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cisco systems dwdm primer oct03
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<p>DWDM Networking PrimerOctober 2003</p> <p>ONS 15454 MSTP</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Agenda</p> <p> Introduction Optical Fundamentals Dense Wavelength Division Multiplexing (DWDM)</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Optical Fundamentals</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Some terminology Decibels (dB): unit of level (relative measure)X dB is 10-X/10 in linear dimension e.g. 3 dB Attenuation = 10-.3 = 0.501 Standard logarithmic unit for the ratio of two quantities. In optical fibers, the ratio is power and represents loss or gain.</p> <p> Decibels-milliwatt (dBm) : Decibel referenced to a milliwattX mW is 10log10(X) in dBm, Y dBm is 10Y/10 in mW. 0dBm=1mW, 17dBm = 50mW</p> <p> Wavelength (): length of a wave in a particular medium. Common unit: nanometers, 10-9m (nm)300nm (blue) to 700nm (red) is visible. In fiber optics primarily use 850, 1310, &amp; 1550nm</p> <p> Frequency ( ): the number of times that a wave is produced within a particular time period. Common unit: TeraHertz, 1012 cycles per second (Thz)Wavelength x frequency = Speed of light 2003, Cisco Systems, Inc. All rights reserved.</p> <p> x =C</p> <p>Some more terminology Attenuation = Loss of power in dB/kmThe extent to which lighting intensity from the source is diminished as it passes through a given length of fiber-optic (FO) cable, tubing or light pipe. This specification determines how well a product transmits light and how much cable can be properly illuminated by a given light source.</p> <p> Chromatic Dispersion = Spread of light pulse inThe separation of light into its different coloured rays.</p> <p>ps/nm-km</p> <p> ITU Grid = Standard set of wavelengths to be used in Fibre Optic communications. Unit Ghz, e.g. 400Ghz, 200Ghz, 100Ghz Optical Signal to Noise Ration (OSNR) = Ratio of optical signal power to noise power for the receiver Lambda = Name of Greek Letter used as Wavelength symbol () Optical Supervisory Channel (OSC) = Management channel 2003, Cisco Systems, Inc. All rights reserved.</p> <p>dB versus dBm</p> <p> dBm used for output power and receive sensitivity (Absolute Value) dB used for power gain or loss (Relative Value)</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Bit Error Rate ( BER)</p> <p> BER is a key objective of the Optical System Design Goal is to get from Tx to Rx with a BER &lt; BER threshold of the Rx BER thresholds are on Data sheets Typical minimum acceptable rate is 10 -12</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Optical BudgetBasic Optical Budget = Output Power Input SensitivityPout = +6 dBm R = -30 dBm</p> <p>Budget = 36 dB</p> <p>Optical Budget is affected by:Fiber attenuation Splices Patch Panels/Connectors Optical components (filters, amplifiers, etc) Bends in fiber Contamination (dirt/oil on connectors) 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Glass Purity</p> <p>Fiber Optics Requires Very High Purity GlassWindow Glass Optical Quality Glass Fiber Optics 1 inch (~3 cm) 10 feet (~3 m) 9 miles (~14 km)</p> <p>Propagation Distance Need to Reduce the Transmitted Light Power by 50% (3 dB) 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Fiber FundamentalsAttenuation Dispersion Nonlinearity Distortion It May Be a Digital Signal, but Its Analog Transmission</p> <p>Transmitted Data Waveform 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Waveform After 1000 Km</p> <p>Analog Transmission EffectsAttenuation:Reduces power level with distance</p> <p>Dispersion and Nonlinearities:Erodes clarity with distance and speed</p> <p>Signal detection and recovery is an analog problem</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Fiber GeometryCore Cladding</p> <p> An optical fiber is made of three sections:The core carries the light signals The cladding keeps the light in the core The coating protects the glass</p> <p>Coating</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Propagation in Fibern20n1 1 Intensity Profile</p> <p>CladdingCore</p> <p> Light propagates by total internal reflections at the core-cladding interface Total internal reflections are lossless Each allowed ray is a mode</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Different Types of Fibern2 Multimode fiberCore diameter varies 50 mm for step index 62.5 mm for graded index Bit rate-distance product &gt;500 MHz-kmn1 Core</p> <p>Cladding</p> <p> Single-mode fiberCore diameter is about 9 mm Bit rate-distance product &gt;100 THz-km</p> <p>n2n1</p> <p>CladdingCore</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Optical SpectrumUV Visible IR 125 GHz/nm</p> <p> LightUltraviolet (UV) Visible Infrared (IR)</p> <p>850 nm 980 nm 1310 nm 1480 nm 1550 nm 1625 nm</p> <p> Communication wavelengths850, 1310, 1550 nm Low-loss wavelengths</p> <p> Specialty wavelengths980, 1480, 1625 nm 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Wavelength:</p> <p> (nanometers) Frequency: (terahertz)</p> <p>C = x </p> <p>Optical Attenuation</p> <p> Specified in loss per kilometer (dB/km)0.40 dB/km at 1310 nm 0.25 dB/km at 1550 nm1550 Window</p> <p> Loss due to absorption by impurities1400 nm peak due to OH ions</p> <p>1310 Window</p> <p> EDFA optical amplifiers available in 1550 window</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Optical Attenuation Pulse amplitude reduction limits how far Attenuation in dB Power is measured in dBm:Examples10dBm 0 dBM -3 dBm -10 dBm -30 dBm 10 mW 1 mW 500 uW 100 uW 1 uW</p> <p>)</p> <p>Pi T 2003, Cisco Systems, Inc. All rights reserved.</p> <p>P0 T</p> <p>Types of Dispersion</p> <p> Chromatic DispersionDifferent wavelengths travel at different speeds Causes spreading of the light pulse</p> <p> Polarization Mode Dispersion (PMD)Single-mode fiber supports two polarization states Fast and slow axes have different group velocities Causes spreading of the light pulse 2003, Cisco Systems, Inc. All rights reserved.</p> <p>A Snapshot on Chromatic Dispersion</p> <p>Interference</p> <p> Affects single channel and DWDM systems A pulse spreads as it travels down the fiber Inter-symbol Interference (ISI) leads to performance impairments Degradation depends on:laser used (spectral width) bit-rate (temporal pulse separation) Different SM types 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Limitations From Chromatic Dispersion Dispersion causes pulse distortion, pulse "smearing" effects Higher bit-rates and shorter pulses are less robust to Chromatic Dispersion Limits "how fast and how far10 Gbps60 Km SMF-28t</p> <p>40 Gbps4 Km SMF-28t 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Combating Chromatic Dispersion</p> <p> Use DSF and NZDSF fibers(G.653 &amp; G.655)</p> <p> Dispersion Compensating Fiber Transmitters with narrow spectral width</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Dispersion Compensating Fiber</p> <p> Dispersion Compensating Fiber:By joining fibers with CD of opposite signs (polarity) and suitable lengths an average dispersion close to zero can be obtained; the compensating fiber can be several kilometers and the reel can be inserted at any point in the link, at the receiver or at the transmitter</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Dispersion Compensation Total Dispersion ControlledCumulative Dispersion (ps/nm) +100 0 -100 -200 -300 -400 -500</p> <p>No Compensation With Compensation</p> <p>Distance from Transmitter (km) Dispersion Shifted Fiber Cable</p> <p>Transmitter Dispersion Compensators 2003, Cisco Systems, Inc. All rights reserved.</p> <p>How Far Can I Go Without Dispersion?</p> <p>Distance (Km) =</p> <p>Specification of Transponder (ps/nm) Coefficient of Dispersion of Fiber (ps/nm*km)</p> <p>A laser signal with dispersion tolerance of 3400 ps/nm is sent across a standard SMF fiber which has a Coefficient of Dispersion of 17 ps/nm*km. It will reach 200 Km at maximum bandwidth.Note that lower speeds will travel farther.</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Polarization Mode Dispersion Caused by ovality of core due to:Manufacturing process Internal stress (cabling) External stress (trucks)</p> <p> Only discovered in the 90s Most older fiber not characterized for PMD 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Polarization Mode Dispersion (PMD)Ey nx Ex ny Spreaded Pulse As It Leaves the Fiber</p> <p>Pulse As It Enters the Fiber</p> <p> The optical pulse tends to broaden as it travels down the fiber; this is a much weaker phenomenon than chromatic dispersion and it is of little relevance at bit rates of 10Gb/s or less</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Combating Polarization Mode Dispersion Factors contributing to PMDBit Rate Fiber core symmetry Environmental factors Bends/stress in fiber Imperfections in fiber</p> <p> Solutions for PMDImproved fibers Regeneration Follow manufacturers recommended installation techniques for the fiber cable</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Types of Single-Mode Fiber SMF-28(e) (standard, 1310 nm optimized, G.652)Most widely deployed so far, introduced in 1986, cheapest</p> <p> DSF (Dispersion Shifted, G.653)Intended for single channel operation at 1550 nm</p> <p> NZDSF (Non-Zero Dispersion Shifted, G.655)For WDM operation, optimized for 1550 nm region TrueWave, FreeLight, LEAF, TeraLight Latest generation fibers developed in mid 90s For better performance with high capacity DWDM systems MetroCor, WideLight Low PMD ULH fibers 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Different Solutions for Different Fiber TypesSMF (G.652) DSF (G.653) NZDSF (G.655) Extended Band (G.652.C) (suppressed attenuation in the traditional water peak region) Good for TDM at 1310 nm OK for TDM at 1550 OK for DWDM (With Dispersion Mgmt) OK for TDM at 1310 nm Good for TDM at 1550 nm Bad for DWDM (C-Band) OK for TDM at 1310 nm Good for TDM at 1550 nm Good for DWDM (C + L Bands) Good for TDM at 1310 nm OK for TDM at 1550 nm OK for DWDM (With Dispersion Mgmt Good for CWDM (&gt;8 wavelengths)</p> <p>The primary Difference is in the Chromatic Dispersion Characteristics 2003, Cisco Systems, Inc. All rights reserved.</p> <p>The 3 Rs of Optical NetworkingA Light Pulse Propagating in a Fiber Experiences 3 Type of Degradations:Pulse as It Enters the Fiber Pulse as It Exits the Fiber</p> <p>Loss of Energy</p> <p>Shape DistortionPhase Variation</p> <p>Loss of Timing (Jitter)(From Various Sources)</p> <p>ts Optimum Sampling Time</p> <p>t</p> <p>ts Optimum Sampling Time</p> <p>t</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>The 3 Rs of Optical Networking (Cont.)The Options to Recover the Signal from Attenuation/Dispersion/Jitter Degradation Are:Pulse as It Enters the Fiber Pulse as It Exits the Fiber</p> <p>Amplify to Boost the Power</p> <p>Re-ShapePhase Variation</p> <p>DCU</p> <p>Phase Re-Alignment</p> <p>Re-Generate</p> <p>O-E-Ots Optimum Sampling Time</p> <p>t</p> <p>ts Optimum Sampling Time</p> <p>t</p> <p>Re-gen, Re-shape and ts Optimum Remove Optical Noise Sampling Time</p> <p>t</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>DWDM</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Agenda</p> <p> Introduction Components Forward Error Correction DWDM Design Summary</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Increasing Network Capacity OptionsMore Fibers (SDM)Same bit rate, more fibers Slow Time to Market Expensive Engineering Limited Rights of Way Duct Exhaust</p> <p>W D M</p> <p>Same fiber &amp; bit rate, more s Fiber Compatibility Fiber Capacity Release Fast Time to Market Lower Cost of Ownership Utilizes existing TDM Equipment</p> <p>Faster Electronics (TDM) 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Higher bit rate, same fiber Electronics more expensive</p> <p>Fiber Networks Time division multiplexingSingle wavelength per fiber Multiple channels per fiber 4 OC-3 channels in OC-12 4 OC-12 channels in OC-48 16 OC-3 channels in OC-48 Channel 1 Channel nSingle Fiber (One Wavelength)</p> <p> Wave division multiplexingMultiple wavelengths per fiber 4, 16, 32, 64 channels per system Multiple channels per fiber 2003, Cisco Systems, Inc. All rights reserved.</p> <p>l1 l2 Single Fiber (Multiple Wavelengths)</p> <p>ln</p> <p>TDM and DWDM Comparison TDM (SONET/SDH)Takes sync and async signals and multiplexes them to a single higher optical bit rate E/O or O/E/O conversion</p> <p>DS-1 DS-3 OC-1 OC-3 OC-12 OC-48</p> <p>SONET ADM</p> <p>Fiber</p> <p> (D)WDMTakes multiple optical signals and multiplexes onto a single fiber No signal format conversionOC-12c OC-48c OC-192c DWDM OADM Fiber</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>DWDM History Early WDM (late 80s)Two widely separated wavelengths (1310, 1550nm)</p> <p> Second generation WDM (early 90s)Two to eight channels in 1550 nm window 400+ GHz spacing</p> <p> DWDM systems (mid 90s)16 to 40 channels in 1550 nm window 100 to 200 GHz spacing</p> <p> Next generation DWDM systems64 to 160 channels in 1550 nm window 50 and 25 GHz spacing 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Why DWDMThe Business CaseConventional TDM Transmission10 Gbps40km 40km 40km 40km 40km 40km 40km 40km 40km1310 1310 1310 1310 1310 1310 1310 1310 TERM TERM RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 TERM TERM RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 TERM TERM RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 TERM TERM RPTR RPTR RPTR RPTR RPTR RPTR RPTR RPTR</p> <p>OC-48 OC-48 OC-48 OC-48</p> <p>DWDM Transmission10 GbpsOA 120 km 120 km OA OA 120 km OA</p> <p>OC-48 OC-48 OC-48 OC-48</p> <p>4 Fibers Pairs 32 Regenerators 2003, Cisco Systems, Inc. All rights reserved.</p> <p>1 Fiber Pair 4 Optical Amplifiers</p> <p>Drivers of WDM Economics Fiber underground/underseaExisting fiber</p> <p> Conduit rights-of-wayLease or purchase</p> <p> DiggingTime-consuming, labor intensive, license $15,000 to $90,000 per Km</p> <p> 3R regeneratorsSpace, power, OPS in POP Re-shape, re-time and re-amplify</p> <p> Simpler network managementDelayering, less complexity, less elements 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Characteristics of a WDM NetworkWavelength Characteristics</p> <p> TransparencyCan carry multiple protocols on same fiber Monitoring can be aware of multiple protocols</p> <p> Wavelength spacing50GHz, 100GHz, 200GHz</p> <p>0 50 100 150 200 250 300 350 400</p> <p>Defines how many and which wavelengths can be used</p> <p> Wavelength capacityExample: 1.25Gb/s, 2.5Gb/s, 10Gb/s</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Optical Transmission BandsBand Wavelength (nm) 820 - 900 1260 1360 1360 1460 1460 1530 1530 1565 1565 1625 1625 1675</p> <p>New Band S-Band C-Band L-Band U-Band</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>ITU Wavelength Grid </p> <p>1530.33 nm 195.9 THz</p> <p>0.80 nm 100 GHz</p> <p>1553.86 nm 193.0 THz</p> <p> ITU-T grid is based on 191.7 THz + 100 GHz It is a standard for laser in DWDM systemsFreq (THz) 192.90 192.85 192.80 192.75 192.70 192.65 192.60 ITU Ch 29 28 27 26 Wave (nm) 15201/252 1554.13 x 1554.54 1554.94 x 1555.34 1555.75 x 1556.15 1556.55 x 15216 x x x x 15800 x x x x 15540 x x x x 15454 x x x x</p> <p> 2003, Cisco Systems, Inc. All rights reserved.</p> <p>Fiber Attenuation CharacteristicsAttenuation vs. Wavelength2.0 dB/Km Fibre Attenuation Curve S-Band:14601530nm L-Band:15651625nm</p> <p>0.5 dB/Km</p> <p>0.2 dB/Km 800 900 1000 1100 1200 1300 1400 1500 1600 C-Band:15301565nm</p> <p>Wavelength i...</p>
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