This ASM implements the Project 25 OTAR Hello message.
This is an RTCM compliant implementation of the Project 25 OTAR Hello.
This ASM only has an AIS Message 26 variant.
Hello (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 zero (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 |
DAC |
10 |
Designated Area Code. Set to 366. |
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Function Identifier |
6 |
Function identifier. Set to 23. |
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KMM Preamble |
Reserved |
3 |
Reserved for future use. Set to 0. |
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Version |
5 |
Version of KMM Preamble Message Body. Set to 0. |
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MFID |
8 |
Manufacturer’s ID, indicates conformance to standard. Set to 0. |
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Algorithm ID |
8 |
Identifies the algorithm used to encrypt payload. Set to (hex) 85 = AES-128. |
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Key ID |
16 |
Identifies the TEK used to encrypt the KMM. |
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Message Indicator |
72 |
Provides the message indicator to synchronize the encryption of the OTAR KMM |
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Encrypted Payload |
OTAR Message ID |
8 |
Identifies the Project 25 “Message ID” type. One of 255 possible values assigned as the message type. Set to (decimal) 7 = Hello |
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Message Length |
16 |
A 16 bit binary number that defines the length (in octets) of the subsequent OTAR fields, including MAC. Set to (decimal) 8. |
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Message Format |
RSP |
2 |
Response Kind defines acknowledgment to be returned to the sender of the KMM. 00 =Rsp Kind 1, 01 = Rsp Kind 2, 10 = Rsp Kind 3 and 11 is undefined. |
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MN |
2 |
Message Number defines the size of the Message Number field in the KMM. 00 = no message number, 10 = a 2 octet message number. Set to (binary) 00 |
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MAC Processing |
2 |
Defines the type of MAC processing performed over the entire KMM. Set to (binary) 00 = No MAC |
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Spare |
1 |
Always zero. |
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Done |
1 |
Indicates if subsequent KMM messages are expected. 1=NOT DONE (more to follow), 0=DONE=default. |
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Destination RSI |
24 |
Radio Set Identifier number |
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Source RSI |
24 |
Radio Set Identifier Number |
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Hello Flag |
8 |
(hex) 00 = Identification Only, (hex) 01 = Rekey Request (UKEK exists) (hex) 02 = Rekey request (UKEK does not exist), (hex) 03-FF = Reserved. |
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Encryption Bit Padding |
40 |
Sufficient spare bits to ensure that the binary data is a multiple of 128 bits for block encryption (128). Set to zero. |
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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 |
336 |
2 Slot Binary Message |
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