Callsign for MLAT aircraft

[nottledim]

I'm trying to understand how VRS and other programs are able to find and display the callsign (flightID) for aircraft which are not equipped with ADS-B. LoganAir for example runs a number of small aircraft which do not seem to be equipped with ADS-B, (they certainly don't transmit postition etc and I can't see any squitters at all). They do transmit mode-s responses particularly DF11 but that doesn't include callsign. Nevertheless VRS knows their callsign as do other programs like modesdeco2. I can't work out where this data comes from. I'd appreciate some enlightenment on this.

[nitro999]

As I understand it the callsign is a part of the Mode S data transmitted from the aircraft and is input by the pilot into the transponder. But I'm sure others who are more technically minded than me will correct me if I am wrong.

[nottledim]

I finally discovered that the data I wanted is in enhanced mode-s message type BDS2.0.

So, problem solved.