Analysis of Converged Network Traffic
Using Time-Sensitive Networking (TSN)

Rick Blair
Schneider Electric
October 10, 2018

What is Convergence?
•••••••••

Merging of multiple traffic types on a single wire
Operational Technology (OT)
Isochronous (motion)
Cyclic (I/O)
Events (Control events and alarms)
Information Technology (IT)Web
Emaildatabase

Controller1

Controller2

Switch1

Drive1

I/O1

HMI

I/O1

I/O2

Drive2

Drive3

Drive4

I/O2

I/O3

Drive3

Line1

Drive1

Drive2

Line2

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Isochronous Traffic Pattern (motion)••••

Cyclic, often at high rates (<= 1 ms)
Synchronized network and application time
Low tolerance to interference
Typically small payloads
tr

cmd1

TX

cmd2

cmd3

ts

tf

cmd4

RX

fbk1

fbk2

fbk3

fbk4

tcyct0Technical Track© 2018 ODVA, Inc.

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3Cyclic Traffic Pattern (I/O)••••

Application cycle times not synchronized with data transmission cycle times
Interference needs to be controlled
Client-Server (e.g. Modbus®)
Pub-Sub (e.g. EtherNet/IP)

TX
RX

out1

out2

out3

out4

in4

in1

in3

in2

tcyc

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4Event Traffic Pattern (Alarms and Control Events)•••

Acyclic traffic
Bandwidth guarantee required to handle bursts (e.g. alarm shower)
Application retries for message loss during excessive message generation

TXRX

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event1
event10event6
event2

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event9www.odva.org

event755

TSN Overview• IEEE 802.1Qav - Forwarding and Queuing Enhancements for Time-Sensitive Streams• IEEE 802.1AS-Rev - Timing and Synchronization for Time-Sensitive Applications• IEEE 802.1Qbu & IEEE 802.3br - Frame preemption• IEEE 802.1Qbv - Enhancements for Scheduled Traffic• IEEE 802.1Qca - Path Control and Reservation• IEEE 802.1Qcc - Stream Reservation Protocol (SRP) Enhancements and Performance Improvements• IEEE 802.1Qci - Per-Stream Filtering and Policing• IEEE 802.1CB - Frame Replication & Elimination for Reliability
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Time-Aware Traffic Shaping•••

Scheduled traffic
Queuing offers guarantee of exclusive network access
Ideal for Isochronous traffic

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QoS Strict Priority

•
•
•
•

Default queuing mechanism for Ethernet bridges (switches)
Higher numbered queues have priority over lower numbered queues
In general, highest numbered queue with message is transmitted nextShaping mechanisms can affect priority queuingTechnical Track© 2018 ODVA, Inc.

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Cut-through Switching•

Advantages– Switch begins forwarding before fully receiving messages– Offers lower latencies over store-and-forward switching•

Caveats– Behavior not specified in standards– Propagates corrupted messages•

Congestion and port speed differences cause fallback to store-andforward behavior

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10Store-and-forward vs. Cut-through switching
SourceDevice

SourceDeviceSW1

ingress
SW1

SW2

TargetDeviceSW3

message

SW1

ingress
SW1

tsw
egressSW1

SW2

TargetDevicemessagetsw
messageegressSW1

tsw
egressSW2messagetsw
messageegressSW2messagetsw
egressSW3

tsw
messageegressSW3

txmt

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messagetxmt

Store-and-forward
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SW3

Cut-throughwww.odva.org

11Interference

P3

P3
3 PortSwitch

P1

P2

P1

ingress P3

ingress P3high priority

messageingress P1
egress P2

in progress

low prioritymessageegress P2in progress

txmt

Interference due to in-progress message
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P2in progress

tsw
ingress P1

3 PortSwitch

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high priority

low priority

txmt

High-priority Interference
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Small Interfering Message
int0

SW1

P1

ingress
P3 – SW1

SW2

P1

P2

SW3
P2

P1

Target Device
P2

int0

tsw
ingress
P1 – SW1
egress
P2 – SW1

HP0

HP0

int0

tsw

tsw
egress
P2 – SW2

int0

HP0

tsw
egress
P2 – SW3tsw
int0

HP0

txmtTechnical Track© 2018 ODVA, Inc.

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Large Interfering Message
int0

SW1

P1ingress
P3 – SW1

SW2P1P2

SW3

P2P1

Target Device

P2

int0

tsw
ingress
P1 – SW1egress
P2 – SW1

HP 0
int0

HP 0tsw
egress
P2 – SW2

int0

HP 0tsw
egress
P2 – SW3

int0

HP 0txmt
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int0

int1

SW1

P1

int2

SW2ingress
P3 – SW1SW3P1

P2Subsequent Interference – Large
Low Priority Messages

P2

P1

Target Device
P2

int0

tswingress
P1 – SW1egress
P2 – SW1
ingress
P3 – SW2egress
P2 – SW2ingress
P3 – SW3

HP 0
int0

HP 0tsw
int1

int1

HP 0

int0

int2

HP 0

tsw
int2

egress
P2 – SW3

int1

int0

txmt
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Subsequent Interference –Small Low Priority Messages
int0

int1

SW1

P1

int2

SW2P1

P2ingress
P3 – SW1SW3P2P1

Target Device
P2int0tsw
ingress
P1 – SW1egress
P2 – SW1

int0

ingress
P3 – SW2

int1

egress
P2 – SW2

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HP 0
HP 0tsw

int1

int0tsw

HP 0tsw

ingress
P3 – SW3

int2

egress
P2 – SW3

int1

int2

int0

HP 0txmt
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Equal Priority Interference
P3

P1

P2

int0

HP 1

HP 1

ingress P3
ingress P1

3 PortSwitch

int0

HP 0tsw
egress P2

HP 0txmt
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Higher Priority Interference
P3

3 PortSwitch

P1

HP 1ingress P3
ingress P1

int0

HP 0tsw
egress P2

P2tsw
int0

HP 1

HP 0txmt
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Scheduled Traffic Interference
Multiple Blocked Messages

In-Progress Message
P3

P3

3 PortSwitchP1

Schedule

ingress P1

int0

SCH 0Schedule

HP 0ingress P1
HP 0egress P2

int0

int0

HP 0
int0

egress P2

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P2

SCH 0txmt

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3 PortSwitchP1

P2HP 0txmt

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TXPutting It All Together

RXMotion Traffic
TX
RX
I/O Traffic

TX
RX
Event Traffic
TX
RXConverged Traffic
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20Summary & Conclusions••••

Simple system used to demonstrate convergenceThree traffic types (motion, I/O & event)Different interference scenarios analyzed
Convergence can affect latencies, but TSN provides mechanisms todetermine if in acceptable range

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21