- AIS is not a GMDSS communication system but it uses VHF radio, a connection to the navigational equipment on board the ship and the ship’s Maritime Mobile Service Identity (MMSI), so it has similar characteristics to GMDSS equipment. Carriage of AIS is required under the regulations of chapter V of SOLAS.
- AIS automatically provides information, including the ship’s identity, type, position, course, speed, navigational status and other safety information, to shore stations and other ships. AIS also receives automatically such information from similarly fitted ships.
- AIS transmits the data continuously with a reporting interval which varies between 2 seconds and 3 minutes depending on the speed of the ship and its rate of turn. The system is self-organizing so that many ships in an area can signal without interfering with one another. It can also work in an assigned mode for shore-based VTS purposes and a polled mode to respond to interrogation for identification.
- There are two classes of AIS, Class A for SOLAS vessels and a simplified version called Class B which is applicable to non-SOLAS vessels.
- AIS standards also include a safety-related text messaging functionality. Certain models of AIS provide preconfigured safety-related messages which include distress alert information. It is recommended that these are not used because they are not recognized internationally and there is no related reception or SAR infrastructure in place to accommodate them. They therefore may not be received, recognized or acted upon by authorities or other mariners.
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