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AIS SAFETY RELATED BROADCAST MESSAGE (MESSAGE 14)

The safety related broadcast message could be variable in length, based on the amount of safety related text. The length should vary between 1 and 5 slots.

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Parameter

Number of bits

Description

Message ID

6

Identifier for Message 14; always 14.

Repeat indicator

2

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

Source ID

30

MMSI number of source station of message

Spare

2

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

Safety related text

Maximum 968

6-bit ASCII

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 the length of the message should not exceed 1 slot

 

 

The table below gives the number of 6-bit-ASCII characters, 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 characters to the numbers given, if possible.  The probability that a message will be successfully sent and received decreases with each additional slot required, especially since received messages cannot be acknowledged:

 

 

Number of slots

Maximum 6-bit ASCII characters

1

16

2

53

3

90

4

128

5

161

 

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