Pablo Guerrero, Iliya Gurov , Kristof Van Laerhoven , Alejandro Buchmann
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Transcript of Pablo Guerrero, Iliya Gurov , Kristof Van Laerhoven , Alejandro Buchmann
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22/10/2012 | Dept. of Computer Science | Databases and Distributed Systems Group | Pablo Guerrero | 1
Pablo Guerrero, Iliya Gurov, Kristof Van Laerhoven, Alejandro Buchmann
Diagnosing the Weakest Link in WSN Testbeds: A Reliability and Cost Analysis of the USB Backchannel
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Testbeds 101
Debugging and reprogramming used often in experimentation Testbed’s goal: to facilitate WSN experimentation through
centralized node reprogramming, and data collection for posterior evaluation.
Expensive scientific instrument: initial acquisition and deployment maintenance and operation
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this work’s topic:“backchannel”
a) (remote) users
b) server
c) sensor network
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USB as Wired Interface to Sensor Nodes
USB (probably) first introduced with Telos design USB-to-serial chip to access MCU node powered via USB port, if connected
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Wired, USB Backchannel
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server
sensor network
without support layer- 1:48 [SignetLab]
USB
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Wired, USB Backchannel
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server
sensor network
with support layer
support layer
Ethernet
USB
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Wired, USB Backchannel
22/10/2012 | Dept. of Computer Science | Databases and Distributed Systems Group | Pablo Guerrero | 6
server
sensor network
with support layer
support layer
Ethernet
USB
- 1:{2..6} [TUDμNet, TWIST]- 1:22 [Indriya]
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Challenges
Permanent, distributed sensor network testbeds require unattended operation. But:
Bug(s) in USB implementation, USB hardware, bootstrap loader, power variations, etc. hard to reproduce!
Goals: high reproducibility, comparability, and availability of nodes
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11.35% 88.65%
Node Reprogramming
Jobs w/o failed nodes
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Systematic Evaluation
Methodology:1. set up backchannel [node(s), cable(s), hub(s)]2. test power and enumeration3. run micro-benchmark
repetitively reprogramming a node (until failure / 1000 times)
Metrics: reprogramming time, [seconds] reprogramming cycles between failures, RCBF, [cycles]
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USB Backchannel Topologies
A Universal Serial Bus is a layeredstar topology: hubs at each star’s center 127 devices max. 7 layers max.
Cables passive: up to 5m long active: up to 12m long
Hubs passive (bus-powered) active (self-powered)
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Node Evaluation:Test Files and Reprogramming Time
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FTDI chip SiLabs chip
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Node Evaluation:Manufacturers
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FTDI chip
SiLabschip
reliability independent of manufacturer and USB chip
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Topology Evaluation:Single Node Tests, Passive Cables
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Repr
ogra
mm
ing
Tim
e pe
r Cyc
le (s
ecs)
Total USB Cable Length (m)
Repr
ogra
mm
ing
Cycle
s Bet
ween
Failu
res
passive cables: up to 10 meters
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Topology Evaluation:Single Node Tests, Active Cables
22/10/2012 | Dept. of Computer Science | Databases and Distributed Systems Group | Pablo Guerrero | 13
Repr
ogra
mm
ing
Cycle
s Bet
ween
Failu
res
Repr
ogra
mm
ing
Tim
e pe
r Cyc
le (s
ecs)
Total USB Cable Length (m)active cables: < 40 m (unreliable) or < 10m (reliable)
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Topology Evaluation:Single Node Tests, Active Hubs + Passive Cables
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Repr
ogra
mm
ing
Cycle
s Bet
ween
Failu
res
Repr
ogra
mm
ing
Tim
e pe
r Cyc
le (s
ecs)
Total USB Cable Length (m)active hubs and passive cables: 54m (unreliable) or 43m (reliable)
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Topology Evaluation:Multi Node Tests, Topologies
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3x3
3x5
6x4
6x6
7x7
8x8
stable topologies: balanced trees
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Topology Evaluation:Multi Node Tests, Microbenchmark
Extensions: maximum parallelism
node grouping
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N1N2N3N4
1st
N1N2N3N4
time
N5N6N7N8
time2nd 3rd 4th
1st 2nd 3rd
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Multi Node Tests:Gateway Selection & Parallelism
slug buffalo pcmax ||° 5 8 59
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4 12 24 48 6413579
111315
slugbuffalopc
more nodes faster gateway needed (*)
real: 36% faster
parallelism can and should be exploited
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Multi Node Tests:Gateway Selection & Parallelism (2)
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Enhancing Backchannel Reliability
Manual node reconnection costly Solution: resort to hub port power control
per port power switching ganged power switching
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Enhancing Backchannel Reliability:Quantification
22/10/2012 | Dept. of Computer Science | Databases and Distributed Systems Group | Pablo Guerrero | 20choose HPPC-enabled hubs
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Conclusions
USB is method of choice for testbed’s backchannels
Standard’s cabling restrictions can be overcome
Stable multi-node topologies can be built
HPPC-enabled USB hubs improve reliability
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