 turn a RNS contains a Radio Network Controller (RNC) and one or more Node B5. A Node B con- 5 Throughout this book we use 'Node B' as noted by the 3GPP specifications. However, we should know that a Node B is just a 3G-BTS performing more functions than a 2G BTS in GSM for example. The UMTS Development Platform nects to the RNC through the lub interface, and it can support either a FDD or TDD or combined dual mode operation. The RNC takes care of handover decisions requiring signalling to the UE; it comprises a combining/splitting function to support macro diversity between different Node Bs. RNCs can interconnect each other through the Iur logical interface. The latter can be conveyed over a direct physical connection between RNCs or through any appropriate transport network. 3G MSC/VLR Core Network 3G-SGSN Iu-CS Iu-PS Node B Node B Node B Node B Figure 3.7 UTRAN architecture example. All UE connections between UTRAN have a serving RNS. When service relocation demands it, a drift RNSs support the serving RNS by providing new radio resources. Figure 3.8 illustrates the role of a RNS (serving or drift) on a per connection basis be- tween a UE and UTRAN. Core Network (CN) Cells Figure 3.8 Serving and drift RNS. UTRAN IDENTIFIERS AND FUNCTIONS 3.4.1 Identifiers The unique RNC-Ids are defined by the operator, and set in the RNC via O&M. The UMTS Network and Radio Access Technology Element Identifiers The PLMN-Id is made of Mobile Country Code (MCC) and Mobile Network Code (MNC): PLMN-Id = MCC + MNC CN Domain Identifies a CN domain edge node for relocation tasks. It is made up of the PLMN-Id and of the LAC or RAC of the first accessed cell in the target RNS. The two CN domain identifiers are: - CN CS Domain-Id = PLMN-Id + LAC CN PS Domain-Id = PLMN-Id + LAC+ RAC RNC-Id together with the PLMN identifier is used to globally iden- tify the RNC. RNC-Id or the RNC-Id together with the PLMN-Id is used as RNC identifier in UTRAN lub, Iur and Iu interfaces. SRNC-Id is the RNC-Id of the Serving RNC. C-RNC-Id is the RNC-Id of 