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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
© 2011 Optelian. All rights reserved. 3
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.
© 2011 Optelian. All rights reserved. 5
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.
© 2011 Optelian. All rights reserved. 6
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.
© 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
Passive
combiner
Wavelength
Contention
• 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)
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
© 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
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
© 2011 Optelian. All rights reserved. 11
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
© 2011 Optelian. All rights reserved. 14
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
Optical Network
wavelength circuit request
signaling
1
2
3
4
done 5
© 2011 Optelian. All rights reserved.
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
© 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
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