Fujitsu Corporation

Junichi Yoshimura

Satoshi Kuroyanagi

Sadao Ibukuro

Atsuhiko Utsumi

Yoshitaka Eguchi

Katsuji Yamaguchi

Katsuo Suzuki

Upon transmission path monitoring, when a monitoring signal responded by one of optical repeaters provided in a main signal transmission path is superposed on an optical main signal and sent out to the main signal transmission path, the optical main signal is branched to optical fibers, that are optical transmission paths, provided separately from the main signal transmission path and each provided with optical repeaters corresponding to the optical repeaters provided in the main signal transmission path, an optical main signal is selected from a desired optical fiber to be monitored from among the optical transmission paths and the monitoring signal is extracted from the optical main signal selected, thereby checking the quality of the desired optical fiber.

Transmission path monitoring method and device

A protection switch is configured for an input optical signal using an n&times;n optical switch. Furthermore, a signal to be added and dropped is also configured using an n&times;n optical switch. Especially, the n&times;n optical switch uses a complete group switch. Thus, a signal can be output from any input port to any output port. Therefore, a more extensible NPE can be configured at an optical signal level, and a switch is simple and less expensive. As a result, unlike the conventional technology, an NPE itself can be simple and less expensive.

Optical node system and switched connection method

A dispersion compensating apparatus compensates for a dispersion which occurs in a submarine optical fiber transmission system that operates on optical amplification relay principles for the purpose of easily repairing an optical fiber cable and dispersion compensating cables. A plurality of optical amplifiers are placed in the optical fiber cable. The dispersion compensating cables are housed in the casing of each of those of the optical amplifiers which are positioned at dispersion compensating intervals over the optical fiber cable. The dispersion compensating intervals range from about 500 to 1000 km, for example, with a certain tolerance. The optical amplifiers are positioned at intervals of several tens km, for example, and are located within that tolerance. Each of the dispersion compensating fibers has a length in the range of from 20 to 30 km, and is wound around a bobbin.

Apparatus for compensating for dispersion in submarine optical

An optical amplification relay transmission system containing, on a transmission line, an optical repeater for amplifying and relaying an optical signal. The object of the present invention is to perform monitoring of the optical transmission line and optical repeater in a short time and to make the construction of the optical repeater simple. The terminal station contains means for transmitting a burst optical signal on a first optical transmission line, and receiving the burst optical signal transmitted back through a second optical transmission line. Each optical repeater contains a first optical coupler for branching the above burst optical signal transmitted through the first optical transmission line, and a second optical coupler for making the branched burst optical signal, flow through the above second optical transmission line.

Relay transmission system including optical amplification

In a current-spare switching control system provided for a data processing system having a current data processor, a spare data processor, a fault supervisor for supervising the fault of these processors, and switching units for switching from the current data processor to the spare data processor or vice versa, the current-spare switching control system includes: a storage unit for temporarily storing data bits from the fault supervisor; a discrimination unit operatively connected to the storage unit and for comparing the data bits with a reference signal and outputting a coincidence signal when the data bits coincides with the reference signal; an AND gate operatively connected to the discrimination unit for inputting the coincidence signal and a write command from the fault supervisor, and outputting a write signal when the coincidence signal coincides with the write command; a register unit operatively connected to the AND gate for inputting a data bit from the fault supervisor and outputting a switching signal to switch from the current data processor to the spare data processor or vice versa.

Current-spare switching control system

A digital communication terminal equipment is coupled between one or a plurality of low-speed group transmission paths and one or a plurality of high-speed group transmission paths. The digital communication terminal equipment comprises a reference part and a supervised part coupled between selected low-speed group transmission paths and high-speed group transmission paths depending on states of first and second switches, and a bit comparison supervision part for detecting a bit error in a transmission signal which is transmitted between the low-speed group transmission path and the high-speed group transmission path. The reference part has a demultiplexer circuit which demultiplexes a high-speed group signal which is received from the high-speed group transmission path via the second switch into a low-speed group signal, a memory for storing the low-speed group signal from the demultiplexer circuit in response to a write clock signal which is multiplexed within the high-speed group signal, a phase locked loop circuit which includes a voltage controlled oscillator and controls a read out from the memory in response to a read clock signal which is derived by smoothing the write clock signal, and a state detector for detecting an unstable change in an input voltage of the voltage controlled oscillator and for outputting a control signal. The control signal has a level for disabling an operation of the bit comparison supervision part when the state detector detects the unstable change in the input voltage of the voltage controlled oscillator.

Digital communication terminal equipment

A phase synchronization pull-in system used in a bit error detecting apparatus includes a monitored circuit for inputting an input signal and processing the input signal when an operation of the monitored circuit is to be monitored, a standard circuit for processing an output of the monitored circuit inversely to the processing in the monitored circuit, a phase synchronization circuit for inputting the input signal of the monitored circuit and adjusting a first delay time of the input signal so that the first delay time coincides with a second delay time of the output of the standard circuit corresponding to the input signal, a bit error detecting circuit for detecting a difference between the input signal, after being delayed through a variable delay circuit, and the output of the standard circuit, bit by bit, and a controller for controlling the adjusting of the first delay time, a monitoring operation, and a phase synchronization pull-in operation. In the phase synchronization pull-in operation, the first delay time is obtained in the phase synchronization circuit based on whether or not a bit error rate measured by setting the delay time is higher than a predetermined value. The controller determines whether or not more than one possible value of the first delay time enables a successful phase synchronization pull-in, and carries out the monitoring operation when a successful phase synchronization pull-in is successfully carried out for only one value of the first delay time.

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Kawasaki, Japan

Junichi Yoshimura