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