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. Agenda Protocol overview Initial experimental result Problem of IEEE 802.11-based Mac Layer Fuzzy Acknowledgement Performance Improvement Future direction

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

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

5. 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

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

7. Second Rule Sub Optimal Path Discard (SPD) rule Target  Avoid forwarding via sub optimal path Intermediate node K will keep track of, h SK h DK hbhb S K D Number of Packets to be discarded by K,

8. 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 m b is called mobility factor Value of m b indicates aggressiveness

9. Initial Experimental Result

10. Problem in MAC Layer 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.

11. Fuzzy ACK

12. Fuzzy Ack (Cont.) Before broadcasting –Sender will set a timer with expiry time: Data tx time + SIFS + ACK tx time +2×MAX_PROP_DELAY Sender switches to monitor the channel immediately Exactly 3 things can happen –No activity –A valid ACK –A short period of bust activities followed by a silence. Duration of silence period  SIFS duration. Duration of the activity  tx time of ACK packet. Fuzzy ACK not vary 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