A method of processing local area network diagnostic data obtained in respect of a local area network, the local area network having at least one user-device located therein operable to communicate via a local area network gateway device with one or more remote devices in a communications network outside the local area network, the local area network gateway device having a wireless interface associated therewith in the local area network, the local area network diagnostic data comprising data packets received via the wireless interface at least some of which carry performance data in one or more header fields relating to one or more predetermined performance characteristics of the local area network, the method comprising: identifying from packets received via the wireless interface a plurality of packets each having an indication that they belong to a particular aggregate group of packets; selecting from the plurality of packets identified as having an indication that they belong to a particular aggregate group of packets at least two packets that carry performance data relating to a performance characteristic of the local area network; identifying from the at least two packets carrying performance data relating to a performance characteristic of the local area network, at least one set of two or more packets sharing the same source and destination addresses; replacing packets identified as being in a set of two or more packets sharing the same source and destination addresses with a single replacement packet having the shared source and destination address and having one or more header fields corresponding to those identified as being in the set of two or more packets; and updating the aggregate group of packets from which the at least two packets that carry performance data were selected by including the replacement packet therein instead of the set of two or more packets having the same source and destination addresses characterised in that the replacement packet conforms to the same protocol as the packets identified as being in a set of two or more packets and/or carries performance data in one or more header fields in a header conforming to the same protocol as the headers of the packets it replaces, such that the replacement packet and/or information contained in the one or more fields in the header can be analysed using the same analysis tool or process as would have been used for the packets identified as being in the set of two or more packets it has replaced if they had not been replaced. identifying from packets received via the wireless interface a plurality of packets each having an indication that they belong to a particular aggregate group of packets; selecting from the plurality of packets identified as having an indication that they belong to a particular aggregate group of packets at least two packets that carry performance data relating to a performance characteristic of the local area network; identifying from the at least two packets carrying performance data relating to a performance characteristic of the local area network, at least one set of two or more packets sharing the same source and destination addresses; replacing packets identified as being in a set of two or more packets sharing the same source and destination addresses with a single replacement packet having the shared source and destination address and having one or more header fields corresponding to those identified as being in the set of two or more packets; and updating the aggregate group of packets from which the at least two packets that carry performance data were selected by including the replacement packet therein instead of the set of two or more packets having the same source and destination addresses characterised in that the replacement packet conforms to the same protocol as the packets identified as being in a set of two or more packets and/or carries performance data in one or more header fields in a header conforming to the same protocol as the headers of the packets it replaces, such that the replacement packet and/or information contained in the one or more fields in the header can be analysed using the same analysis tool or process as would have been used for the packets identified as being in the set of two or more packets it has replaced if they had not been replaced.