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

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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

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© TRLabs / University of Alberta and Siemens AG, CT IC 2 ON, Dominic Schupke, 2004-06-22

Outline

• Introduction

• The p-Cycle Concept

• p-Cycles and Dual Failures

• Network Design

• Results

• Conclusions

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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

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The p-Cycle Concept

A p-cycle in a mesh network:

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The p-Cycle Concept

On-cycle link failure:

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The p-Cycle Concept

Straddling link failure:

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Straddling link

Path 1

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The p-Cycle Concept

Straddling link failure:

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Path 2

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Assumptions on Dual Failures

• Dual failure scenarios:

• Assumption: t1 + t1,rec. < t2

• p-Cycles: trec. ~ 50 ms

t1 t1+t1,rec. t2

First (span)failure

Recovery fromfirst failure

Second failure

t2+t2,rec. t2+t2,rep.t1+t1,rep.

Recoveryfrom second failure (if possible)

Repair offirst failure

Repair ofsecond failure

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Static p-Cycles and Dual Failures

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No recovery for B-C from second failure

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p-Cycle B

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Recovery from second failure

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t2

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p-Cycle B

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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 to s (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)

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Reconfigurable p-Cycles and Dual Failures

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t1

Vulnerableprotectioncapacity

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t1

Vulnerableworkingcapacity

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t1

p-Cycle formed- after t1

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Recovery from second failure

t1

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p-Cycle formed- after t1 and

- before t2

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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

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Network Design

p-Cycle design

Static p-cycles

No R2 optimization R2 optimization

Protect vulnerableworking capacity only

Protect anyvulnerable capacity

Protect vulnerableprotection capacity only

After first failure

Reconfigurable p-cycles

No R2 optimization R2 optimization

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COST239 Case Study Network

• Hypothetical pan-Europeanoptical network ofCOST239 project

• Traffic matrix modifiedto lightpath entries

• Average nodal degree: dav = 4.7

• Three-connected(connected after anydual span failure)

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0 2 4

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Results for Static p-Cycles

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0.5 0.6 0.7 0.8 0.9 1 Dual failure Restorability

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Reconfiguration

σmax=4

σmax=13

σmax=9

smaller σmax

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Results for Reconfigurable p-Cycles

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ic ReconfigurationR2=100%

Vulnerable workingcapacity protected only

Fraction of p-cycleschangeable in form

Only additional p-cycles

100% 5% 0%

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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

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

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