AIS type A is mandatory for vessels 300GT and above and Cargo ships 500GT and above engaged on International voyages and all Passenger Ships irrespective of ships.
AIS type B has a limited functionality and is intended for Non-SOLAS vessels. It is non-mandated by IMO.
Class B is nearly identical to Class A except Class B does not transmit the vessel's IMO number, ETA or destination, navigational status, rate of turn information, sending safety messages (only receive), maximum present static draft and it also has a reporting rate less than Class A.