Abstract: A head-end station for a passive optical network system arranged to transmit and receive TDMA frames having a header portion and a plurality of basic frames, each basic frame includes traffic bits and control bits. The head-end station includes a data transmitter which assembles and transmits downstream frames and also generates a diagnostic signal for transmission in a downstream frame, the station being switchable to a diagnostic mode in which it transmits the diagnostic signal in a downstream frame in the absence of other traffic, and also including a data receiver which receives upstream frames and detects a return of the diagnostic signal. In a preferred example, the head-end station may transmit a diagnostic signal in the header portion of each downstream frame. Also, in a test mode the transmit signal is looped back to the receiver to enable testing of the transmit receive function.

Abstract: An optical fibre communications system includes a head end connected to n customers by an optical fibre network. The head end has a transmitter unit and a receiver unit, and each of the customers has an optical network unit with an optical receiver and a transmitter unit. The head end transmitter and receiver units are connected respectively to the receivers and the transmitter units of the customer optical network units by at least one passive optical network. The head end transmitter unit includes an optical transmitter driven by a sub-carrier multiplexer, the sub-carrier multiplexer having a plurality of input sub-carriers at different frequencies. One of the sub-carriers carries interactive signals provided by a further optical transmitter unit. The remaining sub-carriers carry broadband service signals. Each customer transmitter unit includes an optical transmitter and apparatus for multiplexing interactive signals and control signals to drive the optical transmitter.

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 head-end station for a passive optical network system is arranged to transmit and receive downstream and upstream multiplex data frames. The data frames include a plurality of basic frames, each basic frame including a plurality of traffic bits and a plurality of control bits. The head-end station includes a data receiver having a control processor arranged to receive control data, a control data buffer which provides a parallel data input to the control processor, a traffic interface and a serial-to-parallel converter. The converter receives upstream TDMA multiplexed frames and the parallel output from the converter is connected in parallel to the respective inputs of the control data buffer and the traffic interface. A data transmitter for such a head-end station also includes a control processor, a control buffer and a traffic interface. A parallel-to-serial converter receives the upstream TDMA.

Abstract: A test apparatus is designed for use with a TPON system including a headend station connected via a fibre optic network to a plurality of terminations. The test apparatus is a self-contained unit including a connection for linking the apparatus to a termination, a first detection circuit which detects status signals generated by the termination, and a second detection circuit which detects alarm signals generated in the head-end station and transmitted to the termination in a downstream data frame. The test apparatus in response to the first and second test circuits provides an output which indicates the condition of the termination. In one example, a series of indicator lamps formed on the housing for the test apparatus are lit to provide the appropriate output.

Abstract: A network head-end station (1) is arranged to receive an upstream TDMA frame comprising interleaved optical signals from a plurality of terminations (2) connected to the head-end station (1) by a fibre network (3). The upstream TDMA frame includes a quiet phase during which none of the terminations transmit. The station (1) includes an opto-electronic receiver (4), a DC clamping circuit (10) for the opto-electronic receiver (4) and a clamping pulse generator. The clamping pulse generator is arranged to generate a pulse at a predetermined time falling within the quiet phase to operate the DC clamping circuit to clamp signals received during the remainder of the TDMA frame to a DC reference level received during the quiet phase.

Abstract: A passive optical network includes a head-end station and a plurality of terminations. The terminations are responsive to control signals from the head-end station. The head-end station is arranged to receive frames having a predetermined bit rate and comprising signals transmitted by the terminations. Ranging pulses are transmitted from each of the terminations to the head-end station where the received ranging pulses are sampled at a high sampling rate greater than the predetermined bit rate. The data samples are applied to a processor which determines the phase and amplitude of the ranging pulses and generates control signals for the terminations to modify the phase or timing and amplitude of the transmissions from the terminations. A locally generated marker pulse may be applied to the incoming data frame before it is sampled in the head-end station, the marker pulse providing a phase and amplitude reference for use by the control processor.