Study On RTT-based End-to-end Network Congestion Control

The performance of traditional TCP degrades in wireless network and highbandwidth-delay product (BDP) network. In this research, we proposed a RTT_basedend-to-end network congestion control protocol on the basis of the study of RTTdistribution model.Firstly, we established an end-to-end network model, and proposed a normalizedRTT distribution model based on Gamma distribution. Through the statistical analysisof the RTT samples got from the Internet, we found that RTT obeys exponentialdistribution under the conditon of light network load, while RTT obeys normaldistribution under the condition of heavy network load. The simulation results showedthat RTT obeys normal distribution in wireless network with heavy network load. Thetheory analysis showed that Gamma distribution can be converted into exponentialdistribution and normal distribution under the conditions of given parametersrespectively. In another word, RTT obeys Gamma distribution.Secondly, a SPC_based end-to-end network congestion control protocol (TCPSPC) is proposed in this research. This protocol uses the change of RTT as thefeedback of the network congestion, processes the RTT data with SPC method,estimates the trends of network load, and adjusts the congestion window size withdifferent strategy. The TCP SPC is tested in both QualNet simulation software and theLinux operating system. The results showed that the new protocol can improve thethroughput of wireless network and ensure the fairness of different data flows.Finally, we applied PI control theory in network congestion control, and proposeda PI_based end-to-end network congestion control protocol (TCP PI). This protocolestablishs an end-to-end virtual router model, calculates the difference of real timequeue size and target queue size at the virtual router, uses PI control theory tocalculate the data sending rate at the sender, and controls the router queue length atthe router. This protocol refers the change of queue size as the signal of networkcongestion, which can avoid the effect of wireless link error packet loss comparedwith the traditional TCP in wireless network. Simulation results showed that, the newprotocol can effectively control the queue size in router, improve network stability andthroughput in wireless network and high bandwidth-delay product network.