on points is controlled by dedicated signalling links. One traffic termination point is capable of controlling more than one cell. Iub interface signalling, known as Node B Application Part (NBAP), has two important constituents. These are Common NBAP (C-NBAP) and Dedicated NBAP (D-NBAP), which are used for common and dedicated signalling links respectively. Iur Interface This is a unique interface in WCDMA networks. Iur is an interface between RNC and RNC. There was no such interface in the GSM network (i.e. between BSC and BSC). This interface was designed to support the inter-RNC soft-handover functionality. This interface also supports the mobility between the RNCs, both the common and dedicated channel DL:2110-2170 MHz UL:1920-1980 MHz 2200-2100 MHz 2100-2000 MHz 2000-1900 MHz Figure 1.6 Frequency bands for WCDMA OVERVIEW OF MOBILE NETWORKS traffic and resource management (e.g. transfer of the cell measurements between the cells). The signalling protocol used for this interface is RNSAP (radio network system application part). I Interface This interface connects the RAN to the CN. It is an open interface and handles the switching, routing and control functions for both the CS and PS traffic. Thus, the interface that connects the RAN to the CS part of CN part is known as the Iu-cs interface, while the one that connects the RAN to the PS part of CN is called the Iu-ps interface. Signalling Signalling in the third-generation WCDMA networks is in three planes: the transport plane, the control plane and the user plane. This is because a 3G network is understood in three layers that contain data flows. These three layers are transport, control and user plane layers as shown in Figure 1.7. The transport plane is a means to provide connection between a UE and network (i.e an air-interface). It contains three layers: physical, data and network layers. The physical layer is the WCDMA layer (TDD/FDD), while the data layer is responsible for setting- up/maintaining/deleting the radio link, protection, error corrections 