How to Synchronize HighSpeed Cameras over Ethernet using

How to Synchronize High-Speed Cameras over Ethernet using the Precision Time Protocol a Case Study Nikolaus Kerö

Introduction e Common notion of time is crucial for distributed image processing e Ethernet has become the only viable communication medium a Performance is highly customizable a Bandwidth, fault tolerance, latency, costs, availability, …. a Huge diverse customer base is driving technology innovation e One single communication medium both for and time a R. I. P. Legacy time transfer and sync systems a No more Camera Link, sorry … e Ethernet is inherently asynchronous a Time transfer has to be packet based e PTP – Precision Time Protocol 2

Precision Time Protocol e PTP – Precision Time Protocol a IEEE 1588 -2008 Standard a Generic protocol for highly accurate time transfer over Ethernet a Customizable via PTP-Profiles e Adopted as the only means of time transfer by various industries a Telecom a Power Utility Providers a Finance Service Providers a Broadcasting a Industrial automation e More than 10 different PTP profiles have been published so far 3

Network Based Clock Synchronization Master Time Master Sync message Slave Time 12: 00 1 Offset. M, S 12: 00 T 0, M Slave 1 T 1, S 2 Slave 2 n T 2, S Slave n T 3, M Master Delay Response Slave Delay Request Slave n

Fault Tolerance in PTP e Based on Announce Messages (and their time-outs) a Messages containing information about clock quality e No Master is present (during start-up or Master failure) a All nodes „Announce“ their clock properties a All nodes converge and select THE single Best Master e A better Master enters the network (i. e. after upgrade) a Discovers it has superior clock parameters and announces itself a Takes over as the better Master (current Master backs-off) 5

Accuracy Requirements e Distributed Image Processing a Synchronized exposure of multiple high-speed cameras e Frame Camera a 1 MP resolution @ 20. 000 fps, Exposure +/- 0. 5 lines accurate < 25 ns a 1 MP resolution @ 6 k fps, Exposure +/- 0. 5 lines accurate < 100 ns e Line Camera a 600 k lines / s a Moving object with 60 m/s a 10µm synchronous spatial resolution < 150 ns 6

Meet the PTP Adversaries e PDV – Packet Delay Variations a Queuing and serialization delays a Heavily dependent on network architecture a Mitigated by prioritizing PTP traffic, however … r Accuracy is limited to sub-µs r Upper bound difficult to impossible to define e Asymmetric transmission times a Again: highly network and device dependent a Out-of-Band measurement mandatory e Node dependent inaccuracies a Time stamping resolution a Oscillator quality quantization error r Local clock is free-running in-between two adjustment cycles 7

How to Cope with Packet Delay Variations TS memory IEEE 1588 E 2 E TC P 1 P 2 P n Sync message Master Slave n Slave 2 e IEEE 1588 end-2 -end Transparent Clock 8

PTP Boundary Clock Master Slave II Listen II Master I Slave I Listen I L 1 S 2 M 2 L 2 BC M 3 L 3 M 4 L 4 Mn Ln BMCA for all ports Slave IV Listen IV Slave III BC 2 Listen III 9

PTP Aware Network Topology e Network devices a Standard datacenter products with line rate capabilities a Built-in hardware PTP support (Boundary Clocks) 40 G BC Leaf 1 G 40 G BC BC Spine Leaf Auxilliary Master BC Leaf Grandmaster Slave 1 G 1 PPS Out-of-Band Measurement 10

Filtered Offset viewed from the Slave 11

750 Slaves Out-of_Band Measurement Partially compensated Asymmetry Master and Slave connected to same BC Masters have slightly different performance 3 BCs between Master and Slave 12

E 2 E-TC Performance: 11 Hops 13

E 2 E-TC Performance: 11 Hops 14

Application Requirements e Multi camera image analysis a Time Labels for every frame a Precise point in time for drawing time stamps e Highly synchronized frame capturing a Generation of arbitrary frequencies a Extremely high resolution a User definable phase offset e External synchronization a V-Sync signal from master camera 15

PTP Clock Architecture Digital PLL -16 TIME (2 ns) -10 CLOCK (10 ns) SET-TIME + Shadow SET-TIME (ns) Increment Shadow Increment -10 (10 ns) 16

Digital High Resolution Frequency Generation 17

How to Generate Phase Locked Arbitrary Signals Period [k. Hz] 15 4. 4 79. 5 0. 9 39. 8 610 305 18 Seconds 17. 0 Resolution=2 e-48 ns 1 ns Error after 2. 2 Resolution=2 e-32 ns 1 ns Error after 70 Resolution=2 e-16 ns 1 ns Error after 30 Hours 131 Years

How to Generate Phase Locked Arbitrary Signals 19

Conclusions e PTP is perfectly suited for synchronizing multiple cameras a Robust a minimal configuration a Well proven IEEE Standard e Accuracy a Sub-µs accuracies achievable with standard network devices a sub 10 ns within PTP networks e Versatile Signal Generation a Frame Syncs a Time Labels 20

Thank You for Your Attention Strontium-ion optical clock at NPL UK - 100 ns deviation per 100 years 21

Additional Slides 22

IEEE 1588 Network Devices • • Boundary clocks • + Good for hierarchical systems • + Scale well with the number of devices • ─ Poor for linear systems (large number of daisy chained clocks) • + Can translate between different media. End-to-end transparent clocks • + Can be used for hierarchical systems • ─ Scale poorly with the number of devices (master sees all slaves) • + Good for linear systems (eliminates cascaded servos) 23

End-2 -End TCs - the Final Solution? 1 Master e 2 e TC 2 2 ≠ 1 Slave 1 e 2 e TC Slave 2 24

How to cope with switch delay variations II TS memory IEEE 1588 Switch P 1 P 2 P n Sync message Ingress Path Delay Master Slave n Slave 2 e IEEE 1588 PEER-2 -PEER Transparent Clock 25

Peer Delay Mechanism Master P 2 P TC Slave 12: 00 Sync PDelay_Req T 01 T 02 T 03 PDelay_Resp T 03 T 04 PDelay_Resp Follow_up 26

Extended Monitoring Master Slave 12: 00 Monitoring System Slave 12: 00 T 01 Del_Req + TLV Sync T 02 Del_Req Del_Resp + TLV Del_Resp T 03 Sync T 04 27

Extended Data Processing e Even extended filtering can mitigate PDV effects significantly a Dynamic outlier detection a Servo optimization a Lucky Packet Algorithm e However a Sudden PDV changes/increases may affect accuracy permanently e Use data of more than 1 Master 28