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Paper: IMPORTANT by Bai Sadagopan et al.

Paper: IMPORTANT by Bai Sadagopan et al. Michalis Faloutsos. 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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Paper: IMPORTANT by Bai Sadagopan et al.

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  1. Paper: IMPORTANTby Bai Sadagopan et al. Michalis Faloutsos

  2. 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?

  3. 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)

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

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

  6. 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

  7. 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”

  8. Metrics: Capturing mobility

  9. 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

  10. 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

  11. 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

  12. Which metrics can distinguish mobility? • Average relative speed and spatial dependence are good metrics

  13. Metrics for connectivity • Average link duration distinguished mobility models Why this dip?

  14. Mobility affects protocol performance • AODV and DSDV thruput comparison varies • Proactive (DSDV) protocols sometimes better than reactive Transmission range 250m

  15. Mobility models • What do nodes do when they reach the end of the road?

  16. 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

  17. 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?

  18. Quick calculations • Relative distance in hops? 1000^2/40 = 25000 m^2 • Area of transmission: pi r^2 = 3.14 250^2 = 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”?

  19. 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?

  20. 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

  21. 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

  22. 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!

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