Problems arise when using an Integrated Service Digital Network infrastructure for providing Asymmetrical Digital Subscriber Line technology. These problems do not always occur but depend on the distance between the end-user location and the central location, and the type of network termination, and result in the impossibility for the end-user to make voice calls or to send data. The problems are caused by the Asymmetrical Digital Subscriber Line splitters, which change the transmission characteristics of the Integrated Service Digital Network infrastructure between the end-user location and the central location. The transmission characteristics that are changed by the Asymmetrical Digital Subscriber Line splitters are impedance, propagation time and insertion loss. The deviation is frequency-dependent and falls outside the internationally-defined ranges for these transmission characteristics.