Nippon Telegraph and Telephone Corporation

Hitachi, Ltd.

Nippon Telegraph and Telephone Public Corporation

Seiichi Yamano

Kiyomi Kumozaki

Noriki Miki

Hiroshi Takatori

Ryuichi Watanabe

Haruo Ogiwara

Yasuyuki Okumura

Yoshihiro Takigawa

Osamu Matsuhara

Ryoichi Komiya

Shinichi Aoyagi

A point-to-multipoint communication system is presented to enable a reliable, high quality communication using multiplexed optical signals between a central office equipment and a plurality of subscriber's equipment. The system is provided with a plurality of office transceivers in the central office equipment, and the each of the subscribers is provided with at least one subscriber transceiver. The system is designed so that a redundancy system is built-in by providing one of either the office transceivers, a plurality of subscriber's transceivers or the optical connection device, to connect the two sets of transceivers at all times. One of these redundancy systems provides an operating connection between each of the office transmitters which are connected to the office transceivers and each of the subscriber transmitters which are connected to the subscriber transceivers. Therefore, when a malfunction occurs somewhere in the optical network, the least number of the malfunctioning components need to be switched over the the normally functioning system to maintain continued communication services. The present communication system is designed with the least number of active components, therefore, the failure probability is significantly decreased, and repairs if necessary can be preformed quickly. The overall effect of the present system is that interactive point-to-multipoint communication services of high quality and reliability are provided at reasonable cost.

Point-to-multipoint optical transmission system

Network termination equipment including structure for transmitting signals back for loopback test. This can test all the functions of the unit by executing the loopback test only after having verified the normal operation of the circuits related to a call origination.

Digital service unit

A line equalizer for eliminating a precursor interference component and postcursor interference components from a pulse signal inputted from a transmission line. A precursor equalizer takes a sum of a signal derived from the input pulse signal retarded by a fundamental period and a signal derived from the input pulse signal multiplied by a coefficient a. A decision circuit decides the threshold level of an output pulse signal from the precursor equalizer to output a predetermined signal. A controller controls the coefficient a of the precursor equalizer on the basis of the signal from the decision circuit, etc.

Line equalizer

A floating type DC-DC converter for remote power feeding is connected via a power separating filter to a signal line on which an AC signal is superimposed on DC power. The DC power separated by the power separating filter is stored in an input capacitor and is supplied by a switching operation of a switching element to the primary winding of a transformer and AC power induced in its secondary winding is supplied to an output capacitor after being rectified by a rectifying element. An electrostatic shield layer is interposed between the primary and secondary windings of the transformer and is connected to the capacitor connected to one of the primary and secondary windings. Rectifying element or switching element connecting means is provided by which an AC voltage induced in the winding portion on one side of the center winding point of the other of the primary and secondary windings and an AC voltage induced in the winding portion on the other side of the center winding point of said other winding are made substantially symmetrical with respect to the center winding point, opposite in polarity and substantially equal in amplitude to each other.

DC-DC Converter for remote power feeding

Growing community of inventors

Yokosuka, Japan

Seiichi Yamano