next generation requirements for dwdm network

Verizon copyright 2011 .

Next Generation Requirements for DWDM network Roman Egorov Verizon Laboratories May 3, 2011

2 Verizon copyright 2011

NG Requirements for DWDM network: Outline

•  Optical Transport Network –  Metro vs. Long-Haul Requirements

•  Next Generation DWDM requirements –  Fiber plant, Amplification, ROADM, and Transceivers

•  Current ROADM Node Architecture

•  Next Generation ROADM Architectures –  Colorless –  Colorless and Directionless –  Colorless, Directionless, and Contentionless (CDC)

•  Scaling to beyond 100G –  Flexible Channel Bandwidth

•  Conclusions

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Optical Transport Network: DWDM: Metro vs. LH Requirements

•  Metro DWDM network: –  Optimized towards 1000km of un-regenerated optical reach

–  15 - 20 ROADM pass-throughs for optical path

–  880Gbs transmission capacity per fiber (88 wavelengths @ 10Gbps) up to 8 fiber directions

–  Today: optimized for 10Gbs per channel transmission (intensity modulation)

–  Higher bit rates: 40Gpbs and 100Gbps (phase modulation) can be deployed but fiber capacity is de-rated especially when 100Gbps channels are transmitted (no flexible grid required)

–  Optical amplifiers optimized to support rates of 10G (Raman amplification is not required)

–  ROADM architecture is colored, directional, and has wavelength contention


Optical Transport Network: DWDM: Metro vs. LH Requirements

•  Long-Haul DWDM network: –  Optimized towards 2500km un-regenerated optical reach

–  4 – 8 ROADM pass-throughs for optical path

–  10 Tbs transmission capacity per fiber (100wavelngths @ 100Gbps) up to 8 fiber directions

–  Optimized for 100Gbps per channel transmission

–  Higher bit rates: 400Gbps and 1Tbps can be deployed without de-rating fiber capacity (flexible grid required)

–  Optical amplifiers optimized towards supporting data rates of 100G and beyond (Raman amplification is required)

–  ROADM architecture is colorless, directionless, and contentionless (CDC)


Optical Transport Network: DWDM Transport Node Evolution

•  DWDM introduction to SONET/SDH networks:

–  Needed for Capacity Enhancement –  Support point-to-point topology –  Multiplexing/Demultiplexing at each node

•  Next step for DWDM –  Support multi-node linear and ring

configurations –  Need to support add/drop and pass-

through – OADM –  Channel Add/Drop function is static

•  Reconfigurability + OADM = ROADM –  Wavelength switching –  Channel Add/Drop is dynamic and under

software control –  Additional flexibility

DWDM Multiplexing/Demultiplexing

DWDM Add/Drop


Current ROADM node architectures

•  Current Optical Networks –  Move towards meshed

topologies •  Basic building blocks

–  Optical Splitter/Coupler –  Wavelength Mux/Demux –  Wavelength Selective Switch

(WSS) –  Transmitters w/tunable lasers –  Receivers w/broadband

photo-detectors •  Current ROADM architecture:

–  Limitations: colored architecture

–  Due to Add/Drop structure design and not because of transponder or receiver


NG ROADM node architectures: Colorless

•  In colorless design any wavelength can be assigned to any port on mux/demux structure

–  WSS replaces fixed port mux/demux structure –  Colorless combining requires control of laser side mode

suppression ratio or filter the signal –  Limitations: each Add/Drop structure is unique to each degree


NG ROADM node architectures: Colorless and Directionless

•  Directionless Add/Drop structure allows to direct a channel to any degree of the ROADM

–  Add 1xM coupler to Add structure –  Add 1xM WSS to Drop structure –  No Add/Drop structure is associated w/particular degree –  Limitations: not contention-free


NG ROADM node architectures: Colorless, Directionless, Contentionless

•  Contentionless ROADM design removes wavelength restrictions from Add/Drop structure

–  Transmitter can be assigned to any wavelength and any degree as long as long as the number of channels w/the same wavelength is not more than the number degrees in the node

–  Add/Drop port can be any color and connect to any degree –  Only one Add/Drop structure is needed in the node


NG ROADM node architectures: CDC Example

•  CDC design example –  This design does not use MxN

WSS for add/drop structure •  MxN WSS switch is not

commercially available today

–  Add/Drop structure may be based on using photonic (fiber) switches (with small port counts), optical couplers, and tunable filters

•  This design is scalable in the number of add/drop ports

•  Maintains full flexibility of contentionless design


NG ROADM node Architectures: CDC with Coherent Detection

•  ROADM CDC design with coherent detection:

–  Banded access •  1xN WSS divides

incoming channel into smaller groups

–  All access •  Photonic switch with large

port count

–  Design challenge is to discriminate one channel out of band of channels


NG ROADM Node Architectures: Summary of Evolution

•  ROADM evolution –  Colored, fixed add/drop –  Colorless –  Colorless and Directionless –  Colorless, Directionless, and Contentionless (CDC)


NG ROADM Node Architectures: CDC Architecture

Architecture: •  4-Degree ROADM with

unrestricted add/drop –  Wavelength switching to

route wavelengths between fiber directions

–  Add/drop wavelength routing –  Tunable wavelength selection

in add/drop structure

Benefits •  Any add/drop port can go any

direction with any wavelength •  Each add/drop port can be

assigned any color •  Add/drop wavelength can be

routed to any direction •  No restrictions on color re-use

in add/drop structure

West East

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South

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Transponder Transponder Transponder

Add/drop

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Scaling beyond 100G: Flexible Channel Bandwidth

As bit rates have increased to 100Gb/s (even with more spectrally efficient modulation techniques such as PM-QPSK) most of the available channel bandwidth is being utilized

Problem is manageable at 100 Gb/s, but supporting 400 Gb/s or even 1Tb/s with 50 GHz channel spacing will require very high SNR and will limit optical reach

Network can be future proofed by supporting flexibility in the channel spacing that allows channel bandwidth to be increased with bit rate

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50GHz 50GHz 75GHz 75GHz 150GHz


Scaling Beyond 100G: Options for implementation

•  Single carrier approach: –  Increase constellation size (symbol rate stays the same, bitrate

increases) –  Coded modulation will probably be required (since separating coding

and modulation is not optimal for multi-level signaling) •  TCM as an example is bandwidth efficient modulation

–  Coding gain must outweigh power disadvantage of going to the higher constellation

•  Reach is not comparable to 100G –  Component bandwidth scaling maybe a problem

•  Multiple carrier approach (Super channel): –  Apply OFDM concepts for closer spacing between the carriers –  Technologies are more mature at lower date rates per channel –  Not as efficient spectrum utilization as in single carrier approach –  Requires flexible grid support in WSS

next generation requirements for dwdm network

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