In satellite telecommunication, a downlink is the link from a satellite down to one or more ground stations or receivers, and an uplink is the link from a ground station up to a satellite. Basically any signal from the ground to satellite can be known as Uplink. A space link is a communications link between a spacecraft and its associated ground system or between two spacecrafts. A space link protocol is a communications protocol designed to be used over a space link, or in a network that contains one or multiple space links. The basic data flow over a space link is made of Telemetry(TM) and Telecommand (TC) data. <ref>http://www.esa.int/Our_Activities/Space_Engineering_Technology/Onboard_Computer_and_Data_Handling/Telemetry_Telecommand</ref> Telemetry generally translates to downlink and telecommand to uplink. <br \>