, but the CN definitions have been adopted from the GSM specifications. Major elements of the CN are WMSC/VLR, HLR, MGW (media gateway) on the CS side, and SGSN (serving GPRS support node) and GGSN (gateway GPRS support node) on the PS side. WCDMA Mobile Switching Centre (WMSC) and VLR (Visitor Location Register) The switch and database is responsible for call control activities. WMSC is used for the CS transactions, and the VLR function holds information on the subscriber visiting the region, which includes the mobile's location within the region. OVERVIEW OF MOBILE NETWORKS Gateway Mobile Switching Centre (GMSC) This is the interface between the mobile network and the external CS networks. This estab- lishes the call connections that are coming in and going out of the network. It also finds the correct WMSC/VLR for the call path connection. Home Location Register (HLR) This is the database that contains all the information related to the mobile user and the kind of services subscribed to. A new database entry is made when a new user is added to the system. It also stores the UE location in the system. Serving GPRS Support Node (SGSN) The SGSN maintains an interface between the RAN and the PS domain of the network. This is mainly responsible for mobility management issues like the registration and update of the UE, paging-related activities, and security issues for the PS network. Gateway GPRS Support Node (GGSN) This acts as an interface between the 3G network and the external PS networks. Its functions are similar to the GMSC in the CS domain of CN, but for the PS domain. 1.5.3 Network Management System in 3G Networks As the network technology evolved from 2G to 3G, SO did the network management systems. The NMS in 3G systems will be capable of managing packet-switched data also, as against voice- and circuit-switched data in 2G systems. The management systems in 3G need to be more efficient (i.e. more work possible from the NMS rather than visiting the sites). These systems will be able to optimise the system