Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...

Evaluation of the AODV and DSR Routing Protocols 331.3DSRAODV1.251.2Merit Ratio1.151.11.052 3 4 5 6 7 8 9 10Mean Speed(m/s)Fig. 3. MERIT ratio versus mean speed.4.2 MERIT SpectraIn this section, we present the various MERIT spectra generated for the set ofexperiments where we vary the speed from 2 m/s to 10 m/s.Figure 3 shows that the MERIT ratio computed for DSR and AODV growswith increasing mobility rate. It is clear that as the speed increases, the topologychanges at a faster rate. Since both DSR and AODV are on-demand protocols,a certain delay is experienced before the routes are repaired and the routingcaches/tables are updated to reflect the latest changes in topology. The computedvalues of the MERIT ratio reflect that the paths in the routing table are closerto optimal for scenarios with lower speeds than for scenarios with higher speed,mostly because the topology changes are more frequent and route repairs or routemaintenance is done more frequently. Additionally, we observe that the DSRprotocol yields MERIT ratios that are closer to the optimal cost than AODV.The maximum and average differences between the computed MERIT ratios ofDSR and AODV expressed as a percentage is 1.25 and 0.5136 respectively. Thesedifferences are consistent with the observations made in [2] where the authorssuggest that DSR’s caching is more effective than AODV at lower mobility rateswhere the cached information goes stale more slowly.In Fig. 4, we see that the MERIT ratio increases with respect to the actualpath length. The path length we plot is the average of the actual path lengthsfrom the route trace. The results in the figure indicate that when the actual pathlengths computed by the AODV routing protocol are larger, the MERIT ratio isalso higher. AODV computes paths that are longer than the paths computed byDSR primarily because DSR has access to significantly greater amount of routeinformation than AODV because it employs aggressive caching and promiscuouslistening. AODV has access to less information because it maintains only oneentry per destination in its routing table and relies significantly on a higherfrequency of route discovery flooding to keep its routing table up to date.When the paths between a source-destination pair are longer (more hops),it could result in a higher end-to-end delay. Also, when the speed is higher andthe topology changes at a faster rate, there could be a higher end-to-end delay