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Flash Flooding: Exploiting the Capture Effect Flash Flooding: Exploiting the Capture Effect for Rapid Flooding in Wireless Sensor Networksfor Rapid Flooding in Wireless Sensor Networks

Infocom’09Rio de Janeiro, Brazil

Jiakang Lu and Kamin Whitehouse

Department of Computer Science

University of Virginia

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Classic WSN AlgorithmsClassic WSN Algorithms

• Network floods are common and important operations at the heart of most wireless sensor network algorithms.– Routing tree creation– Time synchronization – Code and data dissemination– Node localization– Group formation

• However, network floods are costly in latency due to …

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……neighborhood contentionneighborhood contention

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CCA+MAC Delay

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…… and low-duty cycleand low-duty cycle

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DRx Tx Tx

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Minimal Interpacket Spacing

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Wake Up

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Related WorkRelated Work• Low-duty cycle CSMA networks

– High latency of an LPL flood• [Polastre 2004], [Buettner 2006]

• Wireless senor networks flooding– Do not explicitly optimize for latency

• [Heinzelman 1999], [Levis 2002], [Hui 2004]

• Real-time communication protocols– Point-to-Point, multicast or data collection

• [He 2003], [Watteyne 2006]

• Rapid wakeup scheduling– Requires phase synchronization

• [Lu 2004], [Li 2005], [Lu 2005], [Keshavarzian 2006]

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Flash OverviewFlash Overview• The Flash flooding protocol exploits the

capture effect to reduce flooding latency by eliminating neighborhood contention– Capture: a radio successfully demodulates one of

multiple overlapping transmissions of the same frequency

– Allow nodes to propagate the message concurrently in a flooding scenario

– Propose three flooding-specific mechanisms to manage transmission concurrency

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OutlineOutline

• Experiment Methodology

• Design of Flash

• Performance evaluation

• Conclusions

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Evaluation MethodologyEvaluation Methodology

• VineLab testbed– 48 Tmote-skys– Office environment

• Trace-based Simulation– Capture-aware simulation framework– Multiple Scales and densities– Statistically verified with the testbed results

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Flash-I: Complete ConcurrencyFlash-I: Complete Concurrency• Carrier sense is completely removed

before transmission– No neighborhood contention

• Tradeoff– Significantly reduce the flooding latency– High network coverage is not guaranteed

TxTx Tx Tx Tx Tx Tx

X-MAC packet trainFlash-I packet train

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Flash-I flooding exampleFlash-I flooding example

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Minimal Interpacket Spacing

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Flash-II: Maintained ConcurrencyFlash-II: Maintained Concurrency

• Flash-II achieves low flooding latency while improving the coverage of Flash-I

• Each node has two phases of flooding:1) Flash-I flood

• With no CCA or MAC delay

2) Neighborhood rebroadcast • With CCA and MAC delay (X-MAC flood)• Reach any nodes that missed the first wave

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Flash-II flooding exampleFlash-II flooding example

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Phase #1 = Flash-I flood

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CCA and MAC delay before local rebroadcast

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Flash-II flooding exampleFlash-II flooding example

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Phase #2 = Local rebroadcast w/ CCA and MAC dealy

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Flash-II Scale SimulationFlash-II Scale Simulation

75%

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Flash-II Density SimulationFlash-II Density Simulation

70%

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1) a small interpacket spacing (IPS)2) a small CCA before the packet train

Flash-III packet train

Flash-III: Controlled ConcurrencyFlash-III: Controlled Concurrency• A fine balance must be achieved to

exploit the capture in a flood

• Flash-III applies a new technique to sense the amount of transmission concurrency

TxTxTx Tx Tx TxTx Tx Tx TxTxTxTx Tx

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X-MAC packet train

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Flash-III flooding exampleFlash-III flooding example

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Flash-III Scale SimulationFlash-III Scale Simulation

75%

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Flash-III Density SimulationFlash-III Density Simulation

80%

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ConclusionsConclusions• Flash is the first network flooding protocol for

wireless networks that explicitly exploits the capture effect to optimize for latency.

• The simplicity of Flash can bring substantial performance improvement in the existing systems and have an immediate and practical impact.

• The empirical study of network-wide capture dynamics and the novel capture-aware simulation framework will inspire new studies on capture in the future.

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Thank youThank you

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Backup slidesBackup slides

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Got D!

cases where capture helpscases where capture helps

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I Got B!

Got D!

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Got A!

cases where collision happenscases where collision happens

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Got B!???

Got D!???