A method and apparatus for transmitting data from a transmitter device to one or more receiver devices connected to the transmitter device via a respective wire connection, the transmitter device being operable to transmit signals onto the wire connections and a further wire connection at different tones, the method comprising: for each tone, allocating signals transmitted on the further wire connection as supporting signals for a particular wire connection, and measuring electromagnetic coupling between the further wire connection and that particular wire connection; using the measurements, determining a power allocation for transmitting a supporting signal on the further wire connection; for one or more of the tones: transmitting a signal onto the particular wire connection, and transmitting a supporting signal onto the further wire connection at the determined transmission power, thereby to cause crosstalk interference in the particular wire connection.