About Congestion Control Is Influenced By Environmental Robustness

With explosive growth of the Internet, the performance of data transmission inthe Internet depends highly on the transport-layer congestion control mechanisms. Forend-toend transport-layer protocols, since the network is regarded as a black box, in-dications for network congestion are necessary for efective congestion control. Thoughthe traditional TCP utilizes only packet loss events for the congestion indication, manyTCP variants that utilize the delay and bandwidth information of the network pathshave been proposed to accommodate recent high-speed, large-bandwidth, and wired-wireless integrated networks. Since the measurement of delay and bandwidth of thenetwork path generally includes the noises and errors, we should deal with them ap-propriately to improve the performance of such TCP variants.In this thesis, we focus on the additional mechanisms to Internet congestion controlto diminish and intentionally utilize measurement noises and errors due to environmen-tal changes. First, we propose to control the degree of dependence on measured valuesof congestion indicators. We then introduce the dynamic parameter setting mecha-nism to control the sensitivity of protocol behavior to the measurement results of thecongestion indicators. Second, we consider adding self-induced oscillation to the datatransmission rate to absorb the ill-efect of the environmental changes. In general, it isdifcult to recognize the sudden changes of the network environment quickly, becausewe cannot avoid the delay in the network measurement. Against this problem, wepropose to add some randomness in determining the increase/decrease slope of datatransmission rate.We confirm the efectiveness of the proposed mechanisms by applying them to TCPSymbiosis, one of the bandwidth-based TCP modifications. Through the simulationexperiments, we show that the former approach can keep the link utilization to be closetoregardless of the degree of measurement noises, and that the latter approach improvesthe link utilization from by absorbing the ill-efect of the environmental changes.