Hitachi, Ltd.

501 Hitachi, Ltd.

Takuji Hamada

Masahiro Takahashi

Hitoshi Fushimi

Seiichi Yasumoto

Sadao Mizokawa

Masakazu Okada

Yoshinori Ohkura

Hiroshi Tomizawa

Katsuhiko Yoneda

Shunji Inada

Hideaki Masuko

Norihiko Sugimoto

Yoshiaki Adachi

Hisao Ogawa

Ken Onuki

Tomoyuki Harada

Shinichi Hanada

Kinshirou Oonishi

Jushi Ide

Kotaro Hirasawa

Shinichiro Yamaguchi

Toshihiko Uchiyama

Shinichi Ueda

Occurrence of significant difference of transmission rate between communication zones can be prevented to maintain the transmission rate of overall network uniform. The radio network system includes a plurality of radio communication control units are connected with each other via radio main line, and each radio communication control unit has a communication function with at least one radio communication terminal arranged within own communication area. Each of the radio communication control units includes means for broadcasting a transmission rate restriction demand to all of other radio communication control units and all of radio communication terminals when data amount stored in a transmission and reception buffer exceeds a predetermined threshold value, and means for lowering a transmission rate when a transmission rate restriction demand is received from any other radio communication control unit within a predetermined period and for increasing the transmission rate when no transmission rate restriction demand is received from any other radio communication control unit.

Radio network system

Radio relay system

A system for transmitting data in high precision by restricting a delay in data transmission time includes a hub. The hub receives through the transmission media a data frame transmitted from a communication device that has a transmission request among a plurality of communication devices, and relays the received data frame to a destination communication device based on a destination address included in the received data frame.

Data transmission method and system for hub-based network

A system for transmitting data in high precision by restricting a delay in data transmission time, and including a hub. The hub receives through transmission media a data frame transmitted from a communication device that has a transmission request among a plurality of communication devices, and relays the received data frame to a destination communication device based on a destination address included in the received data frame.

A data communication system carries out transmission and reception of periodic data between a plurality of computers, and especially an improved data communication system which aims at more effective utilization of a system bus in each computer and which also aims at more effective utilization of a data transmission channel transmitting periodic data, so that the load imposed on the system bus during transfer of periodic data in each computer can be minimized, and the rate of occupation of the data transmission channel during transmission and reception of periodic data can also be minimized.

Cyclic data communication system

A network system includes a transmission line including a plurality of transmission channels, a plurality of transmission equipment connected to the transmission line to effect the transmission and reception of information between each other, and a plurality of devices connected to each of the transmission equipment, thereby effecting the transmission of information between the devices connected to the plurality of transmission equipment. Each of the transmission equipment includes a demultiplexing unit for separating an input signal from the transmission line into a plurality of receiving transmission channels, a channel switch unit for receiving the plurality of receiving transmission channels, outputting designated one of the transmission channels to one of the devices connected to the transmission equipment in question, and receiving transmitting information to form an information transmitting channel and combining it with other channels to be passed to form a plurality of sending transmission channels, and a multiplexing unit for receiving the plurality of sending transmission channels from the channel switch unit to multiplex and output the plurality of sending transmission channels.

Network system

In an annular transmitting system including a ring-like transmission path realized by interconnecting serially a plurality of transmission stations in an annular form, at least one of the transmissions stations generating repetitively a transmitting frame constituted by a plurality of transmission units referred to as time slots, the frame being circulated along the transmission path, wherein transmission of information among transmission stations is performed in such a manner in which each of the transmission stations having a request to send information inserts the information in the slots by dividing the information, which information is ultimately fetched by the transmission station destined to receive that information, a multi-slot access system in which each of the time slots is provided with an area indicating whether the associated time slot is 'free' or 'busy', wherein the transmission station having a request to send information determines that the sending of the information is enabled when it is detected that one time slot located at a particular position within the transmitting frame is 'free' or when it is detected that the time slot succeeding immediately to the 'busy' slot is 'free', to thereby set successively those usable time slots which succeed to the detected 'free' time slot to the 'busy' state and insert the information in these usable time slots.

Multi-slot access system

A ring network data transmission system includes a plurality of transmission apparatuses, at least one terminal connected to each of the transmission apparatuses and double ring transmission paths interconnecting the transmission apparatuses in a ring-like system configuration so that terminals can communicate with one another through the associated transmission apparatuses. When a transmission fault occurs in the network, the transmission apparatus which can serve as the master station issues to all of the other transmission apparatuses a command for searching the fault location. In response to the reception of the command, each of the other transmission apparatuses sends out a monitor signal containing its own address and at the same time checks monitor signal received. Through collation of the address contained in the received monitor signal with the address information arrayed in the order in which the transmission apparatuses are interconnected, the number of bypassed transmission apparatuses existing between each transmission apparatus and the transmission apparatus sending out the monitor signal is determined. By comparing this number with a predetermined maximum permissible number of the stages allowable to be bypassed, the faulty location is detected. With such an operation, automatic reconfiguration operation of double ring configuration can be stabilized.

Method and apparatus for detecting a fault in a ring network data

A loop transmission system having a plurality of data processor connected through respective transmission station with a common loop transmission line is disclosed. This system has a concentrator connected with a plurality of transmission stations through respective loop transmission lines. The concentrator changes the order of connection said loop transmission lines thereby to change the order of connected of said transmission stations on said loop transmission lines.

Loop transmission system having plural stations connected in a variable

A looped data transmission system has a pair of looped transmission lines forming two transmission systems having different transmission directions, and a plurality of stations including at least one control station connected to said transmission lines of the two transmission systems. If a fault occurs in the two transmission lines of the two transmission systems in the same section, a loopback configuration is established such that stations adjacent to the faulty section send signals from one system back to the other system. With the loopback configuration being established, the stations which have received supervisory signals sent from a loopback end station send them back to the transmission line of the other system. When one of the loopback end stations has received a supervisory signal from the direction of the faulty section, it is judged that a portion of the faulty section is recovered, and the result of the judgement is communicated to the control station.

Method of detecting recovery from fault in a data transmission system

A loop type data transmission system based on a token pass principle, wherein a station whose transmission of data is completed passes therethrough a token to the stations located downstream. The station demanding the transmission acquires the right of transmission when received the token, to perform data transmission with a given station. The token signal is classified into a free token representative of the freedom of the line and a busy token representative of occupation of the line. Among a plurality of stations, only one station is destined to execute detection of transmission failure and remedy thereof. This one station is adapted to convert the free token detected upon reconstitution and repeating of the received information into the busy signal and subsequently re-send the free token. The station having sent out the free token after the completed data transmission is transferred to the state for reconstituting and repeating the received information when the busy token returns to that station.

Loop type data transmission system

This invention discloses a loop-back control method for loop-type data transmission systems in which, when a trouble occurs on both transmission lines of two systems, two stations adjacent to the trouble region return signals toward a control station in response to a command from the control station, thereby to separate the trouble region and continue the operation. According to this invention, when the control station detects the occurrence of a trouble on the transmission lines of the two systems, it sends out a broadcast command to search for the trouble point to the transmission lines of both systems and thereafter a loop-back command is issued so that the stations adjacent to the trouble point can loop-back the transmission.

Reconfiguration control method for a loop-type data network

A loop type data highway system in which a plurality of data transmission control stations (abbreviated herein as stations) are connected in cascade to a loop transmission line. Each of the stations responds to a polling frame inquiring of request for reservation of the transmission line. The polling frame is composed of a first field for inquiring of the line reservation request and a second field indicative of whether the line is reserved or not. Each station receives signals inputted from the upstream side along the line and sequentially repeats them to the downstream side along the line without delay. In the station having the line reservation requests, a pattern representative of the line reservation is written in the second field after reception of the first field and sends out the polling frame to the downstream. When the second field as received indicates the non-reserved state of the transmission line, transmission of data is initiated in succession to the second field.

Loop type data highway system

A duplex transmission control system having active and inactive systems for totally controlling a looped transmission line on which computers and terminal devices are connected through respective stations. Each transmission control unit is operable to transmit and receive specific data related to the priority level specified for each unit. Each transmission control unit suspends the transmission of the clock for a certain period in response to the detection of the clock suspension, then transmits the specific priority data. When a transmission control unit detects its own transmitted signal, it is designated as the active system when another transmission control unit receives the signal defining the active system, it is designated as the inactive system.

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Hitachiota, Japan

Takuji Hamada