Multiple Slot Binary Message With Communications State (Message 26)

This message is primarily intended for scheduled binary data transmissions by applying either the SOTDMA or ITDMA access scheme. This multiple slot binary message can contain up to 1 004 data-bits (using 5 slots) depending on the coding method used for the contents, and the destination indication of broadcast or addressed. 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 26 is an Application Specific Message (click on this link for a registry of recognized Application Specific Messages). Where possible, Message 26 should be used in place of Message 6 or 8.

Parameter

Number of bits

Description

Message ID

The identifier for Message 26; always 26

Repeat indicator

Used by the repeater to indicate how many times a message has been repeated. 0-3; default = 0; 3 = do not repeat any more

Source ID

MMSI number of the source station

Destination indicator

0 = Broadcast (no Destination ID field used)
1 = Addressed (Destination ID uses 30 data bits for MMSI)

Binary data flag

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 the Destination ID and 2 spare bits for byte alignment.

Spare bits

0/2

Spare (if Destination ID used)

Binary data

Broadcast Maximum 104

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

Addressed Maximum 72

Application binary data

Broadcast Maximum 88 bits
Addressed Maximum 56 bits

Application specific data

Binary data added by 2nd slot

224

Allows for 32 bits of bit-stuffing

Binary data added by 3rd slot

224

Allows for 32 bits of bit-stuffing

Binary data added by 4th slot

224

Allows for 32 bits of bit-stuffing

Binary data added by 5th slot

224

Allows for 32 bits of bit-stuffing

Spare

Needed for byte alignment

Communication state selector flag

0 = SOTDMA communication state follows
1 = ITDMA communication state follows

Communication state

SOTDMA communication state (see § 3.3.7.2.1, Annex 2), if communication state selector flag is set to 0, or ITDMA communication state (§ 3.3.7.3.2, Annex 2), if communication state selector flag is set to 1

Maximum number of bits

Maximum 1 064

Occupies up to 3 slots, or up to 5 slots when able to use FATDMA reservations. For Class B “SO” mobile AIS stations the length of the message should not exceed 3 slots. Class B “CS” mobile AIS stations should not transmit

The table below gives the maximum number of binary data-bits for settings of destination indicator and coding method flags, such that, the message does not exceed the indicated number of slots.

Destination indicator	Binary data flag	Binary data (maximum bits)
Destination indicator	Binary data flag	1-slot	2-slot	3-slot	4-slot	5-slot
0	0	104	328	552	776	1000
0	1	88	312	536	760	984
1	0	72	296	520	744	968
1	1	56	280	504	728	952

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