Uplinks are connections from a client station to a master station. The decisive factor here is the direction of transmission. In an uplink, the starting point is the client, which transfers a file to the server, and the end point is the server. An uplink is used to transfer files between these two stations in the direction of the server.
The term uplink is known from satellite communication, where the transmission is from a sending ground station to a satellite. The opposite direction is called downlink( DL). The same applies in mobile communications. Uplink is the radio link from the mobile station to the base station, downlink that from the base station to the mobile station. To prevent intermodulation interference between uplink and downlink, there is a guard frequency band between the two frequency bands.
In satellite communications, the frequency ranges for the uplink and the downlink depend on the service. Thus, the higher frequency bands, the Ku band and the Ka band, are used for satellite communications. The Ku band has its downlink between 10.7 GHz and 12.75 GHz and its uplink between 12.7 GHz and 14.8 GHz, and the Ka band between 27.5 GHz and 40.5 GHz. In contrast, satellite-based mobile communications, for example, operate at 1.6 GHz with their LEO satellites, the Low Earth Orbiters (LEO), and other satellite services use C-band frequencies between 3.4 GHz and 5.9 GHz.