M.1371 : Technical characteristics for an automatic identification system using time division multiple access in the VHF maritime mobile frequency band (Rec. ITU-R M.1371-5) | ITU

Table 1: Class A shipborne mobile equipment reporting intervals

Table 1: Class A shipborne mobile equipment reporting intervals (p. 8)
Ship’s dynamic conditions Nominal reporting interval
Ship at anchor or moored and not moving faster than 3 knots 3 min
Ship at anchor or moored and moving faster than 3 knots 10 s
Ship 0-14 knots 10 s
Ship 0-14 knots and changing course 3 1/3 s
Ship 14-23 knots 6 s
Ship 14-23 knots and changing course 2 s
Ship > 23 knots 2 s
Ship > 23 knots and changing course 2 s
Table 2: Reporting intervals for equipment other than Class A shipborne mobile equipment (p. 9)
Platform’s condition Nominal reporting interval Increased reporting interval
Class B "SO" shipborne mobile equipment not moving faster than 2 knots 3 min 3 min
Class B "SO" shipborne mobile equipment moving 2-14 knots 30 s 30 s
Class B "SO" shipborne mobile equipment moving 14-23 knots 15 s 30 s
Class B "SO" shipborne mobile equipment moving >23 knots 5 s 15 s
Class B "CS" shipborne mobile equipment not moving faster than 2 knots 3 min -
Class B "CS" shipborne mobile equipment moving faster than 2 knots 30 s -
Search and rescue aircraft (airborne mobile equipment) 10 s -
Aids to navigation 3 min -
AIS base station 10 s -

Table 48: Message descriptions. Position reports

Table 48: Message descriptions. Position reports (pp. 109-110)
Parameter Number of bits Description
Message ID 6 Identifier for this Message 1, 2 or 3
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 Unique identifier such as MMSI number
Navigational status 4 0 = under way using engine, 1 = at anchor, 2 = not under command, 3 = restricted maneuverability, 4 = constrained by her draught, 5 = moored, 6 = aground, 7 = engaged in fishing, 8 = under way sailing, 9 = reserved for future amendment of navigational status for ships carrying DG, HS, or MP, or IMO hazard or pollutant category C, high speed craft (HSC), 10 = reserved for future amendment of navigational status for ships carrying dangerous goods (DG), harmful substances (HS) or marine pollutants (MP), or IMO hazard or pollutant category A, wing in ground (WIG); 11 = power-driven vessel towing astern (regional use), 12 = power-driven vessel pushing ahead or towing alongside (regional use); 13 = reserved for future use, 14 = AIS-SART (active), MOB-AIS, EPIRB-AIS 15 = undefined = default (also used by AIS-SART, MOB-AIS and EPIRB-AIS under test)
Rate of turn ROTAIS 8 0 to +126 = turning right at up to 708° per min or higher 0 to –126 = turning left at up to 708° per min or higher Values between 0 and 708° per min coded by ROTAIS = 4.733 SQRT(ROTsensor) degrees per min where ROTsensor is the Rate of Turn as input by an external Rate of Turn Indicator (TI). ROTAIS is rounded to the nearest integer value. +127 = turning right at more than 5° per 30 s (No TI available) –127 = turning left at more than 5° per 30 s (No TI available) –128 (80 hex) indicates no turn information available (default). ROT data should not be derived from COG information.
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 The position accuracy (PA) flag should be determined in accordance with Table 50 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 electronic position system (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)
Special manoeuvre indicator 2 0 = not available = default 1 = not engaged in special manoeuvre 2 = engaged in special manoeuvre (i.e. regional passing arrangement on Inland Waterway)
Spare 3 Not used. Should be set to zero. Reserved for future use.
RAIM-flag 1 Receiver autonomous integrity monitoring (RAIM) flag of electronic position fixing device; 0 = RAIM not in use = default; 1 = RAIM in use. See Table 50
Communication state 19 See Table 49
Number of bits 168
Navigational status (from Table 48, p. 109)
Navigational status: Description:
0 Under way using engine
1 At anchor
2 Not under command
3 Restricted maneuverability
4 Constrained by her draught
5 Moored
6 Aground
7 Engaged in fishing
8 Under way sailing
9 Reserved for future amendment of navigational status for ships carrying DG, HS, or MP, or IMO hazard or pollutant category C, high-speed craft (HSC)
10 Reserved for future amendment of navigational status for ships carrying dangerous goods (DG), harmful substances (HS) or marine pollutants (MP), or IMO hazard or pollutant category A, wing in ground (WIG)
11 Power-driven vessel towing astern (regional use)
12 Power-driven vessel pushing ahead or towing alongside (regional use)
13 Reserved for future use
14 AIS-SART (active), MOB-AIS, EPIRB-AIS
15 Undefined = default (also used by AIS-SART, MOB-AIS, and EPIRB-AIS under test)

Table 52: Ship static and voyage related data

Table 52: Ship static and voyage related data (pp. 112-113)
Parameter Number of bits Description
Message ID 6 Identifier for this Message
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
AIS version indicator 2 0 = station compliant with Recommendation ITU-R M.1371-1 1 = station compliant with Recommendation ITU-R M.1371-3 (or later) 2 = station compliant with Recommendation ITU-R M.1371-5 (or later) 3 = station compliant with future editions
IMO number 30 0 = not available = default – Not applicable to SAR aircraft 0000000001-0000999999 not used 0001000000-0009999999 = valid IMO number; 0010000000-1073741823 = official flag state number.
Call sign 42 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 liferafts.
Name 120 Maximum 20 characters 6 bit ASCII, as defined in Table 47 “@@@@@@@@@@@@@@@@@@@@” = not available = default. The Name should be as shown on the station radio license. For SAR aircraft, it should be set to “SAR AIRCRAFT NNNNNNN” where NNNNNNN equals the aircraft registration number.
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
Overall dimension/reference for position 30 Reference point for reported position. Also indicates the dimension of ship (m) (see Fig. 41 and § 3.3.3) 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
ETA 20 Estimated time of arrival; MMDDHHMM UTC Bits 19-16: month; 1-12; 0 = not available = default Bits 15-11: day; 1-31; 0 = not available = default Bits 10-6: hour; 0-23; 24 = not available = default Bits 5-0: minute; 0-59; 60 = not available = default For SAR aircraft, the use of this field may be decided by the responsible administration
Maximum present static draught 8 In 1/10 m, 255 = draught 25.5 m or greater, 0 = not available = default; in accordance with IMO Resolution A.851 Not applicable to SAR aircraft, should be set to 0
Destination 120 Maximum 20 characters using 6-bit ASCII; @@@@@@@@@@@@@@@@@@@@ = not available For SAR aircraft, the use of this field may be decided by the responsible administration
DTE 1 Data terminal equipment (DTE) ready (0 = available, 1 = not available = default) (see § 3.3.1)
Spare 1 Spare. Not used. Should be set to zero. Reserved for future use
Number of bits 424 Occupies 2 slots

Table 53: Identifiers to be used by ships to report their type

Table 53: Identifiers to be used by ships to report their type (p. 114)
Identifier No. Special craft
50 Pilot vessel
51 Search and rescue vessels
52 Tugs
53 Port tenders
54 Vessels with anti-pollution facilities or equipment
55 Law enforcement vessels
56 Spare – for assignments to local vessels
57 Spare – for assignments to local vessels
58 Medical transports (as defined in the 1949 Geneva Conventions and Additional Protocols)
59 Ships and aircraft of States not parties to an armed conflict
Table 53 (continued): Other ships (p. 114)
First digit(1) Second digit(1) First digit(1) Second digit(1)
1 – Reserved for future use 0 – All ships of this type – 0 – Fishing
2 – WIG 1 – Carrying DG, HS, or MP, IMO hazard or pollutant category X(2) – 1 – Towing
3 – See right column 2 – Carrying DG, HS, or MP, IMO hazard or pollutant category Y(2) 3 – Vessel 2 – Towing and length of the tow exceeds 200 m or breadth exceeds 25 m
4 – HSC 3 – Carrying DG, HS, or MP, IMO hazard or pollutant category Z(2) – 3 – Engaged in dredging or underwater operations
5 – See above 4 – Carrying DG, HS, or MP, IMO hazard or pollutant category OS(2) – 4 – Engaged in diving operations
5 – Reserved for future use – 5 – Engaged in military operations 6 – Passenger ships
6 – Reserved for future use – 6 – Sailing 7 – Cargo ships
7 – Reserved for future use – 7 – Pleasure craft 8 – Tanker(s)
8 – Reserved for future use – 8 – Reserved for future use 9 – Other types of ship
9 – No additional information – 9 – Reserved for future use

Table 70: Standard class B equipment position report

Table 70: Standard class B equipment position report (pp. 126-127)
Parameter Number of 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. See § 4.6.1, Annex 2; 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
The PA flag should be determined in accordance with Table 50
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 AIS 1, AIS 2 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 see Table 50
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 (see § 3.3.7.2.1, Annex 2), if communication state selector flag is set to 0, or ITDMA communication state (see § 3.3.7.3.2, Annex 2), if communication state selector flag is set to 1
Because Class B "CS" does not use any Communication State information, this field should be filled with the following value: 1100000000000000110
Number of bits 168 Occupies one slot

Table 71: Extended class B equipment position report

Table 71: Extended class B equipment position report (pages 127-128)
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 The PA flag should be determined in accordance with Table 50
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)
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 47. @@@@@@@@@@@@@@@@@@@@ = not available = default
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
Dimension of ship/reference for position 30 Dimensions of ship in meters and reference point for reported position (see Fig. 41 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, 9-14 = not used, 15 = internal GNSS
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
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