A communication satellite is, in fact, a microwave transmitter/receiver, known as earth stations, or ground stations. The satellite receives transmission on one frequency band(uplink), amplifies or repeat the signal, and transmit it on another frequency (downlink). A single orbiting satellite will operate on a number of frequency bands, called transponder channels, or simply transponders.
Thus, the satellites are transponders that are set in geostationary orbits directly over the equator. These geostationary orbits are 36000 km from the Earth’s surface. At this point, the gravitational force placed on the satellite that wants to filling it out into space.