matthieu clouqueur, wayne d. grover (presenter) clouqueur@trlabs, grover@trlabs

Mesh Restorable Networks with Mesh Restorable Networks with Complete Dual Failure Restorability Complete Dual Failure Restorability and with Selectvely Enhanced Dual-and with Selectvely Enhanced Dual-

Failure Restorability PropertiesFailure Restorability Properties

Matthieu Clouqueur, Wayne D. Grover Matthieu Clouqueur, Wayne D. Grover (presenter)(presenter)

[email protected], [email protected]@trlabs.ca, [email protected]

TRTRLabsLabs and University of Alberta and University of Alberta

Edmonton, AB, CanadaEdmonton, AB, Canada

web site for other related papers: web site for other related papers: www.ee.ualberta.ca/~groverwww.ee.ualberta.ca/~grover

OptiComm 2002OptiComm 2002Boston, MA, USABoston, MA, USA

30/July/200230/July/2002

Matthieu Clouqueur and Wayne D. GroverOptiComm 2002 - Boston, MA, July 20022

OutlineOutline

• Background on Dual Failure Restorability

• Ideas and Motivations

• Research Methods

• Experimental Results

• Conclusions and Impacts


Dual Failures - Really ?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


Background Background re: Dual Failure Restorabilityre: 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


Background: Determination of “R2”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


Prior Finding of High Dual-failure Restorability in Prior Finding of High Dual-failure Restorability in Networks Designed for Single Failure Protection / Networks Designed for Single Failure Protection / Restoration ...Restoration ...

100 %

R1

(Single failure restorability)R2

(Dual failure restorability)

Between 50 % and

99 % R2(i j) on individual scenarios

Non-modular

environment

Modular

Environment

Static behavior 0.53 to 0.75 0.69 to 0.83

First-failure adaptive 0.55 to 0.79 0.87 to 0.91

Fully-adaptive 0.55 to 0.80 0.91 to 0.99

R2 Results for 5 test networks:

70 % to 90 % network

average R2


Research QuestionsResearch 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

newDual-failure restorable service class

“Platinum service class” = assured dual-failure restorability


Three Design Models :

• Dual Failure Minimum Capacity (DFMC): Finds the minimum capacity assignment for full restorability

to dual-failures (R2=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 QuestionsMethods to Investigate these Questions


Complete Dual Failure Restorability at Complete Dual Failure Restorability at Minimum Capacity (DFMC)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


Dual Failure Maximum Restorability at Dual Failure Maximum Restorability at Given Capacity (DFMR)Given Capacity (DFMR)

Minimize:

Total No. of Un-restorable WorkingChannels 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


Multi-service Restorability Design at Multi-service Restorability Design at Minimum Capacity (MRCP)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)


Results with DFMC Results with DFMC (Cost for R2=1 by (Cost for R2=1 by design)design)

• BENCHMARK: Cost of designing for full dual-failure restorability

Network Nodal deg.R2

RedundancyTotal Cap.

Increase / R1

6n14s1 4.67 116.8 % 50.5 %

11n20s1 3.63 258.9 % 87.3 %

11n20s2 3.63 161.3 % 77.1 %

12n18s1 3 268.6 % 84.5 %

12n24s1 4 145.9 % 65.7 %

16n26s1 3.25 248.2 % 94.7 %

– Interpretation: Although average dual-failure restorability levels are quite high with a R1 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


Results with DFMR Results with DFMR (Acheivable R2 vs. (Acheivable R2 vs. Cost)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”


Results with MRCP Results with MRCP (MultiRestorability Service Class Design)(MultiRestorability Service Class Design)

• Results of MRCP confirm that R2 restorability can be guaranteed end to end for selected service paths:

Up to about 20% of demands can be guaranteed R2 =1restorability for a small or negligible capacity increase


Concluding Insights and CommentsConcluding 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...


A Key Insight: A Key Insight: why priority services in a “mesh-why priority services in a “mesh-restorable” will network get restorable” will network get better thanbetter than 1+1 APS 1+1 APS availabilityavailability

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” :-)

matthieu clouqueur, wayne d. grover (presenter) clouqueur@trlabs, grover@trlabs

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