At&t Bell Laboratories

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

Thomas J Starr

Mark W Beckner

Meyer J Zola

David A Pierce

James M Johnson, Jr

Christopher G McHarg

Ralph A Wilson, Iii

Paul D Hunter

Benjamin C Widrevitz

A switching system including a number of switching modules each having a plurality of access ports. Incoming and outgoing packet channels are extended between each switching module and an inter-module packet switch. Each switching module includes a packet switching unit that transmits user information packets, received from the access ports, via the incoming packet channel to the inter-module packet switch, and switches user information packets, received via the outgoing packet channel from the inter-module packet switch, to the access ports for inter-module packet-switched communication. The intermodule packet switch concurrently packet switches user information packets, received on a number of the incoming packet channels, via multiple independent paths to a number of the outgoing packet channels.

Distributed packet switching sytem

A method and apparatus for bus contention resolution for use in a digital communications system wherein a plurality of communications controllers are connected to a shared bus for transmitting information in frames. A priority field is included in each transmitted frame. The bus is monitored such that any time the bus is conveying a frame, the priority field of that frame is known at each of the communications controllers. A given communications controller makes a determination based on the priority fields of a new frame and a present frame being actively conveyed by the shared bus that the new frame is of higher priority than the present frame. Upon such a determination, the given communications controller transmits the new frame. In accordance with a second aspect of the method and apparatus, the bus has the characteristic that when any communications controller connected thereto transmits a predetermined logic value, the bus conveys that predetermined logic value regardless of logic values transmitted by other communications controllers. Each communications controller monitors the bus and counts the number of consecutive bits conveyed thereon having the predetermined logic value. Any communications controller that desires access to the bus consecutively transmits the predetermined logic value a number of times such that the predetermined logic value is conveyed a fixed number of times on the bus. The communications controller then transmits a unique bit sequence but terminates transmission when a difference is detected between a bit transmitted by that communications controller and a bit contemporaneously conveyed by the shared bus.

Method and apparatus for bus contention resolution

A method and apparatus for graceful preemption on a digital communications link used for selective communication from a plurality of user devices. Link controllers are used to implement the enforcement of a protocol on the link. When a first user device is actively communicating over the link, a second user device can gracefully preempt the first user device by having a link controller transmit a preempt character. The link controllers at either end of the link each save values of a set of status variables collectively defining the status of the link controller. When the second user device relinquishes link access, the saved values are used to return the link controllers to their status at the time of preemption such that the first user device can resume communication from the point of interruption without requiring data retransmission.

Method and apparatus for graceful preemption on a digital communications

A bus fault location arrangement for locating the source of a fault condition on a bus connecting a plurality of devices energized by a power supply. When such a fault condition is detected, a bus diagnostic unit included in the arrangement transmits a signal to place a given one of the plurality of devices in a high impedance state. The bus diagnostic unit then transmits a given signal level on the bus. To determine whether the given device is the source of the fault condition, current flow between the device and the power supply is sensed and an error signal is stored when the sensed current exceeds a predetermined magnitude.

Method and apparatus for bus fault location

An arrangement for indicating when different types of electrical components, such as circuit boards and the like, are concurrently joined with connector assemblies. Common to the connector assemblies is a plurality of output conductors which is connected to corresponding plurality of output terminals positioned on each of the connector assemblies, respectively. On each component is a plurality of identification conductors arranged to identify the component through the application of a distinct pattern of potentials on the output conductors when one of the components is joined with one of the connector assemblies. When different types of components are concurrently joined with associated connectors, the identification conductors interconnect all the output conductors, such that only a predetermined pattern of potentials other than the distinct patterns may be applied to the output conductors.

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Wheaton, IL, United States of America

Thomas J Starr