Abstract: 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.

Abstract: Interface apparatus for connection between a data handling device and a data communication medium to enable data to be transferred between the device and the medium, is constituted, inter alia, by a data alignment device (7, 8) coupled in use to the data handling device. A memory (5, 6) is coupled for data transfer to the data alignment device (7, 8) and includes a number of substantially identical subsidiary, First-In-First-Out (FIFO) memories arranged in parallel. The number of subsidiary memories is chosen such that their overall width is at least equal to the longest length of data to be transferred between the memory (5, 6) and the alignment device (7, 8) in a single transfer step and the width of each subsidiary memory is equal to the shortest length of data to be transferred between the memory and the alignment device in a single transfer step.

Abstract: A method and apparatus for synchronizing a clock between first and second logic blocks (20,21) connected via an asynchronous bus (22). The second logic block includes a clock signal generator (9) responsive to an input synchronizing signal to generate a clock signal synchronized with the synchronizing signal. Data is transferred in blocks from the first logic block (20) to the second logic block (21) across the asynchronous bus (22), the receipt of a data block by the second logic block (21) being used to generate the synchronizing signal.

Abstract: A method of inserting an end station (6-8) into a token ring network (2). The end station (6-8) attempts to open into the ring network in one insertion mode, the end station responding to an insertion error code relating to an insertion event, before the end station applies phantom drive, to change from one insertion mode to another insertion mode. A change of insertion mode is a change in at least one of end station speed and end station idling speed.

Abstract: A network interface for an asynchronous cell switched communication network includes a data input, a memory for buffering data received at the data input, and a clock signal generator for providing a clock signal having a frequency which is controlled in accordance with a fill level of the buffer memory. The clock signal is used to control a rate of transfer of data from the buffer memory. Data received at the network interface device is consumed by a buffer, typically a FIFO device. When the buffer fill level exceeds a predetermined level, the clock signal frequency is increased and conversely, when the buffer fill level drops below the predetermined level, the clock signal frequency is decreased.

Abstract: A communication network end station is constituted by a host device including a processor and a memory; a bus; and a communication network interface device connected to the host device via the bus and, in use, to a communication network along which data is transmitted in accordance with a network protocol. The communication network interface device includes a processor which transfers data to and from the network in accordance with the network protocol. The control code for operating the processor is stored in the host device memory. The processor is adapted to route incoming data and associated network protocol information, as it is received, to the host device memory. The bus is capable of transmitting data and associated network protocol information at a speed compatible with the operating speed of the communication network.

Abstract: In a cell switched communication system in which a source is connected to a network for transmission of cells to a network destination via a network element having a plurality of ports, said source generating resource cells containing information concerning a bandwidth allocated to the source for transmitting cells, a method of providing flow control at the network element comprises the steps of: (a) detecting a resource cell as it is received at an input port of the network element; (b) routing the resource cell to a resource cell processing means common to all the ports of the network element; (c) modifying information contained in the resource cell concerning the bandwidth allocation for the source on the basis of a determination of current utilisation of ports of the network element; and, (d) passing the modified resource cell to an output port of the network element for subsequent return to the source.

Abstract: A switch fabric is provided which comprises a shared memory, a number of switch fabric ports, and a switch fabric data controller. The switch fabric data controller routes blocks of data received at one switch fabric port to one or more other switch fabric ports and writes and reads data to and from, respectively, the shared memory. The switch fabric data controller preferentially routes a block of data from the one switch fabric port to the one or more other switch fabric ports without writing the block of data into the shared memory if the one or more other desired switch fabric ports are free or become free within a predetermined period, and otherwise writes the block of data into the shared memory for temporary storage if the one or more other switch fabric ports are busy. In this manner, the switch fabric facilitates "cut-through" of blocks of data across a switch without the need to write the blocks of data to a shared memory, thereby reducing latency.

Abstract: A method and apparatus for synchronizing clock signals on first and second logic blocks connected via an asynchronous bus, wherein the second logic block includes a clock signal generator. The method comprises causing the clock signal on the first logic block to increment a first count; causing the clock signal on the second logic block to increment a second count; comparing the first and second counts; and adjusting the clock signal on the second logic block in response to the result of the comparison to synchronize the two clock signals, wherein the transfer of information between the logic blocks is carried out via the asynchronous bus.

Abstract: 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.

Abstract: A data communication network having a number of end stations connected together for data communication therebetween. At least one network interconnect device receives and transmits data packets. The network interconnect device further includes a memory and a processor, each end station and network interconnect device being adapted to transmit data in accordance with a protocol in which copies of a route recording data packet are transmitted along multiple routes through the network. The memory of the network interconnect device is adapted to store information relating to the manner in which route recording data packets reach the network interconnect device.

Abstract: A termination is provided for a differential transmission line such as unshielded twisted pair (UTP) to isolate a connected device from electromagnetic interference present on the UTP in the form of differential mode and common mode noise. An example of an electromagnetic interference isolator comprises a common mode and a differential mode termination, a common mode choke which exhibits substantially constant impedance over a wide bandwidth and a centre tapped isolation transformer.

Abstract: An end station port (2-6) for connection to a token passing communication system which connects a number of end station ports and in which the communications protocol under which the system operates permits more than one data frame to be transmitted by an end station within a predetermined token holding time comprises a transmit store/frame assembly unit (19) for preparing a data frame, having a length not exceeding a predetermined maximum size, for transmission; and control logic (20) for controlling the passage of data to and from the end station port for transmission on to and receipt from the communication system in use. The control logic (20) transmits a frame prepared by the frame assembly unit (19) when the token is held by the end station port.

Abstract: A method of connecting a new end station to a ring communication system for connecting a number of end stations is constituted by the steps of: i) sensing an attempt by the new end station to attach to the ring; ii) determining whether there is a single end station only existing on the ring; and, iiia) if it is determined that there is more than one end station on the ring, allowing the new end station to attach to the ring and maintaining the ring communication configuration; or b) if it is determined that there is a single end station only on the ring, breaking the ring configuration and setting up two separate communication paths between the new end station and the existing end station.

Abstract: A method of analysing a communication system to locate the source of a fault. The communication system comprises a signal carrying medium (9) coupled to a series of end station ports (2-6) which enable respective end stations (24) to transmit signals onto and receive signals from the medium and a controller (8) to control connection of end stations (24) to the medium via the ports (2-6). The method comprises disconnecting end stations (24) in series from the medium (9) in response to detection of a fault and then detecting whether the fault still exists. A fault analyzer (10) adapted to respond to the detection of a fault causes the controller (8) firstly to disconnect an end station (24) which has previously been characterised as the most likely source of a fault. The controller (8) may disconnect groups of end stations (24) and reconnect subgroups if no fault is present in the group which was not disconnected until the faulty end station is identified.

Abstract: 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.

Abstract: A processor system for connection to a communications network comprises a processor and a memory configurable for operation with the processor in at least two modes, a virtual mode and a protected mode in which operation of the processor and memory is dedicated to data transfer between the processor system and a communications network. A switching device is provided for switching between the virtual and protected modes, which is operable under user program control, in response to a data transfer request generated when data is to be transferred between the memory and the communications network. The switching device then switches to the protected mode, such that there is direct data transfer between the memory and the communications network.

Abstract: 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.

Abstract: 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.

Abstract: 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.