Colorless Devarajan

8/8/2019 Colorless Devarajan

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IntroductionColorless and Directionless ROADM architectures PXC based architecture WSS based architecture

Colorless, Directionless and Contentionless ROADMarchitecturePractical Implementation IssuesConclusion


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Rich MediaServices

Triple PlayServices

BusinessServices

US HQ

India

ScientificResearch

CERN


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Challenges :Services are unpredictable in terms of their bandwidth, routing patternsand requirements.Provisioning high bandwidth connectivity to every single site.Expectations - access to all the contents on demand, at any time and from

anywhere.In this unpredictable business environment, deliver all the services, asquickly as possible.

Solutions:Next gen agile optical network reconfigurable and scalable optical layerROADMs Reconfigurable Optical Add/Drop Multiplexers.Colorless and Directionless architecture.


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In ROADM-driven optical systems, the flexibility of the mesh networkcan be extended by Colorless and Directionless (C&D) feature at everynode in the network

Colorless feature at a local add/drop port - ability of tunabletransponders to have wavelength transparent access to all the DWDM

network portsDirectionless feature at a local add/drop port - ability of tunabletransponders to have non-blocking access to all the DWDM networkports

C&D feature enables efficient use of all the tunable access resources for

on-demand and high bandwidth network configuration and simplify thenetwork architecture


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At a 4 degree node, the architecture consists of:320x320 non-blocking 3D MEMS large optical switches at the coreof PXCA set of AWG based 40 channel Mux/DemuxsTunable transponders at local add/drop ports

PXC based C&D architecture

Sample mesh optical network


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AdvantagesProvides Colorless and Directionless featureProvides Contentionless feature - same wavelengths carrying differentinformation can be received/sent simultaneously with the help of multipletunable transponders from/to different input/output fiber portsEfficient utilization of wavelengths

Provides 100% add/drop at the local portsMinimal loss

ConcernsAs the number of ports N, in NxN core switch grows the number of possible connections increases as N 2

Does not support multicasting can not drop a wavelength from adirection while simultaneously sending the same wavelength to otherdirections along the express path Core switching fabric acts as a single point of failure


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Both the cores are keptactive to avoidchallenges faced whileswitching the entireservicesProtection Switching Card (PSC) - performsthe functions of a 2x1Protection Switch (PS)and also a passivesplitter (S)

Protection is providedper transponder basis

Protection Scheme employed with dual core switching matrix inPXC based architecture


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1

2

3

4

40

Port 1 Port 2 Port 3 Port NPort 4

VOA


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1

2

3

4

40

Port 1 Port 2 Port 3 Port NPort 4

VOA


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The architecture

consists of: 1x9 WSS modules Multi-port splitter

combiners (S/C)

S/C at the localadd/drop siteprovides expansionfacility.

WSS along eachdirection can eitherblock or allow acertain wavelength.

WSS is a betterchoice along eachdirection as it offersintelligentfunctionalities than apassive combiner.


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Advantages:Provides Colorless and Directionless feature at the local add/drop siteWSS can provide Dynamic Channel Equalization and hence maximizesoverall performanceAny wavelength from any direction or originating at that node can bemulticast to all the directions

Offers Pay-as-you-grow approach allows modular growth Scalable in terms of bothnode-degree and number of add/drop wavelengths

Number of WSS modulesrequired at the local add/dropsite depends on the numberof ports in it.


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Concerns:Very expensive on day 1Does not provide contentionless add/drop

Consider 2 differentservices on samewavelength with commonend point no contention

If another service on samewavelength to the sameend point contention

Contention can be avoidedwith multiple WSS & S/Cmodules, but expensive


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CD&C architecture is realized by combining the WSS basedROADMs with PXCThe WSS modules and multi-port splitter combiners are replacedby PXC in the WSS based C&D architecture

CD&C architecture

consists of: WSS modules Multi-port splitter

combiners 320x320 non

blocking 3D MEMSbased PXC


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Provides all the features offered by both PXC based and WSS basedarchitectures

PXC used for the local add/drop provides the Contentionlessadd/drop access in addition to C&D feature

Allows modular growth in number of transponders depending onnumber of add/drop wavelengths at the local add/drop site

Better wavelength utilization

Minimal optical power loss compared to WSS based architecture

Completely eliminates the need for a number of WSS modules andsplitter combiners at the local add/drop site Minimum CAPEX


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Performance analysis

Choice of sub-system technologies

Cost considerationsOther challenges


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Power budgeting and OSNR calculationDistances between the nodes in the sample mesh network -80km

Launch power of a 10Gbps tunable transponder : 1.5dBm - PXC based C&D architecture 4.5dBm - WSS based C&D architecture 4.0dBm - CD&C architecture

Minimum permissible value of the power level, at the APD

receiver is -26dBm


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Every wavelength from a local add site must pass through: Protection Switch Card, PSC ( 3.5dB loss ) 320x320 MEMS switching core ( 2.5dB loss ) 40 channel Mux ( 4dB loss ) Protection Switch PS ( 3.5dB loss )

Every wavelength along the pass-through channels are sent via: 1x2 power splitter ( 3dB loss ) 40 channel Demux ( 4dB loss ) 320x320 MEMS switching core ( 2.5dB loss ) 40 channel Mux ( 4dB loss ) Protection Switch ( 3.5dB loss )

Every wavelength that is to be dropped must pass through: 1x2 power splitter( 3dB loss ) 40 channel Demux ( 4dB loss ) 320x320 MEMS switching core ( 2.5dB loss ) Protection switch ( 3.5dB loss )

Fiber loss for each fiber link of 80km

Total loss of 13.5dB



20.0dB (loss of 0.25dB/km )


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Every wavelength from a local add site must pass through:

Protection switching card, PSC ( 3.5dB loss ) Two WSS modules ( 6dB loss each ) Two 1x8 power splitters ( 9dB loss each )

Every wavelength along the pass-through channels are sent via: 1x8 power splitter ( 9dB loss ) WSS module ( 6dB loss )

Every wavelength that is to be dropped must pass through: Two 1x8 power splitters ( 9dB loss each ) Two WSS modules ( 6dB each ) Protection switching card ( 3.5dB loss )







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Every wavelength from a local add site must pass through: Protection Switch Card, PSC ( 3.5dB loss ) 320x320 MEMS switching core ( 2.5dB loss ) 40 channel Mux ( 4dB loss ) Protection Switch PS ( 3.5dB loss ) WSS module ( 6dB loss )

Every wavelength along the pass-through channels are sent via: 1x8 power splitter ( 9dB loss ) WSS module ( 6dB loss )

Every wavelength that is to be dropped must pass through: 1x2 power splitter ( 3dB loss ) 1x8 power splitter ( 9dB loss ) 40 channel Demux ( 4dB loss ) 320x320 MEMS switching core ( 2.5dB loss ) Protection switch ( 3.5dB loss )







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Launch power of a 10Gbps tunabletransponder : 1.5dBm for the case of PXC based C&D

architecture 4.5dBm for the case of WSS based C&D

architecture 4.0dBm for the case of CD&C architecture

Each channel suffers a specific loss

EDFAs at various locations provide therequired amplification to keep opticalpower level within the limits


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24dB 13dB

18dB

18dB18dB

12dB

20dB 16dB EDFAs are associated with specific noisefigures (NF) which vary with amplificationvalues


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NF = Noise figure of the amplifier h = Plancks constant = 6.634 x 10 -34

f = bandwidth that measures the NF= 0.5nm (62.08GHz)

= optical frequency = 193 THz

CD&C architecture has better OSNRperformance

CD&C ROADM architecture could alsobe 40Gbps ready as it readily providesthe 6dB higher OSNR margin

1

1OSNRprevious_stage +

NF h f Pi/p_current_stage(Watts)

OSNRcurent_stage=

OSNR values at amplifiers along a chosen path


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Plays important roll in the performance of architectureLiquid crystal based switches - stable but slight defect introducesa high power lossBubble based switches high switching speed but lesser coresizeThermo optical waveguides faster switching but constantheating and cooling causes adverse on the deviceMEMS based switches requires vibration free environment butprovides high i/p & o/p port counts, minimal loss, low PDL


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In PXC based & WSS based architectures, cost of implementation isvery expensive

CD&C architecture - relatively lower CAPEXThe overall cost of architecture at a node is calculated by: cost of the devices cost based on number of ports used for a particular add/drop ratio

No. of ports used = (No. of degrees) x (No. of channels per degree) x 2 +(Add/drop ratio) x (No. of d egrees) x (No. of channels per degree) x 2

For PXC based architecture: $ 200 per PXC port

$ 3,000 for a pair of AWG based Mux/DemuxsFor WSS based architecture: $ 9,000 for a 1x9 WSS module

The same costs were considered for CD&C architecture


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At lower add/dropratio, PXC basedarchitecture is veryexpensiveWSS based architecturebecomes expensive asmore no. of wavelengthsadded/droppedAs the add/drop ratioincreases, the CD&Carchitecture is very costeffective


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Complex interconnections between core switches andMux/Demuxs or other components

Integrating core switches with other components reduces complexity, power requirement and space

occupiedHowever, it has the drawback of making it a single-vendor solution

Scalability beyond 8 degrees and 40 channels


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Colorless, Directionless and Contentionless ROADM architectureenabled by the combination of WSS based ROADM and PXC is

proposedPractical implementation issues of CD&C architecture werediscussedCD&C provides

contentionless add/drop along with Colorless and Directionless features dynamic optimization of lightpaths by optical bridge-and-roll elimination of wavelength conversion alternate protection paths

CD&C architecture is a promising solution: Flexibility Ease of provisioning Modular add/drop Minimal pre-planning


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All the reviewers for their comments which led to asignificant improvement of the paper

Prof. Byrav Ramamurthy for the valuable suggestions


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Colorless Devarajan

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