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

16 J. Doshi and P. Kilambipacket that reports their address and bandwidth value.They also have the optionof preventing A from actively maintaining information on them using ablocking bit(explained subsequently). For example in Fig. 1, node F sets theblocking bit and hence prevents A from querying it although it has high fitness.Node A, now adds all the neighborswho responded into its neighbor listand those with blocking bit not set tothe node heap. Now the node beginsthe table buildup procedure. NodeA, for the remainder of its lifetime,keeps polling its neighborhood withhello messages to stay informed of itsneighbors.Fig. 1. Node A’s immediate neighborhoodon its entry into the networkUse of the Blocking bit: This bit maybe set if a node finds the ratio of routinginformation to data informationexceeds some threshold. This safeguardsthe proactive routing overheadof the protocol and hence a node with high fitness is prevented from beingoverloaded (Node F in Fig. 1). The blocking bit is also set when the environmentaround that node is volatile.This forces nodes around it to switch over to reactiverouting, which performs better in such scenarios. In a stable environment,nodes will be encouraged to use active information. Thus the protocol adapts tochanging environment characteristics.4.3 Routing Table BuildupApplication of Fitness functionWe extend the concept of fitness function, discussed earlier, to MANETs. Eachnode uses the fitness function to find its role in the environment and how manynodes it can query. If it has higher fitness, it has to assume a role of facilitatorand allow less fit nodes to communicate. This function F(fitness) is now used toselect the number of nodes to be queried (M) from subsequent hop nodes usingthe formula,M = min(round(F × exp −i2 ×n),n1) (1)where, i is the iteration number (0,1,. . . ,n), n is the sum of number of hop (i+1)nodes to be queried and number of nodes not selected up to i iterations and n1is the number of nodes currently in heap. In Fig.2, Node A selects B, C and Ebased on this fitness function as they have sufficiently high bandwidth. It thenstarts the next iteration of the table buildup by querying these selected nodes.This is explained in the next paragraph(Querying Fit nodes). The exponentialfall-off in the order of 2 is used because it becomes that much more expensiveto maintain nodes proactively with increasing hop radius. This is multiplied byn, as n is dynamic and varies from hop to hop.Thus the fitness is effectively‘scaled’ [11].