ContextAware Cooperative Data Transfer

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• Context-Aware Cooperative Data Transfer
• For Mobile Systems
• Jeffrey Hemmes

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Overview

• Problem Definition and Motivation
• Context-Aware Data Transfer
• System Architecture
• Implementation
• Evaluation
• Conclusions

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Background

• Crisis response systems
• Mobile ad-hoc networks
• Highly dynamic topology
• Device locations change frequently
• Operators work towards a common goal, but...
  different roles may imply different data sets
• Resources may be shared among team members
• Resources limited
• Capabilities vary by device
• Cannot broadcast all data to all devices
• Must limit extraneous data transfers
• Data should still be preserved!

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Objective
Use both system state and dynamic
location information to make real-time node
selection decisions in cooperative storage
systems.
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Context-Aware Data Transfer

• We have
• TeamTrak platform
• Routing protocol containing GPS information
• Basic Idea
• Add system state to routing protocol
• Measure size of data to be transferred
• Use system state for peers to determine if
• sufficient resources available
• Use location history to determine if enough
• time exists to complete data transfer

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System Architecture
Resource Monitor
Routing Table
Route Data
Disk
Batt
GPS Thread
Window Event Handler
Ethernet Thread
Data
Timer
GPS Data
Route Data
Buffer
Buffer
Display
GPS Receiver
Network Card
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Peer Selection

• Nodes initially scored as route packets arrive
• Insufficient storage space/battery life ? score 0
• All others become candidate nodes ? score 1
• State info/node score recorded in routing table
• Location history of candidate nodes recorded
• Linear extrapolation of location history used to
• compute window of opportunity for data transfer
• Node with largest window of opportunity
• selected

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Peer Selection
Wireless Range
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Data Transfer and Recovery

• Each node functions as lightweight file server
• TCP connection established between nodes
• For each file in the data list
• Send an RPC with the file name and size in bytes
• Receiving node sends an acknowledgement
• Transfer data
• When specified number of bytes received,
  receiving node sends another acknowledgement
• Note this only works for single hops!

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Data Transfer and Recovery

• Data may have been transferred from its original
  backup location
• Originating node broadcasts request for any data
  belonging to it
• Nodes holding copies of the data send ACK
• Files transferred back to originating node

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Fault Tolerance

• System is designed to be reasonably fault
  tolerant, but many boundary cases exist
• What happens if
• No suitable peer is found?
• File transfer fails?
• Peers suddenly change direction?
• Data is positioned more than one hop away?
• etc
• This system is fully cooperativewhat about
  permissions and security policies?

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Evaluation
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Conclusions

• Context-aware data transfer allows data
• preservation without excessive transmissions
• Evaluates system state and predicted
  availability
• to make node selection decisions
• May have applications beyond cooperative
• storage

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For More Information

• Jeffrey Hemmes
• Cooperative Computing Lab
• www.cse.nd.edu/jhemmes
• hemmes_at_cse.nd.edu

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Related Work

• Geographic Forwarding
• Static Network Topology
• Routing Protocol Only
• FlashBack
• Measures Relative Location Only
• Determines Proximity via Message Traffic
• Others

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Future Work

• Multihop file transfer protocol over UDP
• Security architecture
• How do failure semantics mesh with permissions
  and security policies?
• What effect does security have on time-critical
  offloads?
• Can this method be used or adapted to choose an
  optimal route instead of a single node?

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Resource Monitor

• Polls battery level every 5 seconds
• Measures available storage space
• Measures size of designated files
• Battery level/free space added to routing packet
• Routing packet broadcast via timer function

Route header
Routing Table Entries
name ttid battery space gateway etc.
Routing Table Entry 1
Routing Table Entry 2
Routing Table Entry 3
Routing Table Entry 4