An apparatus comprising: means for obtaining forwarded traffic volume data (34, 44, 54, 64, 102, 136, 146, 156, 163, 173, 183) and discarded traffic volume data (32, 42, 52, 62, 102, 134, 144, 154, 162, 172, 182), wherein the forwarded traffic volume data relates to an aggregated volume of data forwarded over a point-to-multipoint communication network in each of a plurality of discrete time periods over an observation period and the discarded traffic data relates to a volume of data discarded at a central node of the network in each of the plurality of discrete time periods over the observation period; means for generating calibrated forwarded traffic volume data and calibrated discarded traffic volume data by adding calibration data (104, 105, 131, 141, 151) to the forwarded traffic volume data and the discarded traffic volume data respectively, wherein calibration data is dependent on application of multiple calibration levels; means for filtering multiple instances of said calibrated forwarded traffic volume data and multiple instances of said calibrated discarded traffic volume data to generate respective filtered calibrated forwarded traffic volume data and filtered calibrated discarded traffic volume data, wherein said filtered data are indicative of a distribution of energy present in the respective calibrated traffic volume data and wherein different instances of said calibrated volume data have different calibration levels; means for determining, for each instance of said calibrated forwarded traffic volume data and said calibrated discarded traffic volume data whether periods of relatively high energy are concentrated in calibration data section(s) of the respective calibrated data of said filtered data or in traffic volume data of said filtered data and, if energy is determined to be concentrated in the traffic volume data, determining that the respective volume data has an energy level above the respective calibration level; means for identifying one or more first sample periods within said observation period, wherein said first sample periods correspond to time periods of the observation period where the filtered calibrated discarded traffic volume data has an energy level above a threshold calibration level; and means for determining impact scores for the forwarded traffic volume data and the discarded traffic volume data for each of said one or more first sample periods. means for obtaining forwarded traffic volume data (34, 44, 54, 64, 102, 136, 146, 156, 163, 173, 183) and discarded traffic volume data (32, 42, 52, 62, 102, 134, 144, 154, 162, 172, 182), wherein the forwarded traffic volume data relates to an aggregated volume of data forwarded over a point-to-multipoint communication network in each of a plurality of discrete time periods over an observation period and the discarded traffic data relates to a volume of data discarded at a central node of the network in each of the plurality of discrete time periods over the observation period; means for generating calibrated forwarded traffic volume data and calibrated discarded traffic volume data by adding calibration data (104, 105, 131, 141, 151) to the forwarded traffic volume data and the discarded traffic volume data respectively, wherein calibration data is dependent on application of multiple calibration levels; means for filtering multiple instances of said calibrated forwarded traffic volume data and multiple instances of said calibrated discarded traffic volume data to generate respective filtered calibrated forwarded traffic volume data and filtered calibrated discarded traffic volume data, wherein said filtered data are indicative of a distribution of energy present in the respective calibrated traffic volume data and wherein different instances of said calibrated volume data have different calibration levels; means for determining, for each instance of said calibrated forwarded traffic volume data and said calibrated discarded traffic volume data whether periods of relatively high energy are concentrated in calibration data section(s) of the respective calibrated data of said filtered data or in traffic volume data of said filtered data and, if energy is determined to be concentrated in the traffic volume data, determining that the respective volume data has an energy level above the respective calibration level; means for identifying one or more first sample periods within said observation period, wherein said first sample periods correspond to time periods of the observation period where the filtered calibrated discarded traffic volume data has an energy level above a threshold calibration level; and means for determining impact scores for the forwarded traffic volume data and the discarded traffic volume data for each of said one or more first sample periods.