1. Mesh Restorable Networks with Complete Dual Failure Restorability and with Selectvely Enhanced Dual-Failure Restorability Properties Matthieu Clouqueur, Wayne D. Grover (presenter) clouqueur@trlabs.ca, grover@trlabs.ca TRLabs and University of Alberta Edmonton, AB, Canada web site for other related papers: www.ee.ualberta.ca/~grover OptiComm 2002 Boston, MA, USA 30/July/2002

2. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 2 Outline Background on Dual Failure Restorability Ideas and Motivations Research Methods Experimental Results Conclusions and Impacts

3. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 3 Dual Failures - Really ? Not as “academic” a consideration as we first thought: Sheer fiber route miles –Hermes RailTel estimate of one one cable cut /4 days Span maintenance and upgrade effects –can be much like a first failure in network equivalent effects Span SRLG and nodal bypass effects –cause logical dual failures Availability of paths through single-failure restorable networks: –unavailability doesn’t just vanish... Becomes limited by dual failures

4. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 4 Background re: Dual Failure Restorability Prior work on dual failure restorability analysis of span-restorable mesh networks: (refs: DRCN 01, JSAC 02) –concept of “first failure protection, second failure restoration” (pre-planned reaction) (adaptive reaction) –method for dual failure restorability analysis Some key findings: –1) Span restorable (or “link-protected”) mesh networks designed for R1 = 100%, give very high average R2 values as a side-effect ! –2) Service path availability has far more to do with restorability to dual failures, not the speed of response to a single failure –and …3) Explicit design for R2=100% is very capacity- expensive

5. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 5 Background: Determination of “R2” Case 1: Two failures but no spatial interactions Case 2: Two failures and spatial interactions (competition for spare capacity) Case 3: Two failures with second failure hitting the first restoration pathset Case 4: Two failures isolating a degree-2 node  no outage  may be outage  certain outage  may be outage -> Use computer emulation of all dual failure pairs to analyze R2

6. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 6 Prior Finding of High Dual-failure Restorability in Networks Designed for Single Failure Protection / Restoration... 100 % R 1 (Single failure restorability) R 2 (Dual failure restorability) Between 50 % and 99 % R2(i j) on individual scenarios Non-modular environment Modular Environment Static behavior0.53 to 0.750.69 to 0.83 First-failure adaptive0.55 to 0.790.87 to 0.91 Fully-adaptive0.55 to 0.800.91 to 0.99 R 2 Results for 5 test networks : 70 % to 90 % network average R2

7. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 7 Research Questions Is it possible to enhance the dual span-failure restorability of an R1=1 network design: –purely by a redistribution of the spare capacity ? –to maximize R2 subject to a given budget limit ? Can we structure or allocate the finite R2 levels that are obtained to support a super-high availability service class ? gold silver bronze (economy) Existing QoP paradigm new Dual-failure restorable service class “Platinum service class” = assured dual- failure restorability

8. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 8 Three Design Models : Dual Failure Minimum Capacity (DFMC): Finds the minimum capacity assignment for full restorability to dual-failures (R 2 =100%) Dual Failure Max Restorability (DFMR) Finds the spare capacity placement that maximizes the average restorability to dual-failures for a given spare capacity budget Multi-service Restorability Capacity Placement (MRCP) Finds the minimum capacity assignment and routing that serves demands of multiple service classes including R0 (best-effort), R1 and R2-assured restorability service classes Methods to Investigate these Questions

9. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 9 Complete Dual Failure Restorability at Minimum Capacity (DFMC) Minimize: Total Cost of Capacity Subject to: (1) All demands are routed (2) Working capacity supports (1) (3) Restoration flows for 100% span restoration in the presence of each other span failure (4) Spare capacity to support (3) Note: This is with spare capacity reuse / sharing across non- simultaneous failure scenarios implicit in all cases

10. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 10 Dual Failure Maximum Restorability at Given Capacity (DFMR) Minimize: Total No. of Un-restorable Working Channels over all dual failure scenarios subject to: (1) All demands are routed (2) Working capacity supports (1) (3) Spare capacity less than an allowed Budget (4) Restoration flows as feasible under (4) for all span failures in the presence of each other span failure

11. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 11 Multi-service Restorability Design at Minimum Capacity (MRCP) Define: “R1”, “R2” (and also “R0”)-restorable service demand matrices Minimize: Total Capacity subject to: (1) All demands are routed, (2) Working capacity supports (1) (3) Restoration flows for all dual span failure scenarios for “R2” demands (4) Restoration flows for all single span failures for all “R1” demands (5) Spare capacity to support (3) and (4)

12. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 12 Results with DFMC (Cost for R2=1 by design) BENCHMARK: Cost of designing for full dual-failure restorability –Interpretation: Although average dual-failure restorability levels are quite high with a R 1 design, the capacity cost for making the network restorable to all dual failures is extremely high, (~ 3 x in spare capacity relative to R1=1 design) Large capacity increases are required to provide strictly 100% R2

13. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 13 Results with DFMR (Acheivable R2 vs. Cost) Trade-off between capacity and best acheivable dual-failure restorability: high capacity requirement as R2 =1 is approached (confirms DFMC results) Pure Redistribution of capacity “Budget amount”

14. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 14 Results with MRCP (MultiRestorability Service Class Design) Results of MRCP confirm that R 2 restorability can be guaranteed end to end for selected service paths: Up to about 20% of demands can be guaranteed R 2 =1 restorability for a small or negligible capacity increase

15. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 15 Concluding Insights and Comments Designing for 100% Dual-failure restorability is feasible but very expensive DFMR design method can maximize the network average dual failure restorability (R2) given any total budget for capacity. MRCP design can structure and enhance the R2 ability of an R1- designed network onto specific priority paths: –20 to 40% of all demands per O-D pair could be in this “platinum” service class at very little or no extra capacity cost. And note ! Such R2-restorable service paths will have availability that exceeds that of 1+1 APS...

16. Matthieu Clouqueur and Wayne D. Grover OptiComm 2002 - Boston, MA, July 2002 16 A Key Insight: why priority services in a “mesh-restorable” will network get better than 1+1 APS availability 1+1 APS “1F-P 2F-R” mesh (for a priority path) Normal First failure -> protection Second failure -> outage R2(ij) =0 Normal First failure -> protection Second failure -> restoration ! (adaptive) no outage yet R2(ij) >0 “Takes a licking and keeps on ticking” :-)