ister) contains databases for IMEI. The EIR is the place where mobiles that are missing or stolen are registered. Actually the EIR contains three lists: white, grey and black. The white list contains IMEI for all the authentic mobiles; the grey list has data for faulty mobiles; and the black list contains information about stolen/missing mobiles. Thus, when a call is being made, the number is cross-checked at the EIR. If it is found in the white list, the call goes ahead, but if the number is found in the black list, the call may be blocked. The AC (authentication centre) is mainly responsible for security aspects. As the name suggests, it manages the security information for authentication of subscribers. This infor- mation is usually requested by the VLR and, in coordination with the EIR, it prevents an unauthenticated card from accessing the network. 4.2 CORE NETWORK PLANNING PROCESS The planning process for the core network is slightly different from the radio or transmission network planning processes. It consists of two parts: switch network planning and signalling network planning. In the radio and transmission network planning processes, environmental factors and site selection processes assume great importance. However, these two processes are missing from core network planning, thereby reducing the process to three main steps CORE NETWORK PLANNING PROCESS (network analysis, network dimensioning and detailed planning) before drawing the final core network plan. These steps are shown in Figure 4.2. Network analysis and dimensioning are explained separately for switch and signalling network planning. Network Network Detail Final Core Analysis Dimensioning Planning Network Plan Figure 4.2 Core network planning process 4.2.1 Network Analysis The number of switches (MSCs) in any network is far less than the number of sites or links. Some networks even have only one switch, which means that they cannot be changed on a 'daily basis' as that would have an impact on the performance of the whole network. Switch pl