Clock Synchronization in OMNeT++ Henning Puttnies, Peter Danielis, - - PowerPoint PPT Presentation

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Clock Synchronization in OMNeT++ Henning Puttnies, Peter Danielis, - - PowerPoint PPT Presentation

May 08, 2023 395 likes •586 views

Institute of Applied Microelectronics and Computer Engineering A Simulation Model of IEEE 802.1AS gPTP for Clock Synchronization in OMNeT++ Henning Puttnies, Peter Danielis, Enkhtuvshin Janchivnyambuu, Dirk Timmermann University of Rostock,

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Institute of Applied Microelectronics and Computer Engineering

A Simulation Model of IEEE 802.1AS gPTP for Clock Synchronization in OMNeT++

Henning Puttnies, Peter Danielis, Enkhtuvshin Janchivnyambuu, Dirk Timmermann University of Rostock, Germany

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Institute of Applied Microelectronics and Computer Engineering

  • 1. Motivation

 Real-time Ethernet systems

No open standard established

Only proprietary solutions (expensive)  A standard-based approach is required  IEEE 802.1 Time-Sensitive Networking (TSN) Task Group  gPTP is a part of TSN standards (for sync)

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Institute of Applied Microelectronics and Computer Engineering

  • 2. Basics

 Overview of gPTP protocol

Types of time-aware systems

  • End stations, bridges

Types of ports

  • Master, slave, passive

Time-aware systems only communicate gPTP information directly with other time-aware systems  Hop by hop synchronization

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End station End station Bridge

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Institute of Applied Microelectronics and Computer Engineering

  • 2. Basics

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 Best master clock selection (BMCS)

All time-aware systems participate in BMCS

Announce message: time-synchronization spanning tree vector

Automatic changeover to a secondary grandmaster

End station End station Bridge

Announce Announce

M S M S P

Grandmaster Slave

M

S

Master port Slave port

P

Passive port

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Institute of Applied Microelectronics and Computer Engineering

  • 2. Basics

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 Propagation delay measurement

End station 1 Delay requester time Bridge 1 Delay responder time Pdelay_req Pdelay_resp

t2 t1 t2 t3 t4 tAB tBA

Pdelay_resp_follow_up

t3

Timestamps known by delay requestor

t1 t1 t2 t4 t1 t2 t4 t3

fresponder frequestor r =

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Institute of Applied Microelectronics and Computer Engineering

  • 2. Basics

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 Propagation delay measurement

 Rate ratio

(t12 – t11) (t22 – t21)

r =

End station 2 Slave port Sync Sync

t11 t12 t21 t22

End station 1 Master port (t12 – t11) ≠ (t22 – t21)

r = 1

Clockes1 = Clockes2

r < 1

Clockes1 < Clockes2

r > 1

Clockes1 > Clockes2

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Institute of Applied Microelectronics and Computer Engineering

  • 2. Basics: Transport of Sync. Information

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 correctionField: Composed of propagation delay and residence time  Slave: preciseOriginTimestamp + <delayToGM>  Synced to GM time

Slave Slave port Grandmaster Master port Slave port Sync

te11

Master port Bridge Follow_up

correctionField(1)

Sync Follow_up

correctionField(2)

tb11 tb12 tb31 te21 tb21 tb22 tb41

Compute correctionField(2)

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  • 3. Implementation

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 Scope of the project gPTP simulation model in OMNeT++ using the INET library

 Integrate gPTP model seamlessly with other protocols from INET  Implement only time synchronization and propagation delay

measurement

 Best master clock not part of project

Assumption: GM shall no be selected randomly

 Implement simple clock with constant drift

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Institute of Applied Microelectronics and Computer Engineering

  • 3. Implementation

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 Model of clock with constant drift

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t [s] T(t) = t C(t) = at + b b

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Institute of Applied Microelectronics and Computer Engineering

  • 3. Implementation

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 Model of clock with constant drift

Grandmaster Master port Slave port Sync

te11

Master port Bridge Follow_up Sync Follow_up

tb21 tb31 tb61 te12 tb22 tb32 tb62

Sync Follow_up

tb11 tb51 tb12 tb52

Sync

te21

Follow_up

tb41 te22 tb42

Drift calculation when Sync and Follow_up are received Drift calculation when Sync and Follow_up are sent

Slave Master port

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Institute of Applied Microelectronics and Computer Engineering

  • 3. Implementation

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 Model of gPTP functionalities

  • Eth. interface with gPTP support:

EthernetInferfaceGPTP

  • Simple module for gPTP functions:

etherGPTP

End station End station Bridge M S M S P

Grandmaster Slave

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Institute of Applied Microelectronics and Computer Engineering

 Model of time-aware systems

  • Simple module

tableGPTP

  • Simple module

clock

  • Compound module

EthernetInferfaceGPTP

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  • 3. Implementation

End station End station Bridge M S M S P

Grandmaster Slave

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  • 4. Evaluation: Simulation Setup
  • Same setup as Lim et al.* (BMW + TUM)
  • Evaluation:
  • Propagation delay measurement
  • Time difference to GM

(before resynchronization)

*Hyung-Taek Lim, Daniel Herrscher and Lars Volker “IEEE 802.1AS Time Synchronization in a switched Ethernet based In-Car Network”, IEEE VNC 2011 Clock drift of time-aware systems in domain [ppm]

Master Bridge0 Bridge1 Bridge2 Slave0 Slave1 Slave2 Slave3 Slave4 Slave5 Slave6 Slave7

30

  • 15

20

  • 50

10 50

  • 5
  • 50

40

  • 15
  • 35

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  • 4. Evaluation: Propagation Delay Measurement
  • Converge to 25 ns (absolute difference < 0.5 ns)
  • Lim et al.: +/- 10 ns acceptable

Node Propagation delay[ns] Error (%) Absolute difference [ns] Slave 0

25.43 1.72% 0.43

Slave 1

25.43 1.72% 0.43

Slave 2

24.78

  • 0.88%

0.22

Slave 3

25.29 1.16% 0.29

Slave 4

25.29 1.16% 0.29

Slave 5

24.78

  • 0.88%

0.22

Slave 6

24.78

  • 0.88%

0.22

Slave 7

25.43 1.72% 0.43

Bridge 0

25 0.00% 0.00

Bridge 1

25.43 1.72% 0.43

Bridge 2

24.78

  • 0.88%

0.22

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  • 4. Evaluation: Time Difference to GM

Time difference to GM (before resynchronization)

As expected: e.g., for 125ms and +/- 50ppm  +/- 6.25us

Node Time difference to GM before resynchronization in our implementation [µs] Sync interval 62.5 ms Sync interval 125 ms Bridge 0

2.36 4.24

Slave 0

  • 3.12
  • 6.25

Slave 1

0.63 1.25

Slave 7

  • 2.19
  • 4.37

Bridge 1

  • 0.94
  • 1.87

Slave 2

3.13 6.25

Slave 6

  • 0.94
  • 1.87

Slave 5

2.50 5.00

Bridge 2

1.25 2.50

Slave 3

  • 0.31
  • 0.63

Slave 4

  • 3.12
  • 6.25

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  • 5. Conclusion

 We have contribute

 Simulation model of gPTP  Models for time-aware systems: end-station and bridge  Simple clock model with constant drift

 Comparisons of results to literature  Useful in simulating any networks based on the gPTP  Entire system is publicly available*  Future work: Utilize other the clock models

* https://gitlab.amd.e-technik.uni-rostock.de/peter.danielis/gptp-implementation

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Thank you for your attention. Questions?

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