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

202 S. PatilAfter flooding the query to nodes j hops away, the algorithm continues to thehigher levels of depth in the subsequent iterations in the i-Rule. After the lastiteration, in this case after k hops away, queries are not halted and the search isterminated.4 T-IDEA: Token-Based Iterative-Deepening AlgorithmIterative-deepening search is a good technique to keep a check on the flooding ofthe query by maintaining ‘check-points’ i.e. iterations in the flooding the query.But it does not take into account the energy considerations of the mobile nodes,which is crucial to estimate the network lifetime for any protocol. A betteralgorithm should be adaptive to the energy constraints on the nodes in the adhoc network, by involving nodes which have energy capacity to sustain as alongas possible, thus having a minimal effect on the network lifetime.T-IDEA implements this strategy by querying only a subset of the neighbors,thereby reducing the cost, but selecting neighbors which would convergeto correct results. These neighbors identify themselves as participants in thissearch. We use a token-based scheme in which each node makes local decisionswhether to take part in the search or not. Factors which are primarily functionalin this token-based scheme are energy constraints, query processing capacityetc. The following sections describe the participation algorithm for nodes whichparticipate in this search and the search in the participating nodes of ad hocnetwork.4.1 T-IDEA AlgorithmTo avoid involving highly constrained nodes or nodes who identify themselvesas ‘irrelevant’ for particular search, this algorithm allows any source to querynodes which identify themselves as part of the search and are willing to acceptand forward the queries.Each node in the ad hoc network broadcasts participation token(s) to all ofits neighbors. There are two types of tokens q-tokens and t-tokens. q-token(s)represent the number of query messages, q, for which the node can be the partof the search network and t-token represents the search-TTL for the node i.e. ttime units. Thus, a source would send a query to only those nodes, from which ithas a valid token. Once the node has replied/forwarded its q number of queriesor has been a part for t time-units, it broadcasts a zero-token message sendingits inability to take part in an any more active search query requests.In aggregate, the constained nodes would declare their level of participationin the search operations, by means of number of queries or time-to-search. Incase of t-tokens, sometimes the node receives and processes queries at a veryhigh rate, leading to high energy drain of the ad hoc node capacity. So to reducethe query processing, the node can send a q-token before the expiration of thet-token, to control its energy drainage caused due to high query-processing rate.Similarly if a node has earlier sent a q-token to neighbors, but is receiving queries