e CS core include: average circuit group (CGR) utilisation; total successful BHCA per MSC; call success rate; signalling link utilisation; signalling link load; signalling link availability; VLR database fill ratio; HLR database fill ratio; computer unit load rate; MB load rate; average call setup time; inter-MSC handover success rate. These KPIs may be used to evaluate the performance of the CS core network and for benchmarking. CS Core Network Optimisation Reports Traffic Traffic Field Traffic Maintenance Meas. Meas. Reporting Observ. Observ. Supervision Traffic Information Figure 4.37 Traffic administration functions of network elements 4.7.2 Network Measurements The traffic measurements can be obtained from measurement servers or from a network element's own performance management counters. The network element's own traffic administration capabilities pro- vide measurement counters that enable a printout of more accurate measurement reports. In some cases external measurement tools provide independent verification of network traffic intensity. Alarm moni- toring enables users to find out whether this equipment is available and working to expectations. Traffic Administration Traffic administration functions of network elements (Figure 4.37) cover procedures for collecting infor- mation on the switched calls, finding out the peak busy hour, determining the load of the various units in the exchange and, finding out what the availability of the exchange is. Traffic administration also contains functions for monitoring the system performance, the ratio of failed calls, the load on computer units, the circuit seizure, occupation and release times, for a given circuit group or computer unit. Selected sets of the data used in the configuration of the switches are recovered from the network elements as input for the network parameter build upgrade and tuning. Traffic Measurements Traffic measurements provide information on traffic duration, intensity and distribution of the traffic in the exchange. Such information is