C = Communications
1/. CPDLC - controller/pilot data link communications
2/. Airline operational control via datalink
N = Navigation
1/.Integrated GPS(GNSS) + time reference (updates FMC position)
2/. RNP (required navigation performance) for reduced lateral separation
S = Surveillance
1/. ADS -C
2/. RTA (required time of arrival)
ATM = Air Traffic Management
CNS-ATM is also known as FANS 1/A (Future Air Navigation Systems 1(for Boeing equipment and A for Airbus equipment)
FANS 2/B will be with us soon.
ADS-B (Automatic Depedendent Surveillance - Broadcast) will soon be used in USA, Australia and possibly Indonesia. It is different from CNS ATM in that it is to be used in remote areas, using ground relay stations and will reduce the lateral separation between aircraft from 10 mins (approx 70-80 nms) to 5 nms (using fixed Mach technique). It obviously has great potential for the Indian sub-continent, S.E. Asia and Africa.
All the above require sophisticated aircraft equipment, as well as ATC service. The Aussies have a good write-up on ADS-B, sorry haven't got the website, but try Googling.