Class A

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The operation of Class A AIS transceivers is defined by the equipment and test standard IEC61993-2 Edition 1.

Class A transceivers use the following TDMA access schemes:

Using SOTDMA, units transmit to locate a vacant time slot reserve it, transmit the data and reserve the next time slot automatically. Class A units receive as well as transmit data, receiving when to transmit their own data, as well as receiving data from other ships, AtoNs or base stations and when their next reserved slot is in the AIS slot map.

Class A units have one VHF transmitter, two VHF TDMA receivers and one VHF Digital Selective Calling (DSC) receiver. Class A units must also include links to the shipboard display and sensor systems via standard marine electronic communications. The unit primarily uses GPS, LORAN, Glonas or an internal navigation system to determine its position. The unit connects to shipboard systems through data connections, eg. NMEA 0183/2000/USB, to display information received through AIS.

Access scheme
Transmitter power
Number of receivers
Reporting rate
Number of interfaces
3 (2 x AIS, 1 xDSC)
2 seconds - 3 minutes depending on the speed of the vessel
Mini Keyboard Display (MKD)
6 serial interfaces