ing simulation) are carried out as an additional validation method to validate the accuracy of the calculation results. Figure 6.50 demonstrates that on the one hand the MMPP/D/1 is an accurate model for deriving the required lub bandwidth for the defined TNL performance, i.e. 1% packet loss ratio, and on the other hand demonstrates that the analytical results are all are close to the simulation results form the Rel99 UMTS system simulations. The relative error of the analytical models is below 10%. 6 Dimensioning for Single ATM-Based lub voice traffic only voice traffic only 10000 System simulation Queueing simulation (Opnet) Queueing simulation (Opnet) Analytical calculation Analytical calculation voice traffic demand [kbps] voice traffic demand [kbps] Figure 6.50: Validation of MMPP/D/1 model (voice scenario) Figure 6.51 compares the dimensioning results of the voice only scenario from the OPNET simulation compared with the results derived from different analytical models, i.e. Hyper(2)/D/1 (denoted as (H2/D/1)), M/D/1, and MMPP/D/1. Figure 6.52 shows the relative error of various analytical models. voice only scenario - Rel99 ATM-based lub 10000 system simulation M/D/1 H2/D/1 MMPP/D/1 voice traffic demand [kbps] Figure 6.51: Analytical models vs. simulation for lub bandwidth (voice scenario) As can be seen in Figure 6.51 and Figure 6.52, the M/D/1 model has the lowest accuracy as it assumes Poisson arrivals whose coefficient of variation equals to 1, but the arrival traffic behaves much more bursty with a coefficient of variation larger than 1. In addition, it does not consider the bulk arrival of the packets. The H2/D/1 model improves the accuracy, since it considers the coefficient of variation of the arrival traffic by using the two phases to model this variation by means of introducing two Poisson arrival processes where one Poisson process to model very small packet arrival times and the other to model the larger packet arrival times. Moreover, in order to model the bulk arrival of AAL2 CPS packets, the 