Assignment should be transmitted by a base station when operating as a controlling entity. Other stations can be assigned a transmission schedule, other than the currently used one. If a station is assigned a schedule, it will also enter assigned mode.
Two stations can be assigned simultaneously.
When receiving an assignment schedule, the station should tag it with a time-out, randomly selected between 4 and 8 min after the first transmission.
When a Class A shipborne mobile AIS station receives an assignment it should revert to either the assigned reporting rate or the resulting reporting rate (when slot assignment is used) or the autonomously derived reporting rate (see § 4.3.1, Annex 2), whatever is higher. The Class A shipborne mobile AIS station should indicate that it is in assigned mode (by using the appropriate messages), even if it reverts to a higher autonomously derived reporting rate.
NOTE 1 – The assigning station should monitor the mobile station’s transmissions in order to determine when the mobile station will time-out.
For bounds of assignment settings see Table 16, Annex 2.
Transmissions of Message 16 by base stations using assignment of transmission slots should consider directing transmissions to slots which have previously been reserved by the base station by FATDMA (Message 20).
If continued assignment is required, the new assignment should be transmitted before the start of the last frame of the previous assignment.
|Parameter||Number of bits||Description|
|Message ID||6||Identifier for Message 16. Always 16|
|Repeat indicator||2||Used by the repeater to indicate how many times a message has been repeated. See § 4.6.1, Annex 2; 0-3; 0 = default; 3 = do not repeat any more|
|Source ID||30||MMSI of assigning station|
|Spare||2||Spare. Should be set to zero. Reserved for future use|
|Destination ID A||30||MMSI number. Destination identifier A|
|Offset A||12||Offset from current slot to first assigned slot(1)|
|Increment A||10||Increment to next assigned slot(1)|
|Destination ID B||30||MMSI number. Destination identifier B. Should be omitted if there is assignment to station A, only|
|Offset B||12||Offset from current slot to first assigned slot. Should be omitted if there is assignment to station A, only(1)|
|Increment B||10||Increment to next assigned slot(1). Should be omitted, if there is assignment to station A, only|
|Spare||Maximum 4||Spare. Not used. Should be set to zero. The number of spare bits, which should be 0 or 4, should be adjusted in order to observe byte boundaries. Reserved for future use|
|Number of bits||96 or 144||Should be 96 or 144 bits|
|(1) To assign a reporting rate for a station, the parameter increment should be set to zero. The parameter offset should then be interpreted as the number of reports in a time interval of 10 min.|
When number of reports per 10 min are assigned, only multiples of 20 between 20 and 600 should be used. If a mobile station received a value which is not a multiple of 20 but below 600, it should use the next higher multiple of 20. If a mobile station receives a value greater than 600 it should use 600.
When slot increments are assigned, one of the following increment parameter settings should be used:
0 = see above
1 = 1 125 slots
2 = 375 slots
3 = 225 slots
4 = 125 slots
5 = 75 slots
6 = 45 slots
7 = undefined.
If a station receives the value 7, the station should disregard this assignment. Class B mobile AIS stations should not be assigned a reporting interval of less than 2 s.