Tiny Ad hoc Routing Protocol (TARP)

Ashikur Rahman and Pawel Gburzynski

Department of Computing ScienceUniversity of Alberta

Email: ashikur@cs.ualberta.ca

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 noSession ID

Destination ID

knsDS ,,,,• Packet signature

• Packet Header,

Packet signature + r + h + some more fields

• Packet signatures are stored in DD Cache.

First Rule (Cont.)

hrtT avgr

• Expiry time of an entry, Tr

hrtFT avgcr • Average transmission time, tavg

taavgaavg tCtCt )1(

Initially

C

Lctavg

Second Rule

• Sub Optimal Path Discard (SPD) rule

• Has it’s own (SPD) cache

• Each entry is a tuple, dssddksk CChhDS ,,,,,

Discard Counters

Hop count between <s,k>

Hop count between <d,k>

• Target Avoid forwarding via sub- optimal path

Second Rule (Cont.)

hSKhDK

hbS

K

D

bDKSKds hhhC • Number of Packets to be discarded by K,

bDKSKbds hhhmC

• mb is called mobility factor

• Value of mb indicates aggressiveness

Example: SPD Rule.

S

KL M

DZ

SPD Buffer at:

hb mb

D 0 0

S 0 0

SPD Cache at x:

hb mb hSX CDS hDX CSD

M 0 0 0 0 0 0

L 0 0 0 0 0 0

K 0 0 0 0 0 0

Z 0 0 0 0 0 0

Packet P1 from D to S

S

KL M

DZ

SPD Cache at x:

hb mb hSX CDS hDX CSD

M 0 0 0 0 1 0

L 0 0 0 0 2 0

K 0 0 0 0 3 0

Z 0 0 0 0 1 0

SPD Buffer at:

hb mb

D 0 0

S 2 1

Packet P2 from S to D

S

KL M

DZ

SPD Cache at x:

hb mb hSX CDS hDX CSD

M 2 1 3 2 1 0

L 2 1 2 2 2 0

K 2 1 1 2 3 0

Z 2 1 1 0 1 0

SPD Buffer at:

hb mb

D 2 1

S 2 1

Packet P3 from D to S

S

KL M

DZ

SPD Cache at x:

hb mb hSX CDS hDX CSD

M 2 1 3 2 1 2

L 2 1 2 2 2 2

K 2 1 1 2 3 2

Z 2 1 1 0 1 0

SPD Buffer at:

hb mb

D 2 1

S 2 1

Packet P4 from S to D

S

KL M

DZ

SPD Cache at x:

hb mb hSX CDS hDX CSD

M 2 1 3 2 1 2

L 2 1 2 2 2 2

K 2 1 1 2 3 2->1

Z 2 1 1 0 1 0

SPD Buffer at:

hb mb

D 2 1

S 2 1

Packet P5 from D to S

S

KL M

DZ

SPD Cache at x:

hb mb hSX CDS hDX CSD

M 2 1 3 2->1 1 2

L 2 1 2 2 2 2

K 2 1 1 2 3 1

Z 2 1 1 0 1 0

SPD Buffer at:

hb mb

D 2 1

S 2 1

Packet P6, P7

S

KL M

DZ

SPD Cache at x:

hb mb hSX CDS hDX CSD

M 2 1 3 0 1 2

L 2 1 2 2 2 2

K 2 1 1 2 3 0

Z 2 1 1 0 1 0

SPD Buffer at:

hb mb

D 2 1

S 2 1

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 mb will cause more flooding.

• Higher value of mb will narrow down the width of

the forwarding node strip.

bDKSKtbds hhhtdmC )(

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 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 > RFthreshold retransmit.

)(

)()(

fwdSKD

ackSKD

SKD n

nRF

Effect of RFthreshold

Performance Improvement

Future Direction

• Solution to Hidden node problem yet to be

uncovered.• Incorporation of power consumption into heuristics

facilitating path identification.

Question/Comment