The differences between integration of independent systems and coupling of interdependent systems need to be clearly understood. The aviation system is information bound, and the complexity of the system results largely from the complexity of moving all necessary information in real time to all system participants who have a need for it. In a future automated air traffic management system such as the automated en route air system, air traffic control (ATC) computers would negotiate necessary flight plan revisions directly with aircraft computers. The United Kingdom National Air Traffic Service has supported studies to ensure that a variety of technologies can "play together" in a future environment. The knotty issue of how ATC will cope with a broad mix of aircraft capabilities is more difficult in a constrained economic climate. Airline dispatchers and airline operations centers may coordinate aircraft movements with the System Command Center; revised flight plans are worked out with ATC traffic movements units at ATC facilities.