Implementation of an Available Bandwidth estimator for WAN networks

This thesis presents a control module for software edge routers, called Receive Window Modulation - RWM. Its purpose is to limit congestion phenomena occurring in the network, which cause buffering and packet losses in any of intermediate routers along the path between the end points of an Internet connection. The controller improves end-to-end TCP performance, latency and fairness. It can be deployed in corporate edge routers, so that it does not need any end-point modification. The receiver’s TCP advertised window is modified based on the product of two different estimations: the round-trip time of the TCP connection and the path Available Bandwidth. Both these measurements are passive since round-trip time and Available Bandwidth are estimated by exploiting the existing network traffic. In particular, to estimate the path Available Bandwidth, a statistical method based on the inter-packet arrival time analysis of TCP acknowledgements is proposed. It is not related to the flow throughput, and can be implemented at either the sender or the receiver as a real-time estimation mechanism. Several experiments on both simulations and real network scenarios were conducted to understand whether this estimation was accurate. The comparison between this metric and modern TCP loss-based Congestion Control algorithms, such as CUBIC, showed that our estimations results are promising.