Performance Enhancement of TCP in Dynamic Bandwidth Wired and Wireless Networks

In this paper, we propose a scheme that dynamically adjusts the slow start threshold (ssthresh) of TCP. The ssthresh estimation is used to set an appropriate ssthresh. A good ssthresh would improve the transmission performance of TCP. For the congestion avoidance state, we present a mechanism that probes the available bandwidth. We adjust the congestion window size (cwnd) appropriately by observing the round trip time (RTT) and reset the ssthresh after quick retransmission or timeout using the ssthresh estimation. Then the TCP sender can enhance its performance by using the ssthresh estimation and the observed RTT. Our scheme defines what is considered an efficient transmission rate. It achieves better utilization than other TCP versions. Simulation results show that our scheme effectively improves TCP performance. For example, when the average bottleneck bandwidth is close to 30% of the whole network bandwidth, our scheme improves TCP performance by at least 10%.