An AIS transponder supports situational awareness by transmitting own-ship data and receiving nearby reports. This continuous exchange helps mariners monitor target tracks and identify surrounding traffic as supplementary navigation information.
A 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. AIS 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.
AIS can operate with a minimum display or feed radar, ECDIS and other navigation displays, but remains supplementary to lookout, radar and all available safety information. 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.
