This European Telecommunication Standard (ETS) is the baseline specification for the provision of Return Channel (RC) based on PSTN and ISDN to Digital Video Broadcasting (DVB) systems. It is not intended to specify a return channel solution associated to each broadcast system because the inter-operability of different delivery media to transport the RC is desirable. Therefore the PSTN/ISDN solutions for the RC apply to satellite@ cable@ SMATV@ terrestrial@ MMDS or any future DVB system. The solutions here provided for return channel through PSTN/ISDN are a part of a wider set of alternatives to implement interactive services for DVB systems.