uces in detail the protocol structure and main functions of the IP-based UTRAN. This section introduces two implemented IP-based UTRAN simulation models in this thesis: an exact model and a simplified one. 5.5.1 Exact IP-Based UTRAN Simulation Model This model was implemented as an exact simulation model including the detailed modeling of the IP UTRAN protocol stacks (see section 3.4.1), the main UMTS functions, channels, air interface and the transport network resource management functions. This model was implemented on the basis of the UMTS Rel99 model, by removing the lower AAL/ATM transport layers and replacing them with UDP/IP and Ethernet as the transport layers. Figure 5.6 shows the model architecture for the IP-based UTRAN. Corresponding Nodes Ethernet Ethernet lub (Ethernet Link) Node B Figure 5.6: Modeling of IP-based UTRAN in OPNET Compared to Figure 5.3, it can be seen that the model architecture is similar to the previous UMTS Rel99 simulation model except for the lower UTRAN transport network layers. In the presented node model, the upper application and transport layer modules are 5.5 Simulation Model of IP-Based UTRAN kept for modeling the behavior of UEs and their corresponding nodes. As well the modeling of the UMTS radio network layer protocols (RLC, MAC and FP), the channels, the air interface, and the resource management functions (i.e. CAC, BRA and CTS) are inherited from the developed Rel99 simulation model. However, the modeling of the UTRAN transport network uses the UDP, IP and Ethernet modules to replace the AAL2/ATM modules of the Rel99 simulation model. An overall introduction of this exact IP-based UTRAN simulation model has been published in [LC*07]. More detail description of this simulation model is given in Appendix A.12. 5.5.2 Simplified IP-Based UTRAN Simulation Model In addition to the exact IP-based UTRAN model, a simplified model was implemented with the application of the IP DiffServ QoS scheme in the IP transport network. The main purpose of this simplified simulation mode