An AIS transponder comprises antennas, VHF transceivers, a processor, GNSS timing, sensor interfaces, controls, and integrity testing. These functional parts of a shipborne AIS installation include VHF transmission and reception, processing, positioning or timing input, sensor interfaces, controls and antennas.
This shipborne AIS unit automatically transmits its own data and receives data from other ships, VTS stations and other AIS stations over the AIS VHF data link. The system primarily uses two dedicated VHF channels and time-division access so participating stations can share the radio link; current technical characteristics are specified in ITU-R M.1371-6.
Class A and Class B equipment have different capabilities and reporting behaviour; Class B does not necessarily provide all functions required of Class A equipment.
