assumed that the queue is approximately empty. Let Tp denote the one-way propagation delay of the link. Thus the average round trip time RTTest can be estimated as suggested by Anton Riedl in [Rie04]: (6.39) The above state probabilities P(n) of having n active jobs in the system are given in [Coh79] (j<R) (6.40) E,(R,Rp)p)-(1-p) Figure 6.27 shows the improved results using the above estimated round trip times RTTest for calculating the average transfer delays for the Pareto file size distribution. It is seen obviously that with RTTest, , the calculated mean transfer delays with the M/G/R-PS model fit the simulation results much more accurately. Therefore, it is suggested to apply the above approach for the cases for a highly bursty source traffic where the queuing delay on the bottleneck link is significant. Adjusted & Extended M/G/R-PS Pareto (simulations) Pareto (calculations using RTTest) Figure 6.27: Improvement for Pareto file size distribution with RTTest: ftp scenario, RAB 128 kbps, no CAC, constant file size of 12 kbyte, lub link = 1 E1 line 6.3.8.3 Single RAB with CAC When employing the admission control function (CAC) in the UTRAN, the system can avoid heavy congestions by limiting the number of active simultaneous connections on the link, and thus each user gets a minimum throughput which can guarantee its desired QoS. For 6 Dimensioning for Single ATM-Based lub this case, the M/G/R/N-PS model shall be applied as suggested in section 6.3.7.2 to estimate both average application delay and connection reject ratio (or called blocking probability). The following scenarios validate the M/G/R/N-PS model for an ftp traffic scenario where the CAC function is applied to control the transport resources of the lub interface. In the presented scenario, all users choose the same RAB rate of 128 kbps to transfer data and the CAC guaranteed bandwidth per user connection is set to 96 kbps. For the configured lub link (refer to section 6.3.8.1), the lub user plane allows a maximum of 15 simultaneous user connections. 