Achieving high performance in high capacity data transfers over the Internet has long been a daunting challenge. The current standard of Transmission Control Protocol (TCP), TCP Reno, does not scale efficiently to higher bandwidths. Various congestion controllers have been proposed to alleviate this problem. Most of these controllers primarily use marking/loss or/and delay as distinct feedback signals from the network, and employ separate data transfer control strategies that react to either marking/loss or delay. While these controllers have achieved better performance compared to existing TCP standard, they suffer from various shortcomings. Thus, in our previous work, we designed a congestion control scheme that jointly exploits both delay and marking; D+M (Delay Marking) TCP. We demonstrated that D+M TCP can adapt to highly dynamic network conditions and infrastructure using ns-2 simulations. Yet, an analytical explanation of D+M TCP was needed to explain why it works as observed. Furthermore, D+M TCP needed extensive simulations in order to assess its performance, especially in relation to other high-speed protocols. Therefore, we propose a model for D+M TCP based on distributed resource optimization theory. Based on this model, we argue that D+M TCP solves the network resource allocation problem in an optimal manner. Moreover, we analyze the fairness properties of D+M TCP, and its coexistence with different queue management algorithms. Resource optimization interpretation of D+M TCP allows us to derive equilibrium values of steady state of the controller, and we use ns-2 simulations to verify that the protocol indeed attains the analytical equilibria. Furthermore, dynamics of D+M TCP is also explained in a mathematical framework, and we show that D+M TCP achieves analytical predictions. Modeling the dynamics gives insights to the stability and convergence properties of D+M TCP, as we outline in the thesis. Moreover, we demonstrate that D+M TCP is able to achieve excellent performance in a variety of network conditions and infrastructure. D+M TCP achieved performance superior to most of the existing high-speed TCP versions in terms of link utilization, RTT fairness, goodput, and oscillatory behavior, as confirmed by comparative ns-2 simulations.

This thesis uses a modern control approach to address the Internet traffic control issues in the Transport Layer. Through literature review, we are interested in using the H2/H∞ formulation to obtain the good transient performance of an H2 controller and the good robust property from an H∞ controller while avoiding their deficiencies. The H2/H∞ controller is designed by formulating an optimization problem using the H2-norm and the H∞-norm of the system, which can be solved by an LMI approach using MATLAB. Our design starts with the modeling of a router and the control system by augmenting the network plant function with the Sensitivity function S, the Complementary Sensitivity function T and the Input Sensitivity function U. These sensitivity functions along with their weight functions are used to monitor the closed-loop dynamics of the traffic control. By choosing different combinations of the sensitivity functions, we can obtain the SU, the ST and the STU controllers. Both the window-based and rate-based version of these different types of H2/H∞ controllers have been designed and investigated. We have also proved that these controllers are stable using Lyapunov’s First Method. Next, we verify the performance of the controllers by OPNET simulation using different performance measures of queue length, throughput, queueing delay, packet loss rate and goodput. Our performance evaluation via simulation has demonstrated the robustness and the better transient response such as the rise/fall time and the peak queue value. We have also investigated the controller performances subject to network dynamics as well as through comparison with other controllers. Finally, we have improved these controllers for real-time application. They are capable to update/renew the controller in a short time whenever new network parameter values are detected so that the optimum performance can be maintained.