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

32 P. Narayan and V.R. Syrotiukentire duration of the simulation T . Since DSR and AODV are reactive, the traceis valid only between t start and t stop when data flow actually exists.Only a subsequence of mobile graph G corresponding to the time betweent start and t stop is used to extract actual paths, run the SMP algorithm, and computethe MERIT ratio. Let us denote this subsequence as G ′ = G tstart ...G tstop .For every graph in the mobile graph G ′ , we compute the actual path from thesource to the destination.To compute the MERIT ratio for the mobile graph G ′ , the SMP algorithmrequires the shortest path in each graph of the mobile graph and the shortestpath in the intersection of all subsequences of the graph sequence. We implementDijkstra’s shortest path algorithm to find the shortest hop path in any graph,while computing the cost matrix for the SMP algorithm. We use hop count asthe metric for our implementation of the SMP because both DSR and AODVuse this metric in their path computation.For this work, we consider the cases where we assign the constant values of0, 0.5, 1.0, 1.5 and 2.0 for the update cost. We chose a maximum value of 2.0 forour update cost because we found that the average path length for our simulationexperiments did not exceed 3.5 hops.4 MERIT Spectra for DSR and AODVWe conduct two sets of experiments. In the first set, we measure the MERITratio for different scenarios by varying the degree of mobility. In the second set,we keep the mobility rate constant and measure the MERIT ratio by varyingthe data rate for the CBR flow from the source to the destination.In all cases, our results are averaged over a sufficiently large number of runs toensure a small variance (95% confidence interval). From the confidence intervalcalculations on our experimental results, we find that the MERIT ratio varieswithin 2.85% of the plotted value.4.1 Parameters of InterestThe parameters against which we plot MERIT spectra include:Mean speed: A mean speed of 2 m/s equates to the speed of a pedestrian anda mean speed of 10 m/s corresponds to the speed of a moving vehicle.Data arrival rate: The data arrival rate represents the number of packets sentper second. For our experiments, we use data arrival rates of 2, 4, 6, 8 and10 packets/second, with the traffic being sent out at a constant rate and thepacket size being constant at 64 bytes.Average path length: The average path length for a simulation run denotesthe average actual path length (hop count) over all the paths for the specifiedsource-destination pair.Average end-to-end delay: The average end-to-end delay for a run denotesthe average end-to-end packet delay (in units of number of seconds) computedfrom the router trace for the data packets sent by the candidate protocols.