A method of locating an intermittent electrical fault in an optical undersea transmission system, comprises measuring the time difference between two signals emanating from the fault along two different routes of the system. In one embodiment one of the signals is a voltage transient and the other signal is an optical error signal created in a repeater adjacent the fault as a result of surge protection in the repeater responding to the electrical fault, and in another embodiment both signals are optical signals, once again emanating from adjacent repeaters and caused by the effect of the electrical fault on the adjacent repeaters. It is envisaged that such a transmission system could be permanently provided with apparatus to detect such a fault in which synchronized counters are permanently running and frequently re-set and which stop in response to error signals being received from a fault when it occurs.
The invention relates to a method for pinpointing an interruption in a link for transmitting digital signals between a first station and a second station on the basis of the times of occurrence of signal changes on the link. In accordance with the invention, the method is characterised by generating signal changes after the link has been restored. Preferably, the time of restoration is determined on the basis of data signals received, and a detection signal is fed to the link after the determination of the time of restoration. On the basis of the difference in time of observing restoration and of receiving a detection signal, the location of the interruption is determined. For this purpose, the length of the link need not be known.
A method for pinpointing a short circuit or cable break in a two-wire bus system has the two-wire bus system being subjected at at least one point to a pulse of such a steepness that a reflection occurs at the location of the short circuit and/or cable break. The short circuit or cable break is pinpointed on the basis of the propagation time of the pulse. A circuit includes a pulse generator connected with a gate chain with a shift register, so that the passage of the signal through the gate chain is launched when a pulse is injected into the two-wire bus system. The distance of the short circuit or cable break from the point at which the pulse generator is connected to the two-wire bus system is determined from the number of gates traversed. In addition, a method for pinpointing a cable break, determines that a cable break in the connecting leads of a subscriber has occurred if this subscriber cannot be reached by communication over the bus.
A method for checking lead defects in a two-wire bus system compares the voltage levels on the two wires with certain threshold values, with the comparison being made with the threshold values in the dominant and recessive states. A circuit for performing the method has one input of a first comparator connected with one wire, an input of a second comparator connected with the other wire, and the other inputs of the first and second comparators each being subjected to a voltage that is between the two voltage values on the wires in the dominant and recessive states in normal operation. One input of a third comparator also is connected with one wire, and one input of a fourth comparator is connected with the other wire, with the other inputs of the third and fourth comparators each being subjected to a voltage that is above the maximum voltage value on the wires in the dominant and recessive states during normal operation. The outputs of the first and second comparators are supplied to a subtractor, with a voltage adaptation at the level of the output signal taking place. The output signal of the subtractor is supplied to the input of a fifth comparator, and the output signal of the subtractor also is supplied through a diode to the input of a window comparator. The outputs of the third and fourth comparators also are connected with the input of the window comparator.
A optical submarine cable system having an optical cable comprised of a main optical fiber pair and a sub optical fiber pair; a branching joint box for separating the sub optical fiber pair into a first branching optical fiber pair and a second branching optical fiber pair; a redundant optical cable comprised of extended first and second branching optical fiber pairs; and an end box mounted at the end of the redundant optical cable, so that an expansion of the system and a maintenance and operation of the system are achieved by way of the end box.
A telephone line repeater (28) includes a pattern decoder/recognizer (100) which recognizes, inter alia, an input interrogating signal transmitted on a telephone network (20). The interrogating signal includes an address field (302) having at least one subfield (304) therein. The pattern decoder (100) determines that its repeater (28) is to be tested, if a predetermined subfield (304) of the interrogating signal is configured according to a predetermined select convention. When the repeater (28) recognizes that it is being addressed, a controller (110) causes the addressed repeater to "loop back", returning, in alternating sequence, test-indicative no-operation signals and diagnostic information ("DSM") signals generated by the repeater. Methods for testing a repeater and methods for testing telephone networks are also disclosed.
