Fiber SystemsFiber SystemsDense Wavelength Division Dense Wavelength Division

MultiplexingMultiplexing (DWDM) (DWDM)Tauseef khanTauseef khan

Brief OverviewBrief Overview

►Problems with increasing network demandsProblems with increasing network demands►Solutions proposed & their limitationsSolutions proposed & their limitations►Evolution of DWDMEvolution of DWDM►Technical details Technical details ►DrawbacksDrawbacks►Ongoing ResearchOngoing Research►ConclusionConclusion

Growing Network Usage PatternsGrowing Network Usage Patterns► IssuesIssues

Exponential increase in user demand for bandwidthExponential increase in user demand for bandwidth►Doubling of bandwidth requirement every 6-9 monthsDoubling of bandwidth requirement every 6-9 months

Consistency in quality of services providedConsistency in quality of services provided Keeping the cost of solutions at bayKeeping the cost of solutions at bay

► SolutionsSolutions Increase channel capacity: TDM, WDMIncrease channel capacity: TDM, WDM Statistical multiplexing of users: Multiple optical fibersStatistical multiplexing of users: Multiple optical fibers

Another glimpse at the solutionsAnother glimpse at the solutions

► WDM (Wavelength Division Multiplexing)WDM (Wavelength Division Multiplexing) Use of optical fibers to achieve higher speedsUse of optical fibers to achieve higher speeds Utilize wavelengths to multiplex usersUtilize wavelengths to multiplex users Allow continuous channel allocation per userAllow continuous channel allocation per user Increases the effective bandwidth of existing fiberIncreases the effective bandwidth of existing fiber

► TDM (Time Division Multiplexing)TDM (Time Division Multiplexing) Slotting of channels Slotting of channels simultaneous users simultaneous users Increasing bit rate to maximize utilization of given Increasing bit rate to maximize utilization of given

bandwidthbandwidth

Limitations of current solutionsLimitations of current solutions

► WDMWDM Inefficient usage of full capacity of the optical fiberInefficient usage of full capacity of the optical fiber Capability of carrying signals efficiently over short distances onlyCapability of carrying signals efficiently over short distances only

► Improvements in optical fibers and narrowband lasersImprovements in optical fibers and narrowband lasers Birth of Dense WDM (DWDM) Birth of Dense WDM (DWDM)

► TDMTDM Dependency of Mux-Demux on bit rateDependency of Mux-Demux on bit rate Limitations on bit rates Limitations on bit rates

►how fast can we go? (Decides how small the time slots can be)how fast can we go? (Decides how small the time slots can be)

Evolution of DWDMEvolution of DWDM

Late 1990’s

1996DWDM

Early1990’s

Narrowband WDM

1980’sWideband WDM

16+ channels 16+ channels 100~200 GHz spacing100~200 GHz spacing

2~8 channels2~8 channels200~400 GHz spacing200~400 GHz spacing

2 channels2 channels1310nm, 1550nm1310nm, 1550nm

64+ channels64+ channels25~50 GHz spacing25~50 GHz spacing

What is DWDM?What is DWDM?► DefinitionDefinition

Dense wavelength division multiplexing (DWDM) is a fiber-optic Dense wavelength division multiplexing (DWDM) is a fiber-optic transmission technique that employs light wavelengths to transmission technique that employs light wavelengths to transmit data parallel-by-bit or serial-by-charactertransmit data parallel-by-bit or serial-by-character

How does DWDM fair better?How does DWDM fair better?► No O-E-O requiredNo O-E-O required► Protocol & Bit Rate independenceProtocol & Bit Rate independence► Increased overall capacity at much lower costIncreased overall capacity at much lower cost

Current fiber plant investment can be optimized by a Current fiber plant investment can be optimized by a factor of at least 32factor of at least 32

► TransparencyTransparency Physical layer architecture Physical layer architecture supports both TDM and supports both TDM and

data formats such as ATM, Gigabit Ethernet, etc. data formats such as ATM, Gigabit Ethernet, etc. ► ScalabilityScalability

Utilize abundance of dark fibers in metropolitan areas Utilize abundance of dark fibers in metropolitan areas and enterprise networksand enterprise networks

Capacity ExpansionCapacity Expansion

Basic Components & OperationBasic Components & Operation► Transmitting SideTransmitting Side

Lasers with precise stable Lasers with precise stable wavelengthswavelengths

Optical MultiplexersOptical Multiplexers► On the LinkOn the Link

Optical fiberOptical fiber Optical amplifiersOptical amplifiers

► Receiving SideReceiving Side Photo detectorsPhoto detectors Optical DemultiplexersOptical Demultiplexers

► Optical add/drop Optical add/drop multiplexersmultiplexers

Optical AmplifierOptical Amplifier

► Eliminates O-E-O conversionsEliminates O-E-O conversions► More effective than electronic repeatersMore effective than electronic repeaters► Isolator prevents reflectionIsolator prevents reflection► Light at 980nm or 1480nm is injected via the pump laserLight at 980nm or 1480nm is injected via the pump laser► Gains ~ 30dB; Output Power ~ 17dBGains ~ 30dB; Output Power ~ 17dB

DrawbacksDrawbacks► DispersionDispersion

Chromatic dispersionChromatic dispersion Polarization mode dispersionPolarization mode dispersion

► AttenuationAttenuation Intrinsic: Scattering, Absorption, etc.Intrinsic: Scattering, Absorption, etc. Extrinsic: Manufacturing Stress, Environment, etc.Extrinsic: Manufacturing Stress, Environment, etc.

► Four wave mixingFour wave mixing Non-linear nature of refractive index of optical fiberNon-linear nature of refractive index of optical fiber Limits channel capacity of the DWDM SystemLimits channel capacity of the DWDM System

Ongoing DevelopmentsOngoing Developments► Nortel NetworksNortel Networks

Metro DWDMMetro DWDM OPTera Long Haul 5000 Optical Line SystemOPTera Long Haul 5000 Optical Line System

► Cisco SystemsCisco Systems ONS 15200 Metro DWDM SolutionONS 15200 Metro DWDM Solution

► Lucent TechnologiesLucent Technologies LambdaXtreme TransportLambdaXtreme Transport WaveStar OLS 1.6TWaveStar OLS 1.6T

► Agility Communications & UC Santa BarbaraAgility Communications & UC Santa Barbara Tunable Lasers used for multiple wavelengthsTunable Lasers used for multiple wavelengths

ConclusionConclusion► Robust and simple designRobust and simple design► Works entirely in the Optical domainWorks entirely in the Optical domain► Multiplies the capacity of the network many foldMultiplies the capacity of the network many fold► Cheap ComponentsCheap Components► Handles the present BW demand cost effectivelyHandles the present BW demand cost effectively► Maximum utilization of untapped resourcesMaximum utilization of untapped resources► Best suited for long-haul networksBest suited for long-haul networks

ReferencesReferences

[1] Introducing DWDM [1] Introducing DWDM http://www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_fns.htmhttp://www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_fns.htm

[2] Fundamentals of DWDM Technology [2] Fundamentals of DWDM Technology http://www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_ovr.htmhttp://www.cisco.com/univercd/cc/td/doc/product/mels/dwdm/dwdm_ovr.htm

[3] Dense Wavelength Division Multiplexing (DWDM) [3] Dense Wavelength Division Multiplexing (DWDM) http://www.iec.org/online/tutorials/dwdmhttp://www.iec.org/online/tutorials/dwdm

[4] Dense Wavelength Division Multiplexing (DWDM) Testing [4] Dense Wavelength Division Multiplexing (DWDM) Testing http://www.iec.org/online/tutorials/dwdm_testhttp://www.iec.org/online/tutorials/dwdm_test

[5] “Fiber-Optic Communications Technology” by D.K. Mynbaev, L.L. Scheiner, Pearson [5] “Fiber-Optic Communications Technology” by D.K. Mynbaev, L.L. Scheiner, Pearson Education Asia, 2001 edition Education Asia, 2001 edition

[6] “Dense wave nets' future is cloudy” by Chappell Brown, EETimes [6] “Dense wave nets' future is cloudy” by Chappell Brown, EETimes http://www.eetimes.com/story/OEG20011221S0035http://www.eetimes.com/story/OEG20011221S0035

[7] Cisco Systems [7] Cisco Systems http://www.cisco.com/en/US/products/hw/optical/ps1996/products_quick_reference_guidhttp://www.cisco.com/en/US/products/hw/optical/ps1996/products_quick_reference_guide09186a00800886bb.htmle09186a00800886bb.html

[8] Lucent Technologies [8] Lucent Technologies http://www.lucent.com/products/subcategory/0,,CTID+2021-STID+10482-http://www.lucent.com/products/subcategory/0,,CTID+2021-STID+10482-LOCL+1,00.htmlLOCL+1,00.html

[9] Nortel Networks: “OPTera Long Haul” & “Metro DWDM” [9] Nortel Networks: “OPTera Long Haul” & “Metro DWDM” (http://www.nortelnetworks.com/products/01/optera/long_haul/dwdm/) & (http://www.nortelnetworks.com/products/01/optera/long_haul/dwdm/) & (http://www.nortelnetworks.com/products/library/collateral/12001.25-03-02.pdf)(http://www.nortelnetworks.com/products/library/collateral/12001.25-03-02.pdf)

[10] Agility Communications[10] Agility Communicationshttp://agility.com/intervals/index.phtml?ID=93&f_code=1http://agility.com/intervals/index.phtml?ID=93&f_code=1