Next-Generation ROADMs - · PDF file• Flexible Bandwidth ROADMs and Transmission Beyond...

Next-Generation ROADMs October 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


Wavelength Selective Switch Functionality

Nx1 WSS

. . .

SW 1 VOA 1

VOA M

Common

Port 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.


4-Degree ROADM (Colored)

Tx

Rx

TransceiverColored add ports Colored drop ports

ComOut

ComIn

WSS

ComOut

ComIn

WSS

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.


4-Degree ROADM (Colorless)

ComOut

ComIn

WSS

ComOut

ComIn

WSS

ComOut

ComIn

WSS

ComOut

ComIn

WSS

A

B

C

D

A

. . .

B C D A B C D

WSS WSS WSS WSS

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

Colorless add ports Colorless drop ports

Tx

Rx

Transceiver

• Any transceiver

wavelength

(color) can be

remotely

configured

• The direction is

fixed by fiber

connections.

• Reduced number

of access ports

compared to

colored.


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

Passive

combiner

Wavelength

Contention

• Structure for cross connecting between degrees

remains the same as shown for the 4-degree

ROADM on earlier slide.


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


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

4x1 SW

A

Drop directions

B C D

4x1 SW

4x1 SW

TF TF TF

4x1 SW

4x1 SW

4x1 SW

A

Add directions

B C D

CDC add ports

CDC drop ports


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

Rx

Transceiver

ComOut

ComIn

WSS

ComOut

ComIn

WSS

ComOut

ComIn

WSS

ComOut

ComIn

WSS

A

B

C

D

A

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

B C D A B C D


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.


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


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


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.


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


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

Optical Network

wavelength circuit request

signaling

1

2

3

4

done 5


OpenFlow and SDN

17

R2

R3

R7

R4

R1

R8

R5

R6

s1 s3

s2

s10

s5 s4

s7 s11

s12

s6

s8

s9

OpenFlow Controller

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


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

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