Position Report for Vessels
Position Report for Vessels (FID 0) and Position Report for Aircraft (FID 3) are the only Message 25 payloads that include a 20-bit encrypted ITDMA Communications State. This allows STEDS units to maintain awareness of the planned activity of other STEDS users, thereby avoiding multiple STEDS transmissions during any one slot. Despite this self-organization among STEDS users, they will continue to yield to non-STEDS Class A traffic, who will “see” STEDS transmissions as strictly well-behaved transmissions on the VDL. The FID 0 and FID 3 position reports shall be transmitted once every 30 seconds when the unit has registered a speed over ground (SOG) of less than 3 knots for more than 3 minutes and once every 15 seconds when SOG is 3 knots or greater.