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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