‘from.’ Used to precede the name or identification of the calling station. Frequently used in Morse and telex transmissions.

A system in the GMDSS for transmitting distress alerts from ships and for transmitting associated acknowledgements from shore stations. It is also used for relaying distress alerts and for alerts prior to the broadcast of urgency and safety messages.

The DSC transmission of a distress alert indicates that a mobile unit (ship, aircraft or other vehicle) or person is threatened by grave and imminent danger and requests immediate assistance. It is sent using a DSC format in the bands used for terrestrial radiocommunications or a distress message format, in which case it is relayed through space stations. It is normally followed by a distress call on the associated R/T channel. The distress alert shall provide the identification of the station in distress and its position.

Data Network Identifier. A digital ID downloaded to a ship’s Inmarsat–C terminal, to permit Automated Position Reporting (i.e. to allow polling of the ship’s position).

Disaster Recovery Facility. (ie. AMSA backup facility)

Operating method in which transmission is possible simultaneously in both directions of a telecommunication channel.