Optimization of internet traffic quality of service using robust design and analytic methodologies

Abstract

This thesis is concerned with applying robust design and analytic methodologies for optimizing Internet traffic quality of service (QoS). For the first part of research, a state-of-the-art review on the use of DOE in the field of communication research is presented, and the need for introducing a systematic robust design methodology to simulations (or testbed experiments) is identified in ensuring robust behaviors of a communication network against uncontrollable sources of variation. More specifically, the response surface methodology (RSM) and Taguchi robust design methodology are utilized for the robust design of communication systems or control algorithms. The experimental data for the two methodologies are collected using the well-known ns-2 simulator. First, the RSM, a well-known DOE technique, is used for determining the settings of control parameters of the BLUE active queue management (AQM) scheme such that its performance characteristics become robust against uncontrollable noise variables. In this problem, link utilization and packet loss rate are considered as performance characteristics; operating parameters of BLUE (e.g., freeze time, incremental amount of packet dropping probability, and threshold queue size) as control parameters; and the number of connections and packet size as noise variables. The mean and variance of each response are estimated, and a compromised optimal condition is identified using the dual response approach. Second, the Taguchi robust design methodology is applied for optimizing the Expedited Forwarding (EF) of voice traffic in a Differentiated Services network, and its step-by-step procedures are described in detail. The SN ratio, a robustness measure, is analyzed to determine an optimal design condition for each performance characteristic. The analysis results show that "type of queue scheduling schemes" is a major control factor for ensuring robust behaviors of one-way delay and jitter while "E...