Measure real large wireless networks u Collect every possible information

Measure real large wireless networks u collect every

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Measure real large wireless networks u Collect every possible information » PHY/Link/IP/TCP/App layer trace » Collect every single wireless packet u Need many sniffers for 100% coverage Automatically merge traces u Global view of wireless networks across time, locations, channels, and protocol layers u Enables manual and automatic diagnosis Jigsaw: What Really Happens 12 CSE 222A – Lecture 17: Wireless Networking
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150k square feet u 4 floors 500+ occupants u 150 faculty/staff u 350 students Building-wide WiFi u 39 access points u 802.11b/g » Channel 1, 6, 11 u 10 – 90 active clients anytime u Daily Traffic ~5GB Our lab: EBU3b 13 CSE 222A – Lecture 17: Wireless Networking
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Overlays existing WiFi network ° Series of passive sniffers ° Blanket deployment over 4 floors 39 sensor pods (156 radios) ° 4 radios per pod, cover all channels in use ° Captures all 802.11 activities » Including CRC/PHY events ° Stream back over wired network to centralized storage Jigsaw Deployment
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Jigsaw design Traces synchronization and unification L2 state reconstruction TCP flow reconstruction 15 CSE 222A – Lecture 17: Wireless Networking
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o Frames carry TSF time-stamps o Need a global clock o Estimate the offset between TSF and the global clock for each sniffer Synchronization
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Synchronization Create a virtual global clock u To keep unification working u Critical evidence for analysis » If A and B are transmitting at the same time they could interfere » If A starts transmitting after B has started then A can ± t hear B Require fine time-scales (10- 50us) u NTP is +100 usec accuracy u 802.11 HW clocks (TSF) have 100PPM stability Time (s) TSF diff (us) TSF diff of two sniffers CSE 222A – Lecture 17: Wireless Networking
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Time Ideal Unification CSE 222A – Lecture 17: Wireless Networking
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Time JFrame 1 JFrame 4 JFrame 5 JFrame 3 JFrame 2 Jigsaw unified trace Real Unification CSE 222A – Lecture 17: Wireless Networking
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  • Fall '08
  • Vahdat,A
  • IEEE 802.11, ISM band

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