Physical link:
AIS
msg_ID:
25
Extended description:
Short unscheduled binary data transmission (Broadcast or addressed)
Priority:
4
Access scheme:
RATDMA
ITDMA
FATDMA
CSTDMA
Communication state:
N/A
Transmitted by:
Mobile station
Base station
This message is primarily intended short infrequent data transmissions. The single slot binary message can contain up to 128 data-bits depending on the coding method used for the contents, and the destination indication of broadcast or addressed. The length should not exceed one slot. See application identifiers in § 2.1, Annex 5.
This message should not be acknowledged by either Message 7 or 13.
Table 81 gives the maximum number of binary data-bits for settings of destination indicator and coding method flags, such that, the message does not exceed one slot.
This message should not be acknowledged by either Message 7 or 13.
TABLE 80
| Parameter | Number of bits | Description | |
|---|---|---|---|
| Message ID | 6 | Identifier for Message 25; always 25 | |
| 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; default = 0; 3 = do not repeat any more | |
| Source ID | 30 | MMSI number of source station | |
| Destination indicator | 1 | 0 = Broadcast (no Destination ID field used) 1 = Addressed (Destination ID uses 30 data bits for MMSI) |
|
| Binary data flag | 1 | 0 = unstructured binary data (no Application Identifier bits used) 1 = binary data coded as defined by using the 16-bit Application identifier |
|
| Destination ID | 0/30 | Destination ID (if used) | If Destination indicator = 0 (Broadcast); no data bits are needed for the Destination ID. If Destination indicator = 1; 30 bits are used for Destination ID and spare bits for byte alignment. |
| Spare | 0/2 | Spare (if Destination ID used) | |
| Parameter | Number of bits | Description | ||
|---|---|---|---|---|
| Binary data | Broadcast Maximum 128 Addressed Maximum 96 |
Application identifier (if used) |
16 bits | Should be as described in § 2.1, Annex 5 |
| Application binary data | Broadcast Maximum 112 bits Addressed Maximum 80 bits |
Application specific data | ||
| Maximum number of bits | Maximum 168 | Occupies up to 1 slot subject to the length of sub-field message content Class B “CS” mobile AIS stations should not transmit |
||
Table 81 gives the maximum number of binary data-bits for settings of destination indicator and coding method flags, such that, the message does not exceed one slot.
TABLE 81
| Destination indicator | Coding method | Binary data (maximum bits) |
|---|---|---|
| 0 | 0 | 128 |
| 0 | 1 | 112 |
| 1 | 0 | 96 |
| 1 | 1 | 80 |