Abstract of Thesis presented at COPPE/UFRJ as a partial fulfillment of the requirements for the degree of Doctor of Science (D.Sc.)

Application of Control Algorithms for Treatment of Congestion in Computer Networks

Diana Beatriz Benítez Cáceres

May/2010

Advisors:

Eugenius Kaszkurewicz Amit Bhaya

Department:

Eletrical Engineering

      The speed up growth of the Internet in the last few decades brings as consequence congestion problems. Current Internet congestion control relies on binary adjustment algorithms.
      This work presents and analyzes new proposals of congestion control. The objective of this work is the use of control algorithms to model and to solve the problem of congestion control. First, two techniques based on a more appropriated selection of the parameters of increment and decrement of the dynamic of the AIMD algorithm are introduced according to virtual equilibria. In this context, this work proposes two new TCP-like protocols which control the congestion in a more efficient and fairness way, trading off with a larger number retransmissions. The new protocols use an estimation of the bandwidth and an estimate of the number of users sharing the network.
      This work also studies the congestion control problem from a control perspective, starting from variants of this classical algorithm in order to propose two optimizationbased schemes, which obtains faster convergence to a small neighborhood of the optimal fair full utilization state. The price to be paid for this improvement is that, in addition to the binary feedback information, each source must have knowledge of the sending rates of its neighbors. Simulation results are presented showing that responsiveness and smoothness are improved, even in the presence of delays and timevarying link capacity.