Research Of Improve Data Transmission Performance In DTN Network

Space Delay Tolerant Network(DTN) differ greatly from terrestrial cable network.The terrestrial cable network has small latency and low error rate.So traditional congestion control algorithm in TCP/IP protocol can be well applied.However,space DTN has large latency and high error rate. If using traditional congestion control for TCP / IP protocol as usual, transmission efficiency will be greatly reduced.In order to solve the above problems.Firstly,the thesis summarizes the work to improve the transmission performance in space network.Then,describes the several stages of TCP protocol congestion control algorithm,pointing out the impact of large latency on the slow start phase; the impact of hige error rate to packet loss and the judgment of congestion.Followed, confirmed the validity of its conclusions by use NS2.In order to reduce the effects of large latency to the data transmission, proposed two aspects of improvement based on Vegas algorithm.The one is by expanding the initial window,to get more ACK in unit time,accelerate the growth of congestion window on slow start phase,resulting in greater throughput,the other is take into account the Vegas algorithm may prematurely end the slow start phase, making stay too long in the congestion avoidance phase, which greatly reduces network bandwidth utilization.Thus,the thesis accelerate the growth of the congestion window on Congestion avoidance phase to close to the best congestion window, improving throughput. Through the contrast of NS2 simulation experiment, it can be seen that in a short period of time, improved algorithm can improve the throughput significantly higher than that of traditional Vegas algorithm.In order to determine packet loss causing by congestion or error more accurate,we use the Explicit Congestion Notification(ECN) mechanism to solve the effects of high error rate.According to the router via space link, we can more accurately and more quickly to inform the sender whether congestion occurs. Under the premise of accurately determine the cause of packet loss, congestion further divided state, we able to maximize the use of the bandwidth.By NS2 simulation experiments we can see the improved algorithm is superior to Vegas algorithms in short TCP connections.Finally, based on CCSDS AOS standards and TCP-Splitting techniques,we build a system of space data transmission network. Through TCP-Splitting techniques, making the network inside the space to use the traditional TCP protocol congestion control algorithm, which is used to improved Vegas algorithmthe between the space link. Thus, reducing unnecessary losses and faster file transfer. Transfer small files in the system, we can see that the improved algorithm is superior to Vegas algorithms.