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Low-Power Wireless Bus (LWB)
SenSys 2012Federico Ferrari, Marco Zimmerling(ETH), Luca Mottola(SICS), Lothar Thiele (ETH)
("Potential" BEST PAPER/RUNNER UP)
NSLab study group 2012/11/05Presented by: Yu-Ting
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Outline
• Introduction• Protocol Operation• Evaluation• Discussion
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Comment Part1
• Good writing structure• Clearly explain how this protocol operates
• An extended work of Glossy– Take the efficient flooding advantage of Glossy
• A brand-new and awesome unified solution for WSN communication
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Feature
• Bootstraps quickly and efficiently, while distributing energy costs evenly
• In many-to-one scenarios, LWB operates reliably and efficiently under a wide range of traffic loads, and promptly adapts when traffic demands change
• Supports many-to-many communication without any changes
• Topology-independent• Supports mobile nodes acting as sinks, sources, or both
without any changes or performance loss• Very good energy consumption!
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Comment Part2
• Compare with 7 different protocols– Good to get familiar with important related work
• Seems to beats all the other state-of-art protocols• Clearly describe the scenario and parameters in
evaluation– Use fair choices of parameter for the other protocols– With brief explanation of how other protocols operate
• Multi-Sink is actually not an easy task (few protocols support that)
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Outline
• Introduction• Protocol Operation• Evaluation• Discussion
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Overview
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Operation
• Sink acts as host here• Inter-packet interval (IPI) = 6s here
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Host Failure
• Failure of host: complete absence of communication within Thf
– Upon detect it, nodes switch to the next channel• Hardcode a circular ordered list <channel,
host_id>
• After not receiving stream request for Thf, host also switch the the next channel
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Scheduler
• Determining the round period– Tmin (1s): > total duration of a round Tl
– Tmax (30s): < time of synchronization failing due to clock skew
– dmax (60 slots): number of data slots that the scheduler can map in a single schedule packet (so, # of pkts / round)
– When Topt <Tmin, the network is saturated
• Allocation data slots to streams– where
as: number of data slots the scheduler allocates to streams during a roundrs = T/IPIs
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Outline
• Introduction• Protocol Operation• Evaluation• Discussion
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Metrics
• Metrics1. Data yield: 2. Radio duty cycle
• Protocols
• Testbeds
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Bootstrapping
• Fully bootstrapped: when all source nodes delivered at least one packet to the sink
• LWB, CTP: < 2min; Dozer: >18min• Fairness in energy consumption: only LWB– Battery depletion may cause a network partition
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Many-to-One Scenario:Light/Heavy/Fluctuating Traffic
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Many-to-Many Scenario
• 8 sinks
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Topology Changes - External Interference
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Topology Changes - Node Failures
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Mobile Sink
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Mobile Sources(4) and Mobile Sink(1)
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Real-World Trial
• Many-to-many• One-to-many• Change traffic demands• Change active nodes• 5 mobile nodes
(B,M1~M4) as both sources and sinks
• 7 days during working• B: trigger high rate stream
of all mobile nodes
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Outline
• Introduction• Protocol Operation• Evaluation• Discussion
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Scalability
• The more number of streams, the more consumption of memory and computation time– TelosB can support several hundreds of streams
(each stream with 15bytes/pkt and 13bytes to store in memory)
– [YT] Memory is used to store a burst of received data within 1 round
• The more number of streams, the more saturated the bandwidth is
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Network Diameter
• Difficult to determine the network diameter in advance, which affect the length of data (Td) and schedule (Ts)– Current prototype is 7 hops ([YT] it's not short…)
• When the network spans "several tens" of hops, other approaches may perform better
• Longer slots (Ts,Td) leads to fewer available slots per round and thus bandwidth– Default setting: support 300 streams with IPI=5s,
so double-length slots support at most IPI=10s
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Alternative Scheduling Policies
• Trade off between latency and energy consumption
• LWB-low-latency: adapts the round period T such that the next round occurs immediately after the generation of new packets
• LWB-fixed-period: fixes T = Tmin
• LWB is easy to modify this, unlike others!
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Q&A