Bell Telephone Laboratories

At&t Bell Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Cyrus F Ault

Kristin F Kocan

Clinton D Gibler

A high-speed fiber optic star configuration network uses a processor at the network hub to monitor and control network activity. The hub and the individual nodes of the network cooperate to calibrate node transmitter power levels and node receiver sensitivities. A token passing protocol is used to allocate network access. The token passing is monitored at the hub to detect lost tokens or a babbling bus. The hub processor has the capability to initiate tokens or restore lost tokens and to shut off the transmitter of a node which remains connected to the bus for an excessive period of time. In one embodiment, the circuit elements of the hub are duplicated to provide two separate paths through the hub.

Communication network

A processing system (10) includes a backplane bus (13) that defines a plurality of locations (20-31) implemented as backplane slots each for connecting any option module (41) thereto. Each slot includes contact pins (201a-d) that carry binary logic levels forming a different digital number at each slot. Option modules include their own source of timing signals (220) comprising an oscillator (221) and an identical thermally-sensitive crystal (222) for driving the oscillator. Each option module includes receptacles (207a-d) for the contact pins. The receptacles are connected to the digital input port of a D/A converter (225) whose output port is connected to a heater (224) mounted in physical proximity to the crystal in the crystal's case (223). Depending on which slot an option module is mounted in, the D/A converter receives a different digital input and hence generates a different level of output. The heater generates heat in proportion to the converter's output and hence raises the temperature of the crystal to a different level at each slot, causing the crystal to generate somewhat different fundamental frequency at each slot. Hence option modules connected to different slots generate different fundamental frequencies and therefore emit different harmonic frequencies. Hence the amplitudes of the harmonics emitted by different option modules are non-additive, and radiated emission levels of the processing system equipped with all option modules are no higher than those of the system equipped with only one option module.

Processing system having distributed radiated emissions

A multipoint access data communication system which includes a communication bus, a plurality of transceivers connected to the bus for communication, and a remote collision detector associated with each transceiver for detecting collisions between communications on the medium, has improvements which adapt the transceivers for connection to a plurality of network interface units, and local access arbitrators associated with the transceivers for preventing collisions between transmissions simultaneously attempted by two or more network interface units connected to a transceiver.

Multipoint data communication system with local arbitration

A detection circuit for detecting a mismatch between the output signals of duplicated logic units (10a, 10b). The output terminals of one of the duplicated logic units are correspondingly connected to the output terminals of the other duplicated logic unit, while the power supply leads of the duplicated logic units (10a, 10b) are connected to a positive voltage source (32) through a current imbalance detector. Any mismatch between the output signals of the duplicated logic units (10a, 10b) will result in the detection of a large imbalance of current being supplied to the duplicated logic units (10a, 10b). Upon detection, the detector will generate an error signal.

Mismatch detection circuit for duplicated logic units

A bias field control arrangement for correcting the bias field in accordance with stability range variations in magnetic domain thin film layers. A thin film layer is provided auxiliary to the layers, which auxiliary layer responds to external environmental conditions such as temperature in a manner substantially identical to that of the magnetic domain layers. A pair of register-detectors are defined on the layer in the form of permalloy domain propagating elements, the dimensions of the elements of one being optimized to propagate domains of a diameter larger than that of a domain of a diameter which is optimum in view of the stability range of the layers and the dimensions of the elements of the other being optimized to propagate domains of a diameter smaller than that of the optimum diameter domain. For normal operation, the domains will be propagated along both channels with equal facility and an output comparison section at the output of the detectors produces no control signal. The common bias field of the layers is thus normal and requires no correction. Should the bias field be too low or too high, domains of a diameter will be generated which will fail to propagate properly along one or the other channels. As a result, an output signal is generated which is employed to provide an augmenting or an opposing field to adjust the bias field upward or downward as required. Any errors in the propagation of domains are thus corrected.

Magnetic single-wall domain bias field control arrangement

An adaptable exerciser for a memory system utilizes the error rates of independent memory segments to selectively exercise the segments at different frequencies. Each memory segment has an associated counter which is incremented with errors and decremented at a predetermined rate with time. If the count accumulated in a counter reaches a specified level, the associated memory segment will be exercised at a higher frequency. If the count in any counter should reach a second higher specified level, the associated memory segment is removed from service.

Growing community of inventors

Wheaton, IL, United States of America

Cyrus F Ault