Strategies for Enhanced Dual Failure Restorability with Static or Reconfigurable p -Cycle Networks

1. Strategies for EnhancedDual Failure Restorabilitywith Static or Reconfigurablep-Cycle Networks International Conference on Communications (ICC)Paris, France - June 22, 2004 Dominic A. Schupke*Siemens AG, Corporate TechnologyOtto-Hahn-Ring 6, 81730 Munich, GermanyE-mail: Wayne D. Grover, Matthieu ClouqueurTRLabs and University of Alberta7th Floor, 9107 116 St NW, Edmonton, Alberta, Canada T6G 2V4E-mail: {grover,clouqueur}@trlabs.ca *Results from work at Technische Universität München and TRLabs

2. Outline • Introduction • The p-Cycle Concept • p-Cycles and Dual Failures • Network Design • Results • Conclusions

3. Introduction Preconfigured protection cycles (“p-cycles”): • Applicable in many kinds of networks • High capacity-efficiency • Fast protection switching times • For span-protection:100% restorability against any single span failure Our focus: • Provide enhanced or optimized levelof dual-failure restorability • Static and reconfigurable p-cycles

4. A p-cycle in a mesh network: The p-Cycle Concept A B C E D

5. On-cycle link failure: The p-Cycle Concept A B C E D

6. Straddling link failure: The p-Cycle Concept A Straddling link B C Path 1 E D

7. Straddling link failure: The p-Cycle Concept A Path 2 B C E D

8. Assumptions on Dual Failures • Dual failure scenarios: • Assumption: t1 + t1,rec.< t2 • p-Cycles: trec. ~ 50 ms t1 t1+t1,rec. t2 t2+t2,rec. t1+t1,rep. t2+t2,rep. Recovery fromfirst failure Repair offirst failure Repair ofsecond failure Recoveryfrom second failure (if possible) Second failure First (span)failure

9. Static p-Cycles and Dual Failures t1 A B C E D

10. Static p-Cycles and Dual Failures t1 A t2 B C E D No recovery for B-C from second failure

11. Static p-Cycles and Dual Failures t1 A B p-Cycle A C p-Cycle B E D

12. Static p-Cycles and Dual Failures t1 A B p-Cycle A C t2 p-Cycle B E D Recovery from second failure

13. Susceptibility Concept • p-Cycle susceptible to a dual failure combination:Both failures affect working spans protected by it • p-Cycle protects s working spans Susceptible tos (s-1) failure events • Susceptibility s per p-cycle not larger than given σmax • Restrict when selecting eligible p-cycles for design Other approach: • Failure dispersal concept (see paper)

14. Reconfigurable p-Cycles and Dual Failures t1 A B C E D

15. Reconfigurable p-Cycles and Dual Failures t1 A B C Vulnerableprotectioncapacity E D

16. Reconfigurable p-Cycles and Dual Failures t1 A B C Vulnerableworkingcapacity E D

17. Reconfigurable p-Cycles and Dual Failures t1 A B C • p-Cycle formed • after t1 E D

18. Reconfigurable p-Cycles and Dual Failures t1 A t2 B C • p-Cycle formed • after t1 and • before t2 E D Recovery from second failure

19. Network Design Cost-optimal design: • Length-weighted utilization of network Single-failure restorability: • 100% restorability guaranteed Dual-failure restorability: • R(i,j): Restorable fraction of affected working capacity after dual failure of spans i and j • R2: Average over all dual failure cases

20. Network Design

21. Hypothetical pan-Europeanoptical network ofCOST239 project Traffic matrix modifiedto lightpath entries Average nodal degree: dav= 4.7 Three-connected(connected after anydual span failure) COST239 Case Study Network

22. Results for Static p-Cycles Reconfiguration 0.9 =4 σ max 0.8 0.7 0.6 0.5 smaller Additional Relative Spare Capacity Cost σ 0.4 max 0.3 =9 σ 0.2 max 0.1 =13 σ max 0 0.5 0.6 0.7 0.8 0.9 1 Dualfailure Restorability

23. Results for Reconfigurable p-Cycles 3 Vulnerable workingcapacity protected only Only additional p-cycles 2.5 2 Relative Spare Capacity Cost 1.5 Fraction of p-cycleschangeable in form 100% 5% 0% 1 ReconfigurationR2=100% Static 0.5 0

24. Conclusions Capacity design methods: • Static p-cycles: • Improved dual-failure restorability • Susceptibility viable approach to control restorability • Reconfigurable p-cycles: • Complete dual-failure restorability • Different operational options Outlook: • Reconfigurable p-cycles in networks designed for single-failure restorability only • Multiple protection classes