AIS has the facility to carry arbitrary binary data. These packets are identified with an application specific message (ASM) identifier. The identifier is made up of a DAC and FI, as below.
DAC Designated Area Code FI Function Identiļ¬er
Message types: 6 ABM 8 BBM
12 and 14 correspond to 6 and 8, but are meant for safety related messages and don't use DAC/FI.
Class B CS should not transmit 6,8,12,14. Class B SO can. (ITU-R)