Protection & Restoration of Optical Networks

1. Protection & Restoration of Optical Networks CSE 8344

2. 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 CSE 8344

3. Classification of Schemes CSE 8344

4. 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 CSE 8344

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

6. Dedicated vs. Multiplexed Backup • Dedicated backup • More robust • Less efficient. • Backup multiplexing • Less robust • More efficient. CSE 8344

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

8. 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 CSE 8344

9. 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. CSE 8344

10. 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. CSE 8344

11. 2-Fiber WDM Ring CSE 8344

12. 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. CSE 8344

13. 4-Fiber WDM Ring. CSE 8344

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

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

16. 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 CSE 8344

17. 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. CSE 8344

18. 2X2 Switch CSE 8344

19. 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 CSE 8344

20. Protection Cycles CSE 8344

21. Protection Cycles (cont’d) CSE 8344

22. Network With Default Protection Switching CSE 8344

23. Network After a Link Failure CSE 8344

24. 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. CSE 8344

25. 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. CSE 8344

26. P - cycles CSE 8344

27. 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. CSE 8344

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

29. PANEL: Protection Across Network Layers CSE 8344

30. 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 CSE 8344