A definition of the broadcasting mode is given by using the concepts of audience and programming. There follows a description of the DIDON protocol and the DIODE protocol. The DIODE protocol is a specialized application of the DIDON protocol, when data is broadcast upon request.
The DIODE concept is explained in relation to the various data retrieval systems, and emphasis is placed on its role in learning about audience structure through the use of new mechanisms in collecting user requests.
The DIODE concept is particularly well suited to teletext systems transmitted via cable networks. It allows efficient use of a return channel to remotely control the downloading of teletext pages into multipage decoders built into television sets.