AIS codes · Message types
AIS message types
Every AIS transmission starts with a six-bit message type. Position reports, ship names, base station beacons, safety text and buoy reports are all different types. Each of the 27 has a page here: who sends it, how often, and what to trust in it.
- 1Position report, scheduled (Class A)The standard Class A position report: where the ship is, how fast, which way.Class Adecoded
- 2Position report, assigned schedule (Class A)Same content as type 1, sent on a reporting rate assigned by a base station.Class Adecoded
- 3Position report, response to interrogation (Class A)Same layout as type 1, sent when a station asks the ship to report.Class Adecoded
- 4Base station reportA shore station announcing itself, its position and the UTC date and time.Base stationdecoded
- 5Static and voyage related data (Class A)Name, call sign, IMO number, ship type, dimensions, draught, destination and ETA.Class Adecoded
- 6Binary addressed messageApplication data sent to one named station.Any station
- 7Binary acknowledgeConfirms receipt of up to four type 6 messages.Any station
- 8Binary broadcast messageApplication data sent to everyone in range.Any station
- 9Standard SAR aircraft position reportPosition, altitude, speed and course of a search-and-rescue aircraft.SAR aircraftdecoded
- 10UTC and date inquiryAsks another station to send its UTC time and date.Any station
- 11UTC and date responseReply to a type 10 inquiry, laid out like a base station report.Any stationdecoded
- 12Addressed safety related messageA short free-text safety message sent to one station.Any station
- 13Safety related acknowledgementConfirms receipt of up to four type 12 messages.Any station
- 14Safety related broadcast messageA short free-text safety message sent to everyone in range.Any station
- 15InterrogationRequests a specific message from one or two other stations.Any station
- 16Assignment mode commandA base station assigns reporting slots or intervals to up to two ships.Base station
- 17DGNSS broadcast binary messageDifferential GNSS correction data broadcast by a reference station.Base station
- 18Standard Class B equipment position reportThe Class B equivalent of type 1: position, speed, course and heading.Class Bdecoded
- 19Extended Class B equipment position reportA type 18 plus name, ship type and dimensions in one two-slot message.Class Bdecoded
- 20Data link management messageA base station reserves slots for its own future transmissions.Base station
- 21Aid-to-navigation reportA buoy, beacon, light or virtual mark reporting its identity and position.Aid to navigationdecoded
- 22Channel managementA base station tells ships in a region which channels and power to use.Base station
- 23Group assignment commandA base station assigns a reporting rate to a whole class of ships in an area.Base station
- 24Static data report (Class B)A Class B vessel's name (part A) and type, call sign and dimensions (part B).Class Bdecoded
- 25Single slot binary messageA short application payload in one slot, broadcast or addressed.Any station
- 26Multiple slot binary message with communications stateA longer application payload spread across several slots.Any station
- 27Long-range AIS broadcast messageA compact position report meant to be heard by satellites.Class Adecoded
Message types 1 to 27 are the ones defined in ITU-R M.1371; type 0 is not used. “Decoded” marks the types whose fields the AIS message decoderunpacks; for the rest it reports the type and sender only. For the bigger picture, read how AIS works.