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					                                    Fourth International Workshop on the
                                 Design of Reliable Communication Networks
                                                 (DRCN 2003)


                           21 October 2003


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

Dominic A. Schupke, Matthias C. Scheffel           Wayne D. Grover
       {schupke,scheffel}@lkn.ei.tum.de              {grover@trlabs.ca}




      Munich University of Technology                  TRLabs &
    Institute of Communication Networks           University of Alberta
                                        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




  Technische Universität München
  Institute of Communication Networks                     Matthias C. Scheffel
                                             2
  Prof. Dr.-Ing J. Eberspächer                                    DRCN 2003
                                       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


 Technische Universität München
 Institute of Communication Networks             Matthias C. Scheffel
                                           3
 Prof. Dr.-Ing J. Eberspächer                            DRCN 2003
                                          p-Cycle Concept

Description
•    Network protection strategy
      – Spans
      – (Transit nodes, paths)
•    p-Cycles
      – Preconfigured closed paths
      – Reserved capacity
      – In mesh network

              B                                 E
                                                            Node
                                                            Span
                                 C
                                                            p-Cycle
                                            D
            A
    Technische Universität München
    Institute of Communication Networks                            Matthias C. Scheffel
                                                    4
    Prof. Dr.-Ing J. Eberspächer                                           DRCN 2003
                                        p-Cycle Concept

Span Protection Mechanism
– On-cycle span                                        1 protection path
   • Span is used by p-cycle




           B                                  E
                                                             Node
                                                             Span
                              C
                                                              p-Cycle
                                         D
                                                             Protection path
         A

  Technische Universität München
  Institute of Communication Networks                               Matthias C. Scheffel
                                                  5
  Prof. Dr.-Ing J. Eberspächer                                              DRCN 2003
                                        p-Cycle Concept

Span Protection Mechanism
– On-cycle span                                        1 protection path
   • Span is used by p-cycle

– Straddling span                                      2 protection paths
   • Span’s end nodes lie on p-cycle
   • Span is not used by p-cycle



           B                                  E
                                                             Node
                                                             Span
                              C
                                                              p-Cycle
                                         D                   Protection path
         A

  Technische Universität München
  Institute of Communication Networks                               Matthias C. Scheffel
                                                  6
  Prof. Dr.-Ing J. Eberspächer                                              DRCN 2003
                            p-Cycles in WDM Networks

Full Wavelength Conversion at Nodes

    netVWP Approach
                                              B                         E
•    Different wavelengths along a path

•    Termination of paths at each node             C
                                                             D
 Virtual Wavelength Path VWP
                                              A

 p-Cycle can protect working links
  at any wavelength                                Full conversion
                                                   p-Cycle
+ Capacity-efficient protection                    Working path
– High converter cost
                                                   Wavelength links


    Technische Universität München
    Institute of Communication Networks                 Matthias C. Scheffel
                                          7
    Prof. Dr.-Ing J. Eberspächer                                DRCN 2003
                            p-Cycles in WDM Networks

No Wavelength Conversion at Nodes

    netWP Approach
                                              B                         E
•    Same wavelength along a path

•    No termination along paths                    C
                                                              D
 Wavelength Path WP
                                              A

 p-Cycle can protect working links
  at same wavelength only                          No conversion
                                                   p-Cycle
+ No converter cost                                Working path
– More capacity redundancy
                                                   Wavelength links


    Technische Universität München
    Institute of Communication Networks                 Matthias C. Scheffel
                                          8
    Prof. Dr.-Ing J. Eberspächer                                DRCN 2003
                            p-Cycles in WDM Networks

Partial Wavelength Conversion at Nodes


•    Converter Pool with tunable lasers       B                              E

•    Wavelength conversion for some paths
                                                       C
•    Termination of some paths                                     D
                                              A

•    Idea:                                             Partial conversion
     Make p-cycles accessible
     for working links at different wavelengths
     by providing a small number of converters



    Technische Universität München
    Institute of Communication Networks                    Matthias C. Scheffel
                                          9
    Prof. Dr.-Ing J. Eberspächer                                   DRCN 2003
                      p-Cycles in WDM Networks
Partial Wavelength Conversion at Nodes
wWP_pWP_accessIfRequired &
wWP_pWP_accessFull Approach


p-Cycles without conversion
p-Cycle WP


Converters for p-cycle access
• If Required
• Full                                          B
                                                                      E
Working paths without conversion                    C
Working WP                                               D
                                            A

 Technische Universität München
 Institute of Communication Networks                    Matthias C. Scheffel
                                       10
 Prof. Dr.-Ing J. Eberspächer                                   DRCN 2003
                      p-Cycles in WDM Networks
Partial Wavelength Conversion at Nodes

wWP_pVWP Approach



p-Cycles with full conversion
p-Cycle VWP
(+ straddling span converters)
                                                B
                                                                       E
Working paths without conversion                    C
Working WP                                                D
                                            A




 Technische Universität München
 Institute of Communication Networks                    Matthias C. Scheffel
                                       11
 Prof. Dr.-Ing J. Eberspächer                                   DRCN 2003
                                          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


    Technische Universität München
    Institute of Communication Networks                      Matthias C. Scheffel
                                                 12
    Prof. Dr.-Ing J. Eberspächer                                     DRCN 2003
                                    Case Study Scenario

COST239 Network

•    Pan-European                                   Copenhagen
     optical core network
•    11 nodes, 26 spans               London                   Berlin
                                              Amsterdam
•    Average nodal degree = 4.7
•    1 counterdirectional fiber pair
                                               Luxembourg
     per span                        Brussels
•    32 wavelengths per fiber                                 Prague
•    Given demands
                                                        Zurich
      – Dense matrix                   Paris
      – 1 to 11 lightpaths per node                             Vienna
         (average = 3.2)
      – Symmetry modification                          Milan


    Technische Universität München
    Institute of Communication Networks                   Matthias C. Scheffel
                                             13
    Prof. Dr.-Ing J. Eberspächer                                  DRCN 2003
                                                                             Results

                          Total Cost Comparison
                           1100000
Total cost (in link-km)




                           1000000
                            900000                                                       netWP
                            800000                                                       wWP_pVWP
                            700000                                                       wWP_pWP_accessFull
                            600000
                                                                                         wWP_pWP_accessIfRequired
                            500000
                                                                                         netVWP_fullyEquipped
                            400000
                            300000
                                                                                         netVWP_partiallyEquipped
                            200000
                                       0      100     200        300   400   500   600

                                        Converter cost (in link-km)

                            fullyEquipped = converters for any available wavelength
                            partiallyEquipped = converters for used wavelengths only

                           Technische Universität München
                           Institute of Communication Networks                                       Matthias C. Scheffel
                                                                                   14
                           Prof. Dr.-Ing J. Eberspächer                                                      DRCN 2003
                                                                   Results

                      Capacity-Efficiency Evaluation

                       1.6
Capacity-efficiency




                       1.4
                       1.2
                                                                               netWP
                         1
                                                                               wWP_pVWP
                       0.8
                                                                               wWP_pWP_accessFull
                       0.6
                                                                               wWP_pWP_accessIfRequired
                       0.4
                                                                               netVWP
                       0.2
                         0
                             0      100      200       300   400   500   600

                                 Converter cost (in link-km)

                                                             protection capacity
                                       Capacity-efficiency =
                                                             working capacity

                       Technische Universität München
                       Institute of Communication Networks                                 Matthias C. Scheffel
                                                                          15
                       Prof. Dr.-Ing J. Eberspächer                                                DRCN 2003
                                                                      Results

                       Wavelength Converter Allocation
Number of converters




                        1800
                        1600
                        1400                                                      netWP
                        1200                                                      wWP_pVWP
                        1000                                                      wWP_pWP_accessFull
                         800                                                      wWP_pWP_accessIfRequired
                         600
                                                                                  netVWP_fullyEquipped
                         400
                         200                                                      netVWP_partiallyEquipped
                           0
                                0       100      200      300   400   500   600

                                    Converter cost (in link-km)




                        Technische Universität München
                        Institute of Communication Networks                                  Matthias C. Scheffel
                                                                            16
                        Prof. Dr.-Ing J. Eberspächer                                                 DRCN 2003
                               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

 Technische Universität München
 Institute of Communication Networks                   Matthias C. Scheffel
                                         17
 Prof. Dr.-Ing J. Eberspächer                                  DRCN 2003
            Comparison of p-Cycle Configurations

                                           wWP_          wWP_
                                           pWP_          pWP_       wWP_
                               netVWP                                            netWP
                                          accessIf       access     pVWP
                                          Required        Full
  Protection
                                highest     high        very high   high        very low
  efficiency

  Converters                      most    very few        few       more            no

Tunable lasers
                                    no      yes           yes        yes           n/a
   required

 Termination of
                                   yes     some           yes        yes            no
protection paths

  Wavelength
                                highest     low           high      higher         n/a
   flexibility

    Technische Universität München
    Institute of Communication Networks                                Matthias C. Scheffel
                                                   18
    Prof. Dr.-Ing J. Eberspächer                                               DRCN 2003

				
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