l is to investigate the impact of IP DiffServ QoS on the overall network and end user performances as well as the lub dimensioning. Therefore, this simplified model implements the detailed DiffServ QoS scheme according to the IETF specification (section 3.4.2.1), and deploys the DiffServ-based QoS structure which is presented in section 3.4.2.3. But on the other hand, the modeling of the UMTS radio protocol stacks, the channels, the air interface and the resource management functions are simplified in order to reduce the complexity of the simulation model to be mainly focused on the IP transport network. The simplified IP-based UTRAN simulation model was built based on the standard OPNET IP/Ethernet node model, instead of modifying the Rel99 ATM-based UMTS model. In this simplified model, the UE still consists of the detailed models of the application and the corresponding transport protocol layers. But the models of the UMTS radio protocols (RLC, MAC, and FP) are simplified with only taking the overheads into consideration. For each user connection, the RAB rate can be configured where the data rate of the user is limited by the assigned RAB peak rate. The IP-based transport network is implemented with UDP, IP and Ethernet layers. In the IP layer, the detailed DiffServ QoS function is modeled. The model of the DiffServ is provided in the standard OPNET IP model library. To set up the IP-based UTRAN transport network, the IP Routers are used to connect the Node Bs and the RNC in the simulation scenarios. These IP routers support the IP DiffServ QoS function, Weighted Random Early Detection (WRED) discarding function, various queuing managements like Weighted Fair Queuing (WFQ) scheduler, strict priority scheduler, etc. In these routers, the IP interface shaping is allowed which is used to allocate the IP bandwidth for the corresponding lub link. 5 Introduction of Simulation Models 5.5.3 Summary For the modeling of the IP-based UTRAN network, two simulation models were built within this thesis. The exact IP-based 