DSC (Digital Selective Calling)

Digital Selective Calling is the GMDSS technique for transmitting a digitally coded distress alert or routine call on dedicated VHF, MF, and HF frequencies, addressed by the nine-digit MMSI. VHF DSC uses Channel 70; MF distress uses 2187.5 kHz. A single button press transmits the ship’s identity, position, and nature of distress to all DSC-equipped stations in range and to coast stations, which then coordinate the response. DSC removed the old requirement for continuous aural watchkeeping on a single distress frequency.