IEC 62488-3:2021 applies to power line carrier terminals and networks used to transmit information over power networks including extra high, high and medium voltage (EHV/HV/MV) power lines using both digital and optionally analogue modulation systems in a frequency range between 16 kHz and 1 MHz (see also IEC 62488-1). In many countries, power line carrier (PLC) channels represent a significant part of the utility-owned telecommunication system. A circuit normally routed via a PLC channel can also be routed via a channel using a different transmission medium such as point to point radio, optical fibre or open wire circuit. It is therefore important that the input and output interfaces that are used between terminals in the communication system are standardised. The issues requiring consideration of DPLC and/or APLC devices as parts of a telecommunication network can be found in IEC 62488-1. The scope of this document also includes the description of I/O interfaces and test set-ups that are necessary to qualify characteristics of DPLC or ADPLC terminal at link level.