Abstract: A system for monitoring a network in which a station is connected to the network and includes a transmitter and a receiver. The transmitter outputs a signal modulated with outgoing traffic onto the network and the receiver receives a signal from the network modulated with incoming traffic. The station includes a monitoring circuit which introduces a variable delay in a signal from the transmitter and combines the delayed signal with the received signal so as to produce an output dependent upon the correlation of the signal from the transmitter and the received signal at the given delay. Preferably, the network is an optical network and the delay is introduced by a programmable delay line.

Abstract: A passive, all optical communications network is provided in which a single optical source in a central station serves many outstations (e.g. telephones in customers' premises). Time division multiplexed optical signals from a laser source are transmitted along a single optical fibre from a central station. The signal is split between several secondary fibers at a first splitter (e.g. array of passive couplers) and between further sets of fibres at a second set of splitters. At this stage there are 120 individual fibres to customers' premises. Digital speech or data is sent back to the central station by a laser in the customers' premises operating in a low duty-cycle mode. The 120 data streams are interleaved at the branching points.

Abstract: In a network including an exchange having a masterclock and a number of subscriber stations connected to the exchange, the exchange includes a delay line which receives incoming data. Samples are taken from different taps of the delay line and the tap carrying data in phase with the masterclock is identified and used to output data. In a preferred example, the network is an optical network carrying data cells.

Abstract: A passive, all optical communications network is provided in which a single optical source in a central station serves many outstations (e.g. telephones in customers' premises). Time division multiplexed optical signals from a laser source are transmitted along a single optical fibre (14) from a central station (4). The signal is split between several secondary fibres at a first splitter (10) (e.g. array of passive couplers) and between further sets of fibres at a second set of splitters (12). At this stage there are 120 individual fibres to customers' premises (8). Digital speech or data is sent back to the central station by a laser in the customers' premises operating in a low duty-cycle mode. The 120 data streams are interleaved at the branching points.

Abstract: A passive, all optical communications network is provided in which a single optical source in a central station serves many outstations (e.g., telephones in customers' premises). Time division multiplexed optical signals from a laser source are transmitted along a single optical fibre (14) from a central station (4). The signal is split between several secondary fibres at a first splitter (10) (e.g., an array of passive couplers) and between further sets of fibres at a second set of splitters (12). At this stage there are 120 individual fibres to customers' premises (8). Digital speech or data is sent back to the central station by a laser in the customers' premises operating in a low duty-cycle mode. The 120 data streams are interleaved at the branching points.

Abstract: A passive, all optical communications network is provided in which a single optical source in a central station serves many outstations (e.g. telephones in customers' premises). Time division multiplexed optical signals from a laser source are transmitted along a single optical fibre (14) from a central station (4). The signal is split between several secondary fibers at a first splitter (10) (e.g. array of passive couplers) and between further sets of fibers at a second set of splitters (12). At this stage there are 120 individual fibres to customers' premises (8). Digital speech or data is sent back to the central station by a laser in the customers' premises operating in a low duty-cycle mode. The 120 data streams are interleaved at the branching points.

Abstract: An interface for connecting a station using a time division multiplex format to a time division multi-access system comprising (a) a first channel for converting time division multiplexed signals (112) into bursts (119), (b) a duplex channel for re-constituting bursts (117) into time division multiplex frames (111) and (c) TDMA circuitry for controlling (a) and (b) to operate in conformity with the TDMA. The first channel is preferably adapted to remove unused slots from the multiplex and to collect the used slots over several frames into a single burst. The duplex channel restores the frame format by replacing slots removed by the transmitter.

Abstract: The node of a point to multipoint data telecommunications system needs a receive clock to regenerate the data. The conventional method of regenerating the clock from received signals is difficult because there are gaps when no outstation is active. The invention reduces these problems by synchronizing the receive clock with the master send clock when there is no reception.

Abstract: In a time division multi-access communications system each burst in each slot commences with a preamble and the clocks used to control the sequence of operations are synchronized by means of these preambles. In particular the outstations control their transmissions to the node by timing pre-set delays from the receipt of the preamble. In a preferred embodiment the pre-set delays are adjusted by signals from the node so that bursts arrive at the node in correct sequence.