The term “downlink” is commonly used in the fields of radiocommunications and satellite communications to refer to the communication link that carries data from the network or satellite down to the end user or the Earth’s surface. This is the direction of data transmission that goes from the source (e.g., a network or satellite) to the recipient (e.g., a user’s device).

Conversely, the opposite direction of data transmission, going from the end user or the Earth’s surface to the network or satellite, is referred to as the “uplink.” The uplink is responsible for transmitting data from the user’s device or ground station to the network or satellite.

In the context of fixed-line networks, such as wired broadband or cable internet connections, the terms “downstream” and “upstream” are more commonly used. “Downstream” typically refers to the data flow from the network to the end user’s device, while “upstream” refers to the data flow from the end user’s device back to the network. These terms are essentially equivalent to “downlink” and “uplink” but are specifically used for describing data transfer in wired communication systems.