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

34 P. Narayan and V.R. SyrotiukDSRAODVDSRAODV1.31.351.31.25Merit Ratio1.251.21.151.1Merit Ratio1.21.151.11.0513.51.05101080.8380.662.560.4440.2Path Length (Avg no of hops)2 2Arrival Rate (Packets/sec)Speed (m/s)2 0Delay (secs)Fig. 4. MERIT ratio versus (a) arrival rate and path length; (b) delay and speed.because a greater amount of route maintenance and repair will have to be donewhenever the topology along the path changes. We conclude that in scenarioswhere the mobility rate is higher and in scenarios where the path between thesource and the destination is longer, the paths are further away from the optimal.Since the average delay is affected by the combination of these factors and otherfactors like the network load as well, we can expect to see that higher delayswould lead to higher MERIT ratios.The SMP algorithm used to compute the ideal cost in the MERIT framework,involves a two-valued transition cost. The transition cost can be viewedas a trade-off between the importance of the stability of the path and the lengthof the path. When the cost of updating path information is small, the SMP algorithmplaces more emphasis on searching for the shortest path without regardto whether or not it changes the path. When the cost is larger, the algorithmgives more importance to searching for stable paths since it is costly to changepaths. We observe that MERIT ratios generally increase with an increase in theupdate cost values because the actual routing protocol implementation makesits routing decisions by using only the instantaneous information recorded in itsdata structures at any given time. With a higher cost of update, the importanceof using the past history to make routing decisions is more critical because stablepaths are preferred when the update cost is higher. This is effectively capturedin the higher values obtained for the MERIT ratio with an increase in cost.We see that the MERIT ratio increases with an increase in the data arrivalrate. The path lengths for these scenarios are also noticeably shorter than theones observed for the previous set of experiments. This can be attributed to thefact that both DSR and AODV are on-demand protocols, hence a higher datarate causes the routing tables to be updated more frequently, resulting is smallerpath lengths.Our results clearly indicate that for the scenarios we have considered, DSRprovides paths which are closer to the optimal than AODV. In our experiments,we choose simulation scenarios where we have only one s-t pair, which is communicating.We use a single CBR source that sends data at a steady rate in all