Patent ID: 8818201

Claim:
A method of operating an optical communications system, the system comprising: a distribution network connected to a plurality of terminals; a main network arm with a main head-end unit for communicating with the plurality of terminals in an operational state via the distribution network; a back-up network arm with a back-up head-end unit arranged to allow communication with the plurality of terminals via the distribution network in the event that the main network arm is faulty, the main and back-up network arms having respectively a main repeater and a back-up repeater, at least the back-up repeater being responsive to signals from the back-up head-end unit so that the back-up repeater can be ranged; and the main repeater and the back-up repeater being equidistant from the distribution network; the method comprising: (a) performing a ranging procedure at the head-end unit so as to acquire synchronisation information for scheduling of transmissions from the plurality of terminals; wherein the main head-end unit is located at a first location and the back up head-end unit is located at a second location and that the method further comprises: (b) performing a ranging procedure at the back-up head-end unit in order to acquire synchronisation information in respect of the back-up repeater; (c) if the main network arm is detected to be faulty, using at least part of the synchronisation information acquired in (a) together with the synchronisation information acquired in (b) to schedule transmissions from the plurality of terminals to the back up head-end unit.