It all depends on where you are.
In Saudi Arabia, Jeddah FIR had transmitters and receivers located in the tower base for local work. There were also transmitter/receiver facilities as far north as Tabuk, Riyadh to the east and Abha in the south. As these were huge differences, tropo scatter was used for the long haul, with microwave links feeding the tropo sites.
As this was in the 70s & 80s, the microwave/mux systems were analog, no opportunity to use digital signalling, so equipment status and control was achieved by sending tones up and down the links. Radar data from the distant sites at the edges of the FIR used the same links with massive Racal modems beavering away at 9600 baud! (The really clever bit was the way it was all assembled in Jeddah so a complete radar picture of the whole Kingdom as available for the scope dopes.)