Abstract: A communication system (10) includes a channel (18) that conveys both clear and secure communications and a channel (12) that does not convey clear communications. An interface module (24) resides between these two channels. When a call is attempted through the two channels (12, 18), the module (24) plays a plain-text, audio voice message (54) into the clear side of the call. The message (54) instructs a human operator to take appropriate actions to cause an initiate security setup (ISS) signal (56) to be generated by a secure terminal (28). This message (54) is continuously repeated until the ISS signal (56) is detected at the module (24). The ISS signal (56) includes predetermined frequency components which are notched out of the message (54) so that the ISS signal (56) may be reliably detected at the module (24).

Abstract: This invention discloses a demultiplexer with a first memory element for storing received data bits, a second memory element having individual cells connected to individual remote units (i.e. parallel output) and a logic unit for transferring the appropriate bits from the first to the second memory element in accordance with the received signal configuration. The enabling signal for the second memory element is derived from the demultiplex sync signal.