the controlling RNC. D-RNC-Id is the RNC Id of the Drift RNC. Global RNC-Id = PLMN-Id + RNC-Id Service area Used to uniquely identify an area consisting of one or more cells belonging to the same location area Such an area is called a service area and can be used for indicating the location of a UE to the CN. The Service Area Code (SAC) together with the PLMN-Id and the LAC will constitute the service area identifier. SAI = PLMN-Id + LAC + SAC Used to uniquely identify a cell within an RNS The Cell-Id together with the identifier of the controlling RNC (CRNC-Id) constitutes the UTRAN Cell Identity (UC-Id) UC-Id or C-Id is used to identify a cell in UTRAN lub, Iur and Iu interfaces. UC-Id = RNC-Id + C-Id Local Cell Used to uniquely identify the set of resources within a Node B re- quired to support a cell (as identified by a C-Id). Also used for the initial configuration of a Node B when no C-Id is defined. UE (Radio Network Used as in UTRAN and in signalling messages between UE and Temporary Identities UTRAN. They include: Serving RNC RNTI (s-RNTI), Drift RNC (RNTI) as UE identi- RNTI (d-RNTI), Cell RNTI (c-RNTI), UTRAN RNTI (u-RNTI) See fiers their use in [6] Resource identifiers Radio network control plane identifiers, (see [6]) Transport network control plane identifiers and binding identifier. 3.4.2 System Access Control Through the system access 3G subscribers connect to the UMTS network to use ser- vices and/or facilities. Subscriber system access may be initiated from either the mobile side, e.g. a mobile originated call, or the network side, e.g. a mobile terminated call. In the following we summarize key system access control functions; specifications in [6] describe additional details. 3.4.2.1 Admission and Congestion Control Admission control admits or denies new users, new radio access bearers or new radio links resulting from network tasks, e.g. handover events. It aims to avoid overload situa- The UMTS Development Platform tions and bases its decisions on interference and resource measurements. It a