Where a DF17/18 extended squitter's address and data actually came from.
DF17 is always icaoDirect - it carries no control field, and a DF17
transponder is, by protocol definition, always ICAO-addressed and
broadcasting its own state directly. For DF18, this is derived from the
control field (CF):
icaoDirect (CF=0): ICAO-addressed, direct from the aircraft - same as DF17.
anonymousDirect (CF=1): a self-assigned or anonymous address (e.g. a
ground vehicle's ADS-B-out unit with no Mode-S allocation), direct from
the transmitting participant - icaoHex is not a registered ICAO address.
icaoTisb (CF=2): ICAO-addressed, but ground-station-derived (TIS-B,
fine format) rather than heard directly from the aircraft's own transponder.
anonymousTisb (CF=5): a ground-assigned track-file address (TIS-B, fine
format, non-ICAO) - icaoHex is not a registered ICAO address.
adsr (CF=6): ICAO-addressed, relayed from another data link (e.g. UAT)
by a ground station (ADS-B Rebroadcast).
Where a DF17/18 extended squitter's address and data actually came from. DF17 is always
icaoDirect- it carries no control field, and a DF17 transponder is, by protocol definition, always ICAO-addressed and broadcasting its own state directly. For DF18, this is derived from the control field (CF):icaoDirect(CF=0): ICAO-addressed, direct from the aircraft - same as DF17.anonymousDirect(CF=1): a self-assigned or anonymous address (e.g. a ground vehicle's ADS-B-out unit with no Mode-S allocation), direct from the transmitting participant -icaoHexis not a registered ICAO address.icaoTisb(CF=2): ICAO-addressed, but ground-station-derived (TIS-B, fine format) rather than heard directly from the aircraft's own transponder.anonymousTisb(CF=5): a ground-assigned track-file address (TIS-B, fine format, non-ICAO) -icaoHexis not a registered ICAO address.adsr(CF=6): ICAO-addressed, relayed from another data link (e.g. UAT) by a ground station (ADS-B Rebroadcast).