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© 2003, Cisco Systems, Inc. All rights reserved. DWDM Networking Primer ONS 15454 MSTP DWDM Networking Primer October 2003.

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Presentation on theme: "© 2003, Cisco Systems, Inc. All rights reserved. DWDM Networking Primer ONS 15454 MSTP DWDM Networking Primer October 2003."— Presentation transcript:

1 © 2003, Cisco Systems, Inc. All rights reserved. DWDM Networking Primer ONS MSTP DWDM Networking Primer October 2003

2 © 2003, Cisco Systems, Inc. All rights reserved. Agenda Introduction Optical Fundamentals Dense Wavelength Division Multiplexing (DWDM)

3 © 2003, Cisco Systems, Inc. All rights reserved. Optical Fundamentals

4 © 2003, Cisco Systems, Inc. All rights reserved. Decibels (dB): unit of level (relative measure) X dB is 10 -X/10 in linear dimension e.g. 3 dB Attenuation = = 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  log 10 (X) in dBm, Y dBm is 10 Y/10 in mW. 0dBm=1mW, 17dBm = 50mW Wavelength ( ): length of a wave in a particular medium. Common unit: nanometers, m (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, cycles per second (Thz) Wavelength x frequency = Speed of light  x = C Some terminology

5 © 2003, Cisco Systems, Inc. All rights reserved. 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 Some more terminology

6 © 2003, Cisco Systems, Inc. All rights reserved. dB versus dBm dBm used for output power and receive sensitivity (Absolute Value) dB used for power gain or loss (Relative Value)

7 © 2003, Cisco Systems, Inc. All rights reserved. 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

8 © 2003, Cisco Systems, Inc. All rights reserved. Optical Budget Optical Budget is affected by: Fiber attenuation Splices Patch Panels/Connectors Optical components (filters, amplifiers, etc) Bends in fiber Contamination (dirt/oil on connectors) Basic Optical Budget = Output Power – Input Sensitivity P out = +6 dBmR = -30 dBm Budget = 36 dB

9 © 2003, Cisco Systems, Inc. All rights reserved. Glass Purity Propagation Distance Need to Reduce the Transmitted Light Power by 50% (3 dB) Window Glass1 inch (~3 cm) Optical Quality Glass10 feet (~3 m) Fiber Optics9 miles (~14 km) Fiber Optics Requires Very High Purity Glass

10 © 2003, Cisco Systems, Inc. All rights reserved. Attenuation Dispersion Nonlinearity Waveform After 1000 KmTransmitted Data Waveform Distortion It May Be a Digital Signal, but It’s Analog Transmission Fiber Fundamentals

11 © 2003, Cisco Systems, Inc. All rights reserved. Attenuation: Reduces power level with distance Dispersion and Nonlinearities: Erodes clarity with distance and speed Signal detection and recovery is an analog problem Analog Transmission Effects

12 © 2003, Cisco Systems, Inc. All rights reserved. CladdingCore Coating Fiber Geometry 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

13 © 2003, Cisco Systems, Inc. All rights reserved.  n2n2 n1n1 Cladding  Core Intensity Profile Propagation in Fiber Light propagates by total internal reflections at the core-cladding interface Total internal reflections are lossless Each allowed ray is a mode

14 © 2003, Cisco Systems, Inc. All rights reserved. n2n2 n1n1 Cladding Core n2n2 n1n1 Cladding Core Different Types of Fiber 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

15 © 2003, Cisco Systems, Inc. All rights reserved. Light Ultraviolet (UV) Visible Infrared (IR) Communication wavelengths 850, 1310, 1550 nm Low-loss wavelengths Specialty wavelengths 980, 1480, 1625 nm UV IR Visible 850 nm 980 nm 1310 nm 1480 nm 1550 nm 1625 nm 125 GHz/nm Wavelength:  (nanometers) Frequency:   (terahertz) C =  x Optical Spectrum

16 © 2003, Cisco Systems, Inc. All rights reserved. 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 absorption by impurities 1400 nm peak due to OH ions EDFA optical amplifiers available in 1550 window 1310 Window 1550 Window

17 © 2003, Cisco Systems, Inc. All rights reserved. T T P i P 0 Optical Attenuation Pulse amplitude reduction limits “how far” Attenuation in dB Power is measured in dBm: Examples 10dBm 10 mW 0 dBM 1 mW -3 dBm 500 uW -10 dBm 100 uW -30 dBm 1 uW )

18 © 2003, Cisco Systems, Inc. All rights reserved. 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 Chromatic Dispersion Different wavelengths travel at different speeds Causes spreading of the light pulse Types of Dispersion

19 © 2003, Cisco Systems, Inc. All rights reserved. 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 Interference A Snapshot on Chromatic Dispersion

20 © 2003, Cisco Systems, Inc. All rights reserved. 60 Km SMF-28 4 Km SMF Gbps 40 Gbps Limitations From Chromatic Dispersion t t 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”

21 © 2003, Cisco Systems, Inc. All rights reserved. Combating Chromatic Dispersion Use DSF and NZDSF fibers (G.653 & G.655) Dispersion Compensating Fiber Transmitters with narrow spectral width

22 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. Dispersion Compensation Transmitter Dispersion Compensators Dispersion Shifted Fiber Cable Cumulative Dispersion (ps/nm) Total Dispersion Controlled Distance from Transmitter (km) No Compensation With Compensation

24 © 2003, Cisco Systems, Inc. All rights reserved. How Far Can I Go Without Dispersion? Distance (Km) = Specification of Transponder (ps/nm) 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 © 2003, Cisco Systems, Inc. All rights reserved. Polarization Mode Dispersion Caused by ovality of core due to: Manufacturing process Internal stress (cabling) External stress (trucks) Only discovered in the 90s Most older fiber not characterized for PMD

26 © 2003, Cisco Systems, Inc. All rights reserved. Polarization Mode Dispersion (PMD) 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 nxnx nyny Ex Ey Pulse As It Enters the Fiber Spreaded Pulse As It Leaves the Fiber

27 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. 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 Types of Single-Mode Fiber

29 © 2003, Cisco Systems, Inc. All rights reserved. The primary Difference is in the Chromatic Dispersion Characteristics Different Solutions for Different Fiber Types SMF (G.652) Good for TDM at 1310 nm OK for TDM at 1550 OK for DWDM (With Dispersion Mgmt) DSF (G.653) OK for TDM at 1310 nm Good for TDM at 1550 nm Bad for DWDM (C-Band) NZDSF (G.655) OK for TDM at 1310 nm Good for TDM at 1550 nm Good for DWDM (C + L Bands) Extended Band (G.652.C) (suppressed attenuation in the traditional water peak region) Good for TDM at 1310 nm OK for TDM at 1550 nm OK for DWDM (With Dispersion Mgmt Good for CWDM (>8 wavelengths)

30 © 2003, Cisco Systems, Inc. All rights reserved. The 3 “R”s of Optical Networking A Light Pulse Propagating in a Fiber Experiences 3 Type of Degradations: Loss of Energy Loss of Timing (Jitter) (From Various Sources) Loss of Timing (Jitter) (From Various Sources) t t s Optimum Sampling Time t Phase Variation Shape Distortion Pulse as It Enters the FiberPulse as It Exits the Fiber

31 © 2003, Cisco Systems, Inc. All rights reserved. Re-Shape DCU 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 FiberPulse as It Exits the Fiber Amplify to Boost the Power t t s Optimum Sampling Time t Phase Variation Re-Generate O-E-O Re-gen, Re-shape and Remove Optical Noise t t s Optimum Sampling Time Phase Re-Alignment

32 © 2003, Cisco Systems, Inc. All rights reserved. DWDM

33 © 2003, Cisco Systems, Inc. All rights reserved. Agenda Introduction Components Forward Error Correction DWDM Design Summary

34 © 2003, Cisco Systems, Inc. All rights reserved. Increasing Network Capacity Options Faster Electronics (TDM) Higher bit rate, same fiber Electronics more expensive More Fibers (SDM) Same bit rate, more fibers Slow Time to Market Expensive Engineering Limited Rights of Way Duct Exhaust WDMWDM Same fiber & bit rate, more s Fiber Compatibility Fiber Capacity Release Fast Time to Market Lower Cost of Ownership Utilizes existing TDM Equipment

35 © 2003, Cisco Systems, Inc. All rights reserved. Single Fiber (One Wavelength) Channel 1 Channel n Single Fiber (Multiple Wavelengths) l1 l2 ln 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 OC-3 channels in OC-48 Wave division multiplexing Multiple wavelengths per fiber 4, 16, 32, 64 channels per system Multiple channels per fiber

36 © 2003, Cisco Systems, Inc. All rights reserved. DS-1DS-3OC-1OC-3OC-12OC-48 OC-12cOC-48cOC-192c Fiber DWDMOADM SONETADM Fiber 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

37 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. TERM Conventional TDM Transmission—10 Gbps 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM 40km 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR 1310 RPTR TERM 120 km OC-48 OA 120 km OC-48 DWDM Transmission—10 Gbps 1 Fiber Pair 4 Optical Amplifiers Why DWDM—The Business Case TERM 4 Fibers Pairs 32 Regenerators 40km

39 © 2003, Cisco Systems, Inc. All rights reserved. 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 © 2003, Cisco Systems, Inc. All rights reserved. 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 Characteristics of a WDM Network Wavelength Characteristics

41 © 2003, Cisco Systems, Inc. All rights reserved. Optical Transmission Bands BandWavelength (nm) – 1360 “New Band”1360 – 1460 S-Band1460 – 1530 C-Band1530 – 1565 L-Band1565 – 1625 U-Band1625 – 1675

42 © 2003, Cisco Systems, Inc. All rights reserved. ITU Wavelength Grid ITU-T grid is based on THz GHz It is a standard for laser in DWDM systems nm nm 0.80 nm THz THz 100 GHz

43 © 2003, Cisco Systems, Inc. All rights reserved Wavelength in Nanometers (nm) 0.2 dB/Km 0.5 dB/Km 2.0 dB/Km Attenuation vs. Wavelength S-Band:1460–1530nm L-Band:1565–1625nm C-Band:1530–1565nm Fiber Attenuation Characteristics Fibre Attenuation Curve

44 © 2003, Cisco Systems, Inc. All rights reserved. Ability to put multiple services onto a single wavelength Characteristics of a WDM Network Sub-wavelength Multiplexing or MuxPonding

45 © 2003, Cisco Systems, Inc. All rights reserved. Why DWDM? The Technical Argument DWDM provides enormous amounts of scaleable transmission capacity Unconstrained by speed of available electronics Subject to relaxed dispersion and nonlinearity tolerances Capable of graceful capacity growth

46 © 2003, Cisco Systems, Inc. All rights reserved. Agenda Introduction Components Forward Error Correction DWDM Design

47 © 2003, Cisco Systems, Inc. All rights reserved. Optical Multiplexer Optical De-multiplexer Optical Add/Drop Multiplexer (OADM) Transponder DWDM Components  15xx n

48 © 2003, Cisco Systems, Inc. All rights reserved. Optical Amplifier (EDFA) Optical Attenuator Variable Optical Attenuator Dispersion Compensator (DCM / DCU) More DWDM Components

49 © 2003, Cisco Systems, Inc. All rights reserved. VOAEDFADCM VOAEDFADCM Service Mux (Muxponder) Service Mux (Muxponder) DWDM SYSTEM Typical DWDM Network Architecture

50 © 2003, Cisco Systems, Inc. All rights reserved. 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 Low Cost IR/SR Optics Wavelengths Converted 1 From Optical OLTE To DWDM Mux OEO 2 n

51 © 2003, Cisco Systems, Inc. All rights reserved. Performance Monitoring Performance monitoring performed on a per wavelength basis through transponder No modification of overhead Data transparency is preserved

52 © 2003, Cisco Systems, Inc. All rights reserved. Laser Characteristics c Power Power c DWDM Laser Distributed Feedback (DFB) Active medium Mirror Partially transmitting Mirror Amplified light Non DWDM Laser Fabry Perot Spectrally broad Unstable center/peak wavelength Dominant single laser line Tighter wavelength control

53 © 2003, Cisco Systems, Inc. All rights reserved. DWDM Receiver Requirements Receivers Common to all Transponders Not Specific to wavelength (Broadband) I

54 © 2003, Cisco Systems, Inc. All rights reserved. Optical Amplifier P out = GP in P in EDFA amplifiers Separate amplifiers for C-band and L-band Source of optical noise Simple G G

55 © 2003, Cisco Systems, Inc. All rights reserved. OA Gain Typical Fiber Loss 4 THz 25 THz OA Gain and Fiber Loss OA gain is centered in 1550 window OA bandwidth is less than fiber bandwidth

56 © 2003, Cisco Systems, Inc. All rights reserved. Erbium Doped Fiber Amplifier “Simple” device consisting of four parts: Erbium-doped fiber An optical pump (to invert the population). A coupler An isolator to cut off backpropagating noise IsolatorCouplerIsolatorCoupler Erbium-Doped Fiber (10–50m) Pump Laser Pump Laser Pump Laser Pump Laser

57 © 2003, Cisco Systems, Inc. All rights reserved. Optical Signal-to Noise Ratio (OSNR) Depends on : Optical Amplifier Noise Figure: (OSNR) in = (OSNR) out NF Target : Large Value for X Signal Level Noise Level X dB EDFA Schematic (OSNR) out (OSNR) in NF P in

58 © 2003, Cisco Systems, Inc. All rights reserved. Loss Management: Limitations Erbium Doped Fiber Amplifier Each amplifier adds noise, thus the optical SNR decreases gradually along the chain; we can have only have a finite number of amplifiers and spans and eventually electrical regeneration will be necessary Gain flatness is another key parameter mainly for long amplifier chains Each EDFA at the Output Cuts at Least in a Half (3dB) the OSNR Received at the Input Noise Figure > 3 dB Typically between 4 and 6 Noise Figure > 3 dB Typically between 4 and 6

59 © 2003, Cisco Systems, Inc. All rights reserved.       n      n Dielectric Filter Well established technology, up to 200 layers Optical Filter Technology

60 © 2003, Cisco Systems, Inc. All rights reserved. Multiplexer / Demultiplexer Wavelengths Converted via Transponders Wavelength Multiplexed Signals DWDM Mux DWDM Demux Wavelength Multiplexed Signals Wavelengths separated into individual ITU Specific lambdas Loss of power for each Lambda

61 © 2003, Cisco Systems, Inc. All rights reserved. Optical Add/Drop Filters (OADMs) OADMs allow flexible add/drop of channels Drop Channel Add Channel Drop & Insert Pass Through loss and Add/Drop loss

62 © 2003, Cisco Systems, Inc. All rights reserved. Agenda Introduction Components Forward Error Correction DWDM Design Summary

63 © 2003, Cisco Systems, Inc. All rights reserved. Transmission Errors Errors happen! A old problem of our era (PCs, wireless…) Bursty appearance rather than distributed Noisy medium (ASE, distortion, PMD…) TX/RX instability (spikes, current surges…) Detect is good, correct is better Transmitter Receiver Transmission Channel Information Noise

64 © 2003, Cisco Systems, Inc. All rights reserved. Error Correction Error correcting codes both detect errors and correct them Forward Error Correction (FEC) is a system adds additional information to the data stream corrects eventual errors that are caused by the transmission system. Low BER achievable on noisy medium

65 © 2003, Cisco Systems, Inc. All rights reserved. FEC Performance, Theoretical FEC gain  BER

66 © 2003, Cisco Systems, Inc. All rights reserved. FEC in DWDM Systems FEC implemented on transponders (TX, RX, 3R) No change on the rest of the system IP SDH ATM.... FEC 2.48 G 2.66 G 9.58 G10.66 G IP SDH ATM.... FEC 2.66 G 2.48 G G 9.58 G

67 © 2003, Cisco Systems, Inc. All rights reserved. Agenda Introduction Components Forward Error Correction DWDM Design Summary

68 © 2003, Cisco Systems, Inc. All rights reserved. DWDM Design Topics DWDM Challenges Unidirectional vs. Bidirectional Protection Capacity Distance

69 © 2003, Cisco Systems, Inc. All rights reserved. Transmission Effects Attenuation: Reduces power level with distance Dispersion and nonlinear effects: Erodes clarity with distance and speed Noise and Jitter: Leading to a blurred image

70 © 2003, Cisco Systems, Inc. All rights reserved. OA Solution for Attenuation Loss Optical Amplification

71 © 2003, Cisco Systems, Inc. All rights reserved. Solution For Chromatic Dispersion Length Dispersion +D -D Dispersion Saw Tooth Compensation Saw Tooth Compensation Total dispersion averages to ~ zero Fiber spool DCU

72 © 2003, Cisco Systems, Inc. All rights reserved. Uni Versus Bi-directional DWDM DWDM systems can be implemented in two different ways Bi-directional     Fiber     Uni-directional     Fiber             Uni-directional: wavelengths for one direction travel within one fiber two fibers needed for full-duplex system Bi-directional: a group of wavelengths for each direction single fiber operation for full- duplex system

73 © 2003, Cisco Systems, Inc. All rights reserved. Uni Versus Bi-directional DWDM (cont.) Uni-directional 32 channels system Bi-directional 32 channels system 32 ch full duplex 16 ch full duplex

74 © 2003, Cisco Systems, Inc. All rights reserved. DWDM Protection Review Y-Cable and Line Card Protected Client ProtectedUnprotected Splitter Protected

75 © 2003, Cisco Systems, Inc. All rights reserved. 1 Transponder 1 Client Interface 1 client & 1 trunk laser (one transponder) needed, only 1 path available No protection in case of fiber cut, transponder failure, client failure, etc.. Unprotected

76 © 2003, Cisco Systems, Inc. All rights reserved. 2 Transponders 2 Client interfaces 2 client & 2 trunk lasers (two transponders) needed, two optically unprotected paths Protection via higher layer protocol Client Protected Mode

77 © 2003, Cisco Systems, Inc. All rights reserved. Only 1 client & 1 trunk laser (single transponder) needed Protects against Fiber Breaks Optical Splitter Switch Working lambda protected lambda Optical Splitter Protection

78 © 2003, Cisco Systems, Inc. All rights reserved. 2 client & 2 trunk lasers (two transponders) needed Increased cost & availability 2 Transponders Only one TX active working lambda protected lambda “Y” cable Line Card / Y- Cable Protection

79 © 2003, Cisco Systems, Inc. All rights reserved. Wavelengths Bit Rate Distance Solution Space Designing for Capacity Goal is to maximize transmission capacity and system reach Figure of merit is Gbps Km Long-haul systems push the envelope Metro systems are considerably simpler

80 © 2003, Cisco Systems, Inc. All rights reserved. Designing for Distance Amplifier Spacing G = Gain of Amplifier S P out P noise P in D = Link Distance L = Fiber Loss in a Span Link distance (D) is limited by the minimum acceptable electrical SNR at the receiver Dispersion, Jitter, or optical SNR can be limit Amplifier spacing (S) is set by span loss (L) Closer spacing maximizes link distance (D) Economics dictates maximum hut spacing

81 © 2003, Cisco Systems, Inc. All rights reserved. Link Distance vs. OA Spacing Total System Length (km) Wavelength Capacity (Gb/s) Amp Spacing 60 km 80 km 100 km 120 km 140 km System cost and and link distance both depend strongly on OA spacing

82 © 2003, Cisco Systems, Inc. All rights reserved. OEO Regeneration in DWDM Networks Long Haul OA noise and fiber dispersion limit total distance before regeneration Optical-Electrical-Optical conversion Full 3R functionality: Reamplify, Reshape, Retime Longer spans can be supported using back to back systems

83 © 2003, Cisco Systems, Inc. All rights reserved. Express channels must be regenerated Two complete DWDM terminals needed Provides drop-and- continue functionality Express channels only amplified, not regenerated Reduces size, power and cost Back-to-back DWDM Optical add/drop multiplexer N OADM N N N 3R with Optical Multiplexor and OADM

84 © 2003, Cisco Systems, Inc. All rights reserved. Agenda Introduction Components Forward Error Correction DWDM Design Summary

85 © 2003, Cisco Systems, Inc. All rights reserved. DWDM Benefits DWDM provides hundreds of Gbps of scalable transmission capacity today Provides capacity beyond TDM’s capability Supports incremental, modular growth Transport foundation for next generation networks

86 © 2003, Cisco Systems, Inc. All rights reserved. Metro DWDM Metro DWDM is an emerging market for next generation DWDM equipment The value proposition is very different from the long haul Rapid-service provisioning Protocol/bitrate transparency Carrier Class Optical Protection Metro DWDM is not yet as widely deployed

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