Intelligent Network Investment & Growth Begins With Fiber Characterization

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

2 Fujitsu Proprietary and Confidential All Rights Reserved, ©2006 Fujitsu Network Communications

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


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


Anatomy of Fiber Characterization

Tests?NO

You can only accurately diagnose

and prescribe the correct network with

testing

YES


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


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!


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?


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


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


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!

Fujitsu Proprietary and Confidential All Rights Reserved, ©2006 Fujitsu Network Communications

Practical Considerations In Multi-Gigabit DWDM Network Designs

Jake SentlingarSenior Network Architect – DWDM

December 6, 2006


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


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)


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


Basic Impediments to DWDM Transmission

Total span attenuation

Optical Noise

Dispersion

Non-linear effects


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


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


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


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


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


Basic Dispersion Types

Chromatic

Polarization mode


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


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


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


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


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


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


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


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

Intelligent Network Investment & Growth Begins With Fiber Characterization

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