Eventually every node in the subnet will be able to

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indicating the “distance to itself (0),” and a sequence number. Eventually, every node in the subnet will be able to determine the shortest path to forward a message to all other nodes in the subnet. However (unlike LS based approaches), nodes do not get to know the complete topology of the subnet or even the complete path to the destination. Every node can only determine the best next-hop neighbor for sending a packet to any destination. A third approach to routing is flooding, where the sender simply floods a message (with a sequence number) to all its neighbors. The neighbors in turn flood the message to all their neighbors, and so on. The sequence number is used to keep the flooding in check - every node will rebroadcast a packet indicating the same (source, sequence number)-tuple only once. Ad hoc routing protocols, which typically employ variants of the three basic routing principles, and most often, a combination of the three basic strategies, can be broadly classified into on-demand and proactive proto- cols. Proactive protocols use LS 18 or DV 17 based strategies to maintain a consistent view of the dynamic topology at all times. Reactive or on- demand protocols maintain either no information or partial information Copyright © 2010. World Scientific Publishing Company. All rights reserved. May not be reproduced in any form without permission from the publisher, except fair uses permitted under U.S. or applicable copyright law. EBSCO Publishing : eBook Collection (EBSCOhost) - printed on 2/16/2016 3:46 AM via CGC-GROUP OF COLLEGES (GHARUAN) AN: 340572 ; Beyah, Raheem, Corbett, Cherita, McNair, Janise.; Security in Ad Hoc and Sensor Networks Account: ns224671
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54 M. Ramkumar about the subnet topology. More specific information is determined as and when required, usually by flooding requests to obtain missing topology in- formation. For example, in the ad hoc on-demand DV (AODV) protocol, 19 every node proactively maintains only the one-hop topology information. When- ever a node S desires to send some message to D , S floods a Route-Request (RREQ) packet indicating a sequence number, the destination D , the max- imum number of hops to which the RREQ can be flooded, and a hop-count field (initialized to zero). Every node that rebroadcasts the packet incre- ments the hop-count field by one. The destination D , or some node with the knowledge of a route to D , can instantiate a Route-Response (RREP) packet. Following the receipt of RREP by the source S , even while no node in the path is aware of the complete path between S and D , every node in the path learns the distance (hop-count) to D , and the next hop in the path to D . In the on-demand dynamic source routing (DSR) protocol, 20 nodes do not proactively maintain any topology information. A source S seeking to send a message to a destination D invokes a RREQ packet indicating the source, sequence number, the destination D , and the maximum number of hops. Every node rebroadcasting the RREQ inserts its ID / address in the RREQ. When the RREQ reaches the destination, or some node with the knowledge of a path to the destination, an RREP is invoked. As the RREP
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