Evaluation of TCP performance using NDG loss predictor in wireless networks

Transmission control protocol (TCP), a widely used transport layer protocol performs satisfactorily over the wired networks. The performance of TCP data transmission deteriorates significantly when a TCP connection traverses over wireless networks. It is mainly because of packet losses caused by the high bit error rate of wireless links. Many solutions have been proposed for this problem in the past literature. Most of them have one or the other drawbacks such as violation of TCP's end-to-end principle etc.. In this paper, we consider a new method to improve the performance of TCP over wireless networks. The method employs using normalised delay gradient technique as loss predictor to distinguish congestion losses from that of transmission losses, and thereby evaluate the performance of TCP in wireless networks. A mathematical model representing the sender window size is formulated in such a way that when packet losses occur, TCP checks for the reason. If the losses is due to congestion, reduce the window size to half of the current window size, if the loss is due to transmission, the window size is recovered immediately to the latest value of window size. This method helps in achieving good throughput minimising packet loss. The work involves with estimation of i) round trip time(RTT), ii) sender window dynamics (cwnd), iii) instantaneous queue length at the ingress point of the router, iv) packet loss at the bottleneck link, and v) throughput analysis. The analysis helps in utilising the available wireless network resources more efficiently for proving good quality of service (QoS). For queue management at the bottleneck link, a router which supports RED (random early detection) features is used in the wireless base station. Mat Lab V2009b is used for simulation and analysis of mathematical models.