Optical Performance Monitoring Applications in Transparent Networks - - PowerPoint PPT Presentation

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Optical Performance Monitoring Applications in Transparent Networks

Dan Kilper Advanced Photonics Research Lucent Technologies dkilper@lucent.com

• C. R. Giles, W. Weingartner, A. Azarov, P. Vorreau,

and J. Leuthold

WOCC April 22, 2005 Newark, NJ

2 Old Technology

Ultra-long Transport Systems

Point-to-Point Transparency

Current

ROADM ROADM End Terminal (opaque) End Terminal (opaque)

4000km at 10Gb/s >2000km at 40Gb/s

OA Repeaters

Mitigation of: Noise Dispersion Gain variation Nonlinearity Advanced Technologies: Raman Amplification Dispersion Managed Solitons Dynamic Gain Equalization DPSK, Advanced Modulation Formats

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ULH+ROADM/OXC MESH NETWORK ULH+ROADM/OXC MESH NETWORK

N E S W

λ1 λ2 λ3 λ4 λ5 λ6 λ7

MOADM

A B

ET ET ET ET

C D

λ4 λ5 λ1 λ2 λ3 λ7 λ12 λ6 λ10λ11 λ12 λ10λ11

Operational Complexity + Advanced Technology Advanced Monitoring Transparent Reconfiguration

• Intersecting lines must discover one another and exchange topology information.
• Auto-provisioning must operate across the mesh network.
• Faults are correlated across multiple systems.
• Greater flexibility requires better stability & control

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Optical Network Performance Monitoring

• First Generation: Total power monitoring. Amplifier gain adjustment,

signal presence, link status verification.

• Second Generation: WDM channel presence / power and wavelength.

Auto-provisioning and gain flattening.

• Third Generation: Channel optical SNR / Q-factor, active dispersion
• compensation. Fault isolation, dispersion compensation.
• Fourth Generation: Transparent network management. Channel

performance verification after link concatenation.

• Fifth Generation: In-situ link parameter extraction from detailed

channel signatures. Preplanning / preprovisioning assessment. Resource database creation.

T O D A Y

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Eliminating Regenerators

• Must also consider fault management requirements
• Cost of OADM/ULH technology (DGEF)/OPM < OEO

500 km 500 km 600 km

OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO

1600+ km

OPM OPM

OADM

DGEF

OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO

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3G: DWDM Fault Management

OPM OPM OPM

OEO OEO OEO OEO OEO

OPM OPM OPM OPM OPM OPM

Report BER degradation Read out OPM history: compare actual performance with stored reference Locate degradation: dispatch maintenance

• Advanced technologies/network complexities

– Component alarms may be insufficient

• Need OPM that correlates with end terminal BER

– OPM registers change when end terminal BER alarm triggers

• OPM granularity to suit carrier opex goals

OADM OEO OEO OEO OEO OEO OADM

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Electronic Fault Management

• BER monitoring is sufficient

– No errors in: No errors out – Noise does not propagate past regenerators

• Isolate faults to ~600 km

OSNR: BER Distance

500 km 500 km 600 km

OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO

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Ultra-Long Haul Transmission

1800+ km

• Replace OEOs with OA repeaters: lose fault isolation
• BER at OA repeaters has limited benefit
• Noise propagates through repeaters

Error Free Distance OSNR:

OPM OPM OPM

OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO

Error Free

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5 10 15 20 25 30 10 15 20 25 30 35 OSNR (dB) Node #

‘Good’ ‘Impaired’ Fault Location

BER: 10-12 10-9 Fault Metrics: 10 dB BER drop 10-9 BER threshold

Fault Isolation

• Need sensitivity to wide variety of impairments.
• BER 10-9 gives ~ 4 orders of magnitude

advanced warning in FEC-based links.

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• BER Measurement

– Sensitive to end terminal impairments – Problem: BER in network better than end term.

• Noise loaded BER measurement

– Sensitivity close to BER

• Other methods: OSNR, half-clock, pol.

ext., histograms, tones, autocorrelation, …

– Must show advantage over Q/BER approach

• Cost/sensitivity/impairment coverage

– Target systems that cannot use Q-factor

Q Factor OPM Fault Management Technologies

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Q Factor

• Signal to Noise Ratio Measurement

10G RZ Eye Diagram Vth

Noise Signal Q → + − =

1 1

σ σ µ µ

µ0 σ1 σ0 µ1

( )

                − +         − = 2 2

1 1 4 1

σ µ σ µ

th th th

V erfc V erfc V BER

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Q Factor Monitoring Techniques

(A) Variable threshold, dual decision – eye mapping (B) Variable threshold, use FEC/integrate data (C) Asynchronous histogram methods

• Sensitivity questions

(D) Sampling techniques

Asynch. part

(C)

Vthr

(B) (D) (A)

Vthr Vref

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FEC Error Count Eye Mapping

• Vary voltage threshold across center of eye
• Use commercial 10 Gb/s receiver

1.1 1.2 1.3 1.4 1.5 1.6 1.7

• 10
• 9
• 8
• 7
• 6
• 5
• 4
• 3
• 2

Log(BER) Decision Level (Volts)

Low OSNR High OSNR

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Q-factor vs. time

• Determined measurement noise contributions

under different conditions

• Error due to counting statistics, threshold voltage

accuracy, power fluctuations

2000 4000 6000 8000 10000 13 14 15 16 17 18 19 20 Fixed Decision Level Variable Decision Level

Q-factor (dB) Time (sec)

Vary OSNR

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Dispersion map issues

• Q factor varies with dispersion map
• 10Gb/s: up to 1000 ps/nm

– OK for trend monitoring

• 40 Gb/s: eye closed until end terminal

– Would need per-channel DCM/tunable DCM – Also obstacle to 40G optical networks

… …

+300 ps/nm

Distance node ∆Q sensitivity is weakly dependent

• n magnitude of

Q factor

• 300 ps/nm

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OSNR/Dispersion

• Measure Q-Factor up

to –982 ps/nm accum. dispersion

• OSNR sensitivity only

weakly dependent on dispersion

Use DCMs & SSMF to add dispersion

10 15 20 25 30 35 1 2 3 4 5 6 7 8

|Qmeas - Qbkgd| (dB) OSNR (dB)

0 ps/nm

• 512 ps/nm
• 982 ps/nm

14 16 18 20 22 24 26 28 30 32 34 9 10 11 12 13 14 15 16 17 18 19 20 21 0 ps/nm

• 512 ps/nm
• 982 ps/nm

Q-Factor (dB) OSNR (dB)

Dispersion managed solitons: pulses retain shape throughout transmission!

• Always within receiver

Q-factor range

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Sensitivity varies with monitor location

• OSNR, non-linear impairments accumulate with

distance

• Dispersion follows map

5 10 15 20 25 30 12 14 16 18 20 22 24 26 28 30 32 BER: 10-9 10-14

Q2 (dB) Span #

Pre-compensation: 0 ps/nm

• 300 ps/nm
• 500 ps/nm
• 800 ps/nm

( )

2 2 2 1 ASE ASE P Beat P

σ + +σ D σ

• I

D I Q =

( )2

1 f D D

A P =

DA=Accum. Dispersion f = scaling factor (4 dB @ 800 ps/nm) Dispersion Penalty Calculate “optical” Q on line: Monitor independent: OSNR Drop

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Dispersion faults

• Strongly dependent on map
• Look for discontinuities along path
• Use +/- bands to identify dispersion problems

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 14 16 18 20 22 24 26 28 30 32 Pre-compensation:

• 800 ps/nm

+624 ps/nm

• 624 ps/nm

Q

2 (dB)

Span #

Slope changes in Q trend +/- 624 ps/nm for 10-9 BER degradation

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Performance Polling: Tunable Filter + OA O/E O/E

P P Q Q

• 20 dB

Tap Span loss ~ 20 dB

Filter OA

• Guarantee equal or better sensitivity than end terminal
• Replace entire OEO terminal with single OE, channel

selector, and single channel OA

• O/E provides BER, conventional PM, Q-factor, average

power, channel presence, wavelength drift

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WDM vs. (O)TDM

WDM: Access signals with OE throughout system

OE: Q OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OADM OE: Q

OTDM: OE not available/feasible within network

OPM? O3R OEO OEO OEO OEO OEO OTDM OADM OPM?

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Quality of Service (QoS): per channel BER

QoS Monitoring in Transparent Networks

OEO PM OEO PM OEO PM 600 km 400 km 500 km

How do we monitor in an all-optical network?

OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO OEO

O3R OPM O3R OPM O3R OPM

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Regeneration Applications

• Unambiguous indication of signal quality

– Correlation with common impairments

• Do not need to isolate or measure impairments
• No contingencies on relative impairment

contributions

• Absolute measure of signal quality

– Usually only coarse measure

• Error free/not error free
• Guarantee above threshold: 10-14 BER
• Satisfy operating requirements of system

– System specific: input power, modulation format, etc.

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Optical Regeneration + Monitoring

SOA Filter CW Data Pdata Pcv

1

λ

2

λ

2

λ

For given input power: more or less power will arrive at the output depending on the input signal quality and the filter characteristics

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Unambiguous Quality Indicator: Pout/Pin

• 150 -100
• 50

50 100 150 0.0 0.2 0.4 0.6 0.8 1.0 Monitor Signal (a.u.) Dispersion (ps/nm)

12 14 16 18 20 22 24 26 28 30 0.6 0.8 1.0 OSNR (dB)

Dispersion Unable to isolate noise or dispersion But.... Monitoring signal decreases with decreasing signal quality Noise

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Summary

• Transparent optical networks generate a need for new

system monitoring and management methods

• Focus on applications will drive technology development
• Fault management: Q-factor natural replacement for BER
• Regeneration applications: solutions tied to regeneration

technologies & provide BER trend

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Back-Up Slides

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Is spectral OSNR useful?

1565 1566 1567 1568 1569 1570

• 30
• 20
• 10

Relative Power (dB) Wavelength (nm)

≠ OSNR

Noise Floor, 17 dB & 32 dB

10 Gb/s RZ on 50 GHz grid

Problems:

• Tight channel spacing: overlapping spectra
• Per-channel OSNR (OADM/OXC networks)
• Filters modify spectra (OADM/OXC)
• Poor coverage: MPI, pump RIN transfer, FWM

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Is spectral OSNR useful?

Yes, under following constraints:

• OSNR-degradation is only impairment of interest or major

impairment

• Channels are widely spaced in wavelength

– Or spectral regions reserved for monitoring

• Used for amplifier monitoring (not channel monitoring)

– Don’t follow channels through ROADM/OXC