Xerox Corporation

Robert M Metcalfe

David R Boggs

Charles Patrick Thacker

Eric G Rawson

Butler W Lampson

A data communication system includes a communicating medium and a plurality of transceivers connected to the medium, each including a transmitter for transmitting phase-encoded data onto the medium and a receiver for receiving phase-encoded data communicated on the medium by another transceiver. A digital phase decoder is coupled to the receiver of each transceiver for decoding the data received and applying at its output a decode signal representative of the character of the received data. The decode signal is at a predetermined value whenever data communicated on the medium by another transceiver is received by the subject receiver during the time the subject transmitter is transmitting data onto the medium. Circuitry is included for interrupting the transmission of data whenever the decode signal is detected to be at said predetermined value.

Data communication system

An active T-coupler for fiber optic local networks which permits collision detection wherein two input 36, 44 optical fibers are coupled to photodetectors 360, 440, respectively. Two output 34, 46 optical fibers are coupled to receive light from light sources 340, 460. Driving sources 340, 460 are gate circuits 342, 462, which function in a manner similar to an OR gate, via driver circuits 341, 461. These OR gates receive electrical signals from the host station or an input light fiber detector. Further, the input detectors 360, 440 provide electrical signals to the driving OR gates 342, 462 to pass the signal on, i.e. repeat, or drive OR gate 370 to transmit the signal to the host station. Thus the coupler can act as an optical repeater or transmit originally generated light signals in either the forward or reverse directions. Further, the host station can monitor the electrical signals from the input detectors to detect the occurrence of a data collision while transmitting and thereby react appropriately.

Active T-coupler for fiber optic local networks which permits collision

A repeater is provided for use in a communications network which includes a plurality of transceivers, the repeater being bidirectional and allowing the interconnection of two segments of the network and also allowing longer communications networks to be used by matching or amplifying the signal level of an incoming information packet on one segment and coupling the matched or amplified signal to a succeeding segment. The repeater has two ports that preferably utilize two semiconductor chips, each port having a carrier one-shot which detects the presence of an information packet arriving at that port. If an incoming port's one-shot is triggered by an incoming packet of information, the carrier one-shot for the repeating port and the incoming port transmitter are disabled. If the transceiver coupled to the repeating port detects a collision, this information is fed back to the incoming port which enables the incoming port transmitter thereby causing a collision on the incoming network segment which causes the termination of the transmission of the data packet by a using device already transmitting.

Communications network repeater

Apparatus for enabling communications between two or more data processing stations comprising a communication cable arranged in branched segments including taps distributed thereover. Tied to each tap is a transceiver which on the other side connects to an associated interface stage. Each transceiver includes, in addition to the usual transmitter and receiver sections, a gate which compares the data from the interface stage with the data on the cable and indicates whether such are equal. Should such be unequal, an interference between the transceiver and the cable is indicated, disabling the associated transmitter section. Each interface stage tied to such transceiver also includes an input and an output buffer on the other end thereof interfacing with a using device, such input and output buffers storing both the incoming and outgoing data. The output buffer is connected to a clock-driven shift register which converts the buffered data to a serial stream, feeds such data to a phase encoder, which then connects to the transmitter or driver section of the transceiver. The input buffer is loaded by an input shift register which derives its clock from a phase decoder, the shift register and the phase decoder both connecting to the receiver section. When the station is to start transmitting, the phase decoder detects the presence of other transmissions on the cable and detains the output shift register until no other transmissions are sensed. Once a transmission has begun, if interference is detected and the transmitter section is disabled, a random number generator is used to select an interval of time at the completion of which the next attempted transmission will take place. Concurrently, a counter counts the number of interferences, or collisions, which recur in the attempted transmissions of one data packet and weights the mean of the random number generator accordingly. The input shift register is also connected to an address decoder which enables data transfer to the input buffer only during those times when the data is preceded by an appropriate address.

Growing community of inventors

Palo Alto, CA, United States of America

Robert M Metcalfe