1 Paper: IMPORTANT by 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 = m^2 Area of transmission: pi r^2 = ^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!