This paper presents a comprehensive system modeling and analysis approach for both predicting and controlling queuing delay at an expected value under multi-class traffic in a single buffer. This approach could effectively enhance QoS delivery for delay sensitive applications. Six major contributions are given in the paper: (1) a discrete-time analytical model is developed for capturing multi-class traffic with binomial distribution; (2) a control strategy with dynamic queue thresholds is used in simulation experiments to control the delay at a specified value within the buffer; (3) the feasibility of the system is validated by comparing theoretical analysis with simulation scenarios; (4) the arrival rate can be adjusted for each forthcoming time window during the simulation with multi-packet sources; (5) statistical evaluation is performed to show both efficiency and accuracy of the analytical and simulation results; (6) a graphical user interface is developed that can provide flexible configuration for the simulation and validate input values.