- Mobile uplink/downlink are channels between the satellite and 'end users': mobile satphones, satcom terminals on ships, aircraft etc.
- Feeder uplink/downlink are channels between the satellite and a ground station. The ground station is connected to terrestrial phone/data networks.
When a satphone user calls someone who uses a 'normal' landline, the call is routed from the satphone to the satellite (through the mobile up/downlink), then from the satellite to a ground station (through the feeder up/downlink), and the ground station connects the call to the landline phone network.
Usually, a satellite has many mobile links, and one feeder link. The satellite bundles the data from all mobile links into the one feeder link.