ion counters provide the network design engineer with important information regarding the network's performance. The tasks of measurement data collection may be performed by the operator using the network element's own measurement counters or specialised performance data collection tools like Metrica and Traffica. The network element's own measurement counters can be obtained through direct Man-Machine language (MML) sessions to the network element. The operator also provides other necessary information, i.e. signalling network data, a traffic routing strategy and a current network synchronisation plan. The main task during the network audit phase is to analyse and interpret measurement data received from the operator. The initial switching network performance is analysed in view of the assumed KPIs. The activities also include finding the network busy hour, identification of bottlenecks, modelling the actual network on Direct+, building an upgrade and tuning of the network parameters and making a comparison of actual network usage and penetration forecast. Network Performance Survey The main objectives of a network performance survey are to: analyse active measurements in the network; list or activate important measurements for the project; CS Core Network Optimisation analyse initial values of KPIs; evaluate the call answer rate. Evaluation of Preoptimisation KPIs At the beginning of the project, the initial values of KPIs should be taken and tabulated. This can be done for each module separately or generally for the whole project. Some of the main CS core KPIs are: Call success ratio Call answer rate Drop call ratio Paging success rate LU success rate SS7 link utilisation HO success rate Total number of call attempts Call setup time Circuit group utilisation Circuit blocking A detailed list of KPIs and their definitions is contained in the KPI guide. As an example the evaluation and results of the LU success rate and paging success rate analysis are presented hereafter. Location Update Analysis Location update