Addressed binary message

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

The addressed binary message should be variable in length, based on the amount of binary data. The length should vary between 1 and 5 slots. See application identifiers in § 2.1, Annex 5.

Parameter Number of bits Description  
Message ID 6 Identifier for Message 6; always 6  
Repeat indicator 2 Used by the repeater to indicate how many times a message has been repeated. Refer to § 4.6.1, Annex 2; 0-3; default = 0; 3 = do not repeat any more  
Source ID 30 MMSI number of source station  
Sequence number 2 0-3; refer to § 5.3.1, Annex 2  
Destination ID 30 MMSI number of destination station  
Retransmit flag 1 Retransmit flag should be set upon retransmission: 0 = no retransmission = default; 1 = retransmitted  
Spare 1 Not used. Should be zero. Reserved for future use  
Binary data Maximum 936 Application identifier 16 bits Should be as described in § 2.1, Annex 5
Application data Maximum 920 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;

Additional bit stuffing will be required for these message types. For details refer to transport layer, § 5.2.1, Annex 2.
Table 55 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 8
2 36
3 64
4 92
5 117

These numbers also take bit stuffing into account.