The flow of the RDS is very low, with a value slightly higher than 1 kbit/s (to be compared with what is envisaged for the terrestrial radio digital (RNT), which is 100 times more raised, or with what exists in ADSL, which is approximately 10,000 times higher). The features of the RDS are thus limited to applications which call on data whose coding requires only a few tens of bits repeated very regularly.
The most widespread features on the level of the FM stations which deal with the RDS, in particular the car radios but also, more recently, the mobile phones and the radios digital which have an alphanumeric screen, are the following ones:
- transmission of the name of the station on 8 characters (code PS - Program Service name). As an indication, standard RDS provides that approximately 35% of the flow of the RDS are devoted there, so that the name of the station can be displayed within a period of one second after the selection of a FM station;
- transmission of a list of frequencies corresponding to nearby transmitters also diffusing the station in the course of listening (code AF – Frequency Alternative). Associated with login RDS single allotted by the Council to each station (code pi – Program To identify), this list makes it possible the car radios moving to ensure the continuity of the listening of a station even if the frequency of a FM station changes a geographical zone to another.
- transmission of relative information to the programs of road information (code TA/TP – Program Traffic/Announcement Traffic). This functionality makes it possible a station to inform compatible the FM stations that a road announcement is with the antenna. According to the configuration of the car radio of the driver, this one can automatically commutate reading of one CD to the selection of the last listened station or increase the sound volume of the station in the course of listening throughout this road announcement.
In complement of the essential features of the RDS, other features, more advanced, are also envisaged by standard RDS. Although these features exist since several tens of years, some still know a progressive integration on the level of the car radios while suffering sometimes from a bad ergonomics and an ignorance on behalf of the users. Moreover, certain features today are technologically exceeded whereas others are created to answer new uses (for example RT+, introduced in 2008, which allows the diffusion of information intended for posting, on certain walkmen, of the name of the piece of work in the course of diffusion, the album and the interpreter). Among the many wide features of the RDS, one finds in particular:
- transmission of messages a length being able to reach 64 characters (RT – Radio operator Text). These textual messages diffused to enrich the sound programs by the station usually come to be displayed in complement of the name of the station on the screens laying out of more than two alphanumeric lines. Receivers RDS reconstitute the textual message sent by the station before automatically proposing it to the user or with his request, by sometimes calling on a run on the screen of the FM station when the number of characters of the message exceeds the number of character which the screen can display. While waiting for the generalization of this functionality on the level of the receivers FM, a “diverted” use of the functionality of transmission of the name of the station (the code PS, described previously), is temporarily authorized by the Council within one year an experimental framework since May 19th, 2011 supplemented and prolonged additional on June 12th, 2012. The radios which are declared near the Council can thus transmit a succession of messages of 8 characters instead of name of the station. This practice is called “code ravelling PS” and makes it possible the receivers noncompatible with the functionality “Radio operator Text” to display messages richer all the same than the simple name of the station. However, only a diffusion of textual messages in mode “Radio operator Text” will be in the long term maintained, since the run of the code PS, except standard, is likely to generate dysfunctions on the FM stations (during the alphabetical classification of the radios, for example), besides being able to be completely disabled by the listener.
- the swing automatic (and temporary) of a station towards sound road ads diffused by another radio station (ETERNITY – Enhanced Other Networks –, in partnership with the functionality of transmission of relative information to the programs of road information, already presented). For example, this function allows the listeners who wish it, by activating the function of their car radio (sometimes indicated like “ETERNITY”), to follow the program of a station general practitioner or musical while being automatically informed of the road ads relayed by the station of motorway corresponding to its course. This swing requires a synchronization between the sound diffusion of a road announcement by a station and the diffusion of information ETERNITY on the FM signal in the course of reception. This functionality is thus only available for the stations which have set up a diffusing partnership with a station of the road ads which, moreover, grants a temporary swing of their audience.
- transmission of relative information to the state of the traffic on highway network (TMC – Traffic Chanel Message). With the important development of the GPS receivers, the access to accident or working area, data a dynamic source for preventive information of the motorist about stoppers constitutes a complement of assistance to control. The terrestrial network formed by the sites of diffusion of the FM stations offers a good cover of the French territory while allowing the diffusion of information géo-localised a local scale. This information can be received by certain GPS, which use them then to display them with the screen and to calculate alternative routes in the event of disturbances of the highway network.
More generally, all kinds of data can potentially be transmitted through subcarrier RDS of a service of FM radio. The standard envisages, for example, the principle of the open applications (ODA – Open Dated Applications) or of the transparent channels (CCT – Transparency Dated Channels). However, all these uses remain limited by the important flow that the combination of the features essential of RDS requires (name of the station, follow-up of a station, etc) with some advanced features which come to enrich the services by radio (Radio operator Text for example). Moreover, the use of subcarrier RDS by the services of FM radio authorized by the Council remains subjected to the regulation envisaged by the law of September 30th, 1986 relating to the freedom of communication, like with the existing regulation.