40g dwdm troubleshooting final 42273

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Housekeeping...

Troubleshooting a 40G DWDM Circuit, Step by Step

Case Study

Aaron Deragon Application Engineer, EXFO

January 14, 2014

4 © 2014 EXFO Inc. All rights reserved..

The Problem

› Customer contacted us stating:

› 40G link taking correctable FEC errors

› Initially, errors at one end

› Swapped Tx and Rx fibers, errors appeared at other end

› A problem on the fiber pair is suspected, but not visible


Additional Information

› ~50 km link, including old fiber

› Currently, 17 active DWDM channels including one 40G

non-coherent channel

› Link is using non-coherent 40G cards:

› DQPSK muxponder ($40k USD on Ebay)

› 4 x 10G inputs – 1 x 40G output

› Up to 80 DWDM channels at 40G

› Boost amp

› Pre-amp

› 32-channel WSS (λ selective switch)

› 32-channel DMX (includes variable attenuators)

› CD compensators


The Network

Amplifier

Amplifier


The Network

Amplifier

Amplifier

DCM

DCM


The Network

Amplifier

Amplifier

DCM

DCM

ROADM Functionality

ROADM Functionality


The Network

Amplifier

Amplifier

DCM

DCM

~50km

ROADM Functionality

ROADM Functionality


Hypothesis

› CD not suspected – short, compensated link

› Problem follows fiber, so PMD or ORL suspected

› Some fiber is very old (~20 years), potential PMD

› If ORL, then Tx would be disrupted and cause errors

› Only one fiber seems to be causing issues (errors at one end only)


Goals

› Asked us to help by:

› Determining cause of errors on active link

› Pre-characterizing spare fiber pair to potentially roll to


Equipment

› We used:

› FTB-730 with iOLM

› FTB-5240S-P with WDM Investigator

› FTB-5700

› FOT-930 and FTB-3930

› FIP-400D with cleaning supplies


Our Process

› Larry

› iOLM spare fibers for loss, ORL and length

› UPC patchcord connector for FTB-5700

› Aaron

› OSA monitors all ports to piece story together


Test Results – iOLM Spare Fiber 1

Good Loss Good ORL APC End Event



Good Loss Good ORL APC End Event



Good Loss Good ORL UPC End Event (now)


Test Results – CD and PMD on Fiber 1


Test Results – CD and PMD on Fiber 2


Test Results – OSA at Location A on Fiber 1



40G

40G Channel λ = 1546.924nm OSNR = 35.55dB Power = -7.62dBm Noise floor = -43.16dBm


Test Results – OSA at Location B on Fiber 2

40 G Channel λ = 1546.925nm OSNR = 34.67dB Power = -21.37dBm Noise Floor = -56.03dBm

40G


Actions Taken

› One good spare fiber and one good in-service fiber

› Original testing performed on October 21

› Service rolled to good fibers on October 23

› Error-free operation since


Deeper Dive

› On November 4, testing performed with FTB-5600 QP-OTDR


Spare Fiber – Failed PMD (17 ps)


Active Fiber – WDMI Showed Failing PMD


Conclusion

› iOLM was perfect for single-ended ORL and loss testing

› FTB-5700 was perfect for single-ended PMD testing of dark

fiber

› FTB-5240S-P and WDMI was perfect for in-service, passive

PMD testing

› FTB-5600 QP-OTDR was perfect for identifying the specific

span to replace

› Customer requested iOLM upgrades, WDMI upgrades, trade

for FTB-5700 and possible FTB-5600 purchase ($300K)


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40g dwdm troubleshooting final 42273

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