- ARTCC: Air Route Traffic Control Centers.
- callsign: center.
- e.g. Oakland Center.
- only ~20 ARTCCs in the US.
- TRACON: Terminal Radar Approach Control Facilities.
- callsign: approach, departure.
- e.g. NorCal Approach.
- actc:Airport Control Tower Communications Read more at http://acronymsandslang.com/meaning-of/airports-and-locations/ACTC.html
- callsign: radio.
- not controlling traffic.
- e.g. Oakland Radio, Prescott Radio.
Tower vs ARTCC vs TRACON
Towers handle airport operations, ARTCCs/En-route handle cruise phase, and TRACONs handle climbing and descending aircraft, as well as aircraft transiting between ARTCCs in their controlled areas.
Tower and TRACON
TRACON may be on a separate site or colocate with a tower. For example, California has 5 TRACON, 3 of them colocate with a tower (Santa Barbara, Fresno, Bakersfield) and 2 are independent (Northern California TRACON, near Sacramento; Southern California TRACON, near San Diego).
Clearance Delivery Frequency is initial clearance from ATC before you take off.