affic aggregates at each stage, the dimensioning of a complete tree-structured access network can be derived by performing dimensioning for the basic star network topology at each aggregation stage of the tree-structured access network. In a star-structure access network as shown in (b), the dimensioning task is to determine a necessary bandwidth for each last mile link and the backbone link separately. The analytical models, which have been developed for case (a), are extended and applied in the scenario (b) to dimension the individual links in the network. One important issue for dimensioning the backbone link is overbooking (see Chapter 8), which is to allocate less bandwidth on the backbone link than the total bandwidth request by all the connected last mile links. Usually, the backbone link can be overbooked by taking advantage of the statistical multiplexing gain among traffic from different Node Bs. For a cost-efficient dimensioning of the backbone link, an optimum overbooking is desired to provide balance between the costs and the QoS objectives. In this thesis, overbooking is investigated for a wide variety of scenarios through extensive simulations, with special focus on determining the optimum overbooking for the backbone link. From the investigated results, important factors that have great impact on the overbooking are found. Furthermore, the analytical models are applied in various network scenarios to derive optimum overbooking factors (which represent the degree of overbooking), which are validated by simulations. 1.5 Thesis Overview In chapter 2, the evolution of UMTS networks is introduced. The chapter provides an overview of development of UMTS and emphasizes the technologies of evolved UMTS radio access networks. Chapter 3 gives a detailed introduction of UMTS Terrestrial Radio Access Network (UTRAN) for various UMTS radio access evolutions including their important network elements, internal and external interfaces, channels, and protocol stacks. Special focus on is put on the lub interface, 