Asynchronous Ad-hoc Leader Election in Complete Networks

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Asynchronous Ad-hoc Leader Election in Complete
Networks

• Nolan Irving

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Outline

• Presentation of problem
• Survey of current work
• System description
• Program description
• Data collected
• Conclusions

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Problem Statement

• Ad-hoc network
• No existing backbone to network
• Nodes are resource-poor
• Battery life
• Processing power

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Problem Statement (cont.)

• Leader election
• At any given time, there must be at most one
  leader
• Both links and nodes are unstable
• Cannot safely assume reliable channels
• Network must adapt to frequent changes

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Uses of Ad-hoc Networks

• Rapid network deployment
• Combat situations
• Search rescue

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Why Elect?

• The leader is used to control requests for access
  to limited resources
• Restoration of tokens
• Grant resource requests

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Other Research

• Multihop networks
• Bidirectional links
• Movement-based networks

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Flawed Assumptions

• Algorithms assumed knowledge of number of
  participating processors
• Nearly all research assumed global ordering
• Link representation inappropriate to wireless
  networking

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Other Problems

• Maintenance costs never addressed
• Addition/removal of nodes ignored
• Problem increased by initialization requirement

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Problem Description

• Asynchronous network
• Unknown participants
• No global ordering
• Broadcast communication channel
• CD enabled
• Complete network

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Assumptions

• Communications is a shared broadcast channel
  multiple simultaneous transmissions corrupt
  signal
• Nodes can detect a collision likewise, the
  sender can detect a successful transmission
• Network is single-hop all processors can be
  reached with a single broadcast
• A successful broadcast will reach all
  participating nodes

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Program Framework

• Emulate asynchronous communications using
  priority queue
• Channel class keeps track of simultaneous
  communications and status
• Node class handles communications requests

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Simulation Structure
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Program Framework (cont.)

• Leader election protocol
• Global ordering
• Adding/removing nodes

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Results

• Times were an average of 1000 runs
• Total time is listed in seconds

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Timing Results 1
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Timing Results 2
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Timing Results 3
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Comparison of Results
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Timing Results(0.05 second message duration)
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Summary of Results

• Linear relationship between message length and
  election time
• Polynomial growth of algorithm time and message
  complexity with n

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Conclusions

• Advantages
• System offered a simple asynchronous protocol for
  leader election
• Protocol allows for only one leader
• Maintenance costs minimal
• Handles new additions/dropped nodes easily
• One of very few designs able to handle an unknown
  number of nodes

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Conclusions

• Disadvantages
• Time not strongly bounded
• Delaying technique inefficient
• Will not count participating processors
• Unsuited to extremely large networks

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Sources

• Fundamental Control Algorithms in Ad-hoc
  Networks. Hatzis, et. Al. 1998.
• Leader Election Algorithms for Mobile Ad-hoc
  Networks. Malpani, et. Al. 2000.
• Randomized Initialization Protocols for Ad-hoc
  Networks. Nakano, Koji and Olariu, Stephan.
  2000.
• Randomized Leader Election Protocols for Ad-hoc
  Networks. Nakano, Koji and Olariu, Stephan.
  2000.

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Questions

• ???