Mesh Restorable Networks with Complete
Dual Failure Restorability and with
Selectvely Enhanced Dual-Failure
Restorability Properties
Matthieu Clouqueur, Wayne D. Grover (presenter)
[email protected], [email protected]
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
Outline
• Background on Dual Failure Restorability
• Ideas and Motivations
• Research Methods
• Experimental Results
• Conclusions and Impacts
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
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
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
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 capacityMatthieu Clouqueur and Wayne D. Grover
expensive
OptiComm 2002 - Boston, MA, July 2002
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Background: Determination of “R2”
Case 1: Two failures but no spatial interactions
 no outage
Case 2: Two failures and spatial interactions (competition for spare
capacity)
 may be outage
Case 3: Two failures with second failure hitting the first restoration
 may be outage
pathset
Case 4: Two failures isolating a degree-2 node
 certain outage
-> Use computer emulation of all dual failure pairs to analyze R2
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
Prior Finding of High Dual-failure Restorability in Networks
Designed for Single Failure Protection / Restoration ...
100 %
Between 50 %
and
99 % R2(i j) on
individual
scenarios
R1
(Single failure restorability)
70 % to
90 % network
average R2
R2
(Dual failure restorability)
Non-modular
R2 Results
for 5 test networks:
Modular
environment
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
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
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 ?
“Platinum
service class” =
assured dualfailure
restorability
new
gold
silver
bronze
Dual-failure
restorable
service class
Existing QoP
paradigm
(economy)
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
Methods to Investigate these Questions
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
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
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 nonsimultaneous failure scenarios implicit in all cases
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
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
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
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)
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
Results with DFMC (Cost for R2=1 by design)
• BENCHMARK: Cost of designing for full dual-failure restorability
Network
Nodal deg.
R2
Redundancy
Total 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 %
Large
capacity
increases
are
required to
provide
strictly
100% R2
– 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)
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
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”
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
Results with MRCP
(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 =1
restorability for a small or negligible capacity increase
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
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 R1designed 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...
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Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002
A Key Insight: why priority services in a “mesh-restorable”
will network get better than 1+1 APS availability
“1F-P 2F-R” mesh (for a priority path)
1+1 APS
Normal
Normal
First failure
-> protection
First failure
-> protection
Second
failure ->
outage
Second failure
R2(ij) =0
no outage yet
-> restoration !
(adaptive)
“Takes a licking and keeps on ticking” :-)
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R2(ij) >0
Matthieu Clouqueur and Wayne D. Grover
OptiComm 2002 - Boston, MA, July 2002