At&t Bell Laboratories

Mark W Beckner

Thomas L Hiller

James A Davis

Thomas J Starr

Gilbert A Van Dine

Philip D Olson

Eric J Gausmann

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

An integrated packet switching and circuit switching system comprising a number of switching modules each connected to a corresponding plurality of user terminals. Each switching module includes a time-slot interchange unit for providing circuit-switched communication channels and a control unit that controls the operation of the time-slot interchange unit. Each switching module also includes a packet switching unit used both to provide packet-switched communication channels among the user terminals connected to that switching module, and to switch control information between the user terminals and the control unit to establish circuit-switched calls and packet-switched calls. A time-multiplexed switch interconnects the switching modules to provide circuit-switched communication channels and packet-switched communication channels between user terminals of different switching modules.

Distributed packet switching arrangement

An integrated packet switching and circuit switching system comprising a number of switching modules each connected to a different plurality of user terminals. Each switching module includes a time-slot interchange unit for providing circuit-switched communication channels and a control unit that controls the operation of the time-slot interchange unit. Each switching module also includes a packet switching unit used both to provide packet-switched communication channels among the user terminals connected to that switching module, and to switch control information between the user terminals and the control unit to establish circuit-switched calls and packet-switched calls.

Integrated packet switching and circuit switching system

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.

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Warrenville, IL, United States of America

Mark W Beckner