1. Simulation of 802.11 MAC layer EEL 6507 Fall 2003 Scott Owen & Eric Donnelly

2. Covered in this presentation: Background Approach Simulation Results Conclusions

3. Background Distinguishing features of 802.11 compared to other protocols: – CSMA/CA, instead of the more common CSMA/CD – Exponential backoff algorithm

4. Background Modes: Infrastructure and Ad-hoc – Focus on Ad-hoc mode infrastructure network ad-hoc network AP wired network AP: Access Point

5. Background RTS/CTS – Used to solve “hidden node” problem

6. Background Timing diagram:

7. Background Timing diagram (Our Simulation):

8. Approach Goal: – To create a simulation for the 802.11 MAC layer that would allow various conditions to be tested – As a test case we will investigate the optimum Maximum Transmission Unit (MTU) size, for different device population densities – Coding was done in Matlab

9. Matlab Code State Machine Nodes optionally mobile (random linear path) All nodes aware of each other – Can transmit to any node – Node might not be in range – Node might fall out of range mid-transmission – Hidden nodes possible All nodes have data to transmit at all times (not Poisson)

10. State Machine Ready To TX Tx Rx ACK Tx ACK Wait Tx ACK Rx Rx ACK Wait Backoff

11. Simulation Results

12. Conclusions The goal of a suitable simulation of the 802.11 MAC layer was accomplished Our test experiment relating the optimum MTU to the number of active nodes showed: – Sparsely populated areas are more efficient when all nodes have larger MTU’s – Densely populated areas operate better when all nodes have small MTU’s