Download Asynchronous Ad-hoc Leader Election in Complete Networks

Asynchronous Ad-hoc Leader
Election in Complete Networks
Nolan Irving
Outline
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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
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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
Communications Queue
Channel Class
Election Object
Node 1
Node 2
Node 3
Node 4
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
8.00
7.00
6.00
5.00
4.00
0.05 sec
3.00
2.00
1.00
0.00
5
10
15
20
25
50
100
150
250
Timing Results 2
16.00
14.00
12.00
10.00
8.00
0.10 sec
6.00
4.00
2.00
0.00
5
10
15
20
25
50
100
150
250
Timing Results 3
3.00
2.50
2.00
1.50
0.02 sec
1.00
0.50
0.00
5
10
15
20
25
50
100
150
250
Comparison of Results
16.00
14.00
12.00
10.00
0.10 sec
0.05 sec
0.02 sec
8.00
6.00
4.00
2.00
0.00
5
10
15
20
25
50
100
150
250
Timing Results
(0.05 second message duration)
25.00
20.00
15.00
Average
Worst
10.00
5.00
0.00
5
10
15
20
25
50
100
150
250
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
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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
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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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