ler AAL2 shaping Layer Figure 5.4: Implemented AAL2 QoS Structure The ATM physical layer model is also provided in the OPNET ATM model family. A variety of ATM physical links like E1, STM1 links can be chosen to configure the lub links offering differing link capacities. Moreover, the simulation model provides the possibility of combining a number of ATM links into a virtual link by using Inverse Multiplexing for ATM (IMA) technique. This function is useful if the lub link capacity needs to be extended, e.g. over a bundle of E1 cables. In addition, in the simulation model 300kbps from the total ATM link bandwidth is reserved for the lub control plane, i.e. for transporting the signaling traffic such as NBAP. 5 Introduction of Simulation Models The simulation model allows establishing multiple Node Bs connected to the RNC. With the use of ATM switches or routers, various network topologies can be configured at the lub interface. The possible network topologies are introduced in section 4.2.2. Modeling of the Resource Management Function In section 3.3.4.3, three important resource management functions are introduced. They are Connection Admission Control (CAC), Bit Rate Adaptation (BRA) and Channel Type Switching (CTS). They were implemented in the simulation model according to the concepts described in section 3.3.4.3. For the CAC algorithm, the offered transport resource is based on the assigned bandwidth of the VP or VC, i.e. the Peak Cell Rate (PCR). Each AAL2 connection corresponding to each UMTS DCH is required to reserve a certain amount of ATM bandwidth for the data transmission on the lub interface. This is so-called CAC guaranteed bit rate in section 3.3.4.3. In the simulation model, the CAC guaranteed bit rate is a configurable parameter for setting up the simulation scenarios. For each RAB type, there is an individual setting of the CAC guaranteed bit rate. This means, various RAB types with different peak data rates require different bandwidth reservations on the lub links. In this thesis, the CAC gua