Hitachi, Ltd.

Masahiko Kida

Toyokazu Hashimoto

Susumu Nakayashiki

Hiroyuki Wada

Hisashi Matsumura

Kazuo Yagyu

Isao Nakada

This invention relates to a loop transmission system which has a plurality of stations connected to a loop transmission path to transmit data among the stations. In the transmission frame to be sent out from the sending station, specific information is included for identifying each frame and this information is held in the sending station. When the transmission frame returns to the sending station after being transmitted through the loop transmission path, the specific information in the frame is received and compared with the information held in the station and, if they coincide, it is decided that the transmission frame has been correctly received by the intended receiving station.

Data transmission system adapted to facilitate detection of safe receipt

A method of switching transmission lines for a transmission control system in which a plurality of stations are linked with loop type transmission lines having a stand-by transmission line characterized in that each of the stations is operable to switch the active transmission line to the stand-by transmission line in response to the detection of abnormality in the carrier wave and a station transmitting the carrier wave is operable to halt the transmission of the carrier wave on the active transmission line so that the overall transmission line is switched to the stand-by transmission line, thereby minimizing the system down time.

Method and apparatus for switching loop type transmission lines

In a loop transmission system utilizing specific patterns, a specified station for sending the specific patterns sends a specific pattern S or a specific frame S' which is not delayed in each station in advance of sending a specific pattern G used for data exchanging in each station, thereby ensuring rapid detection of abnormality of the specific pattern G.

Method and system of loop transmission

A loop transmission system including a plurality of stations connected in series in a looped transmission line to transfer data among the stations, wherein the stations include a supervising station and at least one terminal station and the transmission line is duplicated so that when a fault occurs in currently used one of the transmission lines, the other transmission line which has been used as a spare is used for transmission of data, while the supervising station sends out a specific signal to the spare transmission line and the terminal stations each determines one of the transmission lines through which the specific signal is detected, as the spare.

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Hadano, Japan

Masahiko Kida