TCP performance analysis and optimization over DMT based ADSL systems

This paper studies the TCP performance over a DMT based ADSL network. The impact of DMT subchannel bit loading on the TCP throughput performance is studied. The simulation results show that there is a threshold for the signal-to-noise ratio (SNR) gap or bit error rate (BER) above which TCP throughput drops quickly. This threshold takes its value in a wide range depending on the TCP round-trip time as well as channel noise. This suggests that it would be insufficient to set a fixed target BER at, e.g., 10/sup -7/, when calculating the number of bits to be loaded in each subchannel. Instead, the bit loading should take TCP performance into account. Finally a dynamic bit loading scheme is proposed, which jointly optimizes the channel bit rate and TCP throughput performance.