However, at the time of writing, such extended interactivity is only rarely implemented. In spite of the fact that such technologies were developed some twenty years ago (e.g. DVB-RCT), they did not find wide introduction mainly due to the ubiquitous availability of the Internet via broadband (wired and wireless) networks. Furthermore, a return interactive channel in the terrestrial environment requires the allocation of additional radio frequency resources, which due to presence of a number of radiocommunication services (analogue and digital TV broadcasting, radars, etc.)