1. Asynchronous Ad-hoc Leader Election in Complete Networks Nolan Irving

2. Outline Presentation of problem Survey of current work System description Program description Data collected Conclusions

3. Problem Statement Ad-hoc network No existing backbone to network Nodes are resource-poor Battery life Processing power

4. 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

5. Uses of Ad-hoc Networks Rapid network deployment Combat situations Search & rescue

6. Why Elect? The leader is used to control requests for access to limited resources Restoration of tokens Grant resource requests

7. Other Research Multihop networks Bidirectional links Movement-based networks

8. Flawed Assumptions Algorithms assumed knowledge of number of participating processors Nearly all research assumed global ordering Link representation inappropriate to wireless networking

9. Other Problems Maintenance costs never addressed Addition/removal of nodes ignored Problem increased by initialization requirement

10. Problem Description Asynchronous network Unknown participants No global ordering Broadcast communication channel CD enabled Complete network

11. 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

12. Program Framework Emulate asynchronous communications using priority queue Channel class keeps track of simultaneous communications and status Node class handles communications requests

13. Simulation Structure

14. Program Framework (cont.) Leader election protocol Global ordering Adding/removing nodes

15. Results Times were an average of 1000 runs Total time is listed in seconds

16. Timing Results 1

17. Timing Results 2

18. Timing Results 3

19. Comparison of Results

20. Timing Results (0.05 second message duration)

21. Summary of Results Linear relationship between message length and election time Polynomial growth of algorithm time and message complexity with n

22. 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

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

24. 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.

25. Questions ???