The STEDS Message 26 TOI Message format provides for both a broadcast and addressed TOI message variation. The text may be up to 121 6-bit ASCII characters (up to 726 bits). Addressing, when required, shall be performed using the Destination Indicator and Destination ID fields inherent to the Message 26 structure.
NOTE: TOI messages repeat every 15 seconds, until cancelled locally or a cancellation message is received. Cancelling a TOI locally stops transmission of TOI message repetitions and transmits a cancellation message. In the absence of a cancelation message, remote units receiving a TOI will apply Lost Target/Auto Drop processing rules the TOI designation from a target. Cancellation messages repeat four (4) times, 15 seconds apart.
|
Parameter |
Number of bits |
Description |
Encryption Status |
|
Function ID |
5 |
1 = TOI Report |
AES encrypted |
|
Target Type |
4 |
1 = AIS, 2 = Radar, 3 = Manual/Other, 4-15 = undefined |
AES encrypted |
|
Target ID |
20 |
Sender generated ID. |
AES encrypted |
|
MMSI |
30 |
MMSI number of the TOI, if contact type is “AIS”; otherwise all zeros |
AES encrypted |
|
TOI Status Designator |
1 |
0 = cancel; 1 = active |
AES encrypted |
|
Hour |
5 |
0-23 |
AES encrypted |
|
Minute |
6 |
0-59 |
AES encrypted |
|
Second |
6 |
0-59 |
AES encrypted |
|
Longitude |
25 |
Longitude in 1/1000 min (±180 degrees, East = positive, West = negative. 181 degrees = not available = default) |
AES encrypted |
|
Latitude |
24 |
Latitude in 1/1000 min (±90 degrees, North = positive, South = negative, 91 degrees = not available = default) |
AES encrypted |
|
COG |
9 |
Course over ground (0-359°). (511 indicates not available = default). |
AES encrypted |
|
SOG |
7 |
Speed over ground in knots (0-126 knots) with 127 = not available (default) and 126 = 126 kts or higher. |
AES encrypted |
|
Length of Text |
8 |
Length of the text message, expressed as the number of 6-bit ASCII characters |
AES encrypted |
|
Text |
0-726 bits Variable |
Maximum number of 6-bit ASCII characters is 121. |
AES encrypted |
|
Unused bits set to zero |
Variable |
Unused bits set to zero are inserted so that the number of bits in the encrypted field is a multiple of 128 bits. |
AES encrypted |
|
Checksum |
16 |
Cyclic Redundancy Check (CRC) 16-bit polynomial |
AES encrypted |
|
TOTAL |
128 256 384 512 640 768 896 |
128, 256, 384, 512, 640, 768 or 896 encrypted bits |
AES encrypted |
