Modifying the TCP Acknowledgement Mechanism: An Evaluation and Application to Wired and Wireless Networks

Universidad de Los AndesTELECOM BretagneDoctor en Informáticaamoret@ula.vedavid.ros@telecom-bretagne.euNowadays the Transmission Control Protocol (TCP) is omnipresent in the Internet. TCP con- veys roughly 90% of the Internet traffic from applications, such as web, email, file transfers and even multimedia traffic. In this thesis we develop methods and algorithms to improve the fundamental working of TCP: the clocking on data packets through the timely reception of acknowledgements (ACKs). Thus, we study two complementary aspects on data transmission, i.e., the controlling of the congestion of ACKs and the accelerating of the ACKs frequency. First, we describe in detail a mechanism, called ACK congestion control (ACK-CC), allow- ing TCP to deal with the impairments produced by the congestion of ACKs in bandwidth asymmetrical networks. Then, we evaluate the functioning of ACK-CC in both phases of the transmission, namely slow start and congestion avoidance. On the other hand, for the acceleration of the ACKs frequency (and thus the acceleration of data transmission) we assess the ACK division technique, through both simple mathematical modeling and simulation. In this dissertation we also investigate the performance of TCP over WiMAX networks. In WiMAX access networks, a Base Station (BS) serves a number of Subscriber Stations (SSs) forming the so-called last-mile access. Since the bandwidth management in WiMAX systems is centralized at the BS, the SSs have to contend for bandwidth to send their Best Effort traffic (i.e., TCP) in the uplink (from the SS to BS). Hence, we focus on two particular issues: the impact of the WiMAX MAC-layer asymmetry on TCP performance, and the improvement of the bandwidth perception management on the BS to accelerate downlink data transfer