Who's who on the radio
Tower (ATC)
Controls the airfield — issues clearances and instructions (taxi, line-up, take-off, landing). Use “request taxi”.
Approach / Radar
A radar service (Basic, Traffic or Deconfliction). Free-call “inbound” for joining instructions.
“Radio” (Air/Ground, AGCS)
Information only — no instructions or clearances; you stay responsible for your decisions. Use “request taxi information”.
“Information” (FIS, e.g. London Information)
A Flight Information / Basic Service for en-route VFR traffic.
“Ground” (Ground Movement Control)
Controls aircraft and vehicles taxiing on the manoeuvring area — issues taxi instructions and clearances. Found at busier ATC aerodromes; suffix “Ground”.
“Delivery” (Clearance Delivery)
Passes your departure / route clearance before you taxi, to keep the Ground and Tower frequencies clear. Busier aerodromes only; suffix “Delivery”.
Station types — ATC, AFIS & AGCS
ATC — Tower / Approach / Radar
A control service: issues clearances and instructions you must comply with and read back (and provides the agreed service, e.g. separation in controlled airspace).
AFIS — “Information”
Aerodrome Flight Information Service: information and aerodrome instructions, but NOT clearances or separation — decisions and responsibility stay with the pilot.
AGCS — “Radio”
Air/Ground Communication Service: information only (runway in use, known traffic, weather). It cannot issue instructions or clearances — you act at your own discretion.