ol stacks, channels, and transport technologies, whereas the modeling of the UMTS radio interface and the core network are simplified by considering their main impacts on the lub dimensioning. In this way, the complexity of the simulation model can be reduced, which results in an improved simulation efficiency. For modeling the UTRAN network, in addition to the modeling of the basic functions and protocol stacks of the lub interface, several important aspects which are closely related with X. Li, Radio Access Network Dimensioning for 3G UMTS, DOI 10.1007/978-3-8348-8111-3 5 Vieweg+Teubner Verlag | Springer Fachmedien Wiesbaden GmbH 2011 5 Introduction of Simulation Models the network dimensioning as discussed in Chapter 4, i.e. traffic characterization, QoS mechanisms, traffic control, resource managements, and network topology, need to be implemented in the simulation model as well. Moreover, the network-relevant QoS can be defined and evaluated. On the user level, for a detailed modeling of the user behavior and its relevant QoS, the individual user entity needs to be modeled and each user has to be uniquely identified throughout the network for the network resources management and the QoS control. To model different user groups, the simulation models should allow defining various applications and services, different QoS classes, and a variety of transport protocols like UDP, TCP and IP. Another important requirement is that the simulation model should be flexible to choose a transport technology for constructing the transport network in the UTRAN, and easy to configure the transport link bandwidth and the network structure. To model a large UTRAN network, the simulation models should be able to support multiple Node Bs and feasible to configure the number of Node Bs in the network as well as choose the appropriate network topology to connect the Node Bs to the RNC. 5.2 Simulation Model Framework Based on the above requirements, a basic and common framework is designed for building the simulation models for var