Abstract: A device connected to a base of a telephone system by four wires. The device determines the manner in which the wires are used during transmission and reception of electrical signals representing communications. A user places the telephone system in a receive-only mode and provides an indication to the device. The device examines the wires to determine which of the two wires are being used for reception, and the voltage level which is used for receiving the signals. The remaining two wires are deemed to be used for transmission of electrical signals. Communication may be established with an external calibration system to calibrate the transmission and receive voltage levels. The determined information can be used in several environments such as for secure communication for voice and data.

Abstract: A random number generator for generating random numbers. The generator may include two similarly implemented random signal sources, with each source generating a random signal. A difference signal of the two random signals is generated with the result that any common interference signal components are eliminated.