Synchronization Quality of IEEE 802 1 AS in

What is IEEE 802. 1 AS? … it is a clock synchronization protocol IEEE

Clock Synchronization Clocks drift! • Drift rate (r) ti • Synchronization interval (I) •

Clock Drift Model Clock drift rate is caused by: • the non-ideality of the

IEEE 802. 1 AS – Performance Requirements Up to 7 hops precision < 1

IEEE 802. 1 AS – Time Sync Transportation 6

IEEE 802. 1 AS – Time Sync Parameters Origin Timestamp (O) Correction Field (C)

IEEE 802. 1 AS – Neighbor Rate Ratio nri : ratio between frequency of

IEEE 802. 1 AS – Propagation Delay Measurements 10

Two reality bites… Clock Granularity PHY Jitter MAC ti time stamping PHY tp Clock

IEEE 802. 1 AS – Realistic System Model 13

IEEE 802. 1 AS Worst Case Analysis Assumptions: Same value for D, nr in

IEEE 802. 1 AS – OMNe. T++ Simulations 15

Conclusions Precision of 1 ms not achievable for large-scale networks (100 hops) Precision of

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Synchronization Quality of IEEE 802. 1 AS in Large-Scale Industrial Automation Networks Marina Gutiérrez, Wilfried Steiner Radu Dobrin, Sasikumar Punnekkat TTTech Computertechnik AG Vienna, Austria Mälardalen University Västerås, Sweden IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS) www. tttech. com Pittsburgh, 19 April 2017

What is IEEE 802. 1 AS? … it is a clock synchronization protocol IEEE 802. 1 Time Sensitive Networking (TSN) (previously IEEE 802. 1 Audio Video Bridging (AVB)) Adds real-time capabilities to switched Ethernet • Clock synchronization, scheduled traffic, redundancy To be used in Automotive or Industrial Automation Designed for up to 7 -hops large networks 2

Clock Synchronization Clocks drift! • Drift rate (r) ti • Synchronization interval (I) • Synchronization precision (p) I tp 3

Clock Drift Model Clock drift rate is caused by: • the non-ideality of the physical oscillators • environmental conditions -10, 10 4

IEEE 802. 1 AS – Performance Requirements Up to 7 hops precision < 1 ms What happens for n = 100? pi does not depend on n! 5

IEEE 802. 1 AS – Time Sync Transportation 6

IEEE 802. 1 AS – Time Sync Parameters Origin Timestamp (O) Correction Field (C) Rate Ratio (r) 7

IEEE 802. 1 AS – Neighbor Rate Ratio nri : ratio between frequency of two consecutive clocks IEEE 802. 1 AS does not prescribe a method to measure it Measurement should be done within ± 0. 1 ppm 8

IEEE 802. 1 AS – Time Sync Parameters Origin Timestamp (O) Correction Field (C) Rate Ratio (r) 9

IEEE 802. 1 AS – Propagation Delay Measurements 10

IEEE 802. 1 AS – Time Sync Parameters Origin Timestamp (O) Correction Field (C) Rate Ratio (r) 11

Two reality bites… Clock Granularity PHY Jitter MAC ti time stamping PHY tp Clock Granularity = 8 ns max PHY Jitter = 8 ns 12

IEEE 802. 1 AS – Realistic System Model 13

IEEE 802. 1 AS Worst Case Analysis Assumptions: Same value for D, nr in each time-aware system Max error for the measurement of D and nr Max error in the timestamping Neighboring clocks are the fastest and slowest respectively precision = 6. 9 ms 14

IEEE 802. 1 AS – OMNe. T++ Simulations 15

Conclusions Precision of 1 ms not achievable for large-scale networks (100 hops) Precision of 1 ms achievable for medium networks (30 hops) Precision of 2 ms achievable for large-scale networks 16

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