A network analysis system obtains parameter data generated by telecommunications network equipment, in which the parameter data represents operational parameters of the network. The network analysis system processes the parameter data to generate symptom data from test procedures that are applied to the parameter data. Fault data is generated that is representative of faults that may have occurred, on the basis of the symptom data and relationship data representative of the relationship between the symptom data and the faults. The relationship between a symptom and a fault represents likelihood of the symptom being caused by the fault. The system also generates occurrence data that is representative of faults that probably have occurred, on the basis of the fault data.