Abstract: A Raman amplifier for amplifying WDM radiation propagating along an optical fiber, the WDM radiation comprising a plurality of radiation components each having a selected waveband, comprises a plurality of optical radiation generators operable to generate pump radiation of a selected wavelength and power, the radiation being coupled into the fiber to optically amplify the WDM radiation. The generators are wavelength tuneable, and the power of the radiation components of the WDM radiation is measured after it has propagated along the fiber and has been amplified. The wavelength and power of operation of the generators are controlled in dependence upon the measured powers such as to make the measured powers substantially equal in magnitude and of a selected magnitude.

Abstract: A network has a plurality of nodes, wherein at least one of the plurality of nodes includes a switch arranged to carry out a Simple Transit Core Function and three or more of the plurality of nodes include a Single Link Interface which Single Link Interface has associated Output Attributes and/or Input Cognizant Attributes. Each Simple Transit Core Function at one node is not logically connected to another Simple Transit Core Function at another node. Each Simple Transit Core Function at one node is logically connected to at least three Single Link Interfaces at other nodes. The nodes including Single Link Interfaces which are connected to one instance of a node arranged to carry out a Simple Transit Core Function are controlled by respective Intercommunicating Connection Acceptance Control Processes according to the respective Output Attributes and/or Input Cognizant Attributes.

Abstract: An alternative method to the existing manual service creation exploits the properties of genetic programming (GP) to produce service logic programs for an intelligent network. For GP to be of benefit to an intelligent network, it must be able to reduce the time to create a service and reduce the number of implementation errors in the resultant program.

Abstract: A system for checking the correct operation of a wavelength filter comprising a wavelength filter comprising a first selectively reflective element (SRE) for reflecting a first signal of a first wavelength and a second SRE for reflecting a second signal of a different wavelength. The system also detects the second signal reflected by the second selectively reflective element.

Abstract: A tuneable optical filter includes a moveable filter plate and an associated optical region for filtering an input radiation beam to provide corresponding filtered output radiation. The optical region has spatially varying filtration properties. Piezoelectric actuating elements are provided for moving the filter plate and its associated optical region relative to the beam for selecting a portion of the optical region for use in filtering the beam and thereby tuning the filter. The actuating elements are operable when driven by electrical signals to repetitively engage or be in repetitively slidable contact and thereby impart a lateral force to a surface of the filter plate for moving the optical region relative to the beam in at least one dimension. The filter is especially suitable for use in optical communication systems where there arises a need for occasional system reconfiguration involving retuning optical filters of the system.

Abstract: A method of generating a pulse width modulated (PWM) signal receives digital demand data comprising at least one more significant bit and at least one less significant bit. The PWM signal comprises a sequence of one or more frames, each frame comprising a plurality of PWM pulses whose duty cycle is substantially governed by the at least one more significant bit. At least one of its PWM pulses is selected to have its duty cycle modified in response to the at least one less significant bit. Each of the at least one less significant bits uniquely mapping onto the at least one selected PWM pulse of the frame. An apparatus operable according to this method includes an optical attenuator whose optical attenuation is dependent upon its temperature and in which the temperature and, hence, the attenuation is controlled using the above PWM signal.

Abstract: A communications system utilizes, inverse multiplexing to transfer wide band signals over a plurality of narrow band links. To enable efficient use of the available links, incoming data whether or not cell or packet based, is inverse multiplexed in a byte format regardless of packet boundaries into virtual containers. Overhead signals are generated to enable the original data to be reassembled at the receiving end.

Abstract: There is provided an error rate monitor (10) incorporating a counter (30) which is incremented as errors are detected in a data stream passing through an interface unit (20) connected to the counter (30). The counter (30) is also simultaneously decremented at a rate proportional to an exponential of a value presently stored in the counter (30). The monitor (10) thereby provides from the value stored in the counter (30) a measure of error rate in the data stream, the value substantially proportional to a logarithm of error rate in the data stream, thereby providing the monitor (10) with a relatively large error rate monitoring dynamic range.

Abstract: A telecommunications system comprising one or more cross-connects and a plurality of telephone exchanges. Two or more of the telephone exchanges are arranged to communicate with each other via the one or more cross-connects. An adapter provides the telephone exchanges with inter-communication via the one or more cross-connects. The adapter converts traffic between packetized and non-packetized form.

Abstract: In the transmission of speech in mobile telephone services where mobile handsets cooperate with a base station via a radio link, the base station being connected to a mobile switching center which, in turn, is connected to a public network, communication between the handsets and base stations is achieved using a standard selected to minimize bandwidth utilization. Sample standards are GSM and DECT. It has currently been proposed that in utilizing either of these standards a number of encoded speech channels will be multiplexed at the A interface between the base station and the MSC. The multiplex signal would then be converted to a 64 kb/s format at the interface between the MSC and the public network to which the MSC is connected. This proposal has a number of disadvantages.

Abstract: The invention provides a radiation power equalizer for an optical communication system, the equalizer characterized in that it includes: (a) an optical demultiplexer (300) for partitioning information-bearing radiation received at the equalizer into one or more radiation components corresponding to wavelength division multiplexed communication channels of the system; (b) a liquid crystal cell array (310) for selectively transmitting or attenuating said one or more radiation components; (c) an optical multiplexer (330) for combining one or more of the radiation components transmitted or attenuated through the cell array (310) to provide combined radiation; (d) a transmitter erbium-doped fiber amplifier (70) coupled to a PIN diode detector array (120) for measuring radiation power present in said one or more of the radiation components included in the combined radiation and generating one or more corresponding component radiation power indicative signals; and (e) a control module (130) for receiving said one or

Abstract: An Asynchronous Transfer Mode (ATM) multiplexed data stream is terminated at a functional unit. Virtual channel data are being carried in cells in the data stream. A depacketizer has a plurality of cell buffers, each buffer storing the payload data contained in a single cell. The buffers are being loaded in sequence in accordance with a message sequence number carried by each cell and emptied in accordance with a depacketizer algorithm to form a non-continuous data stream. A fill-in cell format generator, on the failure of a valid cell to arrive, causes the replacement of the missing cell by a fill-in cell in the non-continuous data stream. A time-out function generator is started after each cell has been depacketized and sometimes after fill-in replacement cells have been generated.

Abstract: A system for individually controlling the chromatic dispersion of one or more wavelength division multiplexed (WDM) optical signals, chromatic dispersion is compensated a plurality if individually controllable differential optical delay elements. An example of a suitable differential optical delay element is a tunable fiber Bragg grating filter whose spectral response varies along the length of the grating, i.e. is chirped in a non-linear fashion. The system may, in addition, comprise one or more second individually controllable optical delay elements arranged so as to compensate for any unwanted delays across the wavelength band of a signal introduced by a first delay element. Optical circulators may be used to route signals into and between the pluralities of differential optical delay elements. This system has the advantage of providing a compact multi-channel selective differential delay suitable for compensating for chromatic dispersion in a WDM optical communications network.

Abstract: A synchronous digital hierarchy (SDH) telecommunications system for transporting traffic with control bytes for indicating the sources of the traffic. The system comprises a plurality of interconnected nodes each capable of identifying undeliverable traffic by checking the sources indicated by the control bytes. The system also comprises a network management system (NMS) arranged to provide each node with information concerning the expected sources of the traffic. The system acts to identify undeliverable traffic by comparing the sources indicated by the control bytes with the expected sources.

Abstract: In a network of SDH equipments (e.g. synchonous multiplexers add-drop or SMA) for the communication of signals comprising data, a synchronization signal for synchronizing the data and a synchronization status message (SSM) indicating the quality of the source of the synchronization signal, when a synchronization signal is output via a sychronization signal output (SSO) to a stand-alone synchronization equipment (SASE) for conditioning and subsequently input via a synchronization signal input (SSI), the SSM information may be lost. The invention provides means for associating, within the SDH equipment, the revelant SSM with the synchronization signal input at the SSI.

Abstract: A coin validation arrangement, usable for example in pay telephones, uses one or more inductive sensors having a small effective magnetic field so that the inductive sensor responds only to the material of a strip across the coin. Preferably a plurality of inductive sensors are used, mounted at different heights above the floor of a coin guide, at different positions along the coin path. At each position along the coin path there may be either one or a plurality of inductive sensors. Preferably the inductive sensors are surface mount inductors on a printed circuit board which forms part of one wall of the coin guide. Such arrangements are particularly useful for recognizing coins having an outer ring made of a different material from the central disc, and for distinguishing such coins from uniform composition coins.

Abstract: An optical switching arrangement, e.g. an add-drop multiplexer or switch, for receiving an input signal comprising a plurality of input wavelength encoded optical channels. The arrangement includes a selector for selecting from the plurality of input optical channels for forming a plurality of output signals comprising selected ones of the plurality of input optical channels. A combination of input optical channels in any one of the plurality of output signals is different from a combination of input optical channels in the input signal. The selector comprises a plurality of selective reflectors for selectively reflecting optical channels selected from the plurality of input optical channels. The plurality of selective reflectors are arranged to selectively reflect each of the input optical channels selected for forming the plurality of output signals.

Abstract: An optical communications system for communication of a plurality of wavelength multiplexed channels. The communications system comprises a node. The node comprises a plurality of add-drop multiplexers (ADM), one per channel. Each ADM comprises a tributary. The ADMs are interconnected by the tributaries.

Abstract: A data processing system comprising a common memory shared by a first and second data processor circuit, in which each processor circuit executes the same sequence of operational steps and each is connected to the common memory. An isolating device connected between the first data processor circuit and the common memory restricts access by the processor circuit is arranged to execute each operational step a set time period later than the second data processor circuit. A comparator compares the output signals of the two processor circuits in order to detect faulty operation but, before the comparison, the outputs of the second processor circuit are delayed by the set time period.