The protection resulting from features, often inherent in crypto equipment, concealing the presence of valid messages on a communications circuit. The concealing is typically accomplished by causing the circuit to appear to be busy at all times. Two methods of traffic-flow security are as follows: encryption of the sending and receiving addresses, and causing a circuit to appear to be busy at all times by sending dummy traffic. Another common means of traffic flow security is to transmit a continuous encrypted signal, whether or not traffic is being sent.