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AIS BASE STATION REPORT (MESSAGE 4) AND COORDINATED UNIVERSAL TIME AND DATE RESPONSE (MESSAGE 11)
A Base Station Report is used for reporting UTC time and date and, at the same time, position. It is also is used by AIS stations for determining if it is within 120 NM for response to Messages 20 and 23.

Message 11 is only transmitted from a mobile station as a result of a UTC request message (Message 10).

Parameter

Number of bits

Description

Message ID
6 Identifier for this Message 4 or 11
4 = UTC and position report from base station:
11 = UTC and position response from mobile station
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; 0 = default; 3 = do not repeat any more
User ID
30 MMSI number
UTC year
14 1-9999; 0 = UTC year not available = default
UTC month
4 1-12; 0 = UTC month not available = default; 13-15 not used
UTC day
5 1-31; 0 = UTC day not available = default
UTC hour
5 0-23; 24 = UTC hour not available = default; 25-31 not used
UTC minute
6 0-59; 60 = UTC minute not available = default; 61-63 not used
UTC second
6 0-59; 60 = UTC second not available = default; 61-63 not used
Position accuracy
1 1 = high (£10 m)
0 = low (>10 m)
0 = default
Longitude
28 Longitude in 1/10 000 min (±180°, East = positive (as per 2’s complement), West = negative (as per 2’s complement);
181 = (6791AC0h) = not available = default)
Latitude
27 Latitude in 1/10 000 min (±90°, North = positive (as per 2’s complement), South = negative (as per 2’s complement);
91 = (3412140h) = not available = default)
Type of electronic position fixing device
4 Use of differential corrections is defined by field position accuracy above:
0 = undefined (default)
1 = global positioning system (GPS)
2 = GNSS (GLONASS)
3 = combined GPS/GLONASS
4 = Loran-C
5 = Chayka
6 = integrated navigation system
7 = surveyed
8 = Galileo
9-14 = not used
15 = internal GNSS
Transmission control for long-range broadcast message
1 0 = default – Class-A AIS station stops transmission of Message 27 within an AIS base station coverage area.
1 = Request Class-A station to transmit Message 27 within an AIS base station coverage area.
Base station coverage area should be defined by Message 23; If Message 23 is not received, the AIS station which is allowed to transmit on CH75 and 76 should ignore this bit and transmit Message 27.
Spare
9 Not used. Should be set to zero. Reserved for future use
RAIM-flag
1 RAIM (Receiver autonomous integrity monitoring) flag of electronic position fixing device; 0 = RAIM not in use = default; 1 = RAIM in use see Table 50
Communication state
19 SOTDMA communication state
Number of bits
168  
 
(Source: International Telecommunications Union Recommendation ITU-R M.1371-5)