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

Size: px

Start display at page:

Download "A Simulation Model of IEEE 802.1AS gptp for Clock Synchronization in OMNeT++"

Helena Norris
5 years ago
Views:

1 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

1. Motivation Real-time Ethernet systems

2 1. Motivation Real-time Ethernet systems No open standard established Only proprietary solutions (expensive) A standard-based approach is required IEEE Time-Sensitive Networking (TSN) Task Group gptp is a part of TSN standards (for sync) 2

3 2. Basics Overview of gptp protocol End station Bridge End station Types of time-aware systems - End stations, bridges Types of s - Master, slave, passive Time-aware systems only communicate gptp information directly with other time-aware systems Hop by hop synchronization 3

4 2. Basics Best master clock selection (BMCS) Grandmaster End station Announce Announce M S Bridge M S P End station All time-aware systems participate in BMCS Announce message: time-synchronization spanning tree vector Automatic changeover to a secondary grandmaster M S P Master Passive 4

5 2. Basics Propagation delay measurement End station 1 Delay requester time Bridge 1 Delay responder time Timestamps known by delay requestor t1 t1 tab Pdelay_req t2 r = frequestor fresponder t3 tba t4 Pdelay_resp t2 Pdelay_resp_follow_up t1 t2 t4 t3 t1 t2 t4 t3 5

6 2. Basics Propagation delay measurement Rate ratio End station 1 Master End station 2 r = (t12 t11) (t22 t21) t11 Sync r = 1 Clockes1 = Clockes2 t21 r < 1 Clockes1 < Clockes2 t12 Sync t22 r > 1 Clockes1 > Clockes2 (t12 t11) (t22 t21) 6

7 2. Basics: Trans of Sync. Information Grandmaster Master Bridge Master te11 te21 Sync Follow_up correctionfield(1) tb11 tb21 Compute correctionfield(2) tb12 tb22 Sync Follow_up correctionfield(2) tb31 tb41 correctionfield: Composed of propagation delay and residence time : preciseorigintimestamp + <delaytogm> Synced to GM time 7

8 3. Implementation 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 8

9 3. Implementation Model of clock with constant drift C(t) = at + b b T(t) = t t [s] 9

10 3. Implementation Model of clock with constant drift Grandmaster Master Bridge Master Master te11 te12 te21 te22 Sync Follow_up Drift calculation when Sync and Follow_up are received Sync Follow_up tb11 tb12 tb21 tb22 tb31 tb32 tb41 tb42 Sync Follow_up Drift calculation when Sync and Follow_up are sent Sync Follow_up tb51 tb52 tb61 tb62 10

11 3. Implementation Model of gptp functionalities Grandmaster End station M S Bridge M S P End station Eth. interface with gptp sup: EthernetInferfaceGPTP Simple module for gptp functions: ethergptp 11

12 3. Implementation Model of time-aware systems Grandmaster End station M S Bridge M S P End station Simple module tablegptp Simple module clock Compound module EthernetInferfaceGPTP 12

13 4. Evaluation: Simulation Setup Same setup as Lim et al.* (BMW + TUM) Evaluation: Propagation delay measurement Time difference to GM (before resynchronization) Clock drift of time-aware systems in domain [ppm] Master Bridge0 Bridge1 Bridge *Hyung-Taek Lim, Daniel Herrscher and Lars Volker IEEE 802.1AS Time Synchronization in a switched Ethernet based In-Car Network, IEEE VNC

14 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] % % % % % % % % 0.43 Bridge % 0.00 Bridge % 0.43 Bridge %

15 4. Evaluation: Time Difference to GM Time difference to GM (before resynchronization) As expected: e.g., for 125ms and +/- 50ppm +/- 6.25us Time difference to GM before resynchronization Node in our implementation [µs] Sync interval Sync interval 62.5 ms 125 ms Bridge Bridge Bridge

16 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 * 16

17 Thank you for your attention. Questions? 17

Fundamentals of Precision Time Protocol. Rudy Klecka Cisco Systems. October 14, 2015

Fundamentals of Precision Time Protocol Rudy Klecka Cisco Systems October 14, 2015 Abstract This session will provide a general background on IEEE 1588 Precision Time Protocol (PTP), how it works, some