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|
These numbers also take bit stuffing into account.