TYPES OF AUTOMATIC IDENTIFICATION SYSTEMS

ITU-R Recommendation M.1371-1 describes the following types of AIS:

Class A
Shipborne mobile equipment intended for vessels meeting the requirements of IMO AIS carriage requirement.

Class B
Shipborne mobile equipment provides facilities not necessarily in full accord with IMO AIS carriage requirements. The Class B is nearly identical to the Class A, except the Class B:

• Has a reporting rate less than a Class A (e.g. every 30 sec. when under 14 knots, as opposed to every 10 sec. for Class A)
• Does not transmit the vessel's IMO number
• Does not transmit ETA or destination
• Does not transmit navigational status
• Is only required to receive, not transmit, text safety messages
• Is only required to receive, not transmit, application identifiers (binary messages)
• Does not transmit rate of turn information
• Does not transmit maximum present static draught