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AIS position report retransmit

Introduction/Additional information: 

This VDE Protocol Format may be used by VDE Satellites that optionally retransmit AIS position reports as received (AIS Msg. 1, 2, 3), to give better situational awareness for navigation beyond the AIS reception range of ships, e.g., in remote areas.

The satellite should only repeat AIS position reports that contain a repeat indicator value of 0.

The signature authenticates the identity for who received the AIS data and for proper retransmission, not for the authenticity of the single AIS data, however.

Permitted as from: 
01/12/2022
Registrant: 
IALA
Physical link: 
VDE-SAT
Message number (0=VDES-VDE): 
0
DAC or VPFI: 
2
FI / Message ID: 
5
Technical point of contact: 

IALA

G1117-Ed3.0-VHF-Data-Exchange-System-VDES-Overview

State: 
proposal
Number of slots (max): 
1
FEC: 
No
Last modified: 
29/03/2023 - 15:11
Details: 

Parameter

Number of bits

Description

VPFI

16

2

Message ID

16

5

n

8

number of encapsulated AIS position reports

0: unused value

1-255: valid values

Parameter

Number of bits

Description

Time [0]

40

UTC year, month, day and hours, minutes, seconds for the first AIS Message reception, as defined in ITU-R M.1371-5, Message ID 11, starting with year, ending with seconds.

AIS Msg [0]

168

AIS Message [0]: first retransmitted message

Time [1]

40

UTC year, month, day and hours, minutes, seconds for the second AIS Message reception, as defined in ITU-R M.1371-5, Message ID 11, starting with year, ending with seconds.

AIS Msg [1]

168

AIS Message [1]: second retransmitted message

…

…

…

Time [n-1]

40

UTC year, month, day and hours, minutes, seconds for the n-1th AIS Message reception, as defined in ITU-R M.1371-5, Message ID 11, starting with year, ending with seconds.

AIS Msg [n-1]

168

AIS Message [n-1]: n-th retransmitted message

Valid until

32

Unsigned integer number of seconds after the 1st of January

1970 00:00:00 UTC. After the 19th of January 2038 03:14:07

UTC, the number is the number of seconds after this new date (wraps around);

To avoid replay attacks, this value shall be used by the receiving application to verify the validity of the data.

Signature

512

Signature over above data, applied over all bits from the start of the VPI field to the end of the last bit, just before the signature, generated as described for the terrestrial bulletin board, see ITU-R M.2092-1, Annex 4, §4.15

Total number of bits

Variable