A data communications system has a plurality of nodes connected by a plurality of links. A subset of the links and nodes forms a worker path for carrying worker data through the communications system, and a further subset of links and nodes provides a protection path for carrying other data in the absence of a fault in the worker path and for providing an alternative path for the worker data in the event of a fault in the worker path. The alternative path is predetermined prior to the detection of a fault in the worker path.