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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. Since the data content of this binary message is defined by the application, Message 6 is an Application Specific Message (click on this link for a registry of recognized Application Specific Messages).
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Parameter
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Number of bits
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Description
|
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Message ID
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6
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Identifier for Message 6; always 6
|
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Repeat indicator
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2
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Used by the repeater to indicate how many times a message has been repeated. 0-3; default = 0; 3 = do not repeat any more
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Source ID
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30
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MMSI number of the source station
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Sequence number
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2
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0-3
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Destination ID
|
30
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MMSI number of the destination station
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Retransmit flag
|
1
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Retransmit flag should be set upon retransmission: 0 = no retransmission = default; 1 = retransmitted
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Spare
|
1
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Not used. Should be zero. Reserved for future use
|
|
Binary data
|
Maximum
936
|
Application identifier
|
16 bits
|
|
Bit
|
Description
|
|
15-6
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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
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5-0
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Function identifier (FI). The meaning should be determined by the authority which is responsible for the area given in the designated area code
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|
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Application data
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Maximum 920 bits
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Application specific data
|
|
Maximum number of bits
|
Maximum
1 008
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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;
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Additional bit stuffing will be required for these message types. 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:
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Number of slots
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Maximum binary data bytes
|
|
1
|
8
|
|
2
|
36
|
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3
|
64
|
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4
|
92
|
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5
|
117
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(Source: Rec. ITU-R M.1371-5)
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