Transmission Circuit Technology
Medium is the matter or substance that carries a message from one point to another (e.g., copper wire, a thin strand of glass, air in satellite transmission)
Circuit is the path over which data move (includes satellite or microwave transmission).
Line implies a physical connection between two points (e.g., copper wire) (compare with circuit)
Link is an unbroken circuit path between two points
Channel is a circuit or a subdivision of a circuit.