An Efficient Strategy for Wavelength Conversion in WDM p -Cycle Networks

An Efficient Strategy for Wavelength Conversionin WDM p-Cycle Networks

Dominic A. Schupke, Matthias C. Scheffel{schupke,scheffel}@lkn.ei.tum.de

Wayne D. Grover{[email protected]}

Fourth International Workshop on the

Design of Reliable Communication Networks

(DRCN 2003)

Munich University of Technology

Institute of Communication Networks

TRLabs &

University of Alberta

21 October 2003

Technische Universität München Institute of Communication NetworksProf. Dr.-Ing J. Eberspächer

Matthias C. ScheffelDRCN 2003

2

Motivation

• WDM transport networks are becoming more “optical”

– Functions realized in optical domain (e.g. switching)– Routing and wavelength assignment (RWA) problem– High wavelength converter cost

Partial wavelength conversion

• Need for reliability against network failures

– Low capacity redundancy– Fast protection

p-Cycle concept



3

Outline

• p-Cycle Concept

• p-Cycles in WDM Networks

– Full wavelength conversion

– No wavelength conversion

– Partial wavelength conversion

• Implementation

• Case Study Scenario

• Results

• Conclusions / Outlook



4

p-Cycle Concept

Description

• Network protection strategy

– Spans

– (Transit nodes, paths)

• p-Cycles

– Preconfigured closed paths

– Reserved capacity

– In mesh network

B E

C

A

Dp-Cycle

Node

Span



5

p-Cycle Concept

Span Protection Mechanism

– On-cycle span

• Span is used by p-cycle

B E

C

A

Dp-Cycle

Protection path

Node

Span

1 protection path



6

p-Cycle Concept

Span Protection Mechanism

– On-cycle span

• Span is used by p-cycle

– Straddling span

• Span’s end nodes lie on p-cycle

• Span is not used by p-cycle

B E

C

A

D

2 protection paths

1 protection path

p-Cycle

Protection path

Node

Span



7

p-Cycles in WDM Networks

Full Wavelength Conversion at Nodes

• Different wavelengths along a path

• Termination of paths at each node

Virtual Wavelength Path VWP

p-Cycle can protect working links

at any wavelength

+ Capacity-efficient protection

– High converter cost

B E

C

A

D

p-Cycle

Working path

Wavelength links

Full conversion

netVWP Approach



8


No Wavelength Conversion at Nodes

• Same wavelength along a path

• No termination along paths

Wavelength Path WP

p-Cycle can protect working links

at same wavelength only

+ No converter cost– More capacity redundancy

B E

C

A

D

p-Cycle

Working path

Wavelength links

No conversion

netWP Approach



9

Partial Wavelength Conversion at Nodes

• Converter Pool with tunable lasers

• Wavelength conversion for some paths

• Termination of some paths

• Idea:

Make p-cycles accessible

for working links at different wavelengths

by providing a small number of converters


B E

C

A

D

Partial conversion



10


A

E

D

C

B

Working paths without conversion

Working WP

p-Cycles without conversion

p-Cycle WP

Converters for p-cycle access


wWP_pWP_accessIfRequired &wWP_pWP_accessFull Approach

• If Required

• Full



11

A

E

D

C

B


p-Cycles with full conversion

p-Cycle VWP

Working paths without conversion

Working WP


(+ straddling span converters)

wWP_pVWP Approach



12

Implementation

Mathematical Programming

Integer linear program (ILP)

• Objective function:

Minimize ( ∑ working path lengths +

∑ p-cycle lengths +

number of converters • converter cost )

• Constraints:

(1) Provide WP working paths to satisfy the demands

(2) Allocate p-cycles to provide protection for any single span failure

(3) Insert converters according to architecture

(4) Use one wavelength at most once per fiber

Joint optimization of working and protection capacity plus total converter cost



13

COST239 Network

• Pan-European

optical core network• 11 nodes, 26 spans• Average nodal degree = 4.7• 1 counterdirectional fiber pair

per span• 32 wavelengths per fiber• Given demands

– Dense matrix– 1 to 11 lightpaths per node

(average = 3.2) – Symmetry modification

Case Study Scenario

Copenhagen

LondonAmsterdam Berlin

Paris

BrusselsLuxembourg

Prague

Vienna

Zurich

Milan



14

Results

Total Cost Comparison

200000

300000

400000

500000

600000

700000

800000

900000

1000000

1100000

0 100 200 300 400 500 600

Converter cost (in link-km)

To

tal

cost

(in

lin

k-km

)

netWP

wWP_pVWP

wWP_pWP_accessFull

wWP_pWP_accessIfRequired

netVWP_fullyEquipped

netVWP_partiallyEquipped

fullyEquipped = converters for any available wavelength

partiallyEquipped = converters for used wavelengths only



15

Results

Capacity-Efficiency Evaluation

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 100 200 300 400 500 600


Cap

acit

y-ef

fici

ency

netWP

wWP_pVWP

wWP_pWP_accessFull

wWP_pWP_accessIfRequired

netVWP

Capacity-efficiency =protection capacity

working capacity



16

Results

Wavelength Converter Allocation

0200400600800

10001200140016001800

0 100 200 300 400 500 600


Nu

mb

er o

f co

nve

rter

s

netWPwWP_pVWPwWP_pWP_accessFullwWP_pWP_accessIfRequirednetVWP_fullyEquippednetVWP_partiallyEquipped



17

Conclusions / Outlook

• Conclusions:

p-Cycle configurations

in WDM networks with partial wavelength conversion

can reduce the total network cost

– Capacity-efficient protection• Small amount of redundant capacity• More flexibility towards changing demand patterns

– Small number of converters

• Outlook:

Performance evaluation of online routing and protection



18

Comparison of p-Cycle Configurations

netVWP

wWP_

pWP_

accessIf

Required

wWP_

pWP_

access

Full

wWP_

pVWPnetWP

Protection efficiency

highest high very high high very low

Converters most very few few more no

Tunable lasers required

no yes yes yes n/a

Termination of protection paths

yes some yes yes no

Wavelength flexibility

highest low high higher n/a

An Efficient Strategy for Wavelength Conversion in WDM p -Cycle Networks

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