Deploying 40Gbps Wavelengths and BeyondBrian Smith

Confidential

Agenda

What are the future requirements of R&E networks ?

What are the options for upgrading capacity on R&E networks

Some cost comparisons.

Challenges of deploying 40Gb/s wavelengths over 10Gb/s Infrastructure

What about 100G+ ?

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Requirements for Regional Optical Research

Networks

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Requirements

Transparency Carry any service (Ethernet SONET, SAN) at wire speed from GigE to

10GigE and beyond.

Capacity Growth Seamless and cost effective capacity growth which supports emerging

40G wavelength technologies.

Ability to add wavelengths at any supported data rate without affecting existing traffic.

Dynamic Light-path Control Dynamic control plane (e.g UCLP, GMPLS)

Integration with IP/MPLS control plane for dynamic traffic engineering (e.g HOPI).

Client on-demand light paths.

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Options for Future Capacity Growth

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Capacity Growth in RONs

Continue to add 10G wavelengths in existing infrastructure. Up to 320Gb/s capacity with 100GHz spaced DWDM.

Accelerates fiber exhaust

Upgrade to 50GHz 10Gbps system Up to 640Gb/s capacity with 50GHz spaced DWDM.

Needs new terminal equipment.

Service disrupting

Cost effective in the longer term ????

Overlay 40Gb/s wavelengths in existing 10G infrastructure. No service disruption

Expands system capacity – delays requirement to light new fiber.

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Some Cost Comparisons

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Assumptions

Fully dynamic ‘Any-to-Any’ wavelength optical network.

Optical ROADM using WSS technology available at 100GHz and 50GHz.

No penalty associated with cascaded ROADM

Add 40Gbps wavelengths after 75% capacity reached.

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Continue to Add 10G Wavelengths

10Gbps (100GHz)

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# wavelengths

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Cost/Gbps Capacity

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Upgrade to 50GHz 10Gb/s System

10Gbps (50GHz)

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# wavelengths

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au)

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Cost/Gbps Capacity (Gbps)

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Overlay 40Gb/s Wavelengths in Existing 10Gb/s Infrastructure

10Gbps + 40Gbps Overlay (100GHz)

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Cost/Gbps Capacity

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Cost Comparison

Overlaying 40Gb/s wavelengths on an existing 10Gb/s infrastructure leads to lower cost per GigE in the long term.

Higher costs in 50GHz 10Gb/s option mainly due to: Higher cost of 50GHz ROADM compared to 100GHz ROADM

Higher cost of wave-locked MSA transponders (compared to XFP based transponders).

Assuming that 40Gbp/s wavelengths can be supported over an existing 10Gb/s network , this is a bandwidth efficient and cost effective way of delaying the requirement to light a new fiber pair.

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Wavelength Switching Trends

4 8 12 16 20 24 28 32Pass-through Channels

Optical ROADM

ElectronicROADM

Optical ROADM

ElectronicROADM

10G

2.5G

ChannelRate

What are the cost sweet spots today ?

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Wavelength Switching Trends

4 8 12 16 20 24 28 32Pass-through Channels

Optical ROADM

ElectronicROADM

Optical ROADM

ElectronicROADM40G

10G

ChannelRate

How will this change as 10G costs go down ?

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40Gb/s Challenges

Tolerance to Chromatic Dispersion (CD)

Tolerance to Polarization Mode Dispersion (PMD)

OSNR Tolerance

Spectral Width

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Tolerance to Chromatic Dispersion – 40G

6 spans x 80km x 26dB SMF-28 : 32 NRZ modulation format, zero chirp, +FEC.

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-100 -50 0 50 100

Net Dispersion (ps/nm)

dB

Q p

enal

ty

+/- 50 ps/nm

Equivalent to 3km SMF

Dispersion variation with

Temperature (+/- 40 deg)

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Impact of Dispersion Tolerance at 40Gb/s

So what does this mean ?

40Gb/s wavelengths need to have adaptive dispersion compensators.

If you plan to deploy 40Gb/s in the future, consider measuring the net dispersion as accurately as possible

Using other modulation formats (such as Duo-binary) increases the dispersion tolerance window by 3-4 times.

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PMD Tolerance

Some examples

PROTOCOL Max PMD

(1dB penalty)

Average PMD

GigE 220 60

OC48 115 30

10GigE 27 8

40G (NRZ) 7* 2*

* Other non binary modulation techniques can increase the PMD tolerance for 40Gb/s

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PMD Tolerance

So what does this mean ?

Take the 6 spans x 80km SMF-28 example.

Dark Fiber Age Average link DGD (ps)

>1995 2

<1995 10

With older fiber, the 10GigE traffic will see PMD hits on traffic

With new fiber, the 40G traffic can be supported.

Performing a PMD measurement on your fiber plant will define whether 40Gb/s traffic can be supported or not !

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OSNR Tolerance

OSNR required for 40Gb/s is larger than that for 10Gb/s for the same BER.

Reach for 40Gb/s reduced compared to 10Gb/s

CS-RZ modulation format and enhanced FEC coding on the 40Gb/s wavelengths reduces the mismatch in required OSNR.

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Spectral Width

The modulation format used for 40Gb/s will determine the spectral width.

Wavelengths in a fully dynamic network will traverse a cascade of ROADM – Leading to filter pass-band narrowing.

The 40Gb/s modulation format chosen (NRZ, CZ-RZ Duo-binary) must be able to pass through the cascade without distortion.

For this reason, it is likely that the 40Gb/s in a dynamic network will use spectrally efficient modulation formats (Duo-binary, CS-RZ)

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What about 100Gb/s + ?

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100Gb/s

Native 100Gb/s transmission is not likely in the near term Electrical Mux and Demux very challenging at this rate

Availability of optical modulators with sufficient electrical bandwidth

Clock recovery at this rate is extremely difficult

If electro/optic components were available . . . Spectral width ~ 150GHz so wouldn’t fit into a 100GHz pass-band

(<80GHz). Would need >1 bit/symbol coding

Dispersion tolerance ~ ± 10ps/nm.

PMD tolerance < 1ps

OTDM techniques are only approaches currently being developed for ultra high speed transmission.

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100Gbps

Duo-binary, QPSK

Wave-locker

1b/s/Hz

Too many bits/symbol required

Too many bits/symbol required

40Gbps

NRZ/CS-RZ/

Wave-locker

10G overlay

0.4b/s/Hz

Duobinary

Wave-locker

0.8b/s/Hz

Too many bits/symbol required.

No ROADM

1.6b/s/Hz

10Gbps

No issue

NRZ

0.1b/s/Hz

Reduced reach

Wave-locker

NRZ

0.2b/s/Hz

Reduced reach

No ROADMs

Wave-locker

0.4b/s/Hz

100GHz 50GHz 25GHz

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Summary

R&E Regional Optical Networks will require Seamless Capacity Growth and Dynamic Light-path Control.

Deploying 40Gb/s wavelengths in existing 10G networks offers reductions in the cost per GigE as capacity grows.

10G switching will evolve towards Electronic ROADM as component costs continue to fall – Optical ROADM more cost effective for 40G traffic.

If 40Gb/s is to be added to 10Gb/s infrastructure

Need accurate measurements of Dispersion and PMD

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Summary

40Gb/s modulation formats are available that

Improve the OSNR, CD and PMD tolerance

Allow transport through cascaded optical ROADM

The technology for 100Gb/s line rates is under development but not available.

OTDM is the current approach used for single channel ultra high speed transport

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Thank You

Dr Brian Smith

brian.smith@meriton.com