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.