Asynchronous Ad-hoc Leader Election in Complete Networks Nolan 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

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

Timing Results 2

Timing Results 3

Comparison of Results

Timing Results (0.05 second message duration)

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 Leader Election Algorithms for Mobile Ad-hoc Networks. Malpani, et. Al Randomized Initialization Protocols for Ad-hoc Networks. Nakano, Koji and Olariu, Stephan Randomized Leader Election Protocols for Ad-hoc Networks. Nakano, Koji and Olariu, Stephan

Questions ???