broadcast-free collection protocol

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Broadcast-Free Collection Protocol

Daniele Puccinellij, Marco Zunigak, Silvia Giordanoj, Pedro Jos’e Marr’onjkjUniversity of Applied Sciences of Southern Switzerland

kDelft University of Technology

SenSys, 2012MengLin, 2012/12/03

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Outline• Introduction• Model Derivation• Design and Implementation• Experimental Evaluation• Conclusion

Intro/Model/Design/Evaluation/Conclusion

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Introduction• Broadcast-Free collection protocol

– Running data collection protocol without any broadcast and only with unicast traffic

• Broadcasts in asynchronous low-power listening (LPL) are actually more expensive than unicasts in energy footprint

• Broadcasts usually used in– Data dissemination (B or U)– Neighbor discovery (B)– Routing tree formation (B)


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Introduction• Implemented in TinyOS• BFC discovers routes by eavesdropping

on neighbors’ unicast transmissions• Compare with broadcast-based CTP on

duty cycle of the radio (the fraction of radio on-time)

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Broadcast VS Unicast• BoX-MAC (B-MAC + X-MAC)

– Most popular LPL in TinyOS’ MAC layer– Send packet trains to stretch the transmission

duration• Unicast packet trains can be cut short by ack• Broadcast must match the entire wakeup interval

– Broadcast packet is twice as costly as unicast packet


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Broadcast VS Unicast• Data collection protocols

– Unicasts for data traffic– Broadcasts for control traffic to form routing

structure– Trickle algorithm for the management of

broadcast control traffic• First aggressively use beacons to discover a route• Finally converge to a fixed steady-state inter-

beacon interval (IBI)• CTP’s tIBI exponentially increasing from 64 ms to

about 8 minutes


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Modeling the Duty Cycle• Receive checks

• Broadcast transmissions

• Broadcast receptions

• Unicast transmissions

• Unicast receptions


tw The LPL wake up intervaltc The LPL periodic energy check timetrx The packet reception timetIBI The inter-beacon intervaltIPI The inter-packet interval

Ni The number of neighbors of node iFi The ratio of the total number of forwarded packets (local+relay) per locally generated packetΓi the number of transmissions required for every successful reception (the measured ETX)Li The total listening load of node i during the interval tIPI (either intended and unintended receptions)

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Insights Derived from the Model• Roles of nodes

– Leaves (nodes with Fi < 2 that are not within one hop of the sink)

– Relays (nodes with Fi ≥ 2 that are not within one hop of the sink)

– Sink’s neighbors• Optimal tw for Bcast

– [0.5, 2]


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Insights Derived from the Model• Eliminating broadcasts mostly benefits the

lifetime of the sink’s neighbors and leaf nodes


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Insights Derived from the Model• Eliminating broadcasts widens the optimal

wakeup interval range– With broadcast, increasing tw means longer

sleep, but also costlier transmissions– Without broadcast

• Duty cycles being insensitive to change of tw under very low traffic rate scenarios

• Insensitive to out-of-network interference, that is less false busy


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Design and Implementation of BFC• Leverage eavesdropping on neighbors’

unicast transmissions• Connect to a neighbor that already has a

reliable path to the sink• Based on BoX-MAC or any LPL with ack• Assumption

– The sink is always on– Every node injects traffic every tIPI


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Route Discovery• Initialization

– Discover the sink by sending 1~2 unicast pkt to sink; otherwise, goes into hibernation

– Eavesdrop on unicast transmissions every tw

• Parent Selection– Data path validation

• Route assessing: sum up the measured ETXs• Viability flag setting: set flag after sending and

receiving ν consecutive acks– Viable parents advertisement– Simply select workable parents


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Route Discovery• Best Effort Data Delivery

– Not guarantee end-to-end delivery– Set maximum retransmissions and Time to

Live (TTL)• After Nretx=6 unicasts, drop current parent • After TTL=Nmax=32 unicasts, drop packet

– BFC jitter transmissions to alleviate hidden node effects as tw is increased and LPL increases the packet transmission duration?


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Route Maintenance• Route breakage occurs when no longer

has a valid parent• Route failure due to channel dynamics

– Asymmetric for ack and unreliable links• Route failure due to traffic dynamics

– Congestion: reset viability flag or disable ack• Route Repair

– Governed by a Vetting period– New parent accepted

• if measured ETX is the same – Avoid loops Intro/Model/Design/Evaluation/Conclusion

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Design and Implementation of BFC• Adaptive Low Power Listening

– Lock to most active parents causing unbalanced routing tree

– Halves heavily loaded nodes’ tw • Connectivity

– P[overhearing a packet]

psnoop = 1 − 0.5nh

n potential parents

h IPI intervalsIntro/Model/Design/Evaluation/Conclusion

The expected duration of a unicast transmission

Wake up interval

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Snapshots of BFC Operation


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Evaluation• Evaluate on three different testbeds, but

focus on most challenging Motelab (low density and unstable link)

• Compare BFC with CTP• Measure to ensure similar channel

condition in each experiment• Use duty cycle as a key metric• Not much difference in delivery rate and

throughput


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Median and mean for all nodes• Optimal interval for CTP is [1,2]• Much wider and flatter tw for BFC• Sink neighbors’ unicasts are cheaper• Leaves’ unicasts are rare


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Duty cycling savings• Normalizing the results with respect to the

performance of CTP and the optimal duty cycle in CTP


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Impact of the network structure• Place the sink at the edge of the network• Focus on [0.5, 5] sec• BFC still much wider than CTP


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Node insertion• When nodes added or reboot, CTP

aggressively broadcasts to pull a route• For BFC, only cost unicast snoops


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Node removal• Similar to route breakage• CTP might broadcasts to pull a route again• Not easy to evaluate

Intro/Model/Design/Evaluation/ConclusionBFC

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Poor connectivity• CTP commands intense broadcast activity

to pull a route• BFC simply gives up for intervals equal to tseek


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Latency• Use throughput as a proxy for connectivity• 1 tIPI for CTP, 6 tIPI for BFC (middle), 13.5 tIPI for BFC (edge)

• Acceptable One-time delays (43 mins)


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Conclusion• Practical to perform data collection without

broadcast control traffic• Energy efficient for sink’s neighbors and

poor connectivity• Complete research• Nice organization but tedious in writing• Might not be useful in many cases (short

bootstrap time)


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Thanks for Your Listening

broadcast-free collection protocol

Documents

unicast trafficbroadcasts

unicast transmission

broadcastbased ctp

local neighbors

data trafficbroadcasts

interval tipi

unintended receptions

code summary