ding to the introductions given in section 2.3.2 and Appendix A.9. The simulated network model of HSDPA is illustrated in Figure A.8. Compared to the Rel99 simulation model, the way of modeling the UEs, the corresponding nodes in the external networks, and the lub AAL/ATM based transport network is the same as in the Rel99 simulation model. The main differences are the newly introduced HSDPA protocol entities, the HS-DSCH transport channel, the HSDPA air interface, the fast scheduling at the Node B (also called MAC-hs scheduler), and the lub congestion control and flow control functions. External Network Applications TCP/UDP Applications TCP/UDP Core Network Node B Fodes MAC-hs Figure A.8: HSDPA Simulation Model Architecture [WL*06] As highlighted in the figure, the new implemented HSDPA protocol entities are the MAC- d protocol at the RNC and the UE, the MAC-hs protocol at the Node B, and the HS-DSCH FP Appendix at both the RNC and the Node B. In addition to these new protocol entities, the RLC acknowledged mode is used for transmitting the HSDPA traffic. It is modeled including the complete RLC functions like flow control, window mechanisms, error detection and retransmission mechanism based on Selective Repeat ARQ. In the HSDPA, the air interface is different than the one of Rel99 network. As mentioned in section 2.3.2, it offers a much higher peak data rate on the downlink and uses a shorter TTI (2 ms). The modeling the HSDPA air interface is based on deploying the statistical data of the output trace files taken from the dedicated radio simulations provided by the NSN. The trace files provide per-user wireless channel characteristics which are channel dependent and subject to the modeled MAC-hs scheduler in the radio simulations. From the trace files, the statistical data can be obtained for each user on the average user throughput, the probability to transmit n MAC-d PDUs and the probability of retransmissions per TTI. However, the handover UEs are not modeled. Moreover, different flow control and congestio