Madge Networks Limited

Madge Network Limited

David A Pearce

Philip Geoffrey Claridge

Simon Davie Barber

Christopher Guy Sabey

Crispin Nicholas Dent-Young

Jonathan Curnyn

Trevor Warwick

Mark Kenneth Loney

A bridge device (4) for connecting a plurality of communication networks (1-3) around which data is transmitted in frames which include control information defining at least the identity of a destination for data in the frame, each network having at least one end station (8-12). The bridge device comprises a corresponding plurality of data coupling units (13,14) for connection to respective ones of the networks (1-3), each data coupling unit including receive (13) and transmit (14) interfaces for respectively receiving data from and transmitting data onto the connected network. A common store (17) is connected to all the data coupling units for receiving data being transmitted from one network to another. A controller (16,28) controls the routing of data through the bridge device (4) via the common store (17), the controller causing incoming data to be routed to a destination network before the data has been fully stored in the common store, if predetermined conditions are satisfied, the controller being adapted to monitor the amount of free space in the common storage means and to prevent the supply of data to the common store if the available free space is less than a predetermined amount.

Bridge device

Ring communication system and method for connecting a plurality of end

A local area network hub unit (5) has a plurality of switch units (16,17) connected in a ring. Each switch unit (16,17) may be connected to either an adjacent switch unit or to a group of pins of a connector unit (42). Each group of pins of the connector unit may be connected to respective end stations (8,9). Selected groups of two or more switch units (16,17) are connected to a common connector unit (42). Each group of pins of a connector unit (42) maybe coupled by a common coupling unit (7) to their respective end stations.

Local area network hub unit

A jitter generating device for use in a data communication system. The device has a repeating unit with an input and an output connected in use to receive data from the data communication system and to repeat the data onto the data communication system respectively. A clock signal generator generates a clock signal which is fed to the repeating unit to control the rate at which data is output onto the data communication system. A clock phase (jitter) modulating unit modulates the phase of the clock signal output by the clock signal generator.

Data communication systems

A method and apparatus for impedance matching a transmitter to a transmission medium of a communication system during normal operation of the system. The method comprises feeding signals from the transmitter to the transmission medium through a variable impedance; monitoring the potential upstream and downstream of the variable impedance; generating a control signal related to the monitored potentials; and adjusting the impedance of the variable impedance in accordance with the control signal until the monitored potentials satisfy matching conditions in which the transmitter is impedance matched to the transmission medium.

Automatic impedance matching with potential monitoring means

A communication system comprises a signal carrying medium (8) coupled to a series of end station ports (2-5). The end station ports (2-5) enable respective end stations (21) to transmit signals onto and receive signals from the medium (8). A controller (7) is provided to control the connection of the end stations (21) to the medium (8) via the ports (2-5). Monitors (9-12) are connected to the controller (7) to monitor characteristics of signals generated by the end stations (21) coupled to the ports. The monitors (9-12) are connected in parallel to the medium (8) and supply information relating to the monitored signals to the controller (7) in use. This system allows faulty end stations to be identified and removed from the system.

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Buckinghamshire, United Kingdom

David A Pearce