Challenge sync at large scale How to bootstrap u Goal estimate the offset

Challenge sync at large scale how to bootstrap u goal

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Challenge: sync at large - scale How to bootstrap? u Goal: estimate the offset between TSF and the global clock for each sniffer u Time reference from one sniffer to the other Sync across channels u Dual radios on same sniffer slaved to same clock (creates a de facto time linkage) Manage TSF clock skews u Continuously re-adjust offsets when merging frames s T o ∆t 1 ∆t 3 1 2 3 4
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Jigsaw merges 156 traces into one global trace Covers 99% of AP frames, 96% of client frames Starts Jan 24,2006 (Tuesday) Duration 24 hr Total APs 107 (39 CSE) CSE Clients 1026 Active CSE clients anytime 10 - 90 Total Events 2,700M PHY/CRC Errors 48% Valid Frames 52% JFrames 530M Events per Jframe 2.97 Jigsaw in Action CSE 222A – Lecture 17: Wireless Networking
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Jigsaw syncs 99% frames < 20us o Measure sync. quality by max dispersion per Jframe o 20 us is important threshold n 802.11 back-off time is 20us n 802.11 inter frame time is 50 us n Sufficient to infer many 802.11 events CSE 222A – Lecture 17: Wireless Networking
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L2-ACK Beacon
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Hidden Terminals CSE 222A – Lecture 17: Wireless Networking
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packet packet packet Identify a route, forward over links Abstract radio to look like a wired link src A B dst C Multi - hop routing 25 CSE 222A – Lecture 17: Wireless Networking
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For Next Class… Read ExOR paper Submit checkpoint by tonight! 26 CSE 222A – Lecture 17: Wireless Networking
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  • Fall '08
  • Vahdat,A
  • IEEE 802.11, ISM band

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