A Hybrid Approach to Translucent Optical Network Design

Giuseppe Rizzelli(1) Guido Maier(2) Achille Pattavina(3)

Department of Electronics and Information Politecnico di Milano Via Ponzio 34-35 20121 Milan ItalyB (1) rizzellieletpolimiit (2) maiereletpolimiit (3) pattavinaeletpolimiit

Abstract We present a novel design procedure for translucent optical networks Regenerating nodes(RNs) are selected via an Impairment-Aware (IA) ILP formulation exploiting the so-called ldquoconnectivitygraphrdquo while Transponders (TXPs) and DWDM systems are deployed via a greedy heuristic

Introduction

Up to a few years ago most Optical Trans-port Networks (OTNs) in operation were opaqueie hosting opto-electronic regenerating devices(Transponders - TXPs) in the nodes at both endsof each link of the network for every transit-ing lightpath The never-ceasing thrust to in-crease network capacity and throughput is nowa-days sided by a rapidly-increasing sensitivity toCAPEX OPEX and power consumptions Thusmost operators are currently investigating strate-gies to reduce the number of TXPs deployed andactivated in the OTNs exploiting optical bypass ofnetwork nodes offered by new low-cost photonic-switching technology (eg the ROADMs)

The complete elimination of the TXPs froman OTN (the transparent approach) can be ap-plied only to networks of rather limited size be-cause of transmission impairments The translu-cent solution is more scalable and more fre-quently adopted TXPs are deployed in the net-work only where strictly needed in order to setup all the lightpaths requested12 Regeneratorplacement is performed according to two mainstrategies (a)-sparse each node can be as-signed a number of TXPs variable according tothe number of transit lightpaths needing regener-ation at that node (b)-clustered a subset of net-work nodes is selected as ldquoRegenerating Nodes(RNs)rdquo by solving the Regenerators PlacementProblem (RPP)3 and provided by TXPs while therest of the nodes are optically transparent In thispaper we consider only the clustered strategy (b)RPP minimizes the number of regenerating nodesand finds their best location so that a lightpathcan be established between every pair of source-destination nodes requesting it RPP has beenproved to be NP-complete3 and it is just a sub-part of the whole planning procedure

Given the high complexity of the translucent-network design problem it is difficult to find anexact resolution method that can be solved in

useful times on standard computers for realistic-size OTN cases In this paper we would like topresent a novel approach that splits the prob-lem into two subproblems the first solvable by anImpairment-Aware Integer Linear Programming(IA-ILP) formulation and the second heuristicallyThe method has been applied to a large-scaleexample with fast convergence times achievingglobal CAPEX savings

Previous workMany works proposed IA-ILP formulations todeal with the Routing with Regenerators Prob-lem (RRP) where RNs locations are known andlightpaths are routed accordingly under physical-impairment constraints4 Other studies addressthe issue of RPP by modelling propagation im-pairments in terms of maximum distance or max-imum number of links that a lightpath may travelwithout regeneration45 The weakness of thedistance criterion compared to an IA-ILP designstrategy has been demonstrated6

The connectivity graph (see the definition be-low) has been proposed to solve RPP alone78

and jointly with traffic grooming5 An IA-ILPformulation8 considering Amplified SpontaneousEmission (ASE) noise and Polarization Mode Dis-persion (PMD) as signal constraints has alsobeen proposed RNs are not allowed to carry outwavelength conversion and the number of DWDMsystems on each link is pre-assigned This ap-proach minimizes the number of RNs but not thenumber of DWDM systems and TXPs installedMoreover the high IA-ILP complexity makes it ap-plicable only to small-scale cases

Our design method makes use of the connec-tivity graph but differently from previous works(a) the IA-ILP formulation is used to cope onlywith the RPP allowing to reduce the complexity ofthe dimensioning phase (b) more physical layerimpairments are taken into account (c) the num-ber of DWDM systems in the translucent OTN isnot preassigned but rather minimized along with

TXPs minimization (d) the subset of RNs is notpreassigned but computed (e) TXPs are both re-generators and wavelength converters

Translucent-network design procedureWe present our design procedure for translucentOTNs with clustered TXPs The method is di-vided in the two following steps (1) RPP at theend of which the subset of RNs is defined (2)Routing Fiber and Wavelength Assignment withRegenerators Problem (RFWA-RP) by which re-quested lightpaths are routed on the OTN se-lecting their wavelength (or wavelengths in caseof intermediate conversions) and simultaneouslyDWDM systems are allocated to the network linksunder the condition of satisfying all the requestsIn step (2) TXPs can be placed only in the RNsand minimization of resources (TXPs and DWDMsystems) is pursued

Our physical layer impairments model is basedon the computation of Personickrsquos Q-factor for allthe lightpaths9 The computed Q-factor is com-pared to a prefixed signal-quality threshold Qth

to evaluate whether a lightpath needs regener-ation or not Note that Qth=17 dB roughly cor-responds to a BER of 10minus12 (assuming no for-ward error correction) The model used in thispaper takes the following impairments into ac-count ASE noise loss self-phase modulationcross-phase modulation and four wave mixingnon-linear effects Polarization-mode and chro-matic dispersions are considered as totally com-pensated at the receiver The inclusion of otherimpairments in the Q-factor computation wouldnot change our design procedure

We define the transparency island (TI) of agiven OTN node the set of other OTN nodesthat can be reached from that node (following theshortest path) without using TXPs according tothe impairment-model used for planning

As anticipated step (1) is based on the con-nectivity graph the concept7 has been intro-duced and makes use of the transparency is-lands G(NA) is the physical graph of the net-work where N represents the set of nodes andA the set of physical links The connectivity graphGprime(NAprime) is obtained by the following graph trans-formation

bull set Aprime = emptybull add to Aprime a logical link connecting two nodes(i j) isin N if j belongs to the transparencyisland of i and vice versa

Every logical link has the same cost and if there

exists a link in Gprime(NAprime) connecting i to j itmeans that we can set up at least one lightpathin G(NA) between i and j without using regen-erators (they belong to each otherrsquos transparencyisland)

Let us now present the IA-ILP formulationbased on the connectivity-graph Given Gprime(NAprime)and the set S = s d of source-destination nodepairs in N we define the following variables

bull Xsdij Xsd

ij = 1 if the lightpath between (s d) isinS traverses the link (i j) isin Aprime Xsd

ij = 0 oth-erwise

bull Yi Yi = 1 if node i is a regenerator nodeYi = 0 otherwise

The ILP minimizes the objective function

f = α middot

sum(ij)isinAprime

sum(sd)isinS

Xsdij

+ β middotsumiisinN

Yi (1)

f is a total cost function weighting the total light-path length and the number of regenerators withcoefficients α and β respectivelyILP constraints concern flow conservation (Eq 2)and the computation of RNs (Eq 3)

sum(ij)isinAprime

Xsdij minus

sum(jk)isinAprime

Xsdjk =

minus1 if j = s

1 if j = d

0 otherwise

forallj isin N and forall(s d) isin S(2)

sum(ij)isinAprime

Xsdij le Yj

forall(s d) isin S and forallj isin N | j 6= d and j 6= s

(3)

Requested lightpaths are routed on the con-nectivity graph thus a lightpath traversing morethan one logical link needs regeneration at in-termediate nodes Equation 3 means that everynode crossed by a lightpath connecting nodes sand d must be a regenerating node in addition tos and d Since the physical impairments are im-plicitly taken into account in the computation ofGprime(NAprime) working on this graph allows us reduc-ing the complexity of the IA-ILP formulations

Step (2) of our design procedure is RFWA-RP with resource minimization and it is accom-plished by a heuristic algorithm RFWA-RP issolved for each requested lightpath with a greedystrategy run by a network simulator developed in

C++ After all connections have been set up re-generating nodes with no TXPs if any are re-moved from the original RN set

Case-study optimization resultsAs case-study example design experiments havebeen performed using the well known PAN Euro-pean network (28 nodes 41 edges)10 We haveassumed a uniform static matrix of demands in-cluding one bidirectional request for a 10 Gbitsconnection for each pair of network nodes Themaximum capacity of all DWDM systems is set at40 wavelengths (each DWDM system comprisesall the necessary optical amplifiers plus terminalwavelength multiplexer and de-multiplexer) Weassume that more than one line system can beinstalled on each OTN link if needed

For the results presented in this paper β inequation 1 has been chosen much greater than αin order to focus on the minimization of the num-ber of regenerating nodes Results of the dimen-sioning phase are reported in Fig 1 for three dif-ferent values of Qth We used CPLEX 110 on astandard pc with 2GByte of RAM Computationaltime for RPP was approximately 3 5 and 83 sec-onds for 17 19 and 21 dB threshold values re-spectively

Figure 1 reports the results of the opaque ap-proach for comparison clearly showing the effec-tiveness of the translucent approach in reducingthe number of TXPs Due to the fact that the

Workshop on Future Networking ndash G Rizzelli

1

10

100

1000

10000

OPAQUE Hybrid OPAQUE Hybrid OPAQUE Hybrid

28

1

28

3

28

6

4320

364

4320

364

4320

812

108 126 108 124 108 126

Am

ou

nt

of

Re

so

urc

es

Results of Planning PAN Network

Reg Nodes

TXPs

DWDM Syst

15

QTH= 17 dB QTH= 19 dB QTH= 21 dB

Opaque vs Translucent Resources

Fig 1 Network-planning results with static traffic

few regenerationconversion locations are con-strained an optical signal has to traverse withthe same wavelength many links and transparentnodes In order to fulfill the wavelength continuityconstraint clustering TXPs in a small number ofRNs has the side effect of reducing the chances

of wavelength conversion along a given path inthe network This led to install extra DWDM sys-tems compared to the opaque case even if thereare plenty of free usable wavelengths Thus clus-tered strategy is economically effective only whenfully-transparent network nodes have a lower costthan nodes with the capability of hosting TXPs sothat the extra CAPEX due to more DWDM sys-tems is compensated This scenario can becomerealistic when operational costs of hosting regen-erators are high (eg larger area occupation feesin node-housing infrastructures higher energyconsumption costs need for special equipmentfor heat dissipation maintenance costs etc)

We have also carried out planning simulationsby a comprehensive ILP formulation which jointlysolves the RPP and RFWA-RP8 and our Hybridmethod for a 7 8 9 e 10 node networks Thevalues of network diameter and maxmin nodaldegree are constant and the maximum capacityof DWDM systems has been set to 3 Figure2 shows that our Hybrid method has almost thesame performance of the ILP approach particu-larly in terms of RNs and TXPs The number ofDWDM systems needed by the Hybrid method isonly slightly larger than the optimal solution Thisis due to the second step of the algorithm whichis solved by a greedy heuristic The benefit of our

Workshop on Future Networking ndash G Rizzelli

1

10

100

ILP Hybrid ILP Hybrid ILP Hybrid ILP Hybrid

2 2 2 2 3 3

2 2

22 22 22 22

58 58 41 40 34 34 38 46

60 60 62 82

Am

ou

nt

of

Re

so

urc

es

Results of Planning (QTH=17 dB)

Reg Nodes

TXPs

DWDM Syst

23

7 nodes 8 nodes 10 nodes 9 nodes

ILP vs Two-Step Method Resources

Fig 2 ILP vs Hybrid approach Network-planning re-sults

design procedure is showed in Fig 3 ILP methodhas not been able to provide a solution in reason-able time for networks with more than 10 nodeseven with a very small value of number of wave-lengths per DWDM system

Workshop on Future Networking ndash G Rizzelli

1

10

100

1000

10000

ILP Hybrid ILP Hybrid ILP Hybrid ILP Hybrid

2 3

17

3

537

3

4490

4

Co

mp

uta

tio

n t

ime

[s]

Results of Planning (QTH=17dB)

24

7 nodes 8 nodes 10 nodes 9 nodes

ILP vs Two-Step Method Comput Time

Fig 3 ILP vs Hybrid approach Computation times

ConclusionsWe have proposed a two-step planning proce-dure based on an IA-ILP formulation to select theregenerator nodes along with a greedy heuristicto minimize the number of DWDM systems andTXPs deployed in the network The connectiv-ity graph is exploited in order to greatly reducethe computational complexity of the RPP step Infact all the physical impairments are taken intoaccount in the connectivity graph constructionwhich is carried out prior to solve the ILP IA-ILPformulation is thus simplified eliminating any ex-plicit physical-related constraint Thanks to thereduced complexity of the design procedure thephysical model can be complicated beyond theone used in this paper by adding further propaga-tion effects This will be the target of a follow-upof this research

AcknowledgementsThe work described in this paper was carriedout with the support of the BONE-project (rdquoBuild-ing the Future Optical Network in Europerdquo) aNetwork of Excellence funded by the EuropeanCommission through the 7th ICT- Framework Pro-gramme

References1 B Ramamurthy H Feng D Datta J P Her-

itage B Mukherjee Transparent vs opaquevs translucent wavelength-routed optical net-works Proc of OFCNFOEC 1999 SanDiego CA USA

2 G Shen R S Tucker Translucent OpticalNetworks the Way Forward IEEE Commu-nications Magazine vol 45 no 2 pp 48-54February 2007

3 A Sen S Murthy S Bandyopadhyay OnSparse Placement of Regenerator Nodes inTranslucent Optical Networks Proc of IEEEGLOBECOM 2008 New Orleans LA USA

4 Xi Yang B Ramamurthy Sparse Regenera-tion in Translucent Wavelength-Routed Opti-cal Networks Architecture Network Designand Wavelength Routing Photonic NetworkCommunication vol 10 no 1 pp 39-53 July2005

5 A N Patel C Gao J P Jue X WangQ Zhang P Palacharla T Naito Traf-fic Grooming and Regenerator Placementin Impairment-Aware Optical WDM Network Proc of ONDM 2010 Kyoto Japan

6 K Katrinis A Tzanakaki G MarkidisImpairment-Aware WDM Network Dimension-ing with Optimized Regenerator Placement Proc of OFCNFOEC 2009 San Diego CAUSA

7 M S Savasini P Monti M Tacca A Fu-magalli H Waldman Regenerator Placementwith Guaranteed Connectivity in Optical Net-works Proc of ONDM 2007 Athens Greece

8 W Zhang J Tang K Nygard C Wang RE-PARE Regenerator Placement and RoutingEstablishment in Translucent Networks Procof IEEE GLOBECOM 2009 Honolulu HawaiiUSA

9 M Yannuzzi M Quagliotti G Maier E Marin-Tordera X Masip-Bruin S Sanchez-LopezJ Sole-Pareta W Erangoli G Tamiri Perfor-mance of translucent optical networks underdynamic traffic and uncertain physical-layerinformation Proc of ONDM 2009 Braun-schweig Germany

10 S De Maesschalck D Colle I Lievens MPickavet P Demeester C Mauz M JaegerR Inkret B Mikac J Derkacz Pan-EuropeanOptical Transport Networks An Availability-based Comparison Photonic Network Com-munications vol 5 no 3 pp 203-225 May2003

• Introduction
• Previous work
• Translucent-network design procedure
• Case-study optimization results
• Conclusions
• Acknowledgements

C++ After all connections have been set up re-generating nodes with no TXPs if any are re-moved from the original RN set

Case-study optimization resultsAs case-study example design experiments havebeen performed using the well known PAN Euro-pean network (28 nodes 41 edges)10 We haveassumed a uniform static matrix of demands in-cluding one bidirectional request for a 10 Gbitsconnection for each pair of network nodes Themaximum capacity of all DWDM systems is set at40 wavelengths (each DWDM system comprisesall the necessary optical amplifiers plus terminalwavelength multiplexer and de-multiplexer) Weassume that more than one line system can beinstalled on each OTN link if needed

For the results presented in this paper β inequation 1 has been chosen much greater than αin order to focus on the minimization of the num-ber of regenerating nodes Results of the dimen-sioning phase are reported in Fig 1 for three dif-ferent values of Qth We used CPLEX 110 on astandard pc with 2GByte of RAM Computationaltime for RPP was approximately 3 5 and 83 sec-onds for 17 19 and 21 dB threshold values re-spectively

Figure 1 reports the results of the opaque ap-proach for comparison clearly showing the effec-tiveness of the translucent approach in reducingthe number of TXPs Due to the fact that the

Workshop on Future Networking ndash G Rizzelli

1

10

100

1000

10000

OPAQUE Hybrid OPAQUE Hybrid OPAQUE Hybrid

28

1

28

3

28

6

4320

364

4320

364

4320

812

108 126 108 124 108 126

Am

ou

nt

of

Re

so

urc

es

Results of Planning PAN Network

Reg Nodes

TXPs

DWDM Syst

15

QTH= 17 dB QTH= 19 dB QTH= 21 dB

Opaque vs Translucent Resources

Fig 1 Network-planning results with static traffic

few regenerationconversion locations are con-strained an optical signal has to traverse withthe same wavelength many links and transparentnodes In order to fulfill the wavelength continuityconstraint clustering TXPs in a small number ofRNs has the side effect of reducing the chances

of wavelength conversion along a given path inthe network This led to install extra DWDM sys-tems compared to the opaque case even if thereare plenty of free usable wavelengths Thus clus-tered strategy is economically effective only whenfully-transparent network nodes have a lower costthan nodes with the capability of hosting TXPs sothat the extra CAPEX due to more DWDM sys-tems is compensated This scenario can becomerealistic when operational costs of hosting regen-erators are high (eg larger area occupation feesin node-housing infrastructures higher energyconsumption costs need for special equipmentfor heat dissipation maintenance costs etc)

We have also carried out planning simulationsby a comprehensive ILP formulation which jointlysolves the RPP and RFWA-RP8 and our Hybridmethod for a 7 8 9 e 10 node networks Thevalues of network diameter and maxmin nodaldegree are constant and the maximum capacityof DWDM systems has been set to 3 Figure2 shows that our Hybrid method has almost thesame performance of the ILP approach particu-larly in terms of RNs and TXPs The number ofDWDM systems needed by the Hybrid method isonly slightly larger than the optimal solution Thisis due to the second step of the algorithm whichis solved by a greedy heuristic The benefit of our

Workshop on Future Networking ndash G Rizzelli

1

10

100

ILP Hybrid ILP Hybrid ILP Hybrid ILP Hybrid

2 2 2 2 3 3

2 2

22 22 22 22

58 58 41 40 34 34 38 46

60 60 62 82

Am

ou

nt

of

Re

so

urc

es

Results of Planning (QTH=17 dB)

Reg Nodes

TXPs

DWDM Syst

23

7 nodes 8 nodes 10 nodes 9 nodes

ILP vs Two-Step Method Resources

Fig 2 ILP vs Hybrid approach Network-planning re-sults

design procedure is showed in Fig 3 ILP methodhas not been able to provide a solution in reason-able time for networks with more than 10 nodeseven with a very small value of number of wave-lengths per DWDM system

Workshop on Future Networking ndash G Rizzelli

1

10

100

1000

10000

ILP Hybrid ILP Hybrid ILP Hybrid ILP Hybrid

2 3

17

3

537

3

4490

4

Co

mp

uta

tio

n t

ime

[s]

Results of Planning (QTH=17dB)

24

7 nodes 8 nodes 10 nodes 9 nodes

ILP vs Two-Step Method Comput Time

Fig 3 ILP vs Hybrid approach Computation times

ConclusionsWe have proposed a two-step planning proce-dure based on an IA-ILP formulation to select theregenerator nodes along with a greedy heuristicto minimize the number of DWDM systems andTXPs deployed in the network The connectiv-ity graph is exploited in order to greatly reducethe computational complexity of the RPP step Infact all the physical impairments are taken intoaccount in the connectivity graph constructionwhich is carried out prior to solve the ILP IA-ILPformulation is thus simplified eliminating any ex-plicit physical-related constraint Thanks to thereduced complexity of the design procedure thephysical model can be complicated beyond theone used in this paper by adding further propaga-tion effects This will be the target of a follow-upof this research

AcknowledgementsThe work described in this paper was carriedout with the support of the BONE-project (rdquoBuild-ing the Future Optical Network in Europerdquo) aNetwork of Excellence funded by the EuropeanCommission through the 7th ICT- Framework Pro-gramme

References1 B Ramamurthy H Feng D Datta J P Her-

itage B Mukherjee Transparent vs opaquevs translucent wavelength-routed optical net-works Proc of OFCNFOEC 1999 SanDiego CA USA

2 G Shen R S Tucker Translucent OpticalNetworks the Way Forward IEEE Commu-nications Magazine vol 45 no 2 pp 48-54February 2007

3 A Sen S Murthy S Bandyopadhyay OnSparse Placement of Regenerator Nodes inTranslucent Optical Networks Proc of IEEEGLOBECOM 2008 New Orleans LA USA

4 Xi Yang B Ramamurthy Sparse Regenera-tion in Translucent Wavelength-Routed Opti-cal Networks Architecture Network Designand Wavelength Routing Photonic NetworkCommunication vol 10 no 1 pp 39-53 July2005

5 A N Patel C Gao J P Jue X WangQ Zhang P Palacharla T Naito Traf-fic Grooming and Regenerator Placementin Impairment-Aware Optical WDM Network Proc of ONDM 2010 Kyoto Japan

6 K Katrinis A Tzanakaki G MarkidisImpairment-Aware WDM Network Dimension-ing with Optimized Regenerator Placement Proc of OFCNFOEC 2009 San Diego CAUSA

7 M S Savasini P Monti M Tacca A Fu-magalli H Waldman Regenerator Placementwith Guaranteed Connectivity in Optical Net-works Proc of ONDM 2007 Athens Greece

8 W Zhang J Tang K Nygard C Wang RE-PARE Regenerator Placement and RoutingEstablishment in Translucent Networks Procof IEEE GLOBECOM 2009 Honolulu HawaiiUSA

9 M Yannuzzi M Quagliotti G Maier E Marin-Tordera X Masip-Bruin S Sanchez-LopezJ Sole-Pareta W Erangoli G Tamiri Perfor-mance of translucent optical networks underdynamic traffic and uncertain physical-layerinformation Proc of ONDM 2009 Braun-schweig Germany

10 S De Maesschalck D Colle I Lievens MPickavet P Demeester C Mauz M JaegerR Inkret B Mikac J Derkacz Pan-EuropeanOptical Transport Networks An Availability-based Comparison Photonic Network Com-munications vol 5 no 3 pp 203-225 May2003

• Introduction
• Previous work
• Translucent-network design procedure
• Case-study optimization results
• Conclusions
• Acknowledgements

Workshop on Future Networking ndash G Rizzelli

1

10

100

1000

10000

ILP Hybrid ILP Hybrid ILP Hybrid ILP Hybrid

2 3

17

3

537

3

4490

4

Co

mp

uta

tio

n t

ime

[s]

Results of Planning (QTH=17dB)

24

7 nodes 8 nodes 10 nodes 9 nodes

ILP vs Two-Step Method Comput Time

Fig 3 ILP vs Hybrid approach Computation times

ConclusionsWe have proposed a two-step planning proce-dure based on an IA-ILP formulation to select theregenerator nodes along with a greedy heuristicto minimize the number of DWDM systems andTXPs deployed in the network The connectiv-ity graph is exploited in order to greatly reducethe computational complexity of the RPP step Infact all the physical impairments are taken intoaccount in the connectivity graph constructionwhich is carried out prior to solve the ILP IA-ILPformulation is thus simplified eliminating any ex-plicit physical-related constraint Thanks to thereduced complexity of the design procedure thephysical model can be complicated beyond theone used in this paper by adding further propaga-tion effects This will be the target of a follow-upof this research

AcknowledgementsThe work described in this paper was carriedout with the support of the BONE-project (rdquoBuild-ing the Future Optical Network in Europerdquo) aNetwork of Excellence funded by the EuropeanCommission through the 7th ICT- Framework Pro-gramme

References1 B Ramamurthy H Feng D Datta J P Her-

itage B Mukherjee Transparent vs opaquevs translucent wavelength-routed optical net-works Proc of OFCNFOEC 1999 SanDiego CA USA

2 G Shen R S Tucker Translucent OpticalNetworks the Way Forward IEEE Commu-nications Magazine vol 45 no 2 pp 48-54February 2007

3 A Sen S Murthy S Bandyopadhyay OnSparse Placement of Regenerator Nodes inTranslucent Optical Networks Proc of IEEEGLOBECOM 2008 New Orleans LA USA

4 Xi Yang B Ramamurthy Sparse Regenera-tion in Translucent Wavelength-Routed Opti-cal Networks Architecture Network Designand Wavelength Routing Photonic NetworkCommunication vol 10 no 1 pp 39-53 July2005

5 A N Patel C Gao J P Jue X WangQ Zhang P Palacharla T Naito Traf-fic Grooming and Regenerator Placementin Impairment-Aware Optical WDM Network Proc of ONDM 2010 Kyoto Japan

6 K Katrinis A Tzanakaki G MarkidisImpairment-Aware WDM Network Dimension-ing with Optimized Regenerator Placement Proc of OFCNFOEC 2009 San Diego CAUSA

7 M S Savasini P Monti M Tacca A Fu-magalli H Waldman Regenerator Placementwith Guaranteed Connectivity in Optical Net-works Proc of ONDM 2007 Athens Greece

8 W Zhang J Tang K Nygard C Wang RE-PARE Regenerator Placement and RoutingEstablishment in Translucent Networks Procof IEEE GLOBECOM 2009 Honolulu HawaiiUSA

9 M Yannuzzi M Quagliotti G Maier E Marin-Tordera X Masip-Bruin S Sanchez-LopezJ Sole-Pareta W Erangoli G Tamiri Perfor-mance of translucent optical networks underdynamic traffic and uncertain physical-layerinformation Proc of ONDM 2009 Braun-schweig Germany

10 S De Maesschalck D Colle I Lievens MPickavet P Demeester C Mauz M JaegerR Inkret B Mikac J Derkacz Pan-EuropeanOptical Transport Networks An Availability-based Comparison Photonic Network Com-munications vol 5 no 3 pp 203-225 May2003

• Introduction
• Previous work
• Translucent-network design procedure
• Case-study optimization results
• Conclusions
• Acknowledgements