ed for a terminating SMS (short message service) and USSD (unstructured supplementary service data). Observations are an effective tool for testing and solving error situations. As an example the paging success rate for MSC-WAR01 is presented in the Figure 4.39. Core Network Planning and Optimisation MSC-WAR01 Failed Successful 05.04.2001 06.04.2001 07.04.2001 08.04.2001 09.04.2001 10.04.2001 11.04.2001 12.04.2001 Figure 4.38 VLR location updates MSC-WAR01 Failed Success 05.04.2001 06.04.2001 07.04.2001 08.04.2001 09.04.2001 10.04.2001 11.04.2001 12.04.2001 Figure 4.39 Example of the paging success rate analysis CS Core Network Optimisation The paging success rate in the example network is average. The situation can be improved by using greater indoor network coverage on the radio network. The data collected here come from daily measure- ments. It is recommended that hourly measurements should be collected in order to evaluate the need for more resources on the air interface. Call Answer Rate Analysis A call answer rate analysis requires a detailed study of the network clear codes. The main objectives of the call answer rate analysis are to evaluate the call answer rate and identify technical areas for network improvement. To perform a call answer rate there is a need to change the default clear code (CC) groups in the network element. The new grouping of CCs is done by splitting the CC group for normally ended calls into answered calls and technically successful calls and then to introduce a new CC group for radio IF errors. This enables identification of areas with a new grouping of clear codes: Group 1: answered calls (clean code number, e.g. 000'H, normal end of call) Group 2: technical successful calls (clean codes, e.g. 000'H-3FF'H ex. 205H) Group 3: internal congestion (clean code group 400'H-7FF'H) Group 4: external congestion (clean code group 800'H-BFF'H minus radio IF error) Group 5: subscriber error (clean code group COO'H-FFF'H minus radio IF error) Group 6: radio interface error (clean codes 205'H, 