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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

Bits

Description

 

Message ID

6

Identifier for Message 18; always 18

 

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 anymore; should 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 (+180º, East = positive (as per 2's complement)), West = negative (as per 2's complement);
181º (6791AC0h) = not available = default)

 

Latitude

27

Latitude in 1/10 000 min (90º, North = positive (as per 2's complement)), South = negative (as per 2's complement);
91º = (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.1371-5
 

MESSAGE 19: EXTENDED CLASS B EQUIPMENT POSITION REPORT*

Parameter

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.; 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);
91º = (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.
@@@@@@@@@@@@@@@@@@@@ = not available = default

Type of ship and cargo type Provided by
Message 24B

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 Provided by
Message 24B

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 Provided by
Message 24B

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 Provided by
Message 18

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 Provided by Message 18
(Display Flag)

1

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

Assigned mode flag Provided by Message 18 (Display 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: For future equipment: this message is not needed and should not be used. All content is covered by Message 18, Message 24A and 24B.  For legacy equipment: this message should be used by Class B shipborne mobile equipment.

(Source : International Telecommunications Union Recommendation ITU-R M.1371-5)

MESSAGE 24: STATIC DATA REPORT*
Equipment that supports Message 24 part A shall transmit once every 6 min alternating between channels.

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 should be transmitted once every 6 min by Class B “CS” and Class B “SO” shipborne mobile equipment. The message consists of two parts. Message 24B should be transmitted within 1 min following Message 24A.

When the parameter value of dimension of ship/reference for position or type of electronic position fixing device is changed, Class-B :CS” and Class-B “SO” should transmit Message 24B.

When requesting the transmission of a Message 24 from a Class B “CS” or Class B “SO”, the AIS station should respond with part A and part B.

When requesting the transmission of a Message 24 from a Class A, the AIS station should respond with part B, which may contain the vendor ID only.

Parameter

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
For SAR aircraft, it should be set to “SAR AIRCRAFT NNNNNNN” where NNNNNNN equals the aircraft registration number

Number of bits

160

Occupies one-time period

MESSAGE 24 PART B

Parameter

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
Not applicable to SAR aircraft

Vendor ID

42

Unique identification of the Unit by a number as defined by the manufacturer (option; "@@@@@@@" = not available = default)
See vendor Identification field table below

Call sign

42

Call sign of the MMSI-registered vessel. 7 X 6 bit ASCII characters, "@@@@@@@" = not available = default
Craft associated with a parent vessel should use “A” followed by the last 6 digits of the MMSI of the parent vessel. Examples of these craft include towed vessels, rescue boats, tenders, lifeboats and life rafts

Dimension of ship/reference for position.

30

Dimensions of ship in meters and reference point for reported position.
For SAR aircraft, the use of this field may be decided by the responsible administration. If used it should indicate the maximum dimensions of the craft. As default should A = B = C = D be set to “0”.

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, 9-14 = not used, 15 = internal GNSS

Spare

2

 

Number of bits

168

Occupies one-time period

VENDOR IDENTIFICATION FIELD

Bit

Information

Description

(MSB)
41 …...... 24
 (18 bits)

Manufacturer’s ID

The Manufacturer’s ID bits indicate the manufacture’s mnemonic code consisting of three 6 bit ASCII characters.  NMEA mnemonic manufacturer codes should be used for Message 24B Manufacturer ID.

23 …...... 20
(4 bits)

Unit Model Code

The Unit Model Code bits indicate the binary coded series number of the model. The first model of the manufacture uses “1” and the number is incremented at the release of a new model. The code reverts to “1” after reaching to “15”. The “0” is not used

19 …...... 0
                  (LSB)
(20 bits)

Unit Serial Number

The Unit Serial Number bits indicate the manufacture traceable serial number. When the serial number is composed of numeric only, the binary coding should be used. If it includes figure(s), the manufacture can define the coding method. The coding method should be mentioned in the manual