Position Report Payload
The EAIS Position Report Payload format is intended to mirror ITU-R M.1371-5 Message 1 Position Reports format. The table contained here is informational. Implementers should refer back to ITU-R M.1371-[current revision] for most up to date bit usage and descriptions. The EAIS Position Report Payload prior to encryption without bit stuffing is 184 bits in length. Conforming to the AES Encryption scheme with a 128-bit cipher key, the encrypted part of the payload then effectively becomes 256 bits in length to create blocks of 128 bits. The FID 56 position report shall be transmitted once every 30 seconds when the unit has registered a speed over ground (SOG) of less than 3 knots for more than 3 minutes and once every 15 seconds when SOG is 3 knots or greater.
|
Parameter |
Number of bits |
Description |
Encryption Status |
|
DAC |
10 |
Identifier for this message: 366 |
Unencrypted |
|
Function ID |
6 |
Function Identifier: 56 |
Unencrypted |
|
Repeat Indicator |
0 |
Not present in EAIS Position Report Payload |
no bits |
|
User ID |
30 |
MMSI number. |
AES encrypted |
|
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 EPIRBAIS under test) |
AES encrypted |
|
Parameter |
Number of bits |
Description |
Encryption Status |
|
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. |
AES encrypted |
|
SOG |
10 |
Speed over ground in 1/10 knot steps (0-102.2 knots) 1023 = not available, 1022 = 102.2 knots or higher. |
AES encrypted |
|
Position Accuracy |
1 |
The position accuracy (PA) flag 1 = high (≤ 10 m) 0 = low (>10 m) 0 = default |
AES encrypted |
|
Longitude |
28 |
Longitude in 1/10 000 min (±180 degrees, East = positive, West = negative. 181 degrees (6791AC0 hex) = not available = default) |
AES encrypted |
|
Latitude |
27 |
Latitude in 1/10 000 min (±90 degrees, North = positive, South = negative, 91 degrees (3412140 hex) = not available = default) |
AES encrypted |
|
COG |
12 |
Course over ground in 1/10° (0-3599). 3600 (E10 hex) = not available = default; 3 601 – 4 095 should not be used. |
AES encrypted |
|
True Heading |
9 |
Degrees (0-359) (511 indicates not available = default). |
AES encrypted |
|
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) |
AES encrypted |
|
Parameter |
Number of bits |
Description |
Encryption Status |
|
Special maneuver indicator |
2 |
0 = not available = default 1 = not engaged in special maneuver 2 = engaged in special maneuver (i.e. regional passing arrangement on Inland Waterway) |
AES encrypted |
|
Spare |
3 |
Not used. Should be set to zero. |
AES encrypted |
|
RAIM-Flag |
1 |
RAIM (Receiver Autonomous Integrity Monitoring) flag of Electronic Position Fixing Device; 0 = RAIM not in use = default; 1 = RAIM in use) |
AES encrypted |
|
Communication State |
19 |
MSG ID 1 & 2 = SOTDMA communication state as described in 1371-5, Annex 2 MSG ID 3 ITDMA communication state as described in 1371-5, Annex 2 |
AES encrypted |
|
Checksum |
8 |
Exclusive OR (XOR) 8-bit |
AES encrypted |
|
Stuffed bits |
88 |
Stuffed bits are inserted so that the number of bits in the encrypted field is a multiple of 128 bits (256 for this message); set to zero. |
AES encrypted |
|
TOTAL |
272 |
16 unencrypted bits plus 256 encrypted bits |
|
