Method for repeatedly delivering data in a continuous cycle.
A carousel provides a mechanism that allows data to be pushed from a broadcaster to multiple receivers by transmitting a data set repeatedly in a standard format. A set-top box receiver may tune to the data stream at any time and is able to reconstitute the data into a virtual file system.
The carousel may therefore considered as a transport file system or file broadcasting system that allows data files to be transmitted from the broadcaster to multiple receivers or clients simultaneously.
In a unidirectional broadcast environment the receiver is unable to request the retransmission of any data that was missed or received incorrectly. Repeated retransmission of data allows the receiver to cope with random tuning to a channel at an unpredictable time, for instance as the user changes channel.
The carousel cycle period generally determines the maximum time required for a receiver to acquire an application or specific item of data. It is possible to reduce the access time for commonly used files by broadcasting some data elements more often than others.
The standard format for a carousel is known as DSM-CC. This is specified in ISO/IEC 13818-6 and is part of the DAVIC DVB standard for digital video broadcasting.
DSM-CC is an acronym for Data Storage Media Command and Control. The specification provides support for a variety of communication models, including provision for interactive transport control of audio and video streams in a bi-directional environment such as a cable television video on demand system.
The DSM-CC standard specifies two types of carousel, a data carousel and an object carousel. The object carousel extends the more limited data carousel and specifies a standard format for representing a file system directory structure comprising a root directory or service gateway and one or more files and directories.
Files and directories are encapsulated in a DSM-CC object carousel in several layers. Objects are encapsulated in modules, which are carried within download data blocks, within DSM-CC sections encoded in MPEG private sections which are assembled from packets.