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Uplink and downlink are frequencies

Communication from earth station to satellite in uplink and communication from satellite to earth station is downlink

Always uplink freq.>downlink freq.

uplink frequency-1710-1785MHz

downlink frequency-1805-1880

In the sense of a mobile communication:

Downlink frequency is that used by a base station to communicate with the Mobile.

In satellite communication also the same theory exists

downlink is the return path.

Uplink --> 890 MHz - 915 MHz

Downlink --> 935 MHz - 960 MHz