1. SMUCSE 8344 Protection & Restoration of Optical Networks

2. SMUCSE 8344 Terminology Protection –Uses pre-assigned capacity to ensure survivability Restoration –Reroutes the affected traffic after failure occurrence by using available capacity Survivability –Property of a network to be resilient to failures

3. SMUCSE 8344 Classification of Schemes

4. SMUCSE 8344 Reactive / Proactive Reactive –When an existing lightpath fails, a search is initiated to find a new lightpath which does not use the failed components. (After the failure happens) –It cannot guarantee successful recovery, –Longer restoration time Proactive –Backup lightpaths are identified and resources are reserved along the backup lightpaths at the time of establishing the primary lightpath itself. –100% restoration guarantee –Faster recovery

5. SMUCSE 8344 Link Based vs. Path Based Link-based –Shorter restoration time –Less efficient. –Can only fix link failures Path-based –longer restoration time –More efficient.

6. SMUCSE 8344 Dedicated vs. Multiplexed Backup Dedicated backup –More robust –Less efficient. Backup multiplexing –Less robust –More efficient.

7. SMUCSE 8344 Primary Backup MUX Wavelength channel to be shared by a primary and one or more backup paths

8. SMUCSE 8344 Resilience in Optical Networks Linear Systems –1+1 protection –1:1 protection –1:N protection Ring-based –UPSR: Uni-directional Path Switched Rings –BLSR: Bi-directional Line Switched Rings Mesh-based –Optical mesh networks connected by optical cross- connects (OXCs) or optical add/drop multiplexers (OADMs) –Link-based/path-based protection/restoration Hybrid Mesh Rings –Physical: mesh –Logical: ring

9. SMUCSE 8344 Unidirectional WDM Path Protected Rings 1+1 wavelength path selection Signal bridged on both protection and working fiber. Receiver chooses the better signal. Failure: –Destination switches to the operational link. –Revertive /Non revertive switching –No signaling required.

10. SMUCSE 8344 Bidirectional Line switched Ring Shares protection capacity among all the spans on the ring Link failure –Working traffic from 1 fiber looped back onto opposite direction. –Signaling protocol required Node failure –Line switching performed at both sides of the failed node.

11. SMUCSE 8344 2-Fiber WDM Ring

12. SMUCSE 8344 BLSR - 4 Fiber Fibers –2 working –2 protection Protection fiber: no traffic unless failure. Link Failure. –APS channel required to coordinate the switching at both ends of a failure.

13. SMUCSE 8344 4-Fiber WDM Ring.

14. SMUCSE 8344 4-Fiber WDM Ring After a Link Failure

15. SMUCSE 8344 4-Fiber WDM Ring After a Node Failure

16. SMUCSE 8344 Path Layer Mesh Protection Protect Mesh as a single unit Pre-computed routes –1+1 path protection –Protection route per light path –Protection route per failure. On the fly route computation. –Centralized route computation and coordination –Route computation and coordination at end nodes. –Distributed route computation at path ends. Decompose into protection domains. Pure rings P cycles

17. SMUCSE 8344 Mesh Topologies Fibers organized in protection cycles. –Computed offline 4 fibers of each link is terminated by 4 2X2 protection switches Before link failure, switches in normal position. After failure, switches moved to protection state and traffic looped back into the protection cycles.

18. SMUCSE 8344 2X2 Switch

19. SMUCSE 8344 Protection Cycles (cont’d) Criterion for protection cycles. –Recovery from a single link failure in any optical network with arbitrary topology and bi-directional fiber links All protection fibers are used exactly once. In any directed cycle both protection fibers in a pair are not used unless they are in a bridge

20. SMUCSE 8344 Protection Cycles

21. SMUCSE 8344 Protection Cycles (cont’d)

22. SMUCSE 8344 Network With Default Protection Switching

23. SMUCSE 8344 Network After a Link Failure

24. SMUCSE 8344 P –cycles Ring like restoration needed for some client signals. Mesh topologies: bandwidth efficient. P –cycles:Ring like speeds, Mesh like capacity. Addresses the speed limitation of mesh restoration.

25. SMUCSE 8344 P –cycles (cont’d) Cycle oriented pre configuration of spare capacity. Can offer up to 2 restoration paths for a failure scenario. Span Failure –On cycle: similar to BLSR –Off the cycle: 2 paths. Time needed for calculating and connecting restoration path is needed in non-real time.

26. SMUCSE 8344 P - cycles

27. SMUCSE 8344 WDM Recovery Fiber based restoration –Entire traffic carried by a fiber is backed by another fiber. –Bi-directional connection - 4 fibers. WDM based recovery –Protection for each wavelength. –Bi-directional connection - 2 fibers –Allows flexibility in planning the configuration of the network. –Recovery procedure similar to BLSR.

28. SMUCSE 8344 Resilience in Multilayer Networks Why resilience in multilayer networks? –Avoid contention between different single-layer recovery schemes. –Promote cooperation and sharing of spare capacity

29. SMUCSE 8344 PANEL: Protection Across Network Layers

30. SMUCSE 8344 PANEL Guidelines Recovery in the highest layer is recommended when: –Multiple reliability grades need to be provided with fine granularity –Recovery inter-working cannot be implemented –Survivability schemes in the highest layer are more mature than in the lowest layer Recovery in the lowest layer is recommended when: –The number of entities to recover has to be limited/reduced –The lowest layer supports multiple client layers and it is appropriate to provide survivability to all services in a homogeneous way –Survivability schemes in the lowest layer are more mature than in the highest layer –It is difficult to ensure the physical diversity of working and backup paths in the higher layer