1. Mac Support for Broadcast-based Ad hoc Forwarding Scheme Ashikur Rahman and Pawel Gburzynski Department of Computing Science University of Alberta Email: ashikur@cs.ualberta.ca

2. Features & Assumptions Controlled Flooding as a routing scheme Simple Flexible Low cost No control packets Some tunable parameters Fixed communication range Bi-directional flows

3. Protocol in Brief Reactive Broadcast-based Converge to a narrow strip of nodes along the shortest path S D

4. Two controlling rules Duplicate Discard (DD) rule Retransmission Count Source ID Sequence no Session ID Destination ID Packet signature Packet Header, Packet signature + r + h + some more fields

5. Packet signatures are stored in DD Cache. First Rule (Cont.) Expiry time of an entry, T r Average transmission time, t avg Initially

6. Second Rule Sub Optimal Path Discard (SPD) rule Has it’s own (SPD) cache Each entry is a tuple, Discard Counters Hop count between Target Avoid forwarding via sub- optimal path

7. Second Rule (Cont.) h SK h DK hbhb S K D Number of Packets to be discarded by K, m b is called mobility factor Value of m b indicates aggressiveness

8. Second Rule (Cont.) Can be best viewed as series of light bulbs. Nodes on shortest path always turned on Nodes on sub optimal path are periodically turned on/off Frequency of turning on/off varies. S D

9. Second Rule (Cont.) Lower value of m b will cause more flooding. Higher value of m b will narrow down the width of the forwarding node strip. Dynamic quantity The constant need not to be static

10. Experimental Result

11. Couple of MAC Issues Hidden Node Problem A B C Four way handshake RTS/CTS/DATA/ACK ineffective. Does not even use two-way handshake DATA/ACK. Without feedback retransmission is impossible.

12. Fuzzy Acknowledgement Sender will reserve bandwidth for a duration of: –SIFS + ACK tx time Recipient of the packet will send ACK after SIFS Thus Multiple recipients will be allowed to send ACK almost at the same time. Exactly 3 things can happen –No activity –A valid ACK –A short period of burst activities Fuzzy ACK not very reliable, merely gives a hint.

13. Sample Scenario

14. Cross Layer Interaction For Recipient MAC  Should I send ACK? For Sender MAC  Should I retransmit? Retransmission decision is done statistically: RF related to probability of lying on the optimal path If RF > RF threshold  retransmit.

15. Effect of RF threshold

16. Performance Improvement

17. Future Direction Solution to Hidden node problem yet to be uncovered. Incorporation of power consumption into heuristics facilitating path identification.

18. Question/Comment