Text Message (encrypted)
This Message is used to send encrypted text messages.
Usage Notes
- The Message 26 Text Message format provides for both a broadcast and addressed text message. Message addressing, when required, shall be performed using the Destination Indicator and Destination ID fields inherent to the Message 26 structure.
- The text may be up to 142 6-bit ASCII characters (up to 852 bits).
- The addressed version of this message shall have the “ACK Flag” value set by the user. If an ACK is desired, see the Usage Notes of FID 9 for retry procedures.
Encrypted Text Message (Message 26, Addressed)
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Parameter |
# of Bits |
Description |
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Standard Message Header |
Message ID |
6 |
Identifier for Message 26; always 26. |
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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). |
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Source MMSI |
30 |
MMSI number of source station. Varies according to the transmitter ID. |
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Destination Indicator |
1 |
0 = broadcast (no Destination ID field) 1 = Addressed (30 bit Destination ID field). Set to 1 (addressed). |
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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). |
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Destination ID |
30 |
MMSI number of destination station. |
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Spare |
2 |
Not used, Set to zero. |
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Binary Data |
Designated Area Code |
10 |
Designated area code (DAC). This code is based on the maritime identification digits (MID). Set to 366. |
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Function Identifier |
6 |
Function identifier. Set to 17. |
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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. |
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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. |
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ACK Flag |
1 |
Acknowledgement Flag; used to indicate acknowledgement status 0 = no acknowledgement requests = default; 1 = acknowledgement requested. |
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Text length |
8 |
Length of text message in characters. 0 – 142 characters; 143 = unknown = default; 144 – 255 = reserved. |
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Text Message |
0 – 852 |
User Text Message, 6-bit ASCII characters as per ITU 1371. 0 – 142 characters = 0 – 852 bits. |
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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. |
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Checksum |
16 |
16-bit CRC calculated as per EAIS Specification |
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Footer |
Spare |
4 |
Four extra bits to ensure the message ends on a byte boundary. Set to zero. |
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Communications State Selector |
1 |
0 = SOTDMA communication state follows 1 = ITDMA communication state follows |
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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. |
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Total bits |
256 – 1024 |
2 - 5 Slot Binary Message |
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- Message 26 Broadcast Format
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Encrypted Text Message (Message 26, Broadcast)
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Parameter |
# of Bits |
Description |
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Standard Message Header |
Message ID |
6 |
Identifier for Message 26; always 26. |
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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). |
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Source MMSI |
30 |
MMSI number of source station. Varies according to the transmitter ID. |
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Destination Indicator |
1 |
0 = broadcast (no Destination ID field) 1 = Addressed (30 bit Destination ID field). Set to 0 (broadcast). |
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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). |
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Destination ID |
0 |
MMSI number of destination station. Not used. |
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Spare |
0 |
Not used. |
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Binary Data |
Designated Area Code |
10 |
Designated area code (DAC). This code is based on the maritime identification digits (MID). Set to 366. |
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Function Identifier |
6 |
Function identifier. Set to 17. |
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Application Data (encrypted) |
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. |
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Message Linkage ID |
10 |
A source-specific random number, unique across recent binary messages 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 – 1023; 0 = not available. |
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ACK Flag |
1 |
Acknowledgement Flag; used to indicate acknowledgement status 0 = no acknowledgement requests = default; 1 = acknowledgement requested. |
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Text length |
8 |
Length of text message in characters. 0 – 142 characters; 143 = unknown = default; 144 – 255 = reserved. |
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Text Message |
0 – 852 |
User Text Message, 6-bit ASCII characters as per ITU 1371. 0 – 142 characters = 0 – 852 bits. |
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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. |
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Checksum |
16 |
16-bit CRC calculated as per EAIS Specification |
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Footer |
Spare |
4 |
Four extra bits to ensure the message ends on a byte boundary. Set to zero. |
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Communications State Selector |
1 |
0 = SOTDMA communication state follows 1 = ITDMA communication state follows |
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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. |
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Total bits |
224 - 992 |
2 - 5 Slot Binary Message |
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