Digital Equipment Corporation

3com Corporation

Cabletron Systems, Inc.

Quantum Bridge Communications, Inc.

William C Mallard, Jr

Henry S Yang

Jerry D Hutchison

Robert A Curtis

Colby Dill, Iii

Simon A Ginzburg

Michael B Duclos

David X Walls

Jeffrey A Gross

An apparatus and method is disclosed for protecting access to a shared medium in an optical communications system which has plural remote terminals coupled to a central terminal over the shared medium. According to one aspect, if an optical transmitter for an individual remote terminal is active for a first prescribed time interval when it has not been enabled for such transmission, the optical transmitter is disabled. According to another aspect, the continuous time that an individual terminal is enabled to transmit onto the shared medium is monitored. If the enabled transmission for the individual terminal exceeds a second prescribed time interval, the optical transmitter for the individual terminal is disabled.

Method and apparatus for optical media access protection in a passive optical network

An improvement to conventional ATM network paradigms involves the distribution of ATM switching functions across a large number of ATM switching units, each of which may typically provide a limited number of available ports, and by establishing multiple connections between the larger number of ATM switching units in a partially redundant 'chained' configuration analogous to various ring type topologies. A plurality of 'XNODES' each comprising a packet segmentation/reassembly circuit and an ATM switching circuit may be interconnected in various ways to form redundant ATM paths without the need to replicate large and expensive ATM switches.

Redundant ATM interconnect mechanism

A switchable interface for conveniently coupling a network station of the CSMA/CD type to a network having any of a variety of communication media. The invention provides a single interface connector through which connection may be made directly to a twisted-pair medium, using the 10BASE-T protocol, or to a medium of a different type, through an AUI protocol and an appropriate media attachment unit. The interface connector has pin assignments chosen to minimize adverse effects of misconfiguring the station by connecting to a network having a protocol that is different from the one selected in the switchable interface. In one form of the invention, the switchable interface has the ability to determine the protocol being used by the network to which it is connected, and to switch the interface accordingly. Use of the common interface reduces station equipment cost and provides for increased user convenience, since only a single connector is needed to connect to a variety of media types.

Common interface for a network having different communication media

A technique for synchronizing run-length-limited data transmitted over two parallel narrowband communication channels, such as in a token ring local area network using fiber distributed data interface (FDDI) protocols. A serial data stream to be transmitted is demultiplexed onto the two channels by sending sequential blocks of equal numbers of bits over alternate channels. In a receiver-multiplexer, block boundary synchronization is established during connection initialization by using a property of a required HALT code to detect block boundaries received in each channel. Skew compensation is effected by comparing the times of detection of the block boundaries in the two channels, and appropriately controlling a variable delay in at least one of the channels. The technique establishes reliable block boundary synchronization and skew error compensation during connection initialization, and if there is subsequent loss of synchronization, detected transmission errors will eventually result in connection reinitialization and reestablishment of synchronization.

Method and apparatus for transmission of communication signals over two

Data recovery apparatus for receiving two channels of data signal portions skewed in time and recovering from them two data signal portions synchronized with a con, non clock signal. The apparatus includes a phase comparator circuit and a latch circuit associated with each channel of data signals, a single voltage controlled oscillator that generates a clock signal VCO-CLK in response to a VCO control signal and a single charge pumping circuit for generating the VCO control signal. Each phase comparator circuit receives its associated channel of data signal portions and the VCO-CLK signal and generates pump-up/pump-down signals applied to the charge pumping circuit. Each latch circuit is triggered by a selected edge of the VCO-CLK signal, so that the latch circuits respectively provide recovered data signal portions synchronized with the VCO-CLK signal, which may then be recombined in the same sequence as they were originally divided from a common high data-rate signal.

Data recovery apparatus and methods

A circuit for incorporation into LAN-compatible devices uses both the link integrity test (LIT) pulses and the end of frame delimiter (EOF) waveform information in received data transmissions to detect polarity errors on the twisted-pair media to which the devices are connected. The circuit integrates this information and a new auto-polarity detection/correction algorithm with the LIT algorithm of the IEEE 10 Base T standard to provide a stable and reliable twisted-pair link operation. Also, once the circuit is in its normal operational stage, it will not declare that a link is faulty unless it fails to receive a LIT pulse or an EOF waveform within a time-out period that is in accord with the IEEE standard. Therefore, the circuit is quite insensitive to line noise.

Method and means for automatically detecting and correcting a polarlity

A transmission media driving system for receiving high data rate serial binary data signal, dividing the signal into two or more lower data rate signal paths, modified duobinary encoding the signals and transmitting the signals on respective two-conductor transmission lines. The system includes ample encoding circuits for generating control signals and a line driver circuit, associated with each encoding circuit, that is responsive to the control signals to drive one of the transmission lines with the modified duobinary encoded signal through a transformer. The driver circuit includes multiple current sources that are switched to conducting or nonconducting states in response to the control signals to drive currents through a primary winding of the transformer to achieve appropriate levels of the encoded signal.

Transmission media driving system

A squelch circuit is disclosed that distinguishes between noise impulses and valid packets of data transmitted over a transmission line such as a twisted pair media within a local area network. The squelch circuit converts supplied data into a stream of positive and negative pulses and detects a sequence of positive and negative pulses quantified in time based on prior knowledge of the characteristics of a valid packet of data and permits the supplied data to pass if it has the characteristics of a valid packet of data or prohibits the supplied data from passing if it does not have the characteristics of a valid packet of data.

Squelch circuit

A local-area-network device (10) includes a pulse detector (40), which detects positive-voltage pulses on the coaxial cable (14) of the local-area network. Such pulses occur when normal transmission signals reach a short circuit and are reflected. Upon detecting a positive pulse, the pulse detector (40) turns off a transistor switch (Q12) so as to remove power from the receive lines (22) of a receiver (20) in the device (10). Control circuitry (18) can thus conclude, from the simultaneous absences of a receive indication and of a collision indication, that a short circuit has occurred on the line.

Growing community of inventors

Nashua, NH, United States of America

William C Mallard, Jr