In telecommunication, a data transmission circuit is the transmission media and the intervening equipment used for the data transfer between data terminal equipments (DTEs).
Note 1: A data transmission circuit includes any required signal conversion equipment.
Note 2: A data transmission circuit may transfer information in (a) one direction only, (b) either direction but one way at a time, or (c) both directions simultaneously. See duplex (telecommunications).
References
Data transmission circuit Wikipedia(Text) CC BY-SA