a real-world test-bed for mobile ad hoc networks:

1Per Gunningberg©

A Real-World Test-bed for Mobile Ad hoc Networks:

Methodology, Experimentations, Simulation and Results.

Per Gunningberg, Erik Nordström, Christian Rohner, Oskar WiblingUppsala University

2Per Gunningberg©

Background and problem

IETF is standardizing MANET (Mobile Adhoc NETwork) routing protocols:

– One proactive protocol - knowledge about all nodes– One reactive protocol - path on the need basis

Based on experiences from three protocols:– AODV - Adhoc On Demand Distance Vector

(reactive)– DSR - Dynamic Source Routing (reactive)– OLSR - OptiMized Link State Routing(proactive)

Problem: But majority of research done through simulations...

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Part One

A test-bed for evaluating ad hoc routing protocols.

Close to reality

What to measure and how to analyze

Repeatable experiments

Grey Zone Phenomena

Conclusion

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The Uppsala Ad hoc Protocol Evaluation Testbed (APE)

People carrying laptops with 802.11b

Suitable for indoor experiments that are hard to model in simulation

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The Ad hoc Protocol Evaluation Testbed (APE)

Execution environment on top of existing OS.– Runs on Win and Linux

Scenarios with movement choreography.

Emphasizes easy management for scaling.

800++ downloads.

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Laptop instructions (choreography)

node.11.action.0.msg=Test is starting... node.11.action.0.command=start_spyd node.11.action.0.duration=1 node.11.action.1.command=my_iperf c 2 t 330 node.11.action.1.msg=Stay at this location.node.11.action.1.duration=30 node.11.action.2.msg=Start moving! Go to Point A, the end of building. node.11.action.2.duration=75 node.11.action.3.msg=You should have arrived at Point A. Please stay. node.11.action.3.duration=30

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Measurement procedures

Every node collects SNR from every other node it can hear during the test session

Every event is time stamped

Received Packets/Application results are collected at all nodes

Routing state snapshots are collected

Analysis is done after the test session.

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Replaying a scenario

• SNR mapped to virtual distance• Each time interval corresponds to a

topological map

T5025 12510

075

150

Point A

Point D

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APE is a Testbed for…

1. Relative protocol performance comparisons

2. Radio channel effects on ad hoc routing protocols

3. Interactions between hardware, software, protocol, mobility and radio environmentExample: Grey Zone Phenomena

4. Validation of simulation models

5. Generation of traces

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802.11 Gray Zone Phenomena

AA

10 2

3

Broadcast

Unicast

3

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Challenge

Results should be reproducible and comparable between tests

It follows that experiments must be repeatable...

...and therefore stochastic factors need to be dealt with

So – what can we achieve?

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Stochastic Factors in Real World Experiments

Node mobility adds frequent changes in the network topology.– We use choreography and “measure

topology differences”

Variations in hardware and software configuration.– We use identical hardware and software.

Time varying radio environment affects link quality and error rates.

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Topology differences - visual check

RED = Average mobilityGREEN = 25% with lowest mobilityBLUE = 25% with highest mobility

Experiment 1 Experiment 2

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Part Two

Evaluating MANET protocols with the APE testbed, simulation and emulation.

Scenarios

UDP, Ping and TCP

Side-by-side comparison

Faulty protocol constructs

Conclusion

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Coupling Simulation, Emulation and Real World

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Routing protocols ability to adapt

OLSR - Proactive Link state routing. Monitors neighbors and exchange link state info.

AODV - broadcasts to set up path. HELLO or Link feedback to detect link failure.

DSR - broadcasts with source route. Listens to other traffic to find shorter route. RTT measurements and network ACKs.

React to connectivity changes

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Emulation

•Same configuration as Real world

•Table-top emulation

•MAC filters force connectivity changes

•Reduces radio and mobility factors

•Interference reduces bandwidth

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Simulation

•Scenarios recreated in a ns2-simulation using “default” models:

– Transmission range tuned to better match indoors– Mobility with jitter modeled after real world

measurements– Results averaged over 10 runs

•Results provide a baseline

•Can simulations using default (simple) models be used to predict routing protocol performance in complex real world environments?

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Multidimensional Comparison

Three MANET routing protocol implementations:– OOLSR, AODV-UU, DSR-UU

Three traffic types:– UDP (20 pkts/s CBR)– Ping (20 pkts/s CBR)– TCP (File transfer)

Three mobility scenarios:– End node swap, Relay node swap, Roaming node

Three environments (dimensions):– Simulation, Emulation, Real world

3x3x3x(10 runs) = 270 runs

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Experimental Test Environment

•Indoors with offices and corridors

•Four nodes (0, 1, 2, 3)

•Four waypoints (A, B, C, D)

•One data stream from node 3 to node 0

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Relay Node swap

AAA B C D

0 1 2 3

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Scenarios – Relay Node Swap

•End nodes stationary

•Intermediate nodes changes position

•Hop count never smaller than 2

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End node swap

AAA B C D

0 1 2 3

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Scenarios – End Node Swap

•End nodes change positions

•Intermediary nodes stationary

•Hop count changes from 3 to (2) and 1 and back

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Roaming node

AAA B C D

0 1 2

3

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Scenarios – Roaming Node

•Roaming node is source node

•All other nodes stationary

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Results – Relay Node Swap

Simulation Emulation Real World

0

0.2

0.4

0.6

0.8

1

1.2

UDP (Delivery ratio)

AODV-UU DSR-UU OOLSR


0

0.2

0.4

0.6

0.8

1

1.2

Ping (Delivery ratio)



0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

TCP (Mbps)


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Results – End Node Swap


0

0.2

0.4

0.6

0.8

1

1.2




0

0.5

1

1.5

2

2.5

3

TCP (Mbps)


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Results – Roaming Node


0

0.2

0.4

0.6

0.8

1

1.2




0

0.2

0.4

0.6

0.8

1

1.2

Ping (Delivery ratio)



0

0.5

1

1.5

2

2.5

3

3.5

4

TCP (Mbps)


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AODV - UDP - End Node Swap

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OLSR - UDP - End Node Swap

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Observations

Simulation and Emulation similar in absolute CBR performance but not in relative protocol ranking

Real world CBR performance is significantly lower

Discrepancy grows with traffic complexity and scenario

TCP performance is orders of magnitude lower for real world compared to simulation

periods of no-progress time in real world

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Observations (continued)

OLSR tries less hard to re-route and therefore achieves more even performance

•Radio factors account for most of the discrepancy between simulation and real world...

•...but secondary effects, such as cross-layer interactions that are protocol specific, dominate, e.g.:

– Lost HELLOs (AODV)– Excessive buffering (DSR)

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Protocol comparison conclusion

If one protocol performs better than another in simulation, is it possible to assume the same for

the real world?

NO

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Latency - Ping - Relay Node

Simulation Real World

0

500

1000

1500

2000

2500

3000

3500

4000

Relay node swap (Ping) RTT std. dev.


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Conclusions

APE aims to address the lack of real world ad hoc experimental research test-beds

Repeatability addressed at a level that allows relative protocol comparisons

The value of cross-environment evaluation

Revealing of sensing problems leading to instabilities and poor performance

Not visible in simulations

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The End

Paper:

http://www.it.uu.se/research/group/core/publications/GC_technical_report.pdf

APE testbed:http://apetestbed.sourceforge.net/

The Research group:http://www.it.uu.se/research/group/core/

a real-world test-bed for mobile ad hoc networks:

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