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

SAFAR: An Adaptive Bandwidth-Efficient Routing Protocol 17Choice of fitness function: The ratioF(fitness), remains fairly constantthroughout the table buildup procedure.Hence, it makes for a stable fitnessfunction. The node is likely toquery half the nodes if its bandwidthmatches the average.Querying Fit nodesThis involves querying the selectednodes once the fitness function hasbeen applied. In Fig. 2, Node Aqueries nodes B and C with a sendFig. 2. Node A, relaying a send-table messageto nodes B,C and Etable message. This message is a request to these nodes to return their neighborlists back to the source node A. B and C are added to the proactive list(theproactive field in the routing table is set to true). As illustrated in Fig. 2, nodesB, C and E, on receiving a send table message from node A, generate a transfertable packet which reports address and bandwidth information of its neighbors(I,J,K,L,M,G,H respectively) back to A. It also adds A to its update list (i.e. theupdate field in the routing table is set to true). This list is explained in section4.4. Node A, on receiving a table transfer message, updates its routing tableand its heap with the newly found nodes (I, J, K, L, M, G and H).These nodeswill be considered in the next iteration of fitness function application along withthe rejected nodes from the previous query (D). The node A calculates averagebandwidth again using new data in its routing table and recalculates number ofnodes to query. As shown in Fig. 3, nodes J and M are selected.It has to be noted that the Mnodes can be chosen from any hopon the basis of maximum bandwidthvalue. Thus the radius of the activeneighborhood is not maintained uniformly.The procedure of querying fitnodes is applied again on J and M(Fig. 3). At this stage the numberof nodes to query becomes zero andhence the table build-up procedureends.4.4 RoutingFig. 3. Formation of the proactive zoneWhen a node requires a route to the destination (say X), it starts a route discoveryprocedure, which follows a two-stage mechanism as given below.Type-1 messagingThe node, in need of the route, sends a type-1 message to everyone in its proactivelist. If anyone of these queried nodes has a path to the destination,it respondswith a Type-1 reply packet. This packet also reports the maximum cost(lowest