| Wireless ad hoc network consists of many mobile terminals, and it has the characters of centerless, self-organized, multi-hop and dynamic topologies. TCP can't satisfy the characters of wireless ad hoc network is leading to the performance of instability and degradation. There are a set of feasible improvement proposals among the methods of Ad hoc wireless network to improve the performance of TCP, because they adjust the sending rate of packets in accordance with the current network capacity.This thesis presents a proposal which can improve the performance of TCP in Ad hoc wireless network. The new scheme designs a cross-layer interaction mechanism to adjust the TCP congestion control on the basis of bandwidth delay estimation. When a node sends a packet, it measures the bandwidth and delay at the MAC layer and stores the bandwidth delay information in the MAC header of the packets. Then, the available bandwidth and the total delay of the current link can be estimated in the process of packets'forward and the ACK backward transmission. What the cross-layer interactive mechanism can do is supporting MAC layer to complete bandwidth delay estimation and calculate the BDP, realizing the sharing of information between the MAC layer and the TCP layer, responding to the request of the MAC layer and the TCP layer, adjusting TCP congestion window and slow start threshold timely according to the state of TCP. When packets lost at the TCP layer, TCP will modify its congestion window and slow start threshold based on the BDP value obtained from cross-layer interaction mechanism. Because the adjustment of congestion control is according to the state of network, the new scheme can reduce the frequency of the slow start and improve the TCP performance.Simulation results in NS2 show that BDE-TCP reduces the average slow start times, reduces the length of the network layer queue, and improves TCP throughput by 10% to 15% in static scenarios as well as small improvement in dynamic scenarios. |
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