Paper: IMPORTANT by Bai Sadagopan et al.

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Paper IMPORTANTby Bai Sadagopan et al.

• Michalis Faloutsos

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The Problem How important is mobility in ad hoc
performance?

• Mobility has been ignored or downplayed so far
• Questions
• What is the effect of mobility on performance?
• How does mobility affect performance?

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Contribution Mobility is critical

• Mobility affects the performance
• Define a set of parameters (framework)
• Mobility
• Network connectivity
• Protocol structure (building blocks)
• Relative performance of protocols varies with
  mobility
• Mobility affects connectivity (link/path
  stability)

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Motivation and Significance

• W need a systematic approach to simulations
• Warn us varying scenarios gives diff. Results
• Provide a framework to characterize mobility

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Roadmap

• Previous work
• Definition of metrics for mobility and
  connectivity
• Experimental results
• Conclusions
• Paper criticism

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Mobility models and studies

• Way- point model
• Group Mobility (RPGM)
• Groups of nodes that follow a group leader
• Each member has speed similar to leader
• Magnitude, angle (from x-axis)
• Freeway predetermined lanes two way
• Manhattan square lattice two-way traffic
• Prob. 0.5 go straght, 0.25 turn left, 0.25 turn
  right

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Previous studies

• Mobility does matter Pei et al. 11
• Proactive and reactive protocols are similar
  performance johansson et al. 10
• Proactive protocols better throughput, and e2e
  delay, but reactive protocols less overhead Das
  et al. 8 (spot any contradiction?)
• 8 introduced a mobility model limiting change

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Metrics Capturing mobility
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Metrics Spatial and Temporal Dependence

• Spatial Dependence movement similarity of nodes
  close together
• Temporal Dependence similarity of node movement
  with itself in the near past
• Relative Speed as in physics difference of
  vectors

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Metrics for graph connectivity

• Number of link changes how many times there was
  a direct link between two nodes
• Link duration how long a link between nodes
  lasts
• Path availability fraction of time that two
  nodes are connected

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Simulation set up

• Area 1000m x 1000m
• 40 nodes
• 900 sec
• RPGM groups of 1x40, and 4x10
• Speed Vmax 1,5,10,20,30,40,50,60 m/sec
• Range 250m

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Which metrics can distinguish mobility?

• Average relative speed and spatial dependence are
  good metrics

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Metrics for connectivity
Why this dip?

• Average link duration distinguished mobility
  models

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Mobility affects protocol performance

• AODV and DSDV thruput comparison varies
• Proactive (DSDV) protocols sometimes better than
  reactive

Transmission range 250m
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Mobility models

• What do nodes do when they reach the end of the
  road?

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Conclusions

• Mobility affects performance of protocols
• DSR is a well designed protocol with optimized
  parameters
• Other protocols are non-optimized then?
• DSR aggressive caching of routes
• Good for low mobility

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Criticism

• Mobility was examined, but what about other
  parameters
• Average path length of connection
• Average duration of connection
• Speed with respect to connection and simulation
  duration
• Parameters of different protocols, were they
  optimized?

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Quick calculations

• Relative distance in hops? 10002/40 25000 m2
• Area of transmission pi r2 3.14 2502
  196,250
• Average neighborhood 7.85 nodes
• Node density!
• Max straight path length 1000 sqrt(2) / 250
  5.65 hops
• Average path length approx 3 hops
• Is that enough?

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Mean criticism

• We knew that mobility is important
• We knew that DSR seems to perform best
• In one case AODV does better slightly
• Do their results suggest what is the right
  simulation? No.
• They provide some intuitive obseervations
• Building blocks do they actually explain
  something?

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Fair criticism

• Provide a framework, first organized attempt
• Provide metrics
• Do thorough experiments
• Explain they results they see (most of them)
• Intersting work that makes you think

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How could I do things better

• Model topology from a graph theoretic poin of
  view
• More metrics
• Average path length
• Average neighborhood
• Node density
• Path length inflation
• Choice of source-destination pairs (skewed
  distr.)
• Measure disconnectivity scope, duration

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More how to do things better

• Examine the effect of other parameters than just
  mobility
• Show that subtle parameters in protocols can make
  significant changes
• Argue that protocol parameters must be dynamic!