Adding new alternative paths for restoration in WSON network

1. A network management system for managing pre-planned alternative paths in a wavelength switched optical network having a number of nodes and the network management system having:

an input for receiving an indication of a fault affecting a traffic flow, the traffic flow having a working path and two or more pre-planned alternative paths from a source node to a destination node,

a processing part arranged to determine if, after the fault, a number of available alternative paths for the respective traffic flow drops to a threshold, the threshold being at least one, and if so, to determine a new alternative path through the network for the respective traffic flow from the same source node to the same destination node, and

a path set up part arranged to communicate with the nodes along the new alternative path to 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.

2. The network management system of claim 1 , the pre-planned alternative paths comprising any one or more of optically switched shared transponder paths and electrically switched automatic protection paths, and the determination of the number of available alternative paths comprises determination of a number of the protection paths which are active and not alarmed, and a number of the optically switched shared transponder paths which are not yet used.

3. The network management system of claim 1 , at least one of the pre-planned alternative paths adapted to use of a different transponder at the source node to that used by the working path, and the processing part being arranged to determine whether the new alternative path shares the transponder used by the working path or shares the different transponder, so as to provide available alternative paths using two or more different transponders.

4. The network management system of claim 1 , the threshold being one.

5. The network management system of claim 1 , having an internal path computation element for carrying out the determining of the new alternative path.

6. The network management system of claim 1 , being centralized at a single location.

7. The network management system of claim 1 , the path set up part being arranged to set up the new alternative path so that the movement of the traffic flow onto the new alternative path is left under control of the source node, by means of optical switches at nodes along the path where the new alternative path respectively diverges from, and rejoins, a path previously carrying the traffic flow.

8. The network management system of claim 1 , the path set up part being arranged to cause the nodes to remove an existing alternative path if it is no longer available, to free the resources reserved for that path.

9. The network management system of claim 1 , at least some of the nodes having a wavelength conversion capability, and the determination of the new alternative path involving the assignment of a different wavelength for some or all of the path compared to wavelengths used for the pre-planned alternative paths.

10. A method of managing pre-planned alternative paths in a wavelength switched optical network having a number of nodes, the method having the steps of:

receiving an indication of a fault affecting a traffic flow, the traffic flow having a working path and a number of pre-planned alternative paths from a source node to a destination node,

determining if a number of available pre-planned alternative paths for the respective traffic flow drops to a threshold, the threshold being at least one,

if the threshold is reached, determining a new alternative path through the nodes of the network for the respective traffic flow from the same source node to the same destination node, and

setting up the new alternative path in the nodes, to enable one or more of them to move the traffic flow onto the new alternative path in the event of further faults.

11. The method of claim 10 , the pre-planned alternative paths comprising any one or more of optically switched shared transponder paths and electrically switched automatic protection paths, and the determining of the number of available alternative paths comprises determining a number of the protection paths which are active and not alarmed, and a number of the optically switched shared transponder paths which are not yet used.

12. The method of claim 10 , at least one of the pre-planned alternative paths making use of a different transponder at the source node to that used by the working path, and the step of determining the new alternative path comprises determining whether to share the transponder used by the working path or to share the different transponder, so as to provide available alternative paths using two or more different transponders.

13. The method of claim 10 , the threshold being one.

14. The method of claim 10 , the step of determining the new alternative path comprising causing an external path computation element to compute the new alternative path from a source node to a destination node.

15. The method of claim 10 , the setting up step comprising setting up the new alternative path so that the moving of the traffic flow onto the new alternative path is left under control of the source node, by means of optical switches at nodes along the path where the new alternative path respectively diverges from, and rejoins, a path previously carrying the traffic flow.

16. The method of claim 10 , the path set up step comprising reserving resources at the nodes and setting a route status as not used.

17. The method of claim 10 , having the step of causing the nodes to remove an existing alternative path if it is no longer available, to free the resources reserved for that path.

18. A non-transitory computer readable storage medium storing instructions for managing pre-planned alternative paths in a wavelength switched optical network having a number of nodes, the instructions when executed by a set of processors cause the set of processors to:

receive an indication of a fault affecting a traffic flow, the traffic flow having a working path and a number of pre-planned alternative paths from a source node to a destination node;

determine if a number of available pre-planned alternative paths for the respective traffic flow drops to a threshold, the threshold being at least one;

if the threshold is reached, determine a new alternative path through the nodes of the network for the respective traffic flow from the same source node to the same destination node; and

set up the new alternative path in the nodes, to enable one or more of them to move the traffic flow onto the new alternative path in the event of further faults.

19. The non-transitory computer readable storage medium of claim 18 , the pre-planned alternative paths comprising any one or more of optically switched shared transponder paths and electrically switched automatic protection paths; and

the instructions that cause determining of the number of available alternative paths further comprise instructions that when executed by a set of processors cause determining a number of the protection paths which are active and not alarmed, and a number of the optically switched shared transponder paths which are not yet used.

20. The non-transitory computer readable storage medium of claim 18 , at least one of the pre-planned alternative paths making use of a different transponder at the source node to that used by the working path, and the instructions that cause determining the new alternative path further comprise instructions that when executed by a set of processors cause the set of processors to determine whether to share the transponder used by the working path or to share the different transponder, so as to provide available alternative paths using two or more different transponders.

21. The non-transitory computer readable storage medium of claim 18 , the threshold being one.

22. The non-transitory computer readable storage medium of claim 18 , the instructions that cause determining the new alternative path further comprising instructions that when executed by a set of processors cause an external path computation element to compute the new alternative path from a source node to a destination node.

23. The non-transitory computer readable storage medium of claim 18 , the instructions that cause setting up further comprising instructions that when executed by a set of processors cause setting up the new alternative path so that the moving of the traffic flow onto the new alternative path is left under control of the source node, by means of optical switches at nodes along the path where the new alternative path respectively diverges from, and rejoins, a path previously carrying the traffic flow.

24. The non-transitory computer readable storage medium of claim 18 , the instructions that cause path set up further comprising instructions that when executed by a set of processors cause reserving resources at the nodes and setting a route status as not used.

25. The non-transitory computer readable storage medium of claim 18 , further storing instructions that when executed by a set of processors cause the nodes to remove an existing alternative path if it is no longer available, to free the resources reserved for that path.