 quality in a more efficient way. The management systems are also expected to handle both the multi-technology (i.e. 2G to 3G) and multi-vendor environments. 1.5.4 Interfaces and Signalling in 3G Networks As can be seen from Figure 1.5, there are some interfaces and signalling involved in 3G systems. Here, we will briefly discuss interfaces and signalling. Interfaces Uu/WCDMA Air-interface Uu or the WCDMA air-interface is the most important interface in 3G networks. The Uu interface works on WCDMA principles wherein all users are assigned one code, which varies with the transaction. As shown in Figure 1.2, each user has a separate spreading code. Unlike with GSM, here every user uses the same frequency band. There are three variants of the CDMA, which are direct-sequence WCDMA frequency-division duplex THIRD-GENERATION MOBILE NETWORKS (DS-WCDMA-FDD), direct-sequence WCDMA time-division duplex (DS-WCDMA- TDD), and multi-carrier WCDMA (MC-WCDMA). In the initial phase of the WCDMA network rollouts, the FDD variant is used. Initially, 'wideband' was introduced because the Euro-Japanese CDMA version used a wider bandwidth than the American version of CDMA. Frequency Bands in WCDMA-FDD The air-interface transmission directions are separated at different frequencies with a duplex distance of 190 MHz (Figure 1.6). The uplink frequency band is 1920-1980 MHz and the downlink is 2110-2170 MHz. There are several bandwidths defined for the WCDMA system (e.g. 5, 10 and 20 MHz), but 5 MHz is the one that is currently being used in network devel- opment. Although the bandwidth is 5 MHz, the effective bandwidth will be 3.84 MHz, as the guard band takes up 0.6 MHz from each side (i.e. 1.2 MHz in total makes up the guard band). Iub Interface This is the interface that connects the base station to the RNC. This is standardized as an open interface, unlike in the GSM where the interface between the BTS and BSC was not an open one. This consists of common signalling links and traffic termination points. Each of these traffic terminati