We present source tracing as a new viable approach to routing in ad hoc networks where routers communicate the second-to-last hop and distance in preferred paths to destinations. We use two source tracing algorithms, a table-driven protocol (BEST) in which routers maintain routing information for all destinations, and an on-demand routing protocol (DST) in which routers maintain routing information for only those destinations to whom they need to forward data. Simulation experiments are used to

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... compare these protocols with DSR, which has been shown to incur less control overhead than other on-demand routing protocols. The simulations show that DST requires far less control packets to achieve comparable or better average delays and percentage of packet delivered than DSR, and that BEST achieves comparable results to DSR while maintaining routing information for all destinations. to destinations in addition to distances to destinations [11] . This extra information helps remove the "counting-to-infinity" problem that most distance vector routing algorithms suffer from [1]. It also speeds up route convergence when a link failure occurs. On-demand routing protocols have been designed to limit the amount of bandwidth consumed in maintaining up-to-date routes to all destinations in a network by maintaining routes to only those destinations to which the routers need to forward data traffic. The basic approach consists of allowing a router that does not know how to reach a destination to send a flood-search message to obtain the path information it needs. There are several recent examples of this approach (e.g., AODV [14], ABR [17], DSR [10], TORA [12], SSA [5]) and the routing protocols differ on the specific mechanisms used to disseminate flood-search packets and their responses, cache the information heard from other nodes' searches, determine the cost of a link, and determine the existence of a neighbor. However, all the on-demand routing proposals to date use flood search messages that either: (a) give sources the entire paths to destinations, which are then used in source-routed data packets (e.g., DSR); or (b) provide only the distances and next hops to destinations, validating them with sequence numbers (e.g., AODV) or time stamps (e.g., TORA). One problem with source routing is that it results in long data-packet headers as the network size increases; in