Design and analysis of adaptive routing and transport protocols in mobile ad hoc networks

A mobile ad hoc network (MANET) is a collection of mobile computing devices that communicate using wireless links, forming a multihop network without the use of network infrastructure or centralized administration. In this dissertation, we examine routing and transport protocol performance in MANETs and we explore ways of improving that performance.; It is well known that TCP performance in MANETs suffers from TCP's inability to distinguish packet losses due to congestion from losses caused by mobility-induced route failure. We propose a heuristic in which the TCP sender interprets multiple timeouts for the same packet as an indication that the route to the receiver is broken. Rather than doubling the retransmit timeout interval (RTO) on each consecutive timeout, the sender fixes the RTO. The increased rate of packet retransmissions stimulates route repair, reducing the time taken to repair the broken route and re-establish the flow of TCP packets.; UDP performance in MANETs is also problematic. Using simulations, we show that rapid topology changes prevent UDP from fully utilizing available network capacity. To address this issue, we propose an adaptive unreliable packet delivery service, the Adaptive Datagram Protocol. ADP uses acknowledgments from the receiver to clock the transmission of new packets. The sender buffers packets when the application's sending rate exceeds network capacity. If the buffer becomes full, the sender drops excess packets rather than injecting them into the network where they may cause contention. These features enable ADP to attain higher throughputs and use network resources more efficiently than UDP.; We have conducted extensive simulations over a wide range of network loads to test the applicability of our transport protocol proposals to three MANET routing protocols. The network loads were varied to include FTP file transfers, variable-bit-rate video streams, and HTTP traffic. Our results demonstrate that the fixed-RTO heuristic significantly improves TCP performance for routing protocols which respond well to route stimulation, and in situations where route repairs are prolonged or difficult. Our results also show that, in addition to providing higher throughput and greater efficiency than UDP, ADP works well with TCP to achieve an equitable sharing of available bandwidth.