 the radio access network as well as the fast growing number of mobile users and traffic volume, there is a significantly increasing demand for transport capacities in the radio access network. To achieve a cost-efficient design of the UMTS network, the radio access networks have to be dimensioned appropriately for the many types of services which are to be offered. This thesis is dedicated to investigate the dimensioning for the lub interface of different UMTS radio access networks, by simulations as well as analytically. In the framework of this thesis, different UMTS simulation models were developed for the OPNET simulator, according to the 3GPP specifications. Within this work, the simulation models of UMTS Rel99 with the ATM-based UTRAN and UMTS with the IP-based UTRAN were developed. The simulations of HSPA (HSDPA and HSUPA) were using HSPA simulation model established in the context of another project of the Communication Networks working group at the University of Bremen. In this work, these simulation models are used to evaluate the performances of the UMTS networks, and further to provide dimensioning of the transport bandwidths for the lub interface. Moreover, they are used to derive the dimensioning rules and analytical approaches and further to validate the proposed analytical approaches. This thesis proposes a number of novel and elaborate analytical models, algorithms and methodologies, which let UMTS network operators dimension their radio access network bandwidths in order to reduce expenditures, while still being able to offer a desired quality service. For the dimensioning process, different traffic scenarios, evolutions of UMTS radio access networks, transport solutions, QoS mechanisms and network topologies are studied. this thesis, two fundamental types of traffic are distinguished: elastic and circuit-switched traffic, which are associated with data applications and real-time services, respectively. In this thesis for each traffic type different QoS requirements are investigated. The QoS re