This invention relates to systems, methods and computer program code for testing, troubleshooting and evaluation of mobile phone network. We describe a method of processing network data which includes a plurality of session related parameters. The method comprises inputting one or more queries, a query defining a statistic relating to said parameters and to be computed from said network data, formatting a query to define said statistic in terms of one or more intermediate statistics from which said statistic is computable, operating with said formatted query to determine said one or more intermediate statistics, and storing these in a data store for analysis, preferably indexed by said parameters. Preferably entries for the parameters are stored at time positions in a data pipe.