A method of training a digital subscriber line, 'DSL', link comprised in a network in which a modem comprises a DSL interface and a router interface to connect to a router; said router also being connected to a device, the method comprising: the modem performing a line training process on the DSL link, the line training process comprising: a plurality of DSL carriers each transmitting one or more symbols; for each of said plurality of carriers, determining insertion loss and noise level; for each of the plurality of carriers, determining signal to noise ratio, 'SNR' from the insertion loss and noise level; and determining capacity of upstream and downstream links in accordance with the SNRs of each of the carriers; the method also comprising: during the line training process, either: the modem connected to a first powerline adaptor transmitting data to the device via said router connected to a second powerline adaptor; or the modem controlling said router connected to a first powerline adaptor to transmit data, over a powerline, to the device connected to a second powerline adaptor; wherein the powerline adaptors act as an additional time-varying noise source during said data transmission, and wherein the determination of DSL carrier insertion losses and SNRs takes into account this additional time-varying noise source. the modem performing a line training process on the DSL link, the line training process comprising: a plurality of DSL carriers each transmitting one or more symbols; for each of said plurality of carriers, determining insertion loss and noise level; for each of the plurality of carriers, determining signal to noise ratio, 'SNR' from the insertion loss and noise level; and determining capacity of upstream and downstream links in accordance with the SNRs of each of the carriers; the method also comprising: during the line training process, either: the modem connected to a first powerline adaptor transmitting data to the device via said router connected to a second powerline adaptor; or the modem controlling said router connected to a first powerline adaptor to transmit data, over a powerline, to the device connected to a second powerline adaptor; wherein the powerline adaptors act as an additional time-varying noise source during said data transmission, and wherein the determination of DSL carrier insertion losses and SNRs takes into account this additional time-varying noise source. a plurality of DSL carriers each transmitting one or more symbols; for each of said plurality of carriers, determining insertion loss and noise level; for each of the plurality of carriers, determining signal to noise ratio, 'SNR' from the insertion loss and noise level; and determining capacity of upstream and downstream links in accordance with the SNRs of each of the carriers; the modem connected to a first powerline adaptor transmitting data to the device via said router connected to a second powerline adaptor; or the modem controlling said router connected to a first powerline adaptor to transmit data, over a powerline, to the device connected to a second powerline adaptor; wherein the powerline adaptors act as an additional time-varying noise source during said data transmission, and wherein the determination of DSL carrier insertion losses and SNRs takes into account this additional time-varying noise source.