Glossary — communications

GMDSS, DSC, AIS, NAVTEX, VHF channel allocations, satellite networks.

43 terms in this category.

• AIS Aid to Navigation (AIS-AtoN)
  AIS station fitted on a buoy/light/synthetic mark broadcasting position and identity for ECDIS/radar overlay.
• AIS Class A
  The mandatory AIS transponder fitted on SOLAS ships transmitting vessel data at regular intervals and responding to interrogations.
• AIS Class B
  A lower-power AIS transponder used by smaller non-SOLAS vessels, transmitting position and identity data at reduced reporting rates.
• AIS-SART (AIS Search and Rescue Transmitter)
  Survival-craft device that broadcasts AIS Class A position reports when activated, with an MMSI beginning 970, enabling rescuers to plot its position on AIS displays.
• Digital Selective Calling (DSC)
  A standard for transmitting pre-defined digital messages over VHF/MF/HF radio to initiate distress, urgency, or routine calls.
• DSC (Digital Selective Calling)
  Pre-formatted digital distress and safety calling technique transmitting identity, nature of distress, position, and time on dedicated watch-keeping frequencies.
• EGC (Enhanced Group Call)
  Inmarsat satellite broadcast system delivering Maritime Safety Information to all vessels within a defined geographical area simultaneously.
• Enhanced Group Call (EGC)
  Inmarsat-C broadcast service for distributing safety, navigational, and security messages to ships in defined geographic areas.
• Fleet Broadband (FBB)
  An Inmarsat satellite broadband service providing high-speed voice and data communications on mobile maritime terminals.
• Fleet Xpress
  Inmarsat managed broadband service combining Ka-band Global Xpress with L-band FleetBroadband as backup.
• Global Maritime Distress and Safety System (GMDSS)
  An internationally agreed set of safety procedures and communications equipment required on SOLAS ships for distress and safety.
• GMDSS General Operator's Certificate (GOC)
  Highest GMDSS radio operator qualification; required for service in Sea Areas A2/A3/A4.
• GMDSS Restricted Operator's Certificate (ROC)
  GMDSS qualification limited to Sea Area A1 (VHF DSC range only).
• GMDSS Sea Area A1 (Area A1)
  An area within range of at least one VHF DSC coast station providing continuous alerting coverage, typically within 20–50 miles of shore.
• GMDSS Sea Area A2 (Area A2)
  An area beyond A1 but within MF DSC continuous coverage, typically up to 400 nautical miles from shore.
• GMDSS Sea Area A3 (Area A3)
  An area beyond A1 and A2 within coverage of an Inmarsat geostationary satellite, covering most ocean areas between latitudes 70°N and 70°S.
• GMDSS Sea Area A4 (Area A4)
  The polar sea areas beyond GMDSS Area A3, not covered by geostationary satellites, where HF radio is used for distress alerting.
• Inmarsat-C
  Geostationary satellite system providing low-data-rate store-and-forward messaging and EGC SafetyNET broadcasts, recognised under GMDSS for Sea Area A3.
• Iridium GMDSS
  IMO-recognised GMDSS satellite service using Iridium's low Earth orbit constellation, providing global coverage including polar Sea Area A4.
• Iridium GMDSS Service
  Iridium satellite service recognised by IMO since 2020 for GMDSS Sea Areas A1–A4, including polar regions.
• Long Range Identification and Tracking (LRIT)
  A mandatory satellite-based tracking system requiring SOLAS ships to transmit identity and position to flag and port state authorities.
• Long-Range Identification and Tracking (LRIT)
  Mandatory worldwide ship-position-reporting system at 6-hour intervals via Inmarsat-C (or Iridium), separate from AIS.
• METAREA
  One of twenty-one geographic areas for which meteorological services co-ordinate the broadcast of marine weather forecasts.
• MF/HF SSB
  Single-side-band radio in MF (1.6–4 MHz) and HF (4–27 MHz) bands used for medium- and long-range maritime voice and DSC.
• MMSI (Maritime Mobile Service Identity)
  Nine-digit numerical address used to identify ships, coast stations, and devices in DSC, AIS, and satellite distress alerting.
• MOB AIS (Man Overboard AIS)
  Personal AIS beacon worn by crew that activates on water immersion, broadcasting AIS position reports with an MMSI beginning 972 to identify a man-overboard casualty.
• MSI (Maritime Safety Information)
  Umbrella term for navigational warnings, meteorological forecasts, distress relays, SAR information, and piracy reports broadcast to ships under the GMDSS framework.
• NAVAREA
  One of sixteen geographic sea areas defined by IMO/IHO for the co-ordination of worldwide navigational warning broadcasts.
• NAVAREA (NAVAREA)
  One of 21 IMO/IHO-designated sea areas within which a co-ordinating authority issues numbered navigational warnings to mariners.
• Navigational Telex (NAVTEX)
  An automated medium frequency broadcast system transmitting navigational warnings, weather forecasts, and search and rescue notices.
• NAVTEX (Navigational Telex)
  Automated narrow-band direct-printing system broadcasting Maritime Safety Information on 518 kHz (international) and 490 kHz (national) within 200–400 NM of coastal transmitters.
• NAVTEX Frequencies
  International NAVTEX uses 518 kHz (English); national NAVTEX 490 kHz; tropical 4209.5 kHz.
• Radar SART (SART)
  X-band search and rescue transponder that responds to a 9 GHz radar pulse by generating a distinctive 12-dot line on the rescuing vessel's radar display.
• SafetyNET
  The Inmarsat-C broadcast service transmitting maritime safety information including navigational warnings and weather forecasts in GMDSS Areas A3/A4.
• SafetyNET
  Inmarsat-C EGC broadcast service delivering Maritime Safety Information to vessels in ocean areas A3, used as the satellite component of the GMDSS MSI distribution system.
• SafetyNET
  Inmarsat Enhanced Group Call service used to broadcast Maritime Safety Information to GMDSS Sea Areas A3 and A4.
• Starlink Maritime
  SpaceX low-earth-orbit broadband; offers high bandwidth at sea but is not yet GMDSS-recognised.
• Very High Frequency Radio (VHF)
  Marine radio operating in the 156–174 MHz band used for short-range ship-to-ship and ship-to-shore communications.
• Vessel Traffic Service (VTS)
  Shore-based service that monitors and assists vessel movements in defined waters.
• VHF Channel 13
  Bridge-to-bridge channel for navigational coordination, especially in US, Mexican, and some Asian waters.
• VHF Channel 16 (Ch 16)
  The international distress, safety, and calling frequency at 156.8 MHz; all SOLAS ships must maintain a continuous watch on this channel.
• VHF Channel 70 / DSC
  Dedicated VHF DSC channel (156.525 MHz) used to alert and call other stations before voice contact on ch.16.
• VSAT
  Very-Small-Aperture-Terminal satellite communications providing always-on broadband at sea (Ku/Ka band).