A transmission system includes a transmitter (10) and at least one receiver (14) configured to receive signals transmitted therefrom. Carousel-forming data file and directory objects are sent in cycles, with predetermined groups of file and directory objects being formed into respective modules at the transmitter, suitably according to MPEG-2 DSM-CC protocols. Each of the modules is transmitted as a whole, and the receiver is arranged to record received file data and directory objects under a predetermined grouping formulation, at elementary stream or module level.