Parameter

# of Bits

Description

Standard Message Header

Message ID

6

Identifier for Message 26; always 26.

Repeat Indicator

2

Indicates how many times a message has been repeated. 0 – 3; 0 = default; 3 = do not repeat any more. Set to zero (default).

Source MMSI

30

MMSI number of source station. Varies according to the transmitter ID.

Destination Indicator

1

0 = broadcast (no Destination ID field)

1 = Addressed (30 bit Destination ID field). Set to 1 (addressed).

Binary Data Flag

1

0 = unstructured binary data (no Application Identifier bits used)

1 = binary data coded as defined by the 16-bit AI. Set to 1 (structured).

Destination ID

30

MMSI number of destination station.

Spare

2

Not used, Set to zero.

Binary Data

Designated Area Code

10

Designated area code (DAC). This code is based on the maritime identification digits (MID). Set to 366.

Function Identifier

6

Function identifier. Set to 17.

Binary Encrypted Payload

Version

3

Sequential number used to indicate the message version in steps of 1. 0 = test message = default; 1 – 7 = message version. Set to zero.

Message Linkage ID

10

A source-specific random number, unique across recent binary messages equipped with Message Linkage ID. Used to connect the additional information in this Text Message with another ASM. The Message Linkage ID and the source MMSI uniquely identify the sent message. 1 – 1,023; 0 = not available.

ACK Flag

1

Acknowledgement Flag; used to indicate acknowledgement status

0 = no acknowledgement requests = default; 1 = acknowledgement requested.

Text length

8

Length of text message in characters.

0 – 142 characters; 143 = unknown = default; 144 – 255 = reserved.

Text Message

0 – 852

User Text Message, 6-bit ASCII characters as per ITU 1371. 0 – 142 characters = 0 – 852 bits.

Encryption Bit Padding

Variable

Sufficient spare bits to ensure that the binary data is a multiple of 128 bits for block encryption (128, 256, 384, 512, 640, 768, or 896). Set to 0.

Checksum

16

16-bit CRC calculated as per EAIS Specification

Footer

Spare

4

Four extra bits to ensure the message ends on a byte boundary. Set to zero.

Communications State Selector

1

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

Communications State

19

SOTDMA communication state (see ITU 1371-5 § 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.

Total bits

256 –

1024

2 - 5 Slot Binary Message

Parameter

# of Bits

Description

Standard Message Header

Message ID

6

Identifier for Message 26; always 26.

Repeat Indicator

2

Indicates how many times a message has been repeated. 0 – 3; 0 = default; 3 = do not repeat any more. Set to zero (default).

Source MMSI

30

MMSI number of source station. Varies according to the transmitter ID.

Destination Indicator

1

0 = broadcast (no Destination ID field)

1 = Addressed (30 bit Destination ID field). Set to 0 (broadcast).

Binary Data Flag

1

0 = unstructured binary data (no Application Identifier bits used)

1 = binary data coded as defined by the 16-bit AI. Set to 1 (structured).

Destination ID

0

MMSI number of destination station. Not used.