The impact of spurious retransmissions on TCP performance in ad hoc mobile wireless networks

In MANETs, ACK loss can affect TCP communication performance, since end-to-end reliable delivery of data packets is guaranteed by using ACK packets sent from a TCP receiver. This ACK loss may force a TCP sender to produce unnecessary retransmissions (called spurious retransmissions). These spurious retransmissions can also degrade the performance of TCP flows in the network because they will create more channel contention and interferences. These issues have been overlooked and hence require attention. We, therefore, propose new solutions to reduce such spurious retransmissions. Our scheme allows a TCP sender to be correctly informed of the sequence number that the TCP receiver expects to receive (i.e., ACK sequence). This ACK sequence is piggybacked onto routing control packets during a new route discovery process invoked by the TCP receiver. Using the ACK sequence tossed by the routing layer, the TCP sender can reduce spurious retransmissions. We evaluated and compared our scheme with TCP-Reno via simulation on ns-2. Simulation results showed that our proposed solutions outperformed general TCP (for both static and dynamic networks cases under multiple cross TCP traffic) in terms of aggregate throughput and number of spurious retransmissions.