(A) control-theoretic approach to flow control in communication networks

Abstract

This thesis describes flow control algorithms achieving two kinds of max-min fairness properties, that is to say, bandwidth max-min fairness and utility max-min fairness and provides a control-theoretic approach to analyze the stability of proposed algorithms. Our algorithms are scalable in that routers do not need to store any per-flow information of each flow and they use simple first come first serve (FCFS) discipline, stable in that the stability is proven rigorously when there are flows with heterogeneous round-trip delays, and optimal in that the gains used for controllers are optimally adjusted. First, we present a network architecture for the distributed bandwidth max-min flow control of elastic flows and generalize stability conditions to enhance network performance. We suggest two closed-loop system models that approximate our flow control algorithms in continuous-time domain where the purpose of the first algorithm is to achieve the target queue length and that of the second is to achieve the target utilization. The slow convergence of many rate-based flow control algorithms, which use queue lengths as input signals, can be resolved by the second algorithm. Based on these models, we find the conditions for con-troller gains that stabilize closed-loop systems when round-trip delays are equal and extend this result to the case of heterogeneous round-trip delays with the help of Zero exclusion theorem. Second, we revise the proposed algorithms and provide application-performance oriented flow control algorithms. We present a network architecture for the distributed utility max-min flow control of elastic and non-elastic flows where utility values of users (rather than data rates of users) are enforced to achieve max-min fairness. We also provide a distributed link algorithm that does not use the information of users`` utility functions. To show that the proposed algorithm can be stabilized not locally but globally, we found that the use of nonlinear con...