Evaluation of TCP Performance Using NDG Loss Predictor in Wireless Networks

Abstract

Transmission control protocol (TCP), a widely used transport layer protocol provides reliable service and end-to-end congestion control. Performance of TCP is satisfactory in wired networks but fails to perform well in wireless networks. It is because in wireless networks two types of packet losses are important. Congestion loss and transmission loss. Transmission loss can be ignored in wired networks whereas very frequent in wireless networks. Transmission loss is due to random bit error rate (BER). If the packet loss is due to congestion, TCP should react such that it minimises the congestion in the network. If the loss is due to transmission, TCP should continue with its operations. Suppose, a congestion loss is incorrectly classified as transmission loss, the sources will not decrease their sending rate and congestion will build up in the networks causing reduction in the throughput. Similarly, if transmission loss is treated as a congestion loss, the sources will unnecessarily reduce its offered load causing reduction in the throughput. Thus, the impact of such misclassification is considered to be most significant in maintaining the quality of service (QoS) in the wireless networks. To satisfy these challenges, we propose a model based scheme to adopt sending rate to the losses due to congestion and BER. The model distinguishes congestion loss from transmission loss using the scheme proposed in [8], [9]. If the packet loss is due to congestion (Beta = 0), congestion control mechanism is being invoked. If the packet loss is due to transmission (Beta = 0:1), fast-recovery is being used to gain the loss caused by BER and TCP continues its operation. This helps in achieving good throughput in wireless networks. Using this model, we analyse (i) round trip time (RTT), congestion window (cwnd) dynamics, instantaneous queue length at the bottleneck link, the mechanism of packet dropping, and packet loss (ii) delay-RTT, delay-queue (iii) fast recovery of cwnd, and (iv) the throughput. The experimental results show good performance of TCP over the wireless network in presence of BER.