on in case that the user is 5.4 Simulation Model of UMTS Rel99 active again with an increased traffic demand and thus can be switched back to use DCH. In the Re199 simulation model, the CAC, BRA and CTS functions are working together to attain a cost-efficient utilization of the resources in the UMTS radio access network. Duration of an AAL2 connection ATM Link Throughput Figure 5.5: Measuring the CAC guaranteed bit rate RAB 64 kbps RAB 128 kbps RAB 384 kbps Constant distribution Exponential distribution Normal distribution Table 5.1: Measured average ATM link throughput for different RABs QoS Mechanisms in the Transport Network In the AAL2/ATM transport network in UTRAN, there are two basic QoS methods for differentiating the traffic. The first one is on the AAL2-level with the use of AAL2 prioritizations, as explained in Figure 5.4. The second one is on the ATM level by using different ATM VC/VPs with different QoS categories. For example, the delay sensitive traffic can use CBR VCs while the interactive or best effort traffic can use UBR VCs. Both methods can be used in the simulations. Summary The Rel99 Simulation model is a detailed implemented simulation model including the basic UMTS Rel99 functions and protocol stacks with the main focus on the lub interface. The lub transport network is fully modeled with the implemented resource management functions, traffic differentiation and traffic control, QoS mechanisms. It is the simulation model for carrying out performance evaluation and dimensioning for Rel99 network, and also as the basic simulation model for building the other evolved UMTS networks. 5 Introduction of Simulation Models 5.5 Simulation Model of IP-Based UTRAN One important evolution of the UMTS radio access network is the change of the transport technology from the ATM towards IP. In the framework of this thesis, the performances and dimensioning of the IP-based UTRAN are also an important part. Section 2.3.4.1 explains the motivations and advantages of using IP transport and section 3.4 introd