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

Evaluation of the AODV and DSR Routing Protocols 313.4 Mobile Path Computation for DSRTo facilitate the computation of the mobile path for our evaluation of the DSRprotocol, we require the actual paths used by the protocol to route data packetsfrom the source to a destination. In order to obtain this information, we modifythe DSR implementation in ns-2 to trace the primary and secondary cache eachtime an entry is either added to or deleted from the cache.For every simulation run, we gather the route cache trace and use this todetermine the actual path, which DSR would use to route a packet from sourceto destination for a particular time sequenced graph in the mobile graph G. Thisapproach is generalized and can be used to gather route information for protocolimplementations in other network simulators such OpNet or QualNet [15,17].The procedure we adopt to select the actual path is consistent with the algorithmused by the ns-2 implementation of DSR to select a route. For example,Fig. 2 shows a three graph subsequence G i−1 G i G i+1 in a mobile graph for asession between source-destination pair 4-5. The solid path between nodes 4 and5 is the actual route computed by DSR while the dashed path (which coincideswith the last two hops of the actual route) is the shortest hop path.100010001000900790079007800700401211661338007004012161613380070040121616 31360060060050040011151021950040011151021950040011151021930020010018148917530020010018148917530020010018148917500 100 200 300 400 500 600 700 800 900 100000 100 200 300 400 500 600 700 800 900 100000 100 200 300 400 500 600 700 800 900 1000Fig. 2. Subsequence G i−1G iG i+1 of a mobile graph for source-destination 4-5.3.5 Mobile Path Computation for AODVEvery node that implements the AODV protocol maintains a separate routingtable with the next hop information. Each entry in the routing table has anexpiration time and a sequence number. To compute the actual mobile path forAODV, we trace the route table for every node in the simulation whenever anew entry is added or updated in the routing table.One can easily trace the valid path to the destination from the routing tableinformation for each node. The expiration time for each routing table entryis used to judge whether or not the route calculated is stale. We use the samealgorithm used by the ns-2 AODV implementation to calculate the actual mobilepath for our mobile graph.3.6 Computation of the MERIT RatioEvery connection in the connection pattern file has a designated start (t start )and stop time (t stop ). Our mobile graph G consists of a graph sequence for the