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Automatic Identification System (AIS)
Primary Mission Areas:
Services & Reporting:
Maritime Information:
CLASS B AIS REPORTS

Message 18: Standard Class B equipment position report

Parameter

Number of bits

Description

 

Message ID

6

Identifier for Message 18; always 18

 

Repeat indicator

2

Shall be 0 for "CS" transmissions

 

User ID

30

MMSI number

 

Spare

8

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

 

SOG

10

Speed over ground in 1/10 knot steps (0-102.2 knots)
1 023 = not available, 1 022 = 102.2 knots or higher

 

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)

 

COG

12

Course over ground in 1/10= (0-3 599). 3 600 (E10h) = not available = default; 3 601-4 095 should not be used

 

True heading

9

Degrees (0-359) (511 indicates not available = default)

 

Time stamp

6

UTC second when the report was generated by the EPFS (0-59
or 60 if time stamp is not available, which should also be the default value or 61 if positioning system is in manual input mode or 62 if electronic position fixing system operates in estimated (dead reckoning) mode or 63 if the positioning system is inoperative)
61, 62, 63 are not used by "CS" AIS

 

Spare

2

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

 

Class B unit flag

1

0 = Class B SOTDMA unit
1 = Class B "CS" unit

Class B display flag

1

0 = No display available; not capable of displaying Message 12 and 14
1 = Equipped with integrated display displaying Message 12 and 14

Class B DSC flag

1

0 = Not equipped with DSC function
1 = Equipped with DSC function (dedicated or time-shared)

Class B band flag

1

0 = Capable of operating over the upper 525 kHz band of the marine band
1 = Capable of operating over the whole marine band
(irrelevant if "Class B Message 22 flag" is 0)

Class B Message 22 flag

1

0 = No frequency management via Message 22 , operating on AIS1, AIS2 only
1 = Frequency management via Message 22

Mode flag

1

0 = Station operating in autonomous and continuous mode = default
1 = Station operating in assigned mode

 

RAIM-flag

1

RAIM (Receiver autonomous integrity monitoring) flag of electronic position fixing device; 0 = RAIM not in use = default; 1 = RAIM in use

 

Communication state selector flag

1

0 = SOTDMA communication state follows
1 = ITDMA communication state follows
(always "1" for Class-B "CS")

 

Communication state

19

SOTDMA communication state. Because Class B "CS" does not use any Communication State information, this field shall be filled with the following value: 1100000000000000110.

 

Number of bits

168

Occupies one slot

 

(Source : International Telecommunications Union Recommendation ITU-R M.1371-3)

Message 19: Extended Class B equipment position report*

Parameter

Number of bits

Description

Message ID

6

Identifier for Message 19; always 19

Repeat indicator

2

Used by the repeater to indicate how many times a message has been repeated. See § 4.6.1, Annex 2; 0-3; 0 = default; 3 = do not repeat any more

User ID

30

MMSI number

Spare

8

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

SOG

10

Speed over ground in 1/10 knot steps (0-102.2 knots)
1 023 = not available, 1 022 = 102.2 knots or higher

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)

COG

12

Course over ground in 1/10= (0-3 599). 3 600 (E10h) = not available = default; 3 601-4 095 should not be used

True heading

9

Degrees (0-359) (511 indicates not available = default)

Time stamp

6

UTC second when the report was generated by the EPFS (0-59
or 60) if time stamp is not available, which should also be the default value or 61 if positioning system is in manual input mode or 62 if electronic position fixing system operates in estimated (dead reckoning) mode, or 63 if the positioning system is inoperative)

Note: CSTDMA devices do not transmit if position information is not available.

Spare

4

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

Name

120

Maximum 20 characters 6-bit ASCII, as defined in Table 44.
@@@@@@@@@@@@@@@@@@@@ = not available = default

Type of ship and cargo type

8

0 = not available or no ship = default
1-99 = as defined
100-199 = reserved, for regional use
200-255 = reserved, for future use

Dimension of ship/reference for position

30

Dimensions of ship in metres and reference point for reported position (see Fig. 42 and § 3.3.3)

Type of electronic position fixing device

4

0 =?Undefined (default); 1 = GPS, 2 = GLONASS, 3 = combined GPS/GLONASS, 4 = Loran-C, 5 = Chayka, 6 = integrated navigation system, 7 = surveyed; 8 = Galileo, 9-15 = not used

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 47

DTE

1

Data terminal ready (0 = available 1 = not available; = default) (see § 3.3.1)

Assigned mode flag

1

0 = Station operating in autonomous and continuous mode = default
1 = Station operating in assigned mode

Spare

4

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

Number of bits

312

Occupies two slots.


* Note: Class B/CS units autonomously transmit Messages 18 & 24. Message 19 is transmitted only upon a base station poll.

(Source : International Telecommunications Union Recommendation ITU-R M.1371-3)

Message 24: Static Data Report

Message 24 Part A may be used by any AIS station to associate a MMSI with a name.

Message 24 Part A and Part B shall be used by Class B "CS" shipborne mobile equipment. The message consists of two parts. Message 24B shall be transmitted within 1 min following Message 24A.

In case of an interrogation for a Class B "CS" on a Message 24, the response shall include Part A and Part B.

Message 24 Part A

Parameter

Number of bits

Description

Message ID

6

Identifier for Message 24; always 24

Repeat indicator

2

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

User ID

30

MMSI number

Part number

2

Identifier for the message part number; always 0 for Part A

Name

120

Name of the MMSI-registered vessel. Maximum 20 characters 6-bit ASCII, @@@@@@@@@@@@@@@@@@@@ = not
available = default

Number of bits

160

Occupies one-time period

Message 24 Part B

Parameter

Number of bits

Description

Message ID

6

Identifier for Message 24; always 24

Repeat indicator

2

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

User ID

30

MMSI number

Part number

2

Identifier for the message part number; always 1 for Part B

Type of ship and cargo type

8

0 = not available or no ship = default
1-99 = as defined in § 3.3.2
100-199 = reserved, for regional use
200-255 = reserved, for future use

Vendor ID

42

Unique identification of the Unit by a number as defined by the manufacturer (option; "@@@@@@@" = not available = default)

Call sign

42

Call sign of the MMSI-registered vessel. 7 X 6 bit ASCII characters, "@@@@@@@" = not available = default

Dimension of ship/reference for position. Or, for unregistered daughter vessels, use the MMSI of the mother ship.

30

Dimensions of ship in meters and reference point for reported position (see Fig. 42 and § 3.3.3). Or, for an unregistered daughter vessel, use the MMSI of the associated mother ship in this data field

Spare

6

 

Number of bits

168

Occupies one-time period

(Source : International Telecommunications Union Recommendation ITU-R M.1371-3)