Abstract: A method of, and an apparatus for, operating an optical modulator employ an optical attenuation versus voltage response which is cyclic and which includes an input to which the application of a bias voltage moves the modulator's response along the voltage axis to maintain the modulator's response at a desired voltage position. The apparatus comprises a bias voltage generator for generating a bias voltage which comprises the sum of a first and a second voltage component. The first component is fixed during normal operation and is selected to correspond to the expected bias voltage required for maintaining the modulator's response at a desired voltage position. The apparatus further comprises circuitry for detecting the position of the modulator's response and adjusting the second voltage component to maintain the response at the desired voltage position.

Abstract: A telecommunications data transmission system can provide transmission of data blocks using a unidirectional broadband link and a duplex narrowband link between two subscribers, the narrowband link providing control and addressing information regarding the data blocks sent via the broadband link from the first to the second subscriber, the transmission on the broadband link possibly being sent using Motion Picture Expert Group 2 encoding.

Abstract: A photonics system comprising an optical circulator, comprising a plurality of ports; a first port arranged to receive a plurality of spatially separate optical signals each comprising a plurality of wavelengths; the optical circulator arranged to pass the plurality of optical signals to a second port so as to produce them as spatially separate signals; a plurality of optical wavelength filters arranged at the second port, in which each of the plurality of optical wavelength filters is arranged to align with a different one of the plurality of optical signals at the second port, each of the plurality of optical wavelength filters for selectively reflecting a selection of the plurality of wavelengths comprised in the respective optical signal and selectively passing others of the plurality of wavelengths.

Abstract: An SDH network is enclosed in which the occurrence of closed timing loops is prevented by causing each node to stamp the clock signal passing through that node with identifying data. In one embodiment, each node is operative to overstamp any node identifying data from preceding nodes and to indicate that the timing signal is not to be used for synchronization purposes if the node to which it is being sent would result in a closed timing loop. In a second embodiment, node identifying data is added to a list, and if any node reads its own indenting data on that list, then it knows not to use the synchronization signal. By counting the number of nodes through which the signal has passed, a way is provided for preventing the occurrence of synchronization reference chains of excessive length.

Abstract: A copper wire pair linking network terminating equipment in a home with a relatively localized multiplexer, e.g., in a street cabinet, carring high data rate, e.g., VDSL, signals such as ATM and ISDN, combined at the multiplexer. It is necessary for the multiplexer to be provided with a power supply but, in the event of failure of the power supply, VDSL signals could not be generated in the multiplexer. To provide some fall-back in such a case, a metal link from the local exchange to the network terminating equipment is formed, for example, by using relays, thereby permitting ISDN signals to be received in the home even though the higher data rate ATM has now failed.

Abstract: In an optical telecommunications system using wave division multiplexing (WDM) a wavelength add-drop multiplexer (WADM) has an array of adjacently connected filters, each for selecting light of a respective wavelength being transmitted in a multiplexed data stream along an optical fibre, each of the array of filters being adjacently connected to a portion of the array which is a nominally transparent filter and having means for moving the array so that movement between filters in use occurs via the nominally transparent filter portion of the array. Further, in a method of operating a WADM the transition between two filters of an array of filters each for selecting light of a respective wavelength being transmitted in a multiplexed data stream along an optical fibre occurs by way of a nominally transparent filter portion of the array.

Abstract: Inventory maintenance is improved for a system of one or more vending machines by providing one or more vending machines with unique identifiers, and means for collecting and transmitting information concerning goods dispensed and other status to a remote location where processing means provide an efficient service schedule.

Abstract: In a 2-wire connection from a telephone exchange to a subscriber, the connection is made via a subscriber line interface circuit (SLIC) and a termination box, the termination box having a capacitor and a resistor connected in series between the two wires of the connection and between the SLIC and the subscriber. The SLIC includes means to reverse the polarity between the two wires of the connection and there is measuring means whereby the current required to change the capacitor to the opposite polarity may be measured enabling determination of the impedance between the two wires of the connection.

Abstract: An optical reference frequency generator comprises a plurality of Single Sideband Optical Frequency Shifters (SSB-OFS) wherein the SSB-OFSs are connected in pairs, each pair having a common optical frequency input and an optical shift frequency input arranged so that the output from one SSB-OFS of each pair has a positive frequency shift and the output from the other SSB-OFS has a negative frequency shift.

Abstract: In a Telecommunications Infrastructure, an Access Network or Segment of an Access-Layer Infrastructure has a plurality of subscribers or extensions linked to one or more gateways having ports and providing access to/from higher network layers. The linking from the subscribers or extensions to the gateways is carried out by the statistical-multiplexing of ATM cells carried in time-slots formatted onto broadband bearers. A desired gateway is identified by a number carried in the Virtual-Path Identifier field of each ATM cell. The source is identified by a number carried in an additional address field external to the ATM cell but internal to the time-slot. The linking from the gateways to the subscribers or extensions is via a distribution switch. The desired subscriber is identified by the number carried in the additional address field and the source is identified by the number carried in the Virtual Path Identifier field of the cell.

Abstract: A communications network using Asynchronous Transfer Mode has a head end unit connected to a plurality of groups of network terminations wherein the frequency spectrum of the network is divided into a number of frequency bands, one band of which forms a start-up band used for start-up and configuration of a network termination, the remaining bands each being used for communication between the head end unit and the network terminations within a group subsequent to start-up and configuration. The network may be a Passive Optical Network.

Abstract: Scanning based wavelength measurement systems which are suitable for both localised and distributed WDM, High Density WDM, and coherent systems are based around the use of a fixed cavity Fabry-Perot Etalon which when the output of a tuneable laser is passed through it produces a number of reference equispaced transmission maxima. These maxima are used in a Scanning Heterodyne or Scanning Filter based Spectrometer for detection of the wavelength position of the transmitter.

Abstract: The flexibility of a telecommunications switch fabric can be improved by making the fabric multipurpose. Where a switch fabric has two or more switches of different granularities, they may be connected by a terminating device in which the higher granularity circuits from the first switch are terminated and demultiplexed into the lower granularity circuits for the second switch, in addition to the lower granularity circuits from the second switch being multiplexed together to form higher granularity circuits for the first switch.

Abstract: In an SDH telecommunications system, a buffer overfill/underfill problem, which is consequent upon either a synchronization failure or an excessive amount of wander, is overcome by detecting such failure or wander and temporarily changing the mode of operation of a de-synchronizer at a terminating end of the SDH path. A Synchronization Status Messaging Byte (SSMB) is used as an indicator of the quality of the incoming bearer timing.

Abstract: To increase the number of subscriber network ports which may be accessed on a Broadband Integrated Services Digital (B-ISDN) access network using Asynchronous Transfer Mode (ATM) technology where a Concentration Function is provided by statistical multiplexers, a Grooming Function by ATM switches and own-access-network connections is provided by combining "upstream" ports into the core network(s) and the "downstream" ports to subscribers into a common address group. Each subscriber port and each core network(s) access port are allocated a unique OSI Layer 2 address. The access network destination address being carried in the Virtual Path Identifier (VPI) field of each ATM cell formatted according to relevant CCITT recommendations for the User Network Interface (UNI) or the Network to Network Interface (NNI).