Mac Support for Broadcast-based Ad hoc Forwarding Scheme Ashikur Rahman and Pawel Gburzynski Department of Computing Science University of Alberta

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

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

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

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

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

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

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

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

Experimental Result

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.

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.

Sample Scenario

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.

Effect of RF threshold

Performance Improvement

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

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