Depending upon the role and purpose of the ATC tower, ICAO, ANSPs and regional aviation authorities require recording apparatus to be capable of recording and replaying messages or signals transmitted, received, or conveyed through the equipment at the ATC Unit or Aeronautical Radio Station. Basically, this means recording everything said and heard at an ATC Operators position, and what goes in and out of a radio. Where applicable radar data may also need to be recorded.