Abstract: Uncompensated, illegal viewing of a restricted channel at a subscriber's terminal in a subscription CATV system is prevented by including a redundancy check-bit in each subscriber's terminal address, and by providing for a verification of the check-bit before viewing of the program on the channel is permitted.

Abstract: A data transmission method in which a signal receiving side produces a response code for requesting a text in response to a start request made by a signal transmitting side, and produces an acknowledgement code or a text invalid code upon receiving the requested text, dependent upon the validity of the transmission. A standby request signal is set to the signal transmitting side in response to the start request if the receiving side is not ready. The receiving side, when ready, send a transmission request signal to the signal transmitting side for requesting transmission of text. When a first transmission request signal is received following receipt of a start request code, a timer is started at the transmitting side and the text is transmitted. The receiving side can send additional transmission requests, in which case the text is retransmitted without restarting the clock.