Abstract: Telecommunications (e.g. ISDN) wiring is tested by sequentially supplying to each wire at a first location a pulse sequence identifying that wire while connecting to a common potential other wires, and detecting pulses on the wires at a second location while simultaneously providing a return path connection for the pulses to the other wires. The return path connection is provided by connecting between each wire and a local ground at the second location a resistor and a diode poled to be reverse biassed by pulses on the wire. The detected pulses are counted and the result used to drive a LED (light emitting diode) display comprising N green LEDs indicating correct wiring and N(N-1) red LEDs indicating incorrect connections, the LEDs being arranged in an N by N array with the green LEDs along one diagonal.

Abstract: An order wire system which can be used during installation and maintenance of an optical fiber communication system comprises an optical fiber order wire to which engineers can connect at remote sites communication sets each of which includes a microphone and earphone allowing the engineers to communicate with each other. Full duplex and multi-party operation can be achieved with the sets according to the invention and, because the signals are regenerated, the range of operation is considerable. Both analog and digital communication is contemplated and different specific circuits are proposed. In a typical analog configuration, the microphone output is fed to first and second frequency modulators operating respectively at first f.sub.1 and second f.sub.2 center frequencies. The outputs of the modulators are summed and passed to a laser driver and laser which is optically coupled both to the upstream and the downstream side of the order wire.