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ONS 15454 MSTP DWDM Networking Primer October 2003

ONS 15454 MSTP DWDM Networking Primer October 2003. Introduction Optical Fundamentals Dense Wavelength Division Multiplexing (DWDM). Agenda. Optical Fundamentals. Some terminology. Decibels (dB): unit of level (relative measure)

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ONS 15454 MSTP DWDM Networking Primer October 2003

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  1. ONS 15454 MSTPDWDM Networking PrimerOctober 2003

  2. Introduction Optical Fundamentals Dense Wavelength Division Multiplexing (DWDM) Agenda

  3. Optical Fundamentals

  4. 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. • Decibels-milliwatt (dBm) : Decibel referenced to a milliwatt X mW is 10log10(X) in dBm, Y dBm is 10Y/10 in mW. 0dBm=1mW, 17dBm = 50mW • 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, & 1550nm • 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   x  = C

  5. Some more terminology • Attenuation = Loss of power in dB/km • The 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. • Chromatic Dispersion = Spread of light pulse in ps/nm-km • The separation of light into its different coloured rays. • 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

  6. dB versus dBm • dBm used for output power and receive sensitivity (Absolute Value) • dB used for power gain or loss (Relative Value)

  7. Bit Error Rate ( BER) • BER is a key objective of the Optical System Design • Goal is to get from Tx to Rx with a BER < BER threshold of the Rx • BER thresholds are on Data sheets • Typical minimum acceptable rate is 10 -12

  8. Optical Budget Basic Optical Budget = Output Power – Input Sensitivity Optical Budget is affected by: • Fiber attenuation • Splices • Patch Panels/Connectors • Optical components (filters, amplifiers, etc) • Bends in fiber • Contamination (dirt/oil on connectors) Pout = +6 dBm R = -30 dBm Budget = 36 dB

  9. Glass Purity Fiber Optics Requires Very High Purity Glass Window Glass 1 inch (~3 cm) Optical Quality Glass 10 feet (~3 m) Fiber Optics 9 miles (~14 km) Propagation Distance Need to Reduce the Transmitted Light Power by 50% (3 dB)

  10. Fiber Fundamentals Attenuation Dispersion Nonlinearity Distortion It May Be aDigitalSignal, but It’sAnalogTransmission Transmitted Data Waveform Waveform After 1000 Km

  11. Analog Transmission Effects Attenuation: Reduces power level with distance Dispersion and Nonlinearities: Erodes clarity with distance and speed Signal detection and recovery is an analog problem

  12. Fiber Geometry Core Cladding • An optical fiber is made ofthree sections: • The core carries thelight signals • The cladding keeps the lightin the core • The coating protects the glass Coating

  13. Propagation in Fiber n2 Cladding q1 q0 n1 Core Intensity Profile • Light propagates by total internal reflectionsat the core-cladding interface • Total internal reflections are lossless • Each allowed ray is a mode

  14. Different Types of Fiber n2 Cladding • Multimode fiber • Core diameter varies • 50 mm for step index • 62.5 mm for graded index • Bit rate-distance product>500 MHz-km • Single-mode fiber • Core diameter is about 9 mm • Bit rate-distance product>100 THz-km n1 Core n2 Cladding n1 Core

  15. C=¦ xl Wavelength:l (nanometers) Frequency:¦(terahertz) Optical Spectrum IR UV 125 GHz/nm l • Light • Ultraviolet (UV) • Visible • Infrared (IR) • Communication wavelengths • 850, 1310, 1550 nm • Low-loss wavelengths • Specialty wavelengths • 980, 1480, 1625 nm Visible 850 nm 980 nm 1310 nm 1480 nm 1550 nm 1625 nm

  16. Optical Attenuation • Specified in loss per kilometer (dB/km) • 0.40 dB/km at 1310 nm • 0.25 dB/km at 1550 nm • Loss due to absorptionby impurities • 1400 nm peak due to OH ions • EDFA optical amplifiers available in 1550 window 1550 Window 1310 Window

  17. Examples 10dBm 10 mW 1 mW 0 dBM -3 dBm 500 uW -10 dBm 100 uW 1 uW -30 dBm Optical Attenuation • Pulse amplitude reduction limits “how far” • Attenuation in dB • Power is measured in dBm: ) P P i 0 T T

  18. Types of Dispersion • Chromatic Dispersion Different wavelengths travel at different speeds Causes spreading of the light pulse • 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

  19. Interference A Snapshot on Chromatic Dispersion • 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

  20. 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 far” 10 Gbps t 60 Km SMF-28 40 Gbps t 4 Km SMF-28

  21. Combating Chromatic Dispersion • Use DSF and NZDSF fibers • (G.653 & G.655) • Dispersion Compensating Fiber • Transmitters with narrow spectral width

  22. Dispersion Compensating Fiber • 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

  23. Dispersion Compensation Total Dispersion Controlled +100 0 -100 -200 -300 -400 -500 Cumulative Dispersion (ps/nm) No Compensation With Compensation Distance fromTransmitter (km) Dispersion Shifted Fiber Cable Transmitter Dispersion Compensators

  24. How Far Can I Go Without Dispersion? Specification of Transponder (ps/nm) Distance (Km) = Coefficient of Dispersion of Fiber (ps/nm*km) 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.

  25. Polarization Mode Dispersion • Caused by ovality of core due to: • Manufacturing process • Internal stress (cabling) • External stress (trucks) • Only discovered inthe 90s • Most older fiber not characterized for PMD

  26. Ey Ex Pulse As It Enters the Fiber Spreaded Pulse As It Leaves the Fiber Polarization Mode Dispersion (PMD) nx ny • 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

  27. Combating Polarization Mode Dispersion • Factors contributing to PMD • Bit Rate • Fiber core symmetry • Environmental factors • Bends/stress in fiber • Imperfections in fiber • Solutions for PMD • Improved fibers • Regeneration • Follow manufacturer’s recommended installation techniques for the fiber cable

  28. Types of Single-Mode Fiber • SMF-28(e) (standard, 1310 nm optimized, G.652) • Most widely deployed so far, introduced in 1986, cheapest • DSF (Dispersion Shifted, G.653) • Intended for single channel operation at 1550 nm • 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 90’s • For better performance with high capacity DWDM systems • MetroCor, WideLight… • Low PMD ULH fibers

  29. Different Solutions forDifferent Fiber Types The primary Difference is in the Chromatic Dispersion Characteristics

  30. Loss of Energy Shape Distortion Phase Variation Loss of Timing (Jitter) (From Various Sources) t t ts Optimum Sampling Time ts Optimum Sampling Time The 3 “R”s of Optical Networking A Light Pulse Propagating in a Fiber Experiences 3 Type of Degradations: Pulse as It Enters the Fiber Pulse as It Exits the Fiber

  31. Amplify to Boost the Power Re-Shape DCU Phase Re-Alignment O-E-O Re-Generate t Re-gen, Re-shape and Remove Optical Noise ts Optimum Sampling Time t ts Optimum Sampling Time The 3 “R”s 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 Phase Variation t ts Optimum Sampling Time

  32. DWDM

  33. Agenda • Introduction • Components • Forward Error Correction • DWDM Design • Summary

  34. Increasing Network Capacity Options Same bit rate, more fibers Slow Time to Market Expensive Engineering Limited Rights of Way Duct Exhaust More Fibers (SDM) Same fiber & bit rate, more ls Fiber Compatibility Fiber Capacity Release Fast Time to Market Lower Cost of Ownership Utilizes existing TDM Equipment WDM Faster Electronics (TDM) Higher bit rate, same fiber Electronics more expensive

  35. Fiber Networks • Time division multiplexing • Single 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 • Wave division multiplexing • Multiple wavelengths per fiber • 4, 16, 32, 64 channels per system • Multiple channels per fiber Channel 1 Single Fiber (One Wavelength) Channel n l1 l2 Single Fiber (Multiple Wavelengths) ln

  36. 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 • (D)WDM • Takes multiple optical signals and multiplexes onto a single fiber • No signal format conversion DS-1 DS-3 OC-1 OC-3 OC-12 OC-48 SONET ADM Fiber OC-12c OC-48c OC-192c DWDM OADM Fiber

  37. DWDM History • Early WDM (late 80s) • Two widely separated wavelengths (1310, 1550nm) • “Second generation” WDM (early 90s) • Two to eight channels in 1550 nm window • 400+ GHz spacing • DWDM systems (mid 90s) • 16 to 40 channels in 1550 nm window • 100 to 200 GHz spacing • Next generation DWDM systems • 64 to 160 channels in 1550 nm window • 50 and 25 GHz spacing

  38. Why DWDM—The Business Case Conventional TDM Transmission—10 Gbps 40km 40km 40km 40km 40km 40km 40km 40km 40km TERM TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR DWDM Transmission—10 Gbps OC-48 OC-48 OC-48 OC-48 120 km 120 km OC-48 120 km OC-48 OC-48 OC-48 OA OA OA OA 4 Fibers Pairs 32 Regenerators 1 Fiber Pair 4 Optical Amplifiers

  39. Drivers of WDM Economics • Fiber underground/undersea • Existing fiber • Conduit rights-of-way • Lease or purchase • Digging • Time-consuming, labor intensive, license • $15,000 to $90,000 per Km • 3R regenerators • Space, power, OPS in POP • Re-shape, re-time and re-amplify • Simpler network management • Delayering, less complexity, less elements

  40. Characteristics of a WDM NetworkWavelength Characteristics • Transparency • Can carry multiple protocols on same fiber • Monitoring can be aware of multiple protocols • Wavelength spacing • 50GHz, 100GHz, 200GHz • Defines how many and which wavelengths can be used • Wavelength capacity • Example: 1.25Gb/s, 2.5Gb/s, 10Gb/s 0 50 100 150 200 250 300 350 400

  41. Optical Transmission Bands

  42. ITU Wavelength Grid l 1553.86 nm 1530.33 nm 0.80 nm  193.0 THz 195.9 THz 100 GHz • ITU-T l grid is based on 191.7 THz + 100 GHz • It is a standard for laser in DWDM systems

  43. L-Band:1565–1625nm 1600 800 900 1000 1100 1200 1300 1400 1500 C-Band:1530–1565nm Fiber Attenuation Characteristics Attenuation vs. Wavelength S-Band:1460–1530nm 2.0 dB/Km Fibre Attenuation Curve 0.5 dB/Km 0.2 dB/Km Wavelength in Nanometers (nm)

  44. Characteristics of a WDM NetworkSub-wavelength Multiplexing or MuxPonding Ability to put multiple services onto a single wavelength

  45. Why DWDM?The Technical Argument • DWDM provides enormous amounts of scaleable transmission capacity • Unconstrained by speed ofavailable electronics • Subject to relaxed dispersion and nonlinearity tolerances • Capable of graceful capacity growth

  46. Agenda • Introduction • Components • Forward Error Correction • DWDM Design

  47. Optical Add/Drop Multiplexer (OADM) DWDM Components l1 l1...n 850/1310 15xx l2 l3 Transponder Optical Multiplexer l1 l1 l1...n l2 l2 l3 l3 Optical De-multiplexer

  48. More DWDM Components Optical Amplifier (EDFA) Optical Attenuator Variable Optical Attenuator Dispersion Compensator (DCM / DCU)

  49. Typical DWDM Network Architecture DWDM SYSTEM DWDM SYSTEM VOA EDFA DCM DCM EDFA VOA Service Mux (Muxponder) Service Mux (Muxponder)

  50. l2 OEO OEO OEO ln Transponders • Converts broadband optical signals to a specific wavelength via optical to electrical to optical conversion (O-E-O) • Used when Optical LTE (Line Termination Equipment) does not have tight tolerance ITU optics • Performs 2R or 3R regeneration function • Receive Transponders perform reverse function l1 From Optical OLTE To DWDM Mux Low Cost IR/SR Optics Wavelengths Converted

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