This ASM message is used to broadcast data to all targets, and utilizes MITDMA communication state. Multiple messages, or periodically broadcasted messages may be chained together using the MITDMA communication state. The first transmission in the chain will use RATDMA to access the link, and all additional transmission will use slots allocated by the MITDMA communication state. Scheduled broadcast message is defined in Table 26.
Table 26
Scheduled broadcast message
|
Parameter |
Number of bits |
Description |
|---|---|---|
|
Message ID |
4 |
1 - Broadcast message with MITDMA communication state |
|
Retransmit flag |
1 |
0 (reserved for future use) |
|
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 |
|
Session ID |
6 |
The Session ID associates the VDL transmission with a specific PI transaction |
|
Source ID |
32 |
The Unique Identifier of the transmitting station as described in § 2.4, Annex 1. |
|
Data Count |
11 |
1 – Max data count |
|
ASM identifier |
16 |
Application identifier and described in § 6.2 |
|
Binary Data (no FEC / FEC) |
1 slot: 240 / 144 2 slot: 752 / 528 3 slot: 1264 / 912 SAT: N/A / 808 |
Application data as specified by the ASM Identifier. The available length of the binary data is specified by the Link Id. Unused payload data is zero-filled |
|
Communication State |
38 |
MITDMA communication state as described in § 6.4 |
|
Spare bits |
2 |
Spare Bits – reserved for the future |
Table 20
MITDMA communication state parameters
|
Parameter |
Number of bits |
Description |
Minimum |
Maximum |
|---|---|---|---|---|
|
Transmit block counter |
4 |
A decrementing counter used to indicate how many transmissions are left to transmit within the chain A value of 1 indicates this is the last transmission within the chain A value of 0 indicates a recurring transmission. |
0 |
15 |
|
Block Identifier |
4 |
This identifier uniquely identifies the block of data within the transmit chain. This identifier also maps to the acknowledgment for addressed messages. |
0 |
15 |
|
Slot Increment 1 |
8 |
Offset to the next slot to be used, referenced to the current transmission start slot. A value of 0 indicates no additional slot allocations |
20 |
255 |
|
Number of Slots 1 |
2 |
Indicates the number of consecutive slots, which are allocated, starting at the slot increment A value of 0 indicates the 8 bits from Slot Increment 1 become the MSB for the Slot Increment 2 |
0 |
3 |
|
Slot Increment 2 |
8 |
Offset to the next slot to be used, referenced to the slot specified by slot increment 1 (or current transmission slot if the Number of Slots 1 is set to 0) A value of 0 indicates no additional slot allocations |
20 |
255 |
|
Number of Slots 2 |
2 |
Indicates the number of consecutive slots, which are allocated, starting at the slot increment |
1 |
3 |
|
Slot Increment 3 |
8 |
Offset to the next slot to be used, referenced to the slot specified by Slot Increment 2 |
20 |
255 |
|
Number of Slots 3 |
2 |
Indicates the number of consecutive slots, which are allocated, starting at the slot increment |
1 |
3 |
|
Total bits |
38 |
|
|
|
|
*) When combining Slot Increment 1 and Slot Increment 2 as a 16 bit field. This value should not exceed 6 frames. The combining of these values should only be done for recurring period broadcast transmissions. |
||||
Table 22
ASM identifier parameters
|
Bit |
Description |
|---|---|
|
15-6 |
Designated area code (DAC). This code is based on the maritime identification digits (MID). Exceptions are 0 (test) and 1 (international). Although the length is 10 bits, the DAC codes equal to or above 1 000 are reserved for future use |
|
5-0 |
Function identifier. The meaning should be determined by the authority which is responsible for the area given in the designated area code |
Annex 1 2.4 Station identification
Identification and location of all active maritime stations is provided automatically by means of the AIS. All VDES stations should be uniquely identified. For the purpose of identification, a unique numerical identifier is used as defined by the following:
If the unique identifier has a range which is less than or equal to 999999999, then this number is defined by the most recent version of Recommendation ITU-R M.585.
If the unique identifier has a range which is greater than 999999999, then this number is free form.