This ASM message is used to broadcast data to a group of stations as defined by the specified geographical area. The broadcast message does not contain a communication state. These broadcast messages are used for non-periodic transmission of data, and access the link using RATDMA. Geographical multicast message is defined in Table 31.
Table 31
Geographical multicast message
|
Parameter |
Number of bits |
Description |
|---|---|---|
|
Message ID |
4 |
6 – Geographical addressed message with no communication state |
|
Retransmit flag |
1 |
Indicates that this is a retransmission of data |
|
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. |
|
Longitude 1 |
18 |
Longitude of area to which the group assignment applies; upper right corner (north-east); in 1/10 min |
|
Latitude 1 |
17 |
Latitude of area to which the group assignment applies; upper right corner (north‑east); in 1/10 min |
|
Longitude 2 |
18 |
Longitude of area to which the group assignment applies; lower left corner (south-west); in 1/10 min |
|
Latitude 2 |
17 |
Latitude of area to which the group assignment applies; lower left corner (south‑west); in 1/10 min |
|
Data Count |
11 |
1 – Max data count |
|
Spare bits |
2 |
Spare Bits – reserved for the future |
|
ASM identifier |
16 |
Application identifier and described in § 6.2 |
|
Binary Data (no FEC / FEC) |
1 slot: 208 / 112 2 slot: 720 / 496 3 slot: 1232 / 880 SAT: N/A / 776 |
Application data as specified by the ASM Identifier. The available length of the binary data is specified by the Link Id. |
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.