lso serves during initial UE access, RAB assignment/reconfiguration and handover depending on the required events. Finally, it functions depends on UL interference and DL power information located in the controlling RNC. The serving RNC performs admission con- trol towards the Iu interface. Congestion control monitors, detects and handles situations when the system reaches near overload or an overload situation while users remain connected. Thus, when somewhere in the network, limited resources degrade service quality, congestion control brings the system back and restores stability seamlessly. 3.4.2.2 System Information Broadcasting This function provides the mobile station with the access stratum and non-access stra- tum information used by the UE for its operation within the network. 3.4.3 Radio Channel Ciphering and Deciphering This computation function protects radio-transmitted data against unauthorized third parties. Ciphering and deciphering usage may depend on a session key, derived through signalling and/or session dependent information. 3.4.4 Mobility Functions 3.4.4.1 Handover Handover manages radio interface mobility based on radio measurements in order to maintain CN quality of service. It may be directed to/from another system (e.g. UMTS to GSM handover). Control for this function may originate in the network, or may come independently from the UE. Hence, it may be located in the SRNC, the UE, or both. 3.4.4.2 SRNS Relocation This function coordinates events when a SRNS role passes to another RNS. It manages the Iu interface connection mobility from one RNS to another. The SRNC initiates the SRNS relocation, which finds a home in the RNC and CN as illustrated in Figure 3.9. Core Network Core Network Cells Before SRNS After SRNS Relocation Relocation Figure 3.9 A serving RNS relocation example. The UMTS Network and Radio Access Technology 3.4.5 Radio Resource Management and Control Functions Radio resource management concerns the allocation and maintenance of radio commu- nication resources. In UMTS