Asynchronous Ad-hoc Leader Election in Complete

NetworksNolan Irving

Outline

• Presentation of problem

• Survey of current work

• System description

• Program description

• Data collected

• Conclusions

Problem Statement

• Ad-hoc network• No existing backbone to network

• Nodes are resource-poor• Battery life

• Processing power

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

Uses of Ad-hoc Networks

• Rapid network deployment• Combat situations

• Search & rescue

Why Elect?

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

• Grant resource requests

Other Research

• Multihop networks

• Bidirectional links

• Movement-based networks

Flawed Assumptions

• Algorithms assumed knowledge of number of participating processors

• Nearly all research assumed global ordering

• Link representation inappropriate to wireless networking

Other Problems

• Maintenance costs never addressed

• Addition/removal of nodes ignored• Problem increased by initialization requirement

Problem Description

• Asynchronous network

• Unknown participants

• No global ordering

• Broadcast communication channel

• CD enabled

• Complete network

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

Program Framework

• Emulate asynchronous communications using priority queue

• Channel class keeps track of simultaneous communications and status

• Node class handles communications requests

Simulation Structure

N o d e 1 N o d e 2 N o d e 3 N o d e 4

E le c tio n O b je ct

C h a n n e l C la ss

C o m m un ica tio ns Q u e ue

Program Framework (cont.)

• Leader election protocol

• Global ordering

• Adding/removing nodes

Results

• Times were an average of 1000 runs

• Total time is listed in seconds

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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AverageWorst

Summary of Results

• Linear relationship between message length and election time

• Polynomial growth of algorithm time and message complexity with n

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

Conclusions

• Disadvantages• Time not strongly bounded

• Delaying technique inefficient

• Will not count participating processors

• Unsuited to extremely large networks

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.

Questions

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