Robust design of communication systems: The case of expedited forwarding of voice traffic in differentiated services networks

Design of experiments (DOE) is gaining acceptance in the community of telecommunication researchers, especially during the past several years. In this paper, a state-of-the-art review on the use of DOE in the field of communication networks is presented, and the need for introducing a systematic robust design methodology to network simulations or testbed experiments is identified in ensuring robust behaviors of a network against uncontrollable sources of variation. Then, 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 experimental data are collected using the ns-2 simulator, and 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 “EF queue size” is for throughput and loss rate. Finally, a compromised optimal design condition is identified using a desirability function approach adapted to multi-characteristic robust design problems.