tuning approach in section 6.4.3.1 is used to calculate the Hyper-exponential parameters. But the H2/D/1 model does not have any correlation between packet arrivals. Among these three analytical models, the MMPP/D/1 model has the highest accuracy whose error is within 10% 6.4 Dimensioning for Transport Network Performance range. Because the MMPP/D/1 model is derived from the H2/D/1 model, and additionally includes certain correlation of the arrival traffic. By comparing the dimensioning results from the OPNET simulation with the results derived from different analytical models, it can be concluded that in the voice scenario using the MMPP/D/1 model to derive the required lub bandwidth for the 1% packet loss ratio is accurate (less than 10% relative error). voice only scenario - Rel99 ATM-based lub M/D/1 H2/D/1 MMPP/D/1 voice traffic demand [kbps] Figure 6.52: Relative error of the analytical model (voice scenario) For the web traffic only scenario, the corresponding queuing model is MMPP/D/1. Figure 6.53 compares the dimensioning results for a web traffic scenario (with BRA function) obtained from simulations with UMTS Rel99 simulation model and the results derived from MMPP/D/1 model. Figure 6.54 shows the error of the MMPP/D/1 model. It is seen from the results that the MMPP/D/1 model can estimate the required lub bandwidth accurately for the pure web traffic scenario, and the obtained relative error of the analytical model is less than For the mixed traffic scenario, the queuing model MMPP/D/1 with non-preemptive priority shall be applied for dimensioning. Figure 6.55 compare the dimensioning results of web traffic (using BRA) mixed with 10% voice obtained from the simulation with the results derived from the MMPP/D/1 priority model (section 6.4.3.3). It is seen that the dimensioned lub bandwidth derived from the MMPP/D/1 priority model is close to the results obtained from system simulations. 6 Dimensioning for Single ATM-Based lub packet switched traffic (BRA) only System simulation Queueing simulation (Opne