Analysis of Converged Network Traffic Using Time-Sensitive ...

Analysis of Converged Network Traffic

Using Time-Sensitive Networking (TSN)

Rick Blair

Schneider Electric

October 10, 2018

2

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

• Email

• database

Technical Track 2018 Industry Conference & 19th Annual Meeting www.odva.org

© 2018 ODVA, Inc. All rights reserved.

Controller1 Controller2

Switch1

Drive1 I/O1 I/O2 Drive2 Drive3 Drive4

Line1

I/O1 Drive1 Drive2 I/O2 I/O3 Drive3

Line2

HMI

3

Isochronous Traffic Pattern (motion)

• Cyclic, often at high rates (<= 1 ms)

• Synchronized network and application time

• Low tolerance to interference

• Typically small payloads



cmd1TX

RX

t0

tcyc

cmd2 cmd3 cmd4

fbk1 fbk2 fbk3 fbk4

tr ts tf

4

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)



out1TX

RX

tcyc

out2 out3 out4

in1 in2in3in4

5

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



event1TX

RX event10

event6

event9event2 event17 event75

6

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



7

Time-Aware Traffic Shaping



• Scheduled traffic

• Queuing offers guarantee of exclusive network access

• Ideal for Isochronous traffic

8

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 next

• Shaping mechanisms can affect priority queuing



10

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-and-

forward behavior



11

Store-and-forward vs. Cut-through switching



Source Device

SW1 SW2 SW3Target Device

message

tsw

message

tsw

message

tsw

message

ingress SW1

egress SW1

egress SW2

egress SW3

txmt

Source Device

SW1 SW2 SW3Target Device

message

tsw

message

tsw

message

tsw

message

ingress SW1

egress SW1

egress SW2

egress SW3

txmt

Cut-throughStore-and-forward

12

Interference



Interference due to in-progress message High-priority Interference

P13 PortSwitch P2

P3

in progress

tsw

message

ingress P3

ingress P1

egress P2

txmt

in progress message

P13 PortSwitch P2

P3

high priority

low priority

ingress P3

ingress P1

egress P2

txmt

in progress low priority

high priority

13

Small Interfering Message



SW1 SW2 SW3 Target Device

txmt

P1 P2 P1 P2 P1 P2

int0

HP0

ingressP3 – SW1

ingressP1 – SW1

egressP2 – SW1

int0 HP0

int0 HP0

int0 HP0

egressP2 – SW2

egressP2 – SW3

int0

tsw

tsw

tsw tsw

tsw

14

Large Interfering Message




txmt

P1 P2 P1 P2 P1 P2

int0

tsw

HP0

ingressP3 – SW1

ingressP1 – SW1

egressP2 – SW1

tsw

egressP2 – SW2

egressP2 – SW3

int0

int0 HP0

tsw

int0 HP0

int0 HP0

15

Subsequent Interference – Large

Low Priority Messages




txmt

P1 P2 P1 P2 P1 P2

int0

HP0

ingressP3 – SW1

ingressP1 – SW1

egressP2 – SW1

egressP2 – SW2

int0 int1 int2

tsw

int0 HP0

tswingress

P3 – SW2int1

int1 HP0 int0

tsw

int2ingress

P3 – SW3

egressP2 – SW3

int2 HP0 int1 int0

16

Subsequent Interference –

Small Low Priority Messages




txmt

P1 P2 P1 P2 P1 P2

int0

HP0

ingressP3 – SW1

ingressP1 – SW1

egressP2 – SW1

egressP2 – SW2

int0 int1 int2

tsw

HP0

tswingress

P3 – SW2 int1

HP0

tsw

int2ingress

P3 – SW3

egressP2 – SW3

HP0

int1

int0

int0

tsw

int1 int0int2

17

Equal Priority Interference



P13 PortSwitch P2

P3

int0

tsw

HP1

ingress P1

ingress P3

egress P2

txmt

int0

HP0

HP0

HP1

18

Higher Priority Interference



P13 PortSwitch P2

P3

int0

tsw

HP1

ingress P1

ingress P3

egress P2

txmt

int0

HP0

HP0

HP1

tsw

19

Scheduled Traffic Interference



P13 PortSwitch P2

P3

int0ingress P1

Schedule

egress P2 int0

HP0

HP0

SCH0

txmt

P13 PortSwitch P2

P3

int0ingress P1

Schedule

egress P2 int0

HP0

HP0

SCH0

txmt

Multiple Blocked Messages In-Progress Message

20

Putting It All Together



TX

RX

Motion Traffic

TX

RX

TX

RX

TX

RX

I/O Traffic

Event Traffic

Converged Traffic

21

Summary & Conclusions

• Simple system used to demonstrate convergence

• Three traffic types (motion, I/O & event)

• Different interference scenarios analyzed

• Convergence can affect latencies, but TSN provides mechanisms to

determine if in acceptable range



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