This ASM message is used to return message acknowledgments to one or more addressed messages. Note that this message should always use Link ID of 5 (3/4 coding rate). Acknowledgement message is defined in Table 30.
Table 30
Acknowledgment message
|
Parameter |
Number of bits |
Description |
|---|---|---|
|
Message ID |
4 |
5 – Multiple acknowledgment message with no 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. |
|
Destination ID |
32 |
The Unique Identifier of the receiving station as described in § 2.4, Annex 1. |
|
ACK/NACK Mask |
16 |
Specifies which MITDMA block IDs failed. Bit map field with the LSB representing Block ID 0, the MSB representing Block ID 15. “1” indicates a packet failed “0” indicates the packet was received ok |
|
Coding rate adaption request |
2 |
0 (reserved for future use) |
|
Channel Quality Indicator |
8 |
Signal quality |
|
Zero padding (no FEC / FEC) |
1 slot: 249 / 153 SAT: N/A / 817 As required |
Padding bits are added as required to complete the block size. These bits are not available for future use. |
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.