Binary broadcast message

Binary data for broadcast communication
Access scheme: 
Communication state: 
Transmitted by: 
Mobile station
Base station

This message will be variable in length, based on the amount of binary data. The length should vary between 1 and 5 slots.

Parameter Number of bits Description
Message ID 6 Identifier for Message 8; always 8
Repeat indicator 2 Used by the repeater to indicate how many times a message has been repeated. See § 4.6.1, Annex 2; 0-3; default = 0; 3 = do not repeat any more
Source ID 30 MMSI number of source station
Spare 2 Not used. Should be set to zero. Reserved for future use
Binary data Maximum 968 Application identifier 16 bits Should be as described in § 2.1, Annex 5
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

Table 58 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

These numbers also take into account bit stuffing.
Additional bit stuffing will be required for this message type. For details refer to transport layer, § 5.2.1, Annex 2.