Single slot binary message

msg_ID: 
25
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 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