Adding new alternative paths for restoration in wson network

Abstract

A network management system manages preplanned alternative paths in a wavelength switched optical network for a traffic flow having a working path and two or more preplanned alternative paths from a source node to a destination node. A processing part determines if, after the fault, a number of available alternative paths for the respective traffic flow drops to a threshold. If so, a new alternative path is calculated and set up the new alternative path in the nodes, to enable one or more of the nodes to move the traffic flow onto the new alternative path in the event of further faults without waiting for input from the network management system. Thus multiple faults can be handled without the nodes needing to store details of so many such alternative paths. Otherwise, many such alternative paths are needed to take account of many different possible failure locations.