ain in the mobile station. On the uplink, the data from all participating Node Bs is received and forwarded to the RNC. The RNC combines the data streams and transfers the data to the CN. 3. Softer handover is a special case of soft handover where transmissions can run in parallel over different cells of the same Node B. Besides, two Radio Network Layer resource management functions are considered in this thesis, which have direct impact on the UTRAN transport network. Bit Rate Adaptation (BRA) In order to improve the effective utilization of the lub bandwidth on transferring the packet switched data traffic, Bit Rate Adaptation (BRA) is usually applied in the UMTS system, specifically for the best effort or interactive packet traffic. The main function of BRA is to dynamically assign the available RAB for user flows during their transmission according to their QoS requirements and their activity. For example, when the user activity is considerably low, a low RAB rate will be allocated. When the user has larger needs of bandwidth for transmitting a large amount of data, a higher RAB will be assigned if there is still adequate bandwidth left on the link. It has to be noted that BRA is applied only for the Dedicated Channel (DCH) transferring the packet switched traffic, mainly best effort and interactive traffic types. Because the packet switched traffic, not like circuit switched traffic, 3 UMTS Terrestrial Radio Access Network (UTRAN) normally does not utilize the resource all the time, only on demand. Therefore, when the user does not have any traffic or little traffic to transmit, the utilization of the assigned resources will be reduced. By using the BRA mechanism, the resource for each user connection can be dynamically allocated according to the user's traffic demand. In this way the total bandwidth utilization can be improved. The data rate adaptation is realized by performing RAB upgrades to increase the data rate and RAB downgrades to decrease the data rate. The most important issue of BRA is to define t