Time Sensitive Networks - Update from the IIC Testbed forFlexible Manufacturing

Paul Didier, Cisco
Rick Blair, Schneider ElectricOctober 10, 2018

Abstract
The IIC’s TSN for Flexible Manufacturing testbed’s looks to enable Industrial IoT and Industrie
4.0 through deployment of open, standard deterministic networks within production facilities.
Our Goal is to display the value and readiness of Time-Sensitive Networks (new IEEEstandards) supporting real-time control & synchronization of high performance machines.
The testbed is over 2 years old. We have over 25 companies participating, conducted 12plugfests, established 2 testbed instances, developed 2 demonstrators, outlined an OPC UA
Pub/Sub data exchange and produced a whitepaper on industrial traffic type characterizationand mapping. This paper will give an update on the testbed’s activities, an outlook on thereadiness of TSN as a technology and indication where further work is required from thetestbed perspective. In addition, we will review the Industrial Automation traffic typecharacterization and TSN function mapping coming from the Testbed.
As a point, the IIC invites all ODVA members to participate in the activities – without the need to
be an IIC member.

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Agenda•••Testbed Overview
Testbed testing status
Testbed Whitepaper – Characterization of converged traffic and mapping toTSN functions

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Overview of IIC TSN for Flexible Manufacturing
Key Facts:• > 25 Vendors participating (chip makers, switches, automation devicesand testing products)• > 10 Plugfests conducted over the last year in US, Austria and Germany• 2 Testbed locations at NI in Austin TX and at ISW in Stuttgart Germany• 2 Best Testbed Awards: 1st IIC Testbed Showcase (Q1 2017) and IoTSolutions World Congress (2017)• Demonstrations at 6 major shows: IOT SWC, SPS Drives, Hannover
Messe, NI Week, IOT World, DE Forum• Collaboration with multiple standardization bodies: IEC, IEEE, IETF,
AVNU, LNI4.0, OPC and ODVA
Investigated in testbed subgroup:1.
Selection of communication characteristics for Industrial Automation and Control Systems2.
Identification of traffic types with common requirements
3.
Mapping of Ethernet Qos/TSN mechanisms to traffic types
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4Traffic Type Characteristics
Application-derived communication requirements
Traffic TypeDescription

Data Transmission Periodicity• Cyclic/periodic• Acyclic/sporadic - also periodic frames with large periods (1-2 seconds)

PeriodPlanned data transmission interval (“cycle”), range in orders of magnitude of time

Synchronized to network

Indication whether application is synchronized to network time (yes or no)

Data delivery guarantee• Deadline: data delivery of each packet in a stream is guaranteed to occur at all registered receivers ator before a specified time (within a communication cycle)• Latency: data delivery of each packet in a stream is guaranteed to occur at all registered receivers
within a predictable timespan starting when the packet is transmitted by the sender and ending when
the packet is received• Bandwidth: data delivery of each packet in a stream is guaranteed to occur at all registered receivers
if the bandwidth utilization is within the resources reserved by the sender

Tolerance to interference

Application’s tolerance of a certain amount of latency variation of the packet’s transmission (i.e. jitter)

Tolerance to loss

Application’s tolerance to a certain amount of consecutive packet loss in network transmission

Data size

Application payload size to be transmitted (fixed or variable)

Criticality

Criticality of the application data for the operation of the critical parts of the system (high, medium, low)

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5Periodicity

Typical Period

Synchronized
to network

Data
deliveryguarantee

Tolerance tointerference

Tolerance toloss

Traffic Types for Industrial Automation and Control Systems

Isochronous

Periodic< 2msYes

Deadline

0None

Fixed: 30 - 100 Bytes

High

CyclicPeriodic

2 - 20ms

No

Latency<= latency

1-4
FramesFixed: 50 - 1000 Bytes

High

EventsSporadicn.a.

No

Latency<= latency

Yes

Variable: 100 - 1500 Bytes

HighNetwork Control

Periodic

50ms - 1s

No

BandwidthYes

Yes

Variable: 50 - 500 Bytes

High

Config & Diagnostics

Sporadicn.a.

No

Bandwidthn.a.

YesVariable: 500 - 1500 bytes

MediumBest Effort

Sporadicn.a.

No

Nonen.a.

Yes

Variable: 30 - 1500 Bytes

Low

VideoPeriodic

Frame RateNo

Latencyn.a.

Yes

Variable: 1000 - 1500 Bytes

Low

Audio/Voice

Periodic

Sampling rate

No

Latencyn.a.

Yes

Variable: 1000 - 1500 Bytes

Low

Types

Typical application datasize

Criticality

Complete description: https://www.iiconsortium.org/pdf/IIC_TSN_Testbed_Traffic_Whitepaper_20180418.pdf
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6Mapping of Traffic Types to TSN/QoS mechanisms
Now that traffic types found in industrial networks are defined and characterized, wecan identify standard mechanisms (e.g. IEEE 802.1Q Quality of Service) to support
the various traffic types in a converged network. The mapping gives:• Guidance on how to map (Implement/configure)” the traffic type to the Qos/TSNfeatures. IEEE 802.1Q provides a suggestion on how to map the traffic types totraffic classes• 20 years old, and assuming only the QoS (strict priority feature)• Recommendations about which TSN/QoS mechanisms to use• How to parameterize those mechanisms, andThis mapping identifies the TSN features and services that are relevant for eachtraffic type (Industrial Application systems) in a network where the other traffic types
exist.
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Traffic Class Mechanisms
Mechanism

Description and Comment
Strict Priority Forwarding

IEEE 802.1Q

Strict Priority Forwarding suggests that packets are assigned to outbound queues identified by a Traffic Class. The traffic classes
are all prioritized in this way.

Forwarding and Queuing Enhancements for Time-Sensitive Streams – Credit Based Shaping
IEEE 802.1Qav

This mechanism ensures traffic types receive requested bandwidth over other lower priority traffic types, but does not meetother Data Delivery Guarantees outlined. It was particularly designed for Audio/Video traffic types. Credit-based Shaping queues
can also be used to limit a traffic types use of bandwidth as the credit is only replenished over a certain amount of time. WhenScheduled Traffic is introduced, these bandwidth guarantees are not achievable to the same degree as indepently.

Timing and Synchronization for Time-Sensitive Applications
IEEE 802.1AS-Rev

Clock synchronization is required to support scheduled traffic (IEEE 802.1Qbv) and Credit-based shaping ensuring that thenetwork infrastructure and end devices can transmit on a schedule based on a common sense of time. Therefore in the mapping
considerations, it receives the same recommendation type as Scheduled Traffic. It should be noted that the IACS applications
often require time synchronization, but that consideration is not reflected in the mappings.

Enhancements for Scheduled TrafficIEEE 802.1Qbv

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This enhancement enables traffic streams to be communicated in the network without interference and with little or no jitter.
This feature can be used to meet all the data delivery guarantees: deadline, latency and bandwidth.
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Traffic Class Mechanisms
Mechanism

Description and Comment
Frame preemption

IEEE 802.1Qbu &IEEE 802.3br

Frame preemption has two key capabilities. First, in the absence of traffic scheduling (802.1Qbv), frame preemption can be usedto reduce latency and jitter of packet transmission to help meet deadline and latency data delivery guarantees for express frames
in the presence of potentially interfering preemptible frames. Second, in the presence of traffic scheduling, frame preemption isbeneficial to lower priority preemptible traffic by freeing utilizable bandwidth for transmission.

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

SRP contains multiple signaling protocols. This enhancement adds 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 and reception ofdata streams across a network with the requested QoS capability. These end stations are referred to as Talkers (devices thatproduce data streams) and Listeners (devices that consume data streams). This mechanism is used to provide consistent QoS
behavior across the network.

Frame Replication & Elimination for Reliability
IEEE 802.1CB

This mechanism supplies a critical function for industrial networking systems – seamless redundancy from connection or network
infrastructure outage. It is considered an optional mechanism for critical applications where the network topology supportsredundant, non-congruent paths.
Additionally, this protocol contains specifications for Stream Identification. For ingress policing (Rate or Time-based) on Stream ID
is mandatory, this part of the specification is also required

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9Traffic Class Mechanisms
Mechanism

Description and Comment
Per-Stream Filtering and Policing (a.k.a. Ingress Policing)IEEE 802.1Qci

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This mechanism referred to as per stream filtering and policing (PSFP), is used to filter/police ingress frames that do not meet thespecified policies as configured on the relevant managed objects. PSFP is supported by the following policing actions:• Time-based policing. This is supported by the Stream Gate Instance. This identifies the details of the of the time gateparameters. This allows detection of incoming frames during time periods when the stream gate is in the closed state to resultin the stream gate being permanently set to a closed state, until such a time as management action is taken to reset thecondition. The intent is to support applications where the transmission and reception of frames across the network iscoordinated such that frames are received only when the stream gate is open, and hence, a frame received by the stream gatewhen it is in the closed state represents an invalid receive condition [IEEE 802.1Q §8.6.5.1.2]. The Stream Gate Instanceapplies to one or more Streams• Rate-based policing. This is supported by the Flow meter instances. This allows to specify the Committed Information Rate,and Excess Information Rate. These meters apply to specific one or more streams, and allow policing of streams that exceed
the configured rate.
This mechanism is used to protect queues from unwarranted traffic and maintain the established quality of service for specified
traffic and streams. The recommendations below include a type of policing to be applied.

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10Mapping for Traffic Type: Isochronous• Mandatory: Strict Priority Traffic Class 6*• Mandatory: Scheduled traffic (1Qbv) withexclusive gating• Mandatory: Clock Synchronization (1AS-Rev)• Mandatory: Time-based Ingress Policing (Qci ) on
Stream ID to protect the traffic from interference• Mandatory: Stream Reservation (1Qcc) for
consistent configuration throughout the network• Optional: Frame replication (CB) for resiliency• Optional: Cut-Through only for this traffic type –required for some use cases✽Exclusive gating

Queue 7
Queue 6

Queue 5
Queue 4
Queue 3
Queue 2
Queue 1time

Queue 0Isochronous Cycle

Selection of traffic class (priority) for this type has no effect because of the exclusive gating
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Traffic Type Mapping: CyclicTwo Options to support Cyclic:• Strict Priority – In the case there is
no isochronous traffic, strict priority
with recommended Frame
Preemption to minimize interference.
Network traffic analysis (calculus) toverify latency requirements although
guarantees cannot be given.
• Exclusive Gating – In the case there
is isochronous traffic present,
applying Traffic Scheduling to thistraffic type guarantees boundedlatency, albeit some bandwidth loss
for oversampling
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Option: Strict Priority• Mandatory: strict priority Traffic Class 5• Mandatory: Stream Reservation (1Qcc) for consistentconfiguration throughout the network• Mandatory: Rate-based Ingress Policing (Qci)mechanisms• Perform traffic policing if more traffic is sent than it isspecified for a specific data stream• Perform policing or retagging to best-effort if nonconfigured data streams use the same traffic class (PCP)• Recommended: Frame preemption (Qbu). express
traffic• Optional: Frame Replication (CB) for resiliency

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Traffic Type Mapping: CyclicOption: Exclusive Gating••

Mandatory: Strict PriorityTraffic Class 5
Similar mechanisms as in
Isochronous traffic•••excluding cut-throughuse rate-based Ingress Policing

Queue 7

Network control traffic

Gate open

Gate close

Queue 6Isochronous traffic

Queue 5Cyclic traffic

Queue 4
Queue 3
Queue 2
Queue 1
Queue 0

Bandwidth overprovisioning
may be necessaryTechnical Track© 2018 ODVA, Inc.

Partial exclusive gating

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time
Isochronous Type Cycle
Cyclic Traffic Type Cycle

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Traffic Type Mapping: Events
Events traffic type contains packets with similar properties, but there is afundamental difference on latency requirements of the following „subtypes“
Control Events (10-50ms latency)• Mandatory: Strict Priority Traffic Class 4• Mandatory: Stream Reservation (Qcc) for
consistent configuration throughout the network• Mandatory: Rate-based Ingress Policing (Qci)mechanisms• Optional: Frame Replication (CB) for resiliency• Optional: Frame preemption (Qbu) – express
traffic

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Alarms & Operator commands (2000ms latency)• Mandatory: Strict Priority Traffic Class 3• Mandatory: Stream Reservation (Qcc) for
consistent configuration throughout the network• Mandatory: Rate-based Ingress Policing (Qci)mechanisms• Mandatory: Clock Synchronization (1AS-Rev)• Optional: Credit-based Shaping (Qav) - traffic
shaping on endpoints – to better control bursts• Optional: Frame Preemption (Qbu) preemptable traffic

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Cut-Through802.1CB – Frame
Replication

MM

OO

Cyclic - Option: Strict priority

M

5

Cyclic – Option: Scheduled TrafficM

5

Events - ControlM

4Events - Alarms & Operator Commands

M

3Config & Diag.

M

2Network Control

M

7Video, Audio, VoiceM

1OBest Effort

M

0O

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O
M

M

MTM

MR

M

MR

M

O

MR

M

O

MR

O

MR

ROO

M

C

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Reservation/Scheduling802.1AS-Rev Clock
Synch

6

802.1Qav – Credit
Based Shaping

802.1Qbv (exclusivegating)M

802.1Qci – Time-based
Ingress Policing

Traffic Class

IsochronousTypes

802.1Qbu – Frame
Preemption

802.1Q
Strict Priority

Summary of Mappings

O*M
M

CMR

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RM

Legend:•M - Mandatory•
O - Optional•
C – Conditional•
R –Recommended
T – Time-based•
R – Rate-based••* - End devices
15

THANK YOU