AIS Binary Broadcast Message (Message 8)

This message will be variable in length, based on the amount of binary data. The length should vary between 1 and 5 slots. Since the data content of this binary message is defined by the application, Message 8 is an Application Specific Message (click on this link for a registry of recognized Application Specific Messages)

Parameter

Number of bits

Description

Message ID

Identifier for Message 8; always 8

Repeat indicator

Used by the repeater to indicate how many times a message has been repeated. 0-3; default = 0; 3 = do not repeat any more

Source ID

MMSI number of source station

Spare

Not used. Should be set to zero. Reserved for future use

Binary data

Maximum 968

Application identifier

16 bits

Bit	Description
15-6	Designated area code (DAC). This code is based on the maritime identification digits (MID). Exceptions are 0 (test) and 1 (international). Although the length is 10 bits, the DAC codes equal to or above 1 000 are reserved for future use
5-0	Function identifier (FI). The meaning should be determined by the authority which is responsible for the area given in the designated area code

Application data

Maximum 952 bits

Application specific data

Maximum number of bits

Maximum 1 008

Occupies up to 3 slots, or up to 5 slots when able to use FATDMA reservations.
For Class B “SO” mobile AIS stations the length of the message should not exceed 3 slots

For Class B “CS” mobile AIS stations should not transmit

The table below gives the number of binary data bytes (including application ID and application data), so that the whole message fits into a given number of slots. It is recommended that any application minimizes the use of slots by limiting the number of binary data bytes to the numbers given, if possible:

Number of slots	Maximum binary data bytes
1	12
2	40
3	68
4	96
5	121

(Source: Rec. ITU-R M.1371-5)