fer is quite small and stable. (iv) The transmission delay over the lub link is rather low due to a high transmission speed. For transmitting an ATM cell on a 2 Mbps E1 line it is 0.212 ms. The node processing delay such as switching is very small and thus can be neglected. FP PDUs DCH 1 DCH 2 Segmentation Queue Queue Deterministic Deterministic service rate service rate DCH in Figure 6.42: Delay in the UTRAN lub The following gives an example of the UTRAN FP PDU delay, AAL2 queuing delay and ATM cell delay from the simulation. The simulation is set up for one Node B connected with the RNC via a 2 Mbps lub line, transmitting web traffic with an average web page size of 15 kbyte (Pareto page size distribution). In this example, the FP PDU delay is shown for the downlink, i.e. the delay of transporting FP PDUs from the RNC to the Node B, measured at the Node B side. The AAL2 queuing delay is the queuing delay of the AAL2 buffer at the RNC side. The ATM cell delay consists of (iii) the queuing delay in the ATM buffer and (iv) transmission delay on the lub link. Table 6.5 gives the values of the mean and the variance of the ATM cell delay, AAL2 queuing delay and FP PDU delay from the simulation. Mean (s) Variance ATM Cell Delay 0.000521 1.836e-8 AAL2 Queuing Delay 0.090760 0.07549 FP PDU Delay 0.091789 0.07500 Table 6.5: UTRAN Delay Components 6 Dimensioning for Single ATM-Based lub The results from Table 6.5 show that the ATM cell delay is much smaller than the AAL2 queuing delay and the FP PDU delay, while the AAL2 queuing delay is quite close to the PDU delay. The gap between the AAL2 queuing delay and the FP PDU delay is mainly caused by the ATM cell delay and additional segmentation and reassembly delay. Furthermore, the variance of ATM cell delay is rather small, which means that the ATM cell delay is kept quite stable. The results imply that the FP PDU delay is mainly composed by the AAL2 queuing delay. That means, the AAL2 queuing delay can be used to approximate the lub transport delay. 6.4.1.2 System Models