Abstract: A broadband multiport coherent optic data switch comprises a passive optic combiner/splitter, a plurality of port units and a switch control unit connected thereto, each port unit having a coherent optic source tuned to a respective optic frequency, the output of each source carrying thereon control information, including control information received from the control unit, together with switched data, the outputs of the sources being combined and distributed to all of the plurality of port units.

Abstract: Fault location in an optical signal transmission network in which a main optical fibre is divided into a plurality of branch circuits, is simplified. Optical time domain reflectrometry (OTDR) equipment transmits an output signal along the main fibre, and for each branch circuit the signal is caused to be returned to the OTDR equipment from the branch to be modified in a manner unique to that branch.

Abstract: An ATDM switching system comprises a serial to parallel converter arranged to receive incoming packets of data (which include their own routing information) from several input ports in serial form and deliver them, in parallel format, to a Random Access Memory (RAM) in such a way that the packets form queues within the memory, one for each output port. Packets are then transferred in parallel format, one from each queue in turn, to a parallel to serial converter which delivers them to their respective output ports in serial format. The arrangement is such that when the memory becomes full the system can accommodate incoming packets by overwriting data in the longest queue, a technique that can significantly reduce the total number of packets lost during long term operation.

Abstract: For use in a coherent optic switch a coherent optical transceiver has a single coherent receiver for both data recovery and to lock the transmitter to an optical reference input to the receiver. The switch may include polarisation control of the optical input to the receiver and wave division multiplex control of the transmitter frequency. The transmitter and receiver may be constructed as opto-electronic integrated circuits.

Abstract: An ATM telecommunications switch includes a plurality of parallel data switching planes and a parallel control plane, each plane having an equal number of input ports and output ports and a central switching unit to switch each input port to any output port. Data from a single timeslot on the central switching unit is connected to a plurality of output ports in a point to multipoint operation. A multipoint memory stores information regarding the data addresses and a forward transfer store provides additional storage for multipoint cells.

Abstract: An audio processor circuit for treating a digitally encoded incoming signal, the circuit comprising circuitry (3, 12) for sampling the encoded signal at two or more sample frequencies, circuitry (8, 13, 38, 40, 46) for calculating from the sampled values a cross-correlation function relevant to a particular time frame, the value of said function serving to control operation of an adaptive algorithm, in which the sampled signal portions are truncated (2, 5) such that only the arithmetic sign bit of each signal portion contributes to the function calculation.

Abstract: A Contact Smart Card (3) is inserted in a contact card reader and its capacitance is measured by applying a square wave generated by an oscillator (1) to it via a resistor (4). The capacitance effect of the smart card (3) affects the amplitude of the output from the resistor (1) and the output is monitored in an amplitude detector (2) connected to receive the signal output from the resistor (4) and to compare it against a threshold level for the signal previously established and stored for an acceptable card.

Abstract: A communication procedure suitable for a cordless telephone system involves time division duplex radio communication between a handset 11 and a base station 3 using alternating bursts of transmission over a single radio channel. Once a radio link has been set up, initial transmissions carry a synchronisation logical channel S and a signalling logical channel D multiplexed together, but the link may switch to bursts carrying a communications logical channel B for the speech data and the signalling logical channel D. Burst synchronisation is achieved by the asynchronous detection of words in a synchronisation channel S. These words have bit patterns reducing the probability of incorrect asynchronous detection of them. If one part ceases to receive handset signals from the other, it transmits a special signal, informing the other part. This enables both parts to detect the failure of a link at substantially the same time, so that their actions to re-establish the link are synchronised.

Abstract: A meter reading arrangement has an optical fiber transmission path made up of a pair of optical fibers connecting between a meter to be read and a meter interface unit. Light is transmitted over one of the fibers to an indicator on the meter and reflected light is transmitted by the second fiber to a transducer in the interface unit.

Abstract: There is a demand for user access to ISDN services at the two-wire interface point. The frequently raised objection to such access is the problem of determining the location of a fault and hence the responsibility for the fault. This is solved by the use of a voltage sensor responsive to a DC voltage less than a normal line feed voltage within a voltage range not used in normal operation to control a switch operative to disconnect a subscriber termination unit from the line, and to provide a known linear terminating impedance for the line for the duration of the application of the DC voltage.

Abstract: Synchronization of a receiving termination of a telecommunications system with an incoming data stream is carried out from a synchronization signal carried with the data stream. It is possible that a "mimic" of the synchronization signal may occur within the data stream. Two frame alignment detectors operate in worker/standby relationship, one being locked to a detected synchronization signal and the second searching for an alternative signal. Verification is carried out using a cyclic redundancy check.

Abstract: Circuitry is provided for testing telephone lines, the circuitry comprising a loop current ring trip detector and a relay which in operation is used to break normal current to provide an end of call indication, and wherein said relay is also operative in one test mode to switch from said loop current ring detector to a comparator which functions as a test mode detector. The means may also include a second relay which when the circuit is in a second test mode is operated simultaneously with the first relay, the second relay being connected to a bell capacitor the discharge rate of which can be measured by said capacitor, and the comparator output is sequentially monitored to provide information as to the condition of the insulation and regarding bell capacitor and terminal connection.

Abstract: The material similarity of all-silica waveguides or other devices and optical fibers is utilized to establish an epoxy-free fusion interfacing between optical fibers and integrated-optic devices by using laser welding techniques. This is uniquely applicable to all-silica integrated devices since they have virtually identical material properties to those of optical fibers. The method comprises the steps of machining a locating groove in a silica block, fixing a prepared length of the optical fiber in the locating groove, bringing the block and the device into juxtaposition and aligning the block and the device to provide maximum transmission of a signal from the fiber to the device and laser welding the block and the device together.

Abstract: Data is encrypted for transmission over non-secure communication by providing data with a header and a trailer portion containing the full information as to the sender and recipient of the data so as to form a data packet, incrypting the data packet, and providing a further header and trailer portion to form a further data packet. The further header and trailer only contain information identifying the entry and exit nodes at which the further data packet enters and leaves the non-secure network. On arrival at the exit node the further data packet can be decrypted to reconstruct the original packet which is then conveyed to its destination via a local secure network. Padding non-secure network with dummy messages makes it impossible to identify the presence of genuine traffic between particular nodes of the non-secure network. Thus secure data may be sent via commercial non-secure packet switching networks without indicating its presence.

Abstract: The invention concerns an Asynchronous Transfer Mode Switch having a plurality of input stages (IS1 . . . 1SN) each for receiving a digital data transmission stream (DS1 . . . 256) consisting of a series of cells and wherein each input stage of the switch includes a circuit (52) for determining the destination of the cells of that data stream, and a circuit (63) for disassembling each cell into cell elements and for allocating to each cell element routing data to enable it to be routed across the central stages.

Abstract: The telecommunication network is composed to a greater degree of ATM exchanges (ATM) and to a lesser degree of STM exchanges (STM). Information coming from an STM exchange (for example, STM1) ad to be switched to a further STM exchange (for example, STMy) via an ATM exchange (for example, ATM1) are packeted in short cells for through-connection through the ATM exchange (ATM1) in order to reduce the packeting time. These short cells have a shorter length when compared to the standardized message cells used for information transmission between ATM exchanges.

Abstract: The telecommunication network is composed to a greater degree of ATM exchanges (ATM) and to a lesser degree of STM exchanges (STM). Information coming from an STM exchange (for example, STM1) and to be communicated to a further STM exchange (for example, STMy) via an ATM exchange (for example, ATM1) is packeted in message cells of the same length as those message cells used for the transmission between ATM exchanges in order to reduce the packeting time for the through-connection across the ATM exchange (ATM1). However, respective message parts of a plurality of STM time channels (K1 through K4) that are to be through-connected to the same ATM exchange output are multiplexed in a message cell.

Abstract: The telecommunication network is composed to a greater extent of ATM exchanges and to a lesser extent of STM exchanges. For reducing the packeting time for the through-connection across the ATM exchange, information coming from an STM exchange and to be switched via an ATM exchange to a further STM exchange is packeted either into message cells that are shorter in comparison to standardized message cells used for the transmission between ATM exchanges or into message cells of the same length wherein, however, respective message parts of a plurality of STM channels that are to be through-connected to the same ATM output are multiplexed in a message cell. Given local exchanges (ATM-V) having decentralized line units (SLUR) for the connection of subscriber lines, the message cells of a plurality of STM channels are packeted multiplexed thereat without taking the exchange destination into consideration.

Abstract: A data transmission system in which multiplex data is created in accordance with the Synchronous Digital Hierarchy standard includes an add-drop multiplex having a switch across which data streams are switched between a pair of multiplexers and each input and output for a stream has a rejustifier circuit the timing of which is extracted from a timing extract from the other side of the switch.

Abstract: An add/drop multiplex includes a matrix switch, the drop side of which is connected via buses to respective time slot assignment function circuits which are interconnected by at least one bus capable of transferring traffic between the add and the drop functions of the multiplex.