Abstract: The present exemplary embodiment relates to a remote powered node for a hybrid fiber-copper network. The node may be powered using the dormant copper pair(s) linking the node to the telephone exchange to carry a ringer current. The ringer current can be controlled to power all the electrical load of the node. Alternatively, the ringer current may power all of the components common to all customers served by the node, with the customers feeding power to their customer specific components via a UTP cable.

Abstract: The present invention provides a hybrid communications network, in which a customer may be connected to a copper access network or an optical fibre access network by a network node. By providing power from a network terminal, a customer causes the node to be connected to the optical fibre access network; if power is lost or the network terminal disconnected then the node will connect to the copper access network.

Abstract: The present invention relates to a remote powered node for a hybrid fibre-copper network. The node may be powered using the dormant copper pair(s) linking the node to the telephone exchange to carry a ringer current. The ringer current can be controlled to power all the electrical load of the node. Alternatively, the ringer current may power all of the components common to all customers served by the node, with the customers feeding power to their customer specific components via a UTP cable.

Abstract: A distributive communications network includes groups of nodes at different levels. Each set of nodes at one level is connected to an associated node in the level above for transmission and reception of traffic. Traffic is assigned to one of a number of bands of wavelengths according to whether it is local or wider area traffic. At the first level of node local area traffic in the corresponding band of wavelengths is looped back and retransmitted to all of the terminals that are connected to that node. At each level of node, traffic is either passed on to a higher level, or looped back according to the band of wavelengths to which it is assigned. Thus, the wavelength band determines the node level at which the traffic is looped back, and the breadth of terminals ultimately exposed to this traffic. It is possible to re-use bands of wavelengths for communicating between terminals.

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 reflective star coupler for a distributed switch optical network for narrow band and broad band broadcast communication incudes on port terminated in a reflective surface or device, a signal amplifier and/or filter is disposed in the path between the port and the reflective device to reintroduce the light from that port into the coupler in an amplifier state or selectively according to wavelength. The amplifying device may be a semiconductor laser having a reflective coating on one face thereof.

Abstract: Signals, such as television signals, are distributed from a head-end station via a fibre network. The signals are amplitude modulated on carriers at different frequencies, and the different carriers combined to form a composite analogue signal. In the head-end station the composite analogue signal is clipped to reduce the peak-to-mean ratio and the clipped composite signal is digitized. The resulting digital data is transmitted onto the fibre network and is received at an optical receiver. The optical receiver reconstitutes the composite analogue signal for reception by a termination. In one example the composite analogue signal has a bandwidth of one octave or less, and is digitized by sampling at a sampling rate below the Nyquist rate.

Abstract: In a data communication system a signal is coded with n-bit codewords, wherein n is an integer. The codewords are converted to a serial bit-stream and scrambled using a PRBS (Pseudo-Random Binary Sequence) from a PRBS generator (4). The PRBS sequence has a length n x m where m is an integer. At a receiver the serial data is descrambled using a corresponding binary sequence from a PRBS generator (5) matched to that in the transmitter. The descrambling data is decoded in a decoder (6) in synchronism with the binary sequence in the generator (5), thereby maintaining word alignment between the transmitter and the receiver.

Abstract: A system for distributing HDTV signals from a head station to a number of customer stations includes a single head-end optical source having a frequency f.sub.0 and a modulator arranged to receive light from the single optical source. The modulator modulates the light with a sub-carrier multiplex of n channels, where n is an integer greater than 2, the n channels having frequencies f.sub.1, f.sub.2 . . . f.sub.n. The frequencies are separated in frequency-space from each other and from f.sub.0. A broadband passive branched optical network is connected to the output of the modulator and arranged to distribute the modulated signal from the head station to a plurality of customer stations each having a coherent heterodyne receiver.

Abstract: A system for distributing interactive HDTV signals includes a head-end station and a number of customer stations. The head-end station includes at least one optical source. A bidirectional transmissive broadband passive branched optical network distributes HDTV signals from the head-end station to the customer stations. Each customer station includes an optical coupler arranged to couple the subscriber station to a respective arm of the optical network a coherent receiver including a local oscillator laser and a transmitter arranged to modulate light from the local oscillator laser with return data for transmission via the coupler onto the network. The head-end station also includes a broadband optical receiver arranged to receive and demodulate the return data received via the optical network.

Abstract: A method and control system for controlling a signal from each outstation in a multiple access passive optical network including a central node and a plurality of outstations involves monitoring, at the exchange, the value of a parameter of a signal from reach outstation. The value of the parameter is monitored relative to a predetermined discrimination value to detect the signal relative to predetermined first and second reference values defining a range of acceptable values for the parameter. If the value of the parameter for a detected signal falls outside the range, a control signal is transmitted from the node to instruct the relevant outstation to alter the value of the parameter as required to bring the value into the acceptable range for subsequent signals originating from that outstation. The method and system are particularly adapted for controlling the temporal position and the amplitude of outstation signals in a TDM passive optical network.

Abstract: A receiver (2) for selectively extracting one of two or more time division multiplexed channels of digital signals, which channel has been scrambled before multiplexing using a predetermined digital sequence comprising: a clock means (4) arranged to provide clock pulses having a repetition rate dependent on a clock control signal; a digital sequence generator (10) triggered by each clock pulse to provide a generator signal representative of the next digit in the predetermined digital sequence; a sampling means (8) arranged to provide a sampled signal at the clock pulse rate; and a phase lock means (8, 18, 25, 26, 22, 4, 10) controlling the clock control signal whereby the generator sequence is delay-lockable to the sampled signal. The receiver finds particular application with the reception of digital video signals broadcast through a passive optical network.

Abstract: A regenerative node for use with scrambled, time domain multiplexed (TDM) data channels has a delay-lock receiver for locking onto a channel scrambled by its associated scramble sequence or a common scramble sequence; a transmitter slaved to the receiver for providing data to be transmitted by the node which has been scrambled by the another node's scramble sequence or any empty channel signal scrambled by the common scramble sequence in phase synchronism with the TDM channel to which the receiver is locked; and a regenerator for regenerating the received TDM channels or the TDM channels with the transmitted data overwriting the delay-locked channel. A node wishing to set up a call searches and delay-locks to a channel having a channel empty sequence scrambled by the common sequence and once delay-locked to it transmits a signal scrambled by the destination nodes sequence.

Abstract: A signal having a non-uniform probability density is processed for transmission in pulse code modulated form. The signal is quantized using conventional methods and the quantized signal is then coded using a non-sequential coding scheme in which binary codewords for the quantization levels are chosen in accordance with the probability of the quantization levels and number of ON bits in the codeword. Quantization levels of higher probability are assigned codewords with fewer ON bits. An optical network includes a central station having a master clock source. The central station is connected to a remote station including a signal processor arranged to process a signal for return transmission to the central station using minimum power codeword assignment.

Abstract: An optical communications network comprises a number of remote stations connected to a node by optical fiber transmission paths interconnected by power dividers, each remote station including an optical transmitter operating at a peak power and a low duty cycle for a short period. Typically the optical transmitter is enabled to transmit information for only 10% or less of the total time and for a maximum of 500 ns.

Abstract: A node of an optical transmission network, for example a local area network, has a combined by-pass switch and optical modulator. The by-pass switch and modulator (45) comprises an optical switching matrix with two non-intersecting waveguides (W1, W2) connected by a further waveguide (W3). The junctions between the non-intersecting waveguides and the further waveguide perform both modulation of an optical carrier signal and re-routeing of the transmission path along the network.