How does air traffic control communicate?

How does air traffic control communicate?
Above is a typical example of communication from air traffic control. It begins with the callsign – the name of the flight. This is followed by instructions to reduce the speed to 180 knots, no later than four nautical miles before landing. The pilot should then switch to the frequency of 118.700 to communicate with the tower. The pilot repeats the speed and tower frequency and finally the callsign.
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