intelligent network investment & growth begins with fiber characterization
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Intelligent Network Investment & Growth Begins With Fiber Characterization. Dave Hawkins, Senior Director of Professional Services Jake Sentlingar, Senior Network Architect Fujitsu Network Communications. Agenda. Fiber Characterization Overview Dave Hawkins - PowerPoint PPT PresentationTRANSCRIPT
Fujitsu Proprietary and Confidential All Rights Reserved, ©2006 Fujitsu Network Communications
Intelligent Network Investment & Growth Begins With Fiber Characterization
Dave Hawkins, Senior Director of Professional Services
Jake Sentlingar, Senior Network Architect
Fujitsu Network Communications
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Agenda
Fiber Characterization Overview
Dave Hawkins What is Fiber Characterization
Why it’s Essential to Test Fiber
Your Network Investment
Technical Overview of Fiber Testing
Jake Sentlingar DWDM Network Applications
Impediments to DWDM Transmission
DWDM Network Design
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Fiber Characterization
Who needs Fiber Characterization? Anyone considering deployment of a DWDM or high optical carrier (OC)
rate network elements
When?: Before the final network design and investment AND before moving to a 40 G network
What is it? An essential service to protect your future network investment by
letting you know if your embedded fiber will adhere to engineering specifications for critical fiber performance and support the desired network performance
What types of tests are conducted? Optical Time-Domain Optical Loss Chromatic Dispersion Polarization Mode Dispersion
Testing is required for any multi-gigabit network to function properly
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Anatomy of Fiber Characterization
Tests?NO
You can only accurately diagnose
and prescribe the correct network with
testing
YES
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Why Test Optical Fiber
Even if the fiber is originally “perfect”, events occurring during the life of the fiber can cause performance issues: Splicing Weather changes – i.e. repeated freezing & thawing Physical stress – impacts PMD Micro bends & crushed fibers Poor connector mating Dirty fiber or bulk heads
Impurities, imperfections and other variations can distort and scatter light traveling down a fiber This will cause power loss and signal disruption Certain fiber types are problematic even if new
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Do it Now or Do it Later…
Test fiber prior to final design: Guarantee your network
performance for 20 years
Create a benchmark for comparison
in the event of future issues
Or, you will test later to identify
the problem source: Attempt to fix issues, but it will
always be a non-optimized network
You may discover the need for
additional equipment
Or you may discover you bought too
much or even the wrong equipment
Delays are costly!
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Your Long Term Investment..
Investment in a DWDM network means you plan on future expansion DWDM supports 40Gb/s or 1.6 Terabits of
information Don’t buy your equipment without
testing your fiber While problems may not be immediately
apparent, any growth may require additional capital investment Example: You plan to support 32 wavelengths, but your
fiber may only work with 16 or fewer You may now need to double your
investment to achieve your intended capacity
Why buy DWDM and not care how many wavelengths you can put on it?
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Network Investment vs. Fiber Characterization Investment
OADM $60K
Example of Network Investment:
Terminal Basic Node $40K
& Up to 40 Transponders @
$25K each
OADM $60K
OADM $60K
Fiber Characterization investment:
4 spans *~$2500 = $10,000
Network investment
At full capacity (40 transponders): $2.26M
1 2 3 4
The cost of testing fiber is less than .5% of network investment!
Test Test Test Test
Terminal Basic Node $40K
& Up to 40 Transponders @
$25K each
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Potential Investment Impacts When Utilizing Incorrect Data
If you deploy a network using incorrect data, you will spend significantly more than an investment in Fiber Characterization ($10K for 4 spans)
You may also have unnecessary sunk cost in your network Your project will be delayed resulting in lost revenue And, your network will always be sub-optimized
Type of Incorrect Data Impact Solution CostActual loss is higher than
original data used to design the network
Planned amplifier will not
work
Buy 2 new amps per span $4,000 per amp. Plus, the 2 original
amplifiers already purchased cannot be utilized in the network
Actual loss is lower than original data used to design the network
Signal regenerators planned for the network are not
required
No action required but new design is warranted
Purchased $40K signal regenerator per wavelength that is not required
Fiber type provided is incorrect DCM's purchased will not
properly compensate for dispersion and even small
networks may fail
Buy 2 new DCM's per span $7,000 per DCM. Original DCMs
cannot be utilized
Distance is longer than original data
Undercompensate for chromatic dispersion
Transponders will not work on larger network, purchase
2 new DCMs per span.
$7,000 per DCM. Original DCMs cannot be utilized
Distance is shorter than original
data
Overcompensate for
chromatic dispersion
Transponder will not work,
purchase 2 new DCMs per span
$7,000 per DCM. Original DCMs
cannot be utilized
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Testing “Do”s and “Don’t”s
Do test your fiber to ensure it is capable of supporting DWDM or higher OC applications
Do all testing before finalizing design requirements If not performed - 90% chance at least one component will need reordering
Do hire a reliable outside source (other than fiber provider) to test fiber Do establish fiber records for ease in trouble- shooting Do seek a money back guarantee from network provider—many will
offer the guarantee only if you allow them to test the fiber Do re-shoot fiber if you are growing your network
Don’t think your network will not grow! Today, the standard is 40Gb/s and industry projections predict in 3 years that
100Gb/s will be the standard!
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Practical Considerations In Multi-Gigabit DWDM Network Designs
Jake SentlingarSenior Network Architect – DWDM
December 6, 2006
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DWDM Network Applications
Dense Wavelength Division (DWDM) began 20 years ago Utilizes the installed base of single mode fiber
Various fiber types• Differing DWDM-related (chromatic dispersion) characteristics
• Varying conformance to current standards
Plant records subject to relatively large inaccuracies Good to poor fiber deployment and maintenance practices
Metro, regional and long-haul deployments Linear, ring and mesh topologies Protected and unprotected paths per wavelength NOT a single circuit network – much more complex
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DWDM Systems
Multi-wavelength systems
Several to tens of wavelengths per fiber pair
Uni-directional per fiber
Primary operation in the C band (1530 nm to 1565 nm)
Predominantly 100 GHz wavelength spacing
Typically 40 wavelengths
Also operation in the L band (1565 nm to 1625 nm)
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DWDM Transmission Rates per Wavelength
Currently 2.5 Gb/s to 10 Gb/s
40 Gb/s in early 2007
100 Gb/s in 2010
Higher rates as the data market evolves
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Basic Impediments to DWDM Transmission
Total span attenuation
Optical Noise
Dispersion
Non-linear effects
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Total Span Attenuation
Fiber attenuation in the C band = approximately 0.25 dB/km Independent of fiber type
Connectors at fiber panels add 0.5 dB per mated pair Bypass sites Intra-building connections
Splice loss Near 0.1 dB per splice for state-of-the-art fusion splicing, but can be 0.5 dB per splice with older mechanical splicing
Maintenance splices (future fiber cuts) DWDM equipment Sum of these = Total span attenuation
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Amplifier Selection
Total span attenuation determines the required amplifier type Low attenuation = low gain amplifier = limited span length Moderate attenuation = moderate gain amplifier = less limited span High attenuation = high gain amplifier = least limited span length
Important to use the lowest gain amplifier that is necessary to: maximize Optical Signal to Noise Ratio (OSNR)
• I.e., maximize transponder-to-transponder reach before regeneration is required minimize capital expense
While insuring that the selected amplifier can also “recognize” the incoming attenuated DWDM composite signal
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Optical Noise
Amplifiers contribute noise, reducing the OSNR Noise contribution is a function of amplifier type and its input level
Cascading amplifiers reduces OSNR logarithmically Minimum OSNR must be met at the receiver/transponder
To maintain required bit error rate (BER) Over the twenty year service life
Per-wavelength regeneration is required if the minimum OSNR can not be achieved Expensive Avoid if possible
Use the correct amplifier
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OSNR Margin vs. Amplifier Gain
OSNR margin vs. number of spans by amplifier gain
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Number of equal-distant spans
OSNR margin
low gain
moderate gain
high gain
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Impact of the Incorrect Amplifier
Received Composite signal strength is lower than anticipated and lower than the amplifier’s acceptable range DWDM System fails to operate over that span Two new amplifiers must be obtained (one at each end of the span)
Received Composite signal strength is higher than anticipated and higher than the amplifier’s acceptable range Amplifier’s variable attenuators will adjust to proper operating range System operates but OSNR has been sacrificed Regeneration may be unnecessarily specified
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Basic Dispersion Types
Chromatic
Polarization mode
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Chromatic Dispersion
Pulse spreading caused by wavelengths within a pulse traveling at different speeds in the fiber Pulse widens and flattens Higher transmission rates can experience “pulse to pulse
overlap”
Total dispersion accumulated at each node is dependent on Span length Fiber type(s) in the span Residual dispersion at the previous node
Dispersion magnitude and slope in the C band differ by fiber type
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Dispersion by Fiber Type
Graph Dispersion vs. Wavelength by Fiber Type
-15
-10
-5
0
5
10
15
20
25
1400 1450 1500 1550 1600 1650
Wavelength (nm)
Dispersion (ps/nm-km)
SMF
TeraLight
TW-RS
LEAF
TW-Classic
DSF
SMF-LS
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Chromatic Dispersion Effects
Does not generally limit transponder-to-transponder reach at 2.5 Gb/s or below
Must be managed at 10Gb/s to maintain the pulse shape within the eye opening of the receiver/transponder Dispersion compensation modules specific to span fiber type are
often required Important NOT to overcompensate due to potential non-linear
effects
Several times more critical to properly manage at 40 Gb/s than at 10 Gb/s
Networks considering future 40Gb/s should insure that chromatic dispersion values are accurate before network design proceeds
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Polarization Mode Dispersion (PMD)
Pulse distortion caused by differing transmission speeds in the horizontal and vertical polarizations due to non-circular fiber Fiber manufactured prior to the mid-1990s did not have an objective
or standard for PMD Excessive PMD has been discovered in proposed DWDM networks
and alternate fiber paths were necessary (2 month delay)
Does not limit reach at 2.5 Gb/s or below
Should not exceed about 12 ps/nm-sqrt(km) transponder to transponder at 10 Gb/s
Should not exceed about 4 ps/nm-sqrt(km) transponder to transponder at 40 Gb/s
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Nonlinear effects
Energy transfer from one wavelength to another Caused by interaction of light waves with molecules in the silica medium
Stimulated Brillouin scattering (SBS)
Stimulated Raman scattering (SRS)
Also due to dependence of the refractive index on the
intensity of the applied electric field Self Phase Modulation (SPM) increases the pulse spreading also caused by
chromatic dispersion
Cross Phase Modulation (CPM) also increases pulse spreading in a channel
due to the variation on the refractive index with intensity on the other
channels
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Nonlinear effects (cont.)
Limiting launch power into the fiber is necessary to prevent SBS, SRS, SPM and CPM from disabling successful transmission These effects are negligible at controlled and limited launch power OR catastrophic at marginally higher launch power - i.e., they are
non-linear Therefore it is not possible to compensate for greater span
attenuation than anticipated by increasing the launch power into the fiber
Four Wave Mixing (crosstalk) is the creation of unwanted wavelengths due to mixing of launched wavelengths Effect can be reduced by insuring a well-controlled and minimal
amount of chromatic dispersion
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DWDM Network Design
The fiber data provided for each span is assumed by the DWDM network designer to be accurate
Inaccurate data will usually lead to the following: Delayed deployment Higher equipment and installation costs Non-optimized network Reduced 10 Gb/s reachability Potentially fewer usable wavelengths Reduced mesh applications Difficulty in adding future nodes Relatively limited 40 Gb/s deployment Some or all of the above, depending on the particular DWDM
network
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DWDM Network Design
Accurate span data is a key to a successful, timely and financially optimal DWDM network for initial wavelengths
Accurate span data is necessary to insure that the installed DWDM network provides best possible value over the system life Additional wavelengths Higher and higher transmission rates Mesh networks Nodes added or removed or reconfigured Evolving node types
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