Next-Generation ROADMsOctober 1, 2012

Sheldon Walklin

CTO, Optelian

© 2011 Optelian. All rights reserved. 2

Contents

• Introduction• Wavelength Selective Switch• Colorless, Directionless and Contentionless• Flexible Bandwidth ROADMs and Transmission

Beyond 100 Gb/s• ROADM Control, OpenFlow and SDN• Conclusion

© 2011 Optelian. All rights reserved. 3

Wavelength Selective Switch Functionality

Nx1 WSS

. . .

SW 1 VOA 1

VOA M

CommonPort 1 . . .

. . .

. . .. . .

. . .

Port N

SW M

© 2011 Optelian. All rights reserved.

Colorless, Directionless and Contentionless (CDC)

4

Colorless

Any wavelength can be dynamically added/dropped without having to re-fiber a transceiver.

Directionless

A wavelength can be dynamically added/dropped from any direction without having to re-fiber a transceiver.

Contentionless

A wavelength can be re-used on all directions without any restrictions.

© 2011 Optelian. All rights reserved. 5

4-Degree ROADM (Colored)

Tx

RxTransceiver

Colored add ports Colored drop ports

ComOut

ComIn

WS

S

ComOut

ComIn

WS

S

ComOut

ComIn

WSS

ComOut

ComIn

WSS

A

B

C

D

A

. . .. . .. . .. . . . . .. . .. . .. . .

B C D A B C D

• In general, can build an N-degree ROADM using Nx1 WSSs and 1xN splitters.

• The color and direction are fixed by fiber connections.

© 2011 Optelian. All rights reserved. 6

4-Degree ROADM (Colorless)

ComOut

ComIn

WS

S

ComOut

ComIn

WS

S

ComOut

ComIn

WSS

ComOut

ComIn

WSS

A

B

C

D

A

. . .

B C D A B C DWSS WSS WSS WSS

. . . . . . . . .. . . . . . . . . . . .

Colorless add ports Colorless drop ports

Tx

RxTransceiver

• Any transceiver wavelength (color) can be remotely configured

• The direction is fixed by fiber connections.

• Reduced number of access ports compared to colored.

© 2011 Optelian. All rights reserved. 7

Colorless and Directionless

4x1 WSS

1xN WSS. . .

A

Drop directions

B C D

Colorless drop ports

. . .

A

Add directions

B C D

Colorless add ports

Passivecombiner

WavelengthContention

• Structure for cross connecting between degrees remains the same as shown for the 4-degree ROADM on earlier slide.

© 2011 Optelian. All rights reserved. 8

Colorless, Directionless and Contentionless(using NxM WSSs)

4xN WSS. . .

A

drop directions

B C D

Nx4 WSS. . .

A

add directions

B C D

CDC add portsCDC drop ports

© 2011 Optelian. All rights reserved. 9

Colorless, Directionless and Contentionless (using Broadcast-and-Select with Tunable Filters)

4x1SW

A

Drop directions

B C D

4x1SW

4x1SW

TF TF TF

4x1SW

4x1SW

4x1SW

A

Add directions

B C D

CDC add ports

CDC drop ports

© 2011 Optelian. All rights reserved. 10

Colorless, Directionless and Contentionless (using Adjunct NxM Photonic Switches)

• Use NxM photonic switches to upgrade existing colored ROADMs to full CDC functionality

NxM Switch NxM Switch. . . . . .

Colorless add ports Colorless drop ports

Tx

RxTransceiver

ComOut

ComIn

WS

S

ComOut

ComIn

WS

S

ComOut

ComIn

WSS

ComOut

ComIn

WSS

A

B

C

D

A

. . .. . .. . .. . . . . .. . .. . .. . .

B C D A B C D

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Ideal CDC WSS

CDC ROADM(module)

Directions

A B C

D

CDC add portsCDC drop ports

• Concept module

• Non-blocking wavelength switching between any set of ports.

• Per wavelength attenuation control at line egress ports.

• Low insertion loss (up to a few dB)

• Very high reliability.

© 2011 Optelian. All rights reserved. 12

The Benefit of CDC Functionality

• Without CDC, cannot automatically restore optical circuit for failure on Span S1 or S6, or power failure at Node R2 or R4.

• CDC allows more flexibility to remotely reroute optical circuit when optimizing network utilization.

• Consideration: OTN and/or Layer 2+ protection and switching capabilities may reduce need for optical circuit dynamic routing.

R2

R3

R7

R4

R1

R8

R5

R6

s1s3

s2

s10

s5s4

s7s11

s12

s6

s8

s9

© 2011 Optelian. All rights reserved. 13

Flexible Bandwidth ROADMs

• Flexible bandwidth (FB) ROADMs (aka gridless ROADMs) allow the passband center and/or width to be dynamically adjusted.

• Many people advocate that FB ROADMs will be required to support bit rates beyond 100G.

1 2 3 4

Ch1 Ch2 Ch3 Ch4 Ch5

5 6

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Considerations for Transmission Beyond 100 Gb/s

• For 40G and 100G transmission, the client interface has transitioned to parallel optics, while the line interface has retained single-carrier optics for improved transmission capacity. Parallel optics will likely be required on the line interface for bit rates approaching 1 Tb/s and beyond.

• Multi-carrier channels or superchannels are likely to be used for long-haul transmission beyond 100 Gb/s, with PDM-QPSK used for each constituent carrier. PDM-xQAM may be used in Metro (shorter distance) applications.

• Although FB ROADMs may provide improved spectral efficiency, they are not required for transmission beyond 100 Gb/s.

© 2011 Optelian. All rights reserved.

ROADM Control

15

Automated Optical Layer• Controls the power level of each wavelength at ROADM

ports to a set target (Automatic Power Balancing)• Span or link gain control

Automated Wavelength Circuit Provisioning• Impairment-aware path computation (wavelength routing)• ROADM switch configuration

© 2011 Optelian. All rights reserved.

Automated Wavelength Circuit Provisioning

16

Connection Controller

Path Computation

Element

A-to-Z circuit request with

routing constraints

viable route(s) and required regen

location(s)

impairment-aware

OpticalNetwork

OpticalNetwork

wavelength circuit request

signaling

12

3

4

done5

© 2011 Optelian. All rights reserved.

OpenFlow and SDN

17

R2

R3

R7

R4

R1

R8

R5

R6

s1s3

s2

s10

s5s4

s7s11

s12

s6

s8

s9

OpenFlowController

App

App

App • Centralized dynamic control

• Simple flow table entry at each ROADM for wavelength connection

• Smart Apps – must be aware of topology, resource availability and state, fiber properties, impairment modeling, etc.

• Opportunity for OpenFlow applications to have multi-layer control and visibility

• Apps can evolve independently of physical network

© 2011 Optelian. All rights reserved. 18

Conclusion

• Current generation ROADMs use WSS modules and have colored or colorless access ports.

• CDC functionality generally has a higher capital cost and lower access port density, but may provide lower operational costs.

• FB ROADMs may provide improved spectral efficiency, but are not required to achieve transmission beyond 100 Gb/s

• Multi-carrier channels or superchannels will likely be used for long-haul transmission beyond 100 Gb/s, with PDM-QPSK used for each constituent carrier. PDM-xQAM may see application in the Metro

• Automated ROADM networks are well-suited to centralized control, making OpenFlow a good match. This could also facilitate multi-layer control.

Thank You