Navigation Center Website Top Header Banner
Home | LNMs | Nav Rules | AIS | NAIS Data Request | MSI Data Downloads | GPS Constellation Status | GPS Testing | Almanacs | USCG Int'l Ice Patrol | Contact Us | Search
Automatic Identification System
Mission Areas
Subscribe / Report (free)
Maritime Information

Print friendly version  
AIS SINGLE SLOT BINARY MESSAGE (MESSAGE 25)

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.  This message should not be acknowledged by either Message 7 or 13.  Since the data content of this binary message is defined by the application, Message 25 is an Application Specific Message (click on this link for a registry of recognized Application Specific Messages).

 

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. 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)

Binary data

Broadcast Maximum 128
Addressed Maximum 96

Application identifier
(if used)

16 bits

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 (FI). The meaning should be determined by the authority which is responsible for the area given in the designated area code

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.

 

Destination indicator

Coding method

Binary data (maximum bits)

0

0

128

0

1

112

1

0

96

1

1

80

 

(Source: Rec. ITU-R M.1371-5)