In data transmission, it is a secondary channel in which the direction of transmission is constrained to be opposite to that of the primary, i.e., the forward (user-information) channel. The direction of transmission in the backward channel is restricted by the control interchange circuit that controls the direction of transmission in the primary channel.
in data transmission it is a secondary channel in which the direction of transmission is constrained to be opposite to that of the primary ie the forward (user-information) channel the direction of transmission in the backward channel is restricted by the control interchange circuit that controls the direction of transmission in the primary channel