What a GDS is, who the players are, and how an agency conversation reaches an airline.
A Global Distribution System is a neutral marketplace that connects travel agencies to airline inventory, fares and ticketing. The agency terminal sends short coded entries (cryptic commands) to the host, the host answers with formatted screens. Amadeus, Sabre and Travelport+ are the three global systems in daily agency use.
Every entry starts with an action code, then qualifiers. AN20SEPCAILHR = action AN (availability neutral) + date 20SEP + origin CAI + destination LHR. Learning the action codes is 80% of the work; the qualifiers repeat across commands.
AN20SEPCAILHRNeutral availability CAI→LHR on 20 September120SEPCAILHRAvailability display CAI→LHRA20SEPCAILHRAvailability display CAI→LHREverything you do in GDS LAB is simulated. No airline is contacted, no seat is held, no ticket is issued. The value is muscle memory: the same entries, the same error messages, the same workflow discipline.