect each other, for example, time-aware-shaping andcredit-based-shaping, and the TSN mechanisms applied to one traffic type can influence othertraffic types, such as frame preemption. For this reason, the analysis considers the interaction ofdifferent mechanisms and traffic types in a converged network. The choice of mechanisms forany traffic type suffice even when some traffic types are not available. The selection of
mechanisms and configuration options for a traffic type does not invalidate the quality of service
traffic types with same or higher criticality receive.
We assume the reader has a solid understanding of Ethernet (i.e. Layer 2) networking concepts,
such as quality-of-service, input and output queueing, policing of network traffic and more.

MAPPING OVERVIEWThis section provides an overview of the mappings for each traffic type that are detailed later.
The mappings that support each specific traffic type are structured and include:






the recommendation type,the TSN mechanism,
configuration considerations that are relevant to the use of the mechanism,
the type of device the mechanism would be implemented upon andcontext and reasoning behind the recommendation.

The sections below give more detail and context regarding these parameters. The TSN
Mechanism section describes the TSN mechanisms applied and also gives a general overview ofwhat the mechanism provides. Later, in each traffic type mapping, specific reasons themechanism is mapped are described in the context of that traffic type.

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RECOMMENDATION TYPESThe recommendation types are:

Mandatory (M): the type of device(s) must support the capability on some or all of the
network ports,
Recommended (R): the device(s) should support the capability on some or all of the
network ports,
Optional (O): the device(s) may support the capability on some or all of the network ports
orConditional (C): the device(s) support for the capability on some or all ports is conditional,
where conditions are explained in the subsequent context section for each mapping.

TSN MECHANISMS
Each of the TSN mechanisms presented in “Table: Set of IEEE TSN Enhancements” are used tosome extent in the mappings. We describe the mechanism and how it is used to support key
traffic type characteristics. Because some latency-based Data Delivery Guarantees may require
lower latency than standard “store and forward” network infrastructure can provide we describe
an additional mechanism: cut-through switching. This concept is not currently an IEEE
standardized feature.

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Mechanism
IEEE 802.1Q Strict
Priority

TSN Mechanisms
Description and Comments
Strict Priority Forwarding
The 802.1Q standard lays out a mechanism of identifying traffic forwarding priority
and drop eligibility with the Priority Code Point (PCP) in the VLAN tag as outlined inIEEE 802.1Q 2018 Section 6.9.3. It also specifies Traffic Class as the means to placea frame in an output queue. Strict Priority Forwarding suggests that packets are
assigned to outbound queues identified by a Traffic Class (respectively in bridges)
by their PCP value. If a bridge supports more than 1 outbound queue, frames inqueues with a higher Traffic Class are forwarded before frames in queues with alower Traffic Class, if other mechanisms such as Traffic Scheduling (.1Qbv) or
Credit-based Shaping (.1Qav) are not in place. This mechanism is considered amandatory default feature for all bridges supporting IEEE 802.1Q. Each of thetraffic types are assigned at least a Traffic Class value to indicate which QoS
mechanisms the networking queuing and forwarding functions should apply to thepacket.
We do not recommend the number of queues a bridging device must have, but
assume that two or more queues are required to support traffic scheduling andseparate scheduled traffic from unscheduled traffic.

IEEE 802.1Qav

Forwarding and Queuing Enhancements for Time-Sensitive Streams
Credit-based shaping was formally included in IEEE 802.1Q—Section 34. It
identifies a means to reserve bandwidth along a network path through a StreamReservation protocol and enforced via a queue management mechanism that
ensures an amount of bandwidth is available for certain specified traffic. It was
designed for Audio/Video traffic types. This mechanism ensures specified traffic
types receive requested and allocated bandwidth over lower priority traffic types,
but does not meet all Data Delivery Guarantees outlined, such as Deadline or
Latency.
Credit-based shaping queues can also be used to limit a traffic type’s use of
bandwidth as the credit is used and only replenished over time.

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Mechanism
IEEE 802.1AS-Rev

TSN Mechanisms
Description and Comments
Timing and Synchronization for Time-Sensitive Applications
This mechanism is based on the Precision Time Protocol (a.k.a. PTP) referred to as
Clock Synchronization. It is used to ensure that the synchronization requirements
are met for time-sensitive applications, such as audio, video, and control acrossnetworks. It is a profile or derivation of the IEEE 1588 Precision Timing Protocol.
Clock synchronization is required to support scheduled traffic (IEEE 802.1Qbv),
ensuring that the network infrastructure and end-devices can transmit on aschedule based on a common sense of time. Therefore, in the mapping
considerations, it receives the same recommendation type as 802.1Qbv. IACS
applications often require time synchronization, but that is not reflected in the
mappings.

IEEE 802.1Qbv

Enhancements for Scheduled Traffic
Scheduled Traffic enables support for scheduled network traffic as specified in IEEE
802.1Q 2018 section 8.6.8.4. This enhancement enables traffic streams to becommunicated in the network without interference and with little jitter. Thisfeature can be used to meet all the Data Delivery Guarantees (deadline, latency
and bandwidth). Bandwidth guarantees may be met with other mechanisms, suchas .1Qav Credit-based Shaping, but their ability to maintain bandwidth guarantees
diminishes with the presence of Scheduled Traffic as the exclusive time-based
queueing takes priority.
Scheduled Traffic queues can be used to limit a traffic types use of bandwidth as
the queue is only open a certain amount of time.
We recommend this mechanism include a concept of Exclusive Gating, whichsuggests that only one queue (i.e. Traffic Class) has access to forwarding
mechanisms at scheduled times. This is used for the Iscohronous traffic type
Mapping.

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Mechanism
IEEE 802.1Qbu & IEEE
802.3br

TSN Mechanisms
Description and Comments
Frame preemption
Frame Preemption standards allow higher priority “express” frames to interrupt a
lower-priority preemptible frames currently in transmission and resume thepreempted frame’s transmission after higher priority frames are transmitted. The
802.1Qbu portion has been incorporated into the IEEE 802.1Q standard (seesections 6.7.1, 6.7.2, 8.6.8 and Annex S). The Ethernet-specific specifications aredefined in IEEE 802.3br.
Frame preemption has two key capabilities. First, in the absence of Scheduled
Traffic (802.1Qbv), frame preemption can be used to reduce latency and jitter ofpacket transmission to help meet deadline and latency Data Delivery Guarantees
for express frames in the presence of potentially interfering preemptible frames. It
cannot guarantee delivery to the same degree as with Scheduled Traffic due to thepresence of other express traffic and traffic transmission delays due totransmitting frames too small to be preemptible thus causing delays and jitter.
Second, in the presence of Scheduled Traffic, frame preemption is beneficial tolower priority preemptible traffic by freeing utilizable bandwidth for transmission.
Preempting lower priority traffic allows the passage of non-express frames thatmight otherwise be too large to egress in the time allotted, thereby increasing theamount of usable bandwidth for lower priority traffic.

IEEE 802.1Qcc

Stream Reservation Protocol (SRP) Enhancements and Performance
Improvements
This standard has been approved and will be incorporated into IEEE 802.1Q in thenext revision. It provides enhancements to the configuration of time-sensitive
streams into the SRP. SRP includes the following: description of three configuration models: centralized, decentralized, hybrid, specification of MSRPv1 and MIBs for hybrid model,
 definition of bridge-managed objects and MIBs for centralized configuration
model and
 YANG module with four core structures to be used for CNC/CUC API
SRP contains multiple signaling protocols. This enhancement specifies the Multiple
Stream Registration Protocol (MSRP) as a signaling protocol that enables the ability
to reserve network resources for devices that will guarantee the transmission andreception of data streams across a network with the requested QoS capability.
These end-devices are called Talkers (devices that produce data streams) and
Listeners (devices that consume data streams).
SRP also specifies the use of different configuration models and mechanisms tocommunicate required flows. Considerations for management and configuration
are out of the scope.
This mechanism is used to provide consistent QoS behavior across the network.

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Mechanism
IEEE 802.1Qci

TSN Mechanisms
Description and Comments
Per-Stream Filtering and Policing (PSFP and a.k.a. Ingress Policing)This enhancement to PSFP establishes time-based policing and has been included
into IEEE 802.1Q-2018. Per stream filtering and policing (PSFP) is used to filter
frames at the ingress port that do not meet the configured policies. PSFP supports
the following policing actions: Time-based policing: This allows detection of incoming frames during periods
when the stream gate is in the closed state. The intent is to support
applications where the transmission and reception of frames across the
network is coordinated such that frames are received only when the stream
gate is open, and hence, a frame received by the stream gate when it is in theclosed state represents an invalid receive condition [IEEE 802.1Q §8.6.5.1.2].
The Stream Gate Instance applies to one or more Streams. This complements
1Qbv, which applies to egress port.
 Rate-based policing: This is supported by the Flow meter instances. This
enables specification of the Committed Information Rate and Excess
Information Rate. These meters apply to one or more streams and allow
policing of streams that exceed the configured rate.
 Burst-based policing. This is supported by the Flow meter instances, indicating
the length of supported burst (back-to back sending of streams).
 Frame length-based policing. Flow Meter instance allows the specification offiltering criteria based on the maximum frame lengths.
Stream filter instance table (IEEE 802.1Q-2018 §8.6.5.1.1) specifies which filtering
actions shall be applied to network traffic with varying granularity. It allows theapplication of policers (Stream Gate Instance and Flow meters)
 per stream and by Traffic Class.
The PSFP in 802.1Q refers to the 802.1CB standard for identifying a stream. This
specification allows for a variety of granularity levels in the policing. For example,
use of null-stream stream identification could be used to police a whole Traffic
Class. Or specifying a unique stream identification can be used to create a moregranular policy. As this specification affects hardware resources, further work
should be specified in TSN profiles.
This mechanism is used to protect queues from unwarranted traffic and tomaintain the established quality of service for specified traffic and streams. The
recommendations below include a type of policing to be applied.
To limit the bandwidth usage for a traffic type either by a single device or throughthe accumulation of traffic, policing traffic utilization at both ingress (through
PSFP) and egress (through either IEEE 802.1Qav Credit-Based Shaping or IEEE
802.1Qbv Traffic Scheduling) should be used.

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Mechanism
IEEE 802.1CB

TSN Mechanisms
Description and Comments
Frame Replication & Elimination for Reliability
This mechanism is part of the formal TSN set of enhancements and supplies a
critical function for industrial networking systems –seamless redundancy fromconnection or network infrastructure outage. As stated in IEEE 802.1CB “Thisstandard specifies procedures, managed objects, and protocols for bridges and end
systems that provide identification and replication of packets for redundanttransmission, identification of duplicate packets, and elimination of duplicate
packets." When applied on a network with redundant, non-congruous paths, it
ensures that the packets arrive at their destination without interruption even if linkor network infrastructure occurs.
Loss of packets through congestion is eliminated in a properly functioning TSN
network via the Scheduled Traffic function. The loss of packets due to network orlink outages is mitigated through the Frame Replication and Elimination function.
The Per-Stream Filtering and Policing mechanisms specifies that the stream
identification portion of this standard is applicable when PSFP is used. For thisreason, it is not mentioned in the recommendations for PSFP. Recommendations
for PSFP below therefore only reference the frame replication and elimination
aspects of this mechanism.

Cut-throughCut-Through Switching
Cut-through switching is not an IEEE standard nor is there a working group at IEEE
working on this. Cut-through switching is a means to further reduce latency as abridge can transmit frames before the frame is fully received. In other words, it
begins transmitting as soon as enough header information is received to determine
to which outbound port the frame should be transmitted. Store and Forward
bridges must wait until a frame is fully received before transmitting thereby
increasing latency.
This mechanism is used to reduce latency. To ensure the outbound queue isavailable, this feature is best used in combination with Traffic Scheduling. To
protect the capability from mis-use or inappropriate frames, the PSFP mechanism
should also be engaged.
Standardization is required before interoperability between bridges and end-points
can be expected.
Table 13: Description of TSN Mechanisms

MAPPED DEVICE TYPES
We recommend two type of devices: end-devices and bridges. The mappings recommend TSN
features for each. In many industrial and manufacturing networks, end-devices are combinedwith end-devices in multi-port end-devices capable of bridging communication. In this case, themultiport end-device should be seen as both a bridge and an end-device with a virtual link

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between the end-device and the bridge. The recommendation for end-devices or bridges would
then apply to this device.

TRAFFIC TYPES MAPPINGS
Each section below maps TSN Mechanisms to the relevant traffic types. The order in which thoseare presented are in a priority that reflects the Traffic Class mappings recommended for the
traffic type. Traffic scheduling with time-based exclusive gating introduces a superseding form ofpriority over the Priority Code Point/Traffic Class and Strict Priority mechanisms. Therefore,
Network Control is presented as the first traffic type, but any scheduled traffic (i.e. IEEE
802.1Qbv) by default of exclusive gating, is given priority regardless of the traffic class.

MAPPING TRAFFIC TYPE: NETWORK CONTROLThis traffic type requires bandwidth and latency guarantees. Additional constraints need to beconsidered for this traffic type, for example clock synchronization (i.e. IEEE 802.1AS-Rev) frames
shall not be preempted. The timestamp integrity of the clock synchronization mechanism orother network control protocols may be invalidated by the frame preemption.
The following mechanisms can be used to implement this traffic type:
1. Mandatory: QoS Strict priority, treated with highest priority Traffic Class 7 applicable tobridges.
Frames from this traffic type are usually small, sporadic and the bandwidth requirements arelow. The highest priority (traffic class [IEEE 802.1Q]) ensures that these frames are minimallydelayed by other traffic types. When Qbv scheduling mechanisms are in place, the strictpriority has an effect only in the case when scheduled queues are closed and multiple othernon-scheduled queues are opened at the same time—and have a frame ready fortransmission at the same time. In this case, Strict Priority queueing gives Network Control
packets priority. Clock Synchronization (IEEE 802.AS-Rev clause 8.4.4) specifies that PTP
frames do not carry VLAN-Tags, but they shall be identified by the PTP-Ether Type and treatedwith a specific priority (still under discussion).
No user application should send data associated with the highest Traffic Class.
2. Conditional: If Frame Preemption is in effect, then network control traffic (i.e. IEEE 802.1ASRev) queues are considered Express Traffic, applicable to bridges.
Typically, Precision Time Protocol (PTP), i.e. IEEE 802.1AS-Rev, frames are too small to beconsidered for pre-emption, but that may change. The standard does not specify any
considerations for preemption. If PTP is preempted without specifications on how,
implementations may vary and could cause PTP integrity issues.
Therefore, PTP traffic should not be preempted as that may interfere with the timesynchronization function. Therefore, if preemption (IEEE 802.1Qbu) is used, the traffic class
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associated with this traffic type shall be configured as express and not preemptable. This
recommendation may be changed if PTP frame size is limited so that they may not be
preempted or the standard specifies how PTP frames are preempted to avoid impacting PTP
functionality.
3. Conditional: Cut-through switching, Store-and-Forward handling, applicable to bridges.
If switches with cut-through capabilities are used, network control traffic shall be configured
to use the store-and-forward mechanism. Network control traffic is typically exchanged
between the neighboring bridging devices and therefore not appropriate for cut-throughtransmission.

MAPPING TRAFFIC TYPE: ISOCHRONOUS
Data Delivery Guarantees and no Tolerance to Interference are key characteristics of isochronous
traffic. These deadline guarantees are dependent on the application cycle time. Networks withfewer hops naturally can support smaller cycle times. Additionally, scheduling or network analysis
mechanisms (“network calculus”) are needed to determine whether a set of applications’requirements regarding Data Delivery Guarantees and Tolerance to Interference can be met.
Regardless of those mechanisms or tools, a set of TSN quality of service capabilities in the
networking infrastructure is required to meet those requirements while still maintaining
guarantees for other traffic types.
To guarantee negligible jitter or interference, there shall be a guarantee of no interfering frames
from frames from other traffic types delay Isochronous traffic along its transmission path. Thiscan be achieved by guaranteeing that no traffic class other than the one used for Isochronous
traffic is allowed to transmit during the period when this traffic type is scheduled forcommunication. The following mechanisms can be used to implement this traffic type:
1. Mandatory: QoS–Strict priority, treated with high priority (Traffic Class 6) applicable tobridges.
Exclusive gating supersedes the priority suggested by Traffic Class. As isochronous traffic uses
exclusive gating (see Figure 1) the selection of the priority has no effect. Although
Isochronous traffic has a higher priority than network control, we recommend using trafficclass 6 instead of 7 as network control is assumed to always be present in a network whereas
isochronous may not. In that case, other traffic types may use this traffic class.
2. Mandatory: Scheduled Traffic mechanism (802.1Qbv) applicable to bridges and end-devices.
Exclusive gating is needed to satisfy the above defined Data Delivery Guarantee (deadline)
and Tolerance to Interference (no jitter) for Isochronous traffic by ensuring no interference
from other traffic types. End-devices should send the isochronous frames at a specific timewith negligible jitter. Although Scheduled Traffic (802.1Qbv) is meant for bridges, themechanism (or something similar) is needed on end-devices too.
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Note: Other mechanisms, for example Frame Preemption, in specific scenarios may achieve
similar or sufficient results, but are not the focus of this paper as they would not achieve theguarantees in a converged network scenario. A “Mandatory” recommendation therefore
ensures the requirements are fulfilled.
3. Mandatory: Clock Synchronization (IEEE 802.1AS-Rev) applicable to bridges and end-devices.
Clock synchronization is necessary for the coordination of the scheduled events (e.g. IEEE
802.Qbv gate-events and message-transmission times on end-devices).
4. Mandatory: Per-Stream Filtering and Policing (IEEE 802.1Qci) with Time-based policing
applicable to bridges.
Mechanisms are needed to protect the Scheduled Traffic from interference by messages
introduced by misconfigured or faulty devices at ingress points for the network
infrastructure. PSFP provides mechanisms to protect against following error scenarios:more traffic is sent than specified either because of a misconfiguration or device behavior,traffic is sent outside the time window as a result of a clock synchronization error andstops other traffic types or unexpected frames (e.g. Denial of Service attacks) from using
the Scheduled Traffic queues. This may be because of legacy configurations or incorrectly
configured devices.

Note that PSFP has options to drop frames or reassign the frame’s Traffic Class.
5. Mandatory: Stream Reservation (IEEE 802.1Qcc) is applicable to bridges.
A network configuration function is needed that will receive information from applications
and end-devices about the traffic types that will be supported. This function must haveknowledge of the topology (or at least neighbors) and capabilities of the infrastructure. With
this information, it will determine if requirements can be met and generate a schedule for its
particular area of responsibility. This network configuration function may be implemented byusing the centralized, distributed or hybrid configuration model. We do not address these
implementations here.
The configuration function will ensure:The schedule of the time windows within each bridge device shall be done such that theforwarding of these frames along the transmission path can be conducted with required
latency and negligible jitter. For example, between any two neighboring devices, thesending time of Scheduled Traffic must match the receiver’s PSFP (“ingress policing”).
Consistent exclusive gating (see Figure 1) shall be configured. Exclusive gating closes allother queues during the gate open and gate close events for the queue assigned to thistraffic type. Gate open intervals shall be calculated so that all engineered Scheduled
Traffic can be forwarded within the interval (i.e. at least 100% of the required bandwidth

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for Scheduled Traffic is reserved). Traffic scheduling (IEEE 802.1Q-2018 section 8.6.8.4)
specifies that the device shall check if there is enough time interval left to transmit theframe completely before the gate closes, before start of transmission of an unscheduled
frame the device. This is called “guard-banding” (described in more detail in IEEE 802.1Q
Annex Q).
Prohibit collisions or overlapping between multiple isochronous streams in an unintended
manner. These scheduled streams should be separated in time within the same queue.
Ensure exclusive gating for Scheduled Traffic does not significantly delay the frames fromthe Network Control traffic, which includes PTP for clock synchronization. In other words,
exclusive gates must be open less than the timeout intervals used by network control
protocols.

6. Optional: Frame Replication and Elimination (IEEE 802.1CB) for redundancy applicable tobridges and end-devices
Depending on network topology and an application’s Tolerance to Loss requirements, it is
optional whether replication and elimination of frames on redundant, non-congruous pathsin the network is used.
7. Optional: Cut-Through switching is applicable to bridges
When applications require cycles in the range of < 250 µsec and medium-to-large line
topologies with more than 25 bridged endpoints, cut-through functionality may berequired to meet latency requirements. This depends on the frame size, number ofbridges, topology and link speed. This feature is needed to overcome the latency
limitations caused by the store-and-forward delay and may even be required in case of
1Gbit/s link speeds.
Cut-through propagation is guaranteed only in combination with the exclusive gating
feature of scheduled traffic, otherwise there are no guaranties that a cut-through frame
is using a switch port which is occupied (in use) by another frame.
If Cut-Through forwarding is employed, it is not possible for a switch implementation todetermine frame length before transmitting. It is thus possible that a Cut-Through frame
violates a gate-close event of its assigned queue by being too large. Faulty devices or
misconfiguration can lead to such scenarios and it is highly recommended a switch
implement mechanisms to prevent fault propagation, such as truncating the transmissionof the frame, thereby invalidates the offending frame.

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Exclusive gating for Isochronous traffic

Queue 7

Network control traffic

Gate close

Gate open

Isochronous traffic

Queue 6
Queue 5

Queue 4
Queue 3
Queue 2
Queue 1time

Queue 0Pattern I Cycle
Pattern II Cycle (Network Cycle)

Figure 1: Exclusive gating for Isochronous traffic.

MAPPING TRAFFIC TYPE: CYCLICThe Cyclic traffic type requires bounded latency where a limited amount of interference can be
tolerated.
The mapping recommendations assume that isochronous traffic will be present in the networkand therefore traffic scheduling (.1Qbv) is required and present in the network infrastructure,
though isochronous traffic may not be present, as typically found in existing deployments.
Therefore, other traffic shaping mechanisms may be used to achieve the traffic typerequirements without the use of traffic scheduling (.1Qbv). This is reflected in the two options
outlined for the Cyclic traffic type.
Depending on the parameters (period, latency and bandwidth) the following alternative
implementation options are possible:Strict Priority. This option uses strict priority QoS in the network by assigning Cyclic Traffic
to the queue with the second highest traffic class (out of the queues that do not use
exclusive gating) where only Network Control and Isochronous traffic types have higher
priority. In this case, it is assumed that a network configuration function can analyze (e.g.,
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Control traffic type and the interference from lower priority traffic already intransmission.
Optionally frame preemption mechanisms may be deployed to help satisfy the latency
requirements by reducing the interference from lower priority traffic classes intransmission.
Advantages: No oversampling (see below) is used –bandwidth reservation is not wasted
Disadvantages: Strong impact on communication latency from traffic types ofnumerically equal or higher Traffic Class. Adding streams of type Network Control (e.g.
extending the network), isochronous or cyclic (e.g. potential future application updates)
affect the maximum latency and communication jitter.


Scheduled Traffic. Traffic Scheduling may be used for Cyclic traffic to guarantee bandwidthand bounded latency. As end-devices may not be time synchronized for the purpose of
message (or frame) exchange although they may use time synchronization for thetimestamping of events at the application level. Therefore, the network cannot assume
arrival of the packets in a timely manner. A schedule can be created whereby exclusive
gates are opened frequently enough (gating cycle is time between gate open and the nextgate open) where latency would be bounded to the network communication latency plus
1 gating cycle. In this case the network from the first switch (edge switch) through to thelisteners will forward the traffic as scheduled. Oversampling, where the gating cycle is lessthan the application cycle, may be required to achieve the application’s required bounded
latency. Oversampling leads to unused bandwidth as the exclusive gates are not always
used.
Advantages: This approach delivers guaranteed bandwidth, and no interference fromother traffic types. Optionally, the Traffic Class gate may be left open beyond the exclusive
gate to lower the latency for a portion of the Cyclic frames. But the bounded latency is
still dependent on the gating cycle and the implied oversampling defines the amount of
unused bandwidth. Figure 2 shows an example of the configuration, where exclusive
gating is used and the gate left open for cyclic traffic (Traffic Class 5).
Disadvantages: Depending on the configured gating cycle, this option leads to either:bounded latency is greater than application cycle time if the gating cycle is equivalent
to the application cycle time (i.e. no unused bandwidth) or
unused bandwidth when the gating cycle is smaller than the application cycle.

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Exclusive gating for complete Pattern I

Exclusive gating for one portion of Pattern II

Queue 7

Network control traffic

Gate close

Gate open

Queue 6Isochronous traffic

Queue 5Cyclic traffic

Queue 4
Queue 3
Queue 2
Queue 1
Queue 0time
Pattern I Cycle
Pattern II Cycle (Network Cycle)

Figure 2: Exclusive gating for Cyclic traffic.

MECHANISMS FOR IMPLEMENTING OPTION STRICT PRIORITY:
1. Mandatory: QoS—Strict priority, treated with priority Traffic Class 5 applicable to bridges:
First and second highest traffic classes are used for Network Control and Isochronous traffic.
Cyclic traffic receives priority over all other traffic except Network Control or when
Isochronous traffic is in-use.
2. Mandatory: Per-Stream Filtering and Policing (IEEE 802.1Qci) with Rate-based policing isapplicable to bridges: This mechanism is needed to protect the traffic potential interferenceby: policing traffic if more traffic is sent than specified for a specific data stream and policing or retagging to best-effort (or lower priority) if non-configured data streams use
the same traffic class (PCP).
3. Mandatory: Stream Reservation (IEEE 802.1Qcc) is applicable to bridges: A “network
configuration” function is needed which will receive information from applications and/or
end-devices about the traffic types that will be supported for PSFP configuration.
4. Recommended: Frame preemption (IEEE 802.1Qbu), where cyclic queues are marked as
Express Traffic is applicable to bridges and end-devices: Frame preemption can be used tolimit the interference from lower traffic classes with frames in transmission at the time Cyclictraffic is available for transmission. Isochronous traffic uses exclusive gating and is not
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affected by preemption. End-devices must also support this as they may receive pre-empted
frames.
5. Optional: Frame Replication and Elimination (IEEE 802.1CB) for redundancy applicable tobridges and end-devices Depending on network topology and an application’s Tolerance toLoss requirements, the replication and elimination of frames so as to conduct them on
redundant, non-congruous paths within the network is optional.
We recommended that a configuration mechanism is applied to analyze network traffic
requirements (i.e. Network Calculus) to determine whether the latency requirements can be met.

MECHANISMS FOR IMPLEMENTING OPTION SCHEDULED TRAFFIC:
These are the union of mechanisms for Cyclic Traffic-Option and mechanisms needed for
Isochronous traffic when applicable to bridges, with the following exceptions:
Per-Stream Filtering and Policing (IEEE 802.1Qci) with Rate-based policing should be used. It may
be applicable to use Time-based policing on interlinks between bridges after the traffic has beenRate-based policed on ingress to the network.
Cut-through should not be applied to this traffic type. Depending on network topology and an
application’s Tolerance to Loss requirements, a means to guarantee packet delivery should beconsidered. Therefore, the replication and elimination of frames so as to conduct them on
redundant, non-congruous paths within the network (IEEE 802.1CB) is considered optional.

MAPPING TRAFFIC TYPE: EVENTSThe Event traffic type contains traffic with the same characteristics, but there are two application
categories that differ in the latency and Tolerance to Loss requirements:Applications that send “Alarms and Operator Commands”—tolerate latency up to 2
seconds and can contain large frames up to 1500 bytes. In case of alarm showers, a
relatively high number of frames are issued. Forwarding of up to 2000 frames per second
should be guarantee-able, even though more frames may be generated. The applications
can tolerate frame loss in such scenarios.
Applications that send Control Events—require latency in the range of 10 ~ 50ms andhave short frames up to 200 bytes. Frame loss is to be minimized.

As the Data Delivery Guarantee (latency) requirement of the application categories differ
significantly, and to guarantee the latency of the Control Event traffic under the condition that ashower of alarm traffic is active, two Traffic Classes shall be used, one for the Control Events andsecond for Alarms and Operator Commands.

TRAFFIC TYPE: EVENTS—CONTROL EVENTS
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1. Mandatory: QoS—Strict priority, treated with priority Traffic Class 4 applicable to bridges.
2. Mandatory: Per-Stream Filtering and Policing (IEEE 802.1Qci) with Rate-based policing isapplicable to bridges
As Control Events data is sporadic, some upper bound for accumulated the worst casebandwidth usage shall be given by the application.
3. Mandatory: Stream Reservation (IEEE 802.1Qcc) is applicable to bridges.
A “network configuration” function is needed which will receive information fromapplications and/or end-devices about the traffic types that will be supported for PSFP
configuration.
4. Optional: Frame Replication and Elimination (IEEE 802.1CB) for redundancy applicable tobridges.
Depending on network topology and an application’s Tolerance to Loss requirements, thereplication and elimination of frames so as to conduct them on redundant, non-congruous
paths within the network is optional.
5. Optional: Frame Preemption (IEEE 802.1Qbu), where Control Event queues are “Express
Traffic” is applicable to bridges and end-devices
In case that preemption is available in the network components, the traffic class associatedto Control Events shall be configured as Express Traffic and thereby non-preemptable. This
traffic has small frames (up to 200 Bytes), and will not significantly affect the Network Control
and Cyclic traffic types.

TRAFFIC TYPE: EVENTS—ALARMS AND OPERATOR COMMANDS
Mechanisms for implementing this traffic type for Alarms and Operator Commands applicationsare:
1. Mandatory: QoS—Strict priority, treated with priority Traffic Class 3 applicable to bridges
In some cases, more bandwidth is intentionally generated than reserved. In such a case thistraffic will utilize the bandwidth intended to be used by the traffic with lower traffic classes(priorities).
2. Mandatory: Clock Synchronization (IEEE 802.1AS-Rev) applicable to bridges and end-devices.
Clock Synchronization is necessary for timestamping and observing sequence of events on
end-devices.
3. Mandatory: Per-Stream Filtering and Policing (IEEE 802.1Qci) with Rate-based policing isapplicable to bridges.

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PSFP is used to manage the bandwidth of end-device data streams at their ingress into the
network and the accumulated traffic type bandwidth utilization along the network path. For
the case that alarm applications are designed to send more data than the bandwidthreservation (e.g., in case of alarm showers exceed the 2000 frames/second), the PSFP
mechanism is mandatory to perform rate limitation. PSFP also allows for the re-marking oftraffic exceeding bandwidth utilization rates allowing the traffic to be handled as lower
priority traffic or to be dropped altogether. This option may be an advantage to other policing
mechanisms.
4. Mandatory: Stream Reservation (IEEE 802.1Qcc) is applicable to bridges and end-devices.
A network configuration function is needed that will receive information from applications
and end-devices about the traffic types that will be supported for PSFP configuration.
5. Optional: Credit-Based Shaping (IEEE 802.1Qav) is applicable to bridges and end-devices.
To maintain the reserved bandwidth, credit-based shaping may be used. This enables bridges
and end-points to queue frames that exceed credits allocated. It provides end-device more
flexibility on how to handle alarm bursts.
6. Optional: Frame Preemption (IEEE 802.1Qbu), where Alarms and Operator Command queues
are “Preemptable”, is applicable to bridges.
When frame preemption is available in the network components, the traffic class associatedto Alarms and Operator Commands shall be configured as preemptable traffic to minimize
the interference effect on Cyclic, Network Control and Control Events traffic types. This also
increases available bandwidth for this traffic type as the packet can be distributed over small
amounts of available time.

MAPPING TRAFFIC TYPE: CONFIGURATION & DIAGNOSTICS
This traffic type requires bandwidth guarantees. Due to the relaxed latency requirements(100ms) this traffic type can be considered as sporadic (non-cyclic) traffic.
Necessary mechanisms for implementing this traffic type:
1. Mandatory: QoS—Strict priority, treated with priority Traffic Class 2 applicable to bridges
Maintains the higher priority of other traffic types.
2. Mandatory: Per-Stream Filtering and Policing (IEEE 802.1Qci) with Rate-based policing isapplicable to bridges.
3. Mandatory: Stream Reservation (IEEE 802.1Qcc) is applicable to bridges.

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4. Optional: Frame Preemption (IEEE 802.1Qbu), where the Configuration and Diagnostics
queue(s) are “Preemptable”, is applicable to bridges

MAPPING TRAFFIC TYPE: BEST EFFORTThis traffic type uses all the remaining bandwidth. In some cases, it is required to have somebandwidth guarantees. Following mechanisms can be used to implementing this traffic type:
1. Mandatory: QoS—Strict priority, treated with priority Traffic Class 0 applicable to bridges
2. Optional: Frame Preemption (IEEE 802.1Qbu), where the Best Effort queue(s) are“Preemptable”, is applicable to bridges

MAPPING TRAFFIC TYPES: VIDEO & AUDIO
These two traffic types are intended for human consumption.
As this traffic is less critical than ICAS traffic, it will use a lower traffic class but higher than Best
Effort.
As both traffic types have similar characteristics (the difference is on the absolute value of thelatency requirement), there should be one Traffic Class for both these traffic types.
Mechanisms for implementing these two traffic types are:
1. Mandatory: QoS - Strict priority, treated with priority Traffic Class 1 applicable to bridges
2. Recommended: Credit-Based Shaping (IEEE 802.1Qav) is applicable to bridges and enddevices
In professional audio/video-based systems credit-based shaping is used to maintain somelatency upper bounds. The given guarantees are possible when these frames use trafficclasses with higher priorities. In the case of converged industrial network, additional trafficwith scheduling, and preemption is introduced, and these Audio-Video Bridging, AVB (IEEE802.1QAV), guarantees are not achievable to the same degree. In this situation latencies forthis traffic type depend on application-specific factors such as rate and length of scheduled
data streams with exclusive gating, number of streams, network load and usage ofpreemption.
In this case, credit-based shaping will contribute that one talker/sender (within this traffictype) will not monopolize the bandwidth left over for this traffic type (at least the video traffic
will not cause longer latencies in the audio traffic).
3. Mandatory: Per-Stream Filtering and Policing (IEEE 802.1Qci) with rate-based policing isapplicable to bridges.
4. Mandatory: Stream Reservation (IEEE 802.1Qcc) is applicable to bridges.
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5. Optional: Frame Preemption (IEEE 802.1Qbu), where the Video and Audio queue(s) are“Preemptable”, is applicable to bridges.

MAPPING SUMMARY

Cut-Through802.1CB—Frame Replication

M

M

O

O

Cyclic—Option: Strict
PriorityM

5

Cyclic—Option:
Scheduled TrafficM

5

Events—Control

M

4

Events—Alarms &Operator Commands

M

3

Config & Diag.

M

2

Network Control

M

7Video, Audio, Voice

M

1

O

Best Effort

M

0

O

O

M

M

MT

M

MR

M

MR

M

O

MR

M

O

MR

O

MR

R

O
O

M

C

Reservation/Scheduling802.1AS-Rev Clock Synch

6802.1Qav—Credit Based
Shaping

802.1Qbv (exclusive gating)M

802.1Qci—Ingress Policing

Traffic Class

IsochronousTypes

802.1Qbu—Frame
Preemption

802.1Q
Strict Priority

This table summarizes the traffic type mappings described above.

O

M
M

C
MR

R

M

Table 14: Summary of Traffic Type Mappings

Legend: M: Mandatory O: Optional
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C: Conditional
R: Recommended
T: Time-based
R: Rate-based

Our selection of the mechanisms for support of traffic types considers the presence of the traffic
types in combination, e.g. Network Control type will always be present. As well, in some use
cases there is no Isochronous traffic, nonetheless our selection considers it.
In case that there are devices that do not support eight (priority) queues, the mapping of thetraffic types to the priority queues shall consider the following:






Mandatory: Network Control shall have a separate queue and have the highest priority
Mandatory: Isochronous shall have a separate queue
Recommended: Cyclic shall have a separate queue (in case that Isochronous traffic is notpresent)
Cyclic, Control Events, Alarms and Operator Commands and Configuration andDiagnostics Traffic Types can be mapped in one queue
Best Effort, Audio and Video Traffic Types can be mapped in one queue

SUMMARY
We have documented the types of traffic found in typical manufacturing ICAS and the network
performance characteristics they need. We presented a suitable mapping of the traffic types to
QoS capabilities, including the TSN capabilities. This mapping should help vendors deliverinteroperable and certifiable devices and network infrastructure to the industry overall.
With the enhanced QoS capabilities from IEEE 802.1 TSN, the manufacturing ecosystem has achance to converge devices and applications onto a single, open, standard Ethernet network inways not possible before. This convergence leads to greater openness to IoT innovations
demanded by customers. That is the overall goal of the IIC and the companies working in thistestbed.

AUTHORS AND LEGAL NOTICEThis document is a work product of the Industrial Internet Consortium Time-Sensitive Networking
Testbed.
Authors: The following persons have written substantial portions of material content in thisdocument:

Astrit Ademaj (TTTech)David Puffer (B&R)
Dietmar Bruckner (B&R)

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







George Ditzel (Schneider Electric)
Ludwig Leurs (Bosch Rexroth)Marius-Petru Stanica (ABB)
Paul Didier (Cisco)René Hummen (Belden/Hirschmann)
Richard Blair (Schneider Electric)
Thomas Enzinger (B&R)

Contributors: The following persons contributed valuable ideas and feedback that significantly
improved the content and quality of this document:Florian Frick (ISW)
Jeff Lund (Cisco)Andreas Papa
Paul Andrews

Technical Editor: Stephen Mellor (IIC staff) oversaw the process of organizing the contributionsof the above Authors and Contributors into an integrated document.

Copyright© 2019 Industrial Internet Consortium, now incorporating OpenFog, is a program of
Object Management Group, Inc. (“OMG”).
All copying, distribution and use are subject to the limited License, Permission, Disclaimer andother terms stated in the Industrial Internet Consortium Use of Information – Terms, Conditions& Notices, as posted at http://www.iiconsortium.org/legal/index.htm#use_info. If you do not
accept these Terms, you are not permitted to use the document.

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