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

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

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

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 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,

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

Initial Experimental Result

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.

Fuzzy ACK

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.

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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