Envirostore: A Cooperative Storage System for Disconnected Operation in Sensor Networks

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Envirostore A Cooperative Storage System for
Disconnected Operation in Sensor Networks

• Infocom07
• AuthorsLiqian Luo, Chengdu Huang, Tarek
  Abdelzaher
• John Stankovic
• Presented By Rohini Kurkal
• Under Guidance of Dr.Bin Tang

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Contents

• Introduction
• System Design
• Implementation
• Performance Evaluation
• Possible Extensions

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Introduction

• Applications
• -Environmental monitoring/data logging
• No real time communication b/w sensor and sink
• Disconnected system
• EnviroStore - cooperative storage system for
  sensor networks suitable for disconnected
  operation
• It is storage-centric rather than
  communication-centric
• Major concern -maximizing effective storage
  capacity
• Implemented in nesC for TinyOS and evaluated in
  TOSSIM

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Storage centric paradigm

• Should be simple and lightweight
• Micaz has only an 8MHz 8-bit processor and a 4KB
  RAM,
• Iris has 8KB RAM, 512KB Measurement Flash Memory
• Sensor nodes do not maintain files but just
  writes data to collection station and never read
  the data they write
• Data redistributionmust improve overall storage
  utilization

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System Design

• Sink process that runs on a users PC,
  identified by a regular IP address and a well
  known TCP port
• Data mule-collects data wirelessly from
  encountered nodes and dumps these data later to
  the base station
• Two types of data mules
• - Intentionally relay data b/w the sink and
  the sensor nodes
• - Opportunistic data upload

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System Model
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System Design

• Data redistribution is used to maximize the
  effective storage space of the sensor network
• In-network Data Redistribution
• Sensor nodes are in a single network
• Overloaded nodes offload data to neighboring
  empty nodes
• Cross-partition Data Redistribution
• Disconnected network
• Overloaded nodes upload to data mules
• Data Mules offload to under-loaded nodes

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In-network data redistribution

• Uses lazy-offload scheme to save energy
  postpones data balancing until the storage
  overflows
• Overloaded nodes should satisfy below conditions
• Ri lt RTH and Ri - Ri gt
  Rimbalance
• Where ,
• Ri Remaining Storage size
• RTH Threshold to delay data transfer
• Rimbalance Parameter to allow local
  imbalances
• Ri Average remaining storage

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Contd..

• Bad Idea
• Selecting neighbor with largest remaining free
  space
• This can cause data ping-pong
• Prevent data ping pong - bound the amount of data
  transfer
• Remaining storage remaining node energy must be
  checked
• Node should not invoke or accept data
  redistribution unless its estimated energy
  lifetime gt estimated storage lifetime

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Cross-partition data redistribution

• Uses data mules
• Discriminate nodes (overloaded and under-loaded)
• Data mule calculates its free storage value Rm
  as the weighted sum aR(1-a)Rm.
• a 1 mule favors redistribution to
  neighborhood
• a 0 emphasizes upload
• Conserve power and reduce message collision,
  nodes use back-off timers

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Transition state of sensor node
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System Architecture of sensor nodes
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Implementation

• Implemented using nesC in Tinyos
• Local storage space of nodes is organized into a
  circular buffers
• Uses
• It consumes minimum code and data memory
• organizes space as continuous data chunk
• eliminates the need for free space management
  mechanisms
• prolongs flash lifetime by balancing write access
  to different locations

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Log Files

• Log-array file
• Simultaneously written by different nodes
• Generates a sequence of log items
• Logs attributes of environmental events
  independently monitored by multiple nodes
• Log-sequence file
• one writer at a time
• Multiple nodes must coordinate with each other
• Maintains unique continuous serial numbers
• Used in EnviroSuite

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Log-Array File
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Log-Sequence File
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PerformanceEvaluation

• Basic deployment configuration field of 80 80
  ft2 ,
• 36 nodes were deployed
• Two Scenarios
• Scenarios 1 Single Disconnected
• sensor network
• Scenario 2 Partitioned
• sensor network with data mules

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Comparison of data storing rate at different time
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Why EnviroStore is different ?

• Used for disconnected sensor networks
• Extra constraint of limited energy use lazy
  offload
• Resource limitation of individual nodes
• Load balancing must be dependent only on local
  information
• Has additional challenge of redistributing data
  between entities that are disconnected

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Possible Extensions

• use of controllable data mules to optimize data
  redistribution and upload
• data replacement policies to maximize the total
  amount of information instead of just the amount
  of stored data
• performance evaluation of EnviroStore on real
  hardware platform

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