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Evolving Metro/Regional ROADM
Architectures to 400G and beyond
ECOC Market Watch
London
September 2013
Paul Momtahan
Director of Transport Solution Marketing
Evolving Metro/Regional to 400G Agenda
Metro/Regional Market Drivers
Moving beyond 100G
ROADM Architecture
Evolution
Cost Effective CDC for the Metro
Metro/Regional Market Drivers Traffic Growth & 100G
Worldwide Annual Growth in Traffic Volume on Metro Networks
% of Respondents
Operator Timelines for Wide-Scale Metro 100G Deployment
% of Respondents
Source: Metro Packet-Optical Transport 2.0 Survey, Heavy Reading, March 2013
Traffic growth is driving operators to start adopting 100G in the metro
Metro/Regional Market Drivers Inter-Data Centre Traffic
Inter-data centre traffic is growing at >30% CAGR
32
44 45
57 62
0
10
20
30
40
50
60
70
Amsterdam Frankfurt Paris NYC London
# o
f C
olo
ca
tion D
ata
centr
es
Inter-data centre traffic is likely to drive the need for higher speed lambdas in the metro
Metro/Regional Market Drivers Metro vs. Long Haul
Local
Exchange
Hub Office
Metro / Regional
Long Haul
Consumer: Hubbed & Asymmetrical
Enterprise: Some meshed, more symmetrical
nX 10Gs
Short distances
Few OLAs
Traditional Metro Consumer/Enterprise
Meshed
Symmetrical Traffic
nX 100/400Gs
Long Distances
Numerous OLAs
Core Network Hub to Hub
Meshed
Symmetrical
nX 100/400Gs
Short distances
Few OLAs
New Metro Layer Data Centre to Data Centre
Will have 10G, 100G and 400G
Focus on Flexibility and Cost
Coherent Only
Performance & Flexibility
Moving beyond 100G 16QAM & Superchannels
16QAM doubles spectral efficiency but is at least four times more sensitive to OSNR
– Technology is limited to 30Gbaud today, thus requiring 2x200Gbps for 400G
16QAM
4x100Gb
137.5 GHz
2x200Gb
75 GHz
1x400Gb
75 GHz 100
Gb
50 G
Hz
100
Gb
50 G
Hz
100
Gb
50 G
Hz
Superchannels & Flexgrid
Superchannels and flexgrid enable a further 33% boost in spectral efficiency by combing two
200Gbps lambdas in 75Ghz
Moving beyond 100G Impact of 10G on 16QAM
The metro is still dominated by 10G however 16QAM is severely impacted by crosstalk (i.e. XPM) from 10G
0 2 4 6 8 10
With 10G & DCMs
Coherent Only
# of 40km/10dB spans (ROADM cascades)
400G (2x200G) reach with 3dB margin
ROADM Architecture Evolution Broadcast & Select
SPLITTER
SPLITTER
SPLITTER
SPLITTER
SPLITTER
Broadcast & Select has been the dominant architecture for multi-degree ROADM
WSS
WSS
WSS
WSS
WSS
As the number of degrees
increases so does the
splitter loss, lowering OSNR
WSS Isolation:
Non-selected channels leak
through and create cross talk
ROADM Architecture Evolution Route & Select
Route & Select does not suffer from splitter scaling or WSS isolation problem
WSS
WSS
WSS
WSS
WSS
WSS
WSS
WSS
WSS
WSS
ROADM Architecture Evolution 400G Reach: Route & Select vs. Broadcast & Select
If we get rid of 10G and Dispersion Compensation, Broadcast and Select can
deliver 400G performance comparable with Route & Select
However as the number of degrees (size of splitter & WSS) increases Broadcast &
Select performance will degrade
Amplifier OSNR Broadcast & Select Isolation (20D ROADM)
Route and Select
R&S has better 400G performance as # of degree scales
16
ROADM Architecture Evolution Broadcast & Select vs. Route & Select Broadcast & Select Advantages
– Cost-effective (1xWSS per Degree)
– Filter narrowing (1xWSS per pass-through) - No longer an issue with next gen WSS
– Support for optical Broadcast/Multicast schemes
– Good 400G performance if no 10G/DCMs and degree count is not too high
Route & Select Advantages
– No loss in splitter (advantage for 400G & high-degree ROADM)
– No leakage from non-selected channels at egress (advantage for 16QAM/400G)
– Scales to support high degree counts (mesh, CD/CDC) without impacting 400G performance
00.20.40.60.8
11.21.41.61.8
B&S, no CD R&S with CD R&S with CDC
Recent Tellabs Study on North American metro
Rela
tive C
ost of O
ptical Layer
Add/Drop Number of Degrees (DWDM Line)
Directionless Colourless Contention-less 2D 4D 6D 8D 10D >10D
ROADM Architecture Evolution ROADM Decision Criteria for 400G
Drivers for colourless & directionless:
– Layer 0 Restoration
– Network Defragmentation/Optimisation (SDN)
– Fast Provisioning (pre-installed transponders)
Drivers for contention-less:
– Minimises blocking in highly loaded network
– Network blocking not node contention is likely to be the main source of blocking in metro networks
Drivers for more DWDM line degrees
– Meshing in the metro, extending to access
– C&D (each directionless eats a degree)
– CDC (max 16 add/drop ports per “degree”)
Add/Drop Number of Degrees (DWDM Line)
Directionless Colourless Contention-less 2D 4D 6D 8D 10D >10D
Add/Drop Number of Degrees (DWDM Line)
Directionless Colourless Contention-less 2D 4D 6D 8D 10D >10D
Broadcast & Select
Route & Select
Cost Effective CDC for the Metro High Port Count MCS
MCS MCS MCS
16 Add/drops
degree 1 degree 2 degree 8
Scalable
– 16 add/drops per WSS port
High loss across MCS
– EDFA array required
– 2xEDFA for each degree (input & output)
– 16xEDFA for eight degree system
Decreased Performance
– EDFAs add noise
– Mixing of 16 sources (SMSR)
Cost Effective CDC for the Metro Low Port Count MCS
MCS MCS MCS
4~8 Add/drops
degree 1 degree 2 degree 8
Cost per add/drop port drops by 30%~50%
– Reduced loss across MCS
– Enables EDFAs to be eliminated
Better performance:
– No noise from EDFA
– Mixing of fewer add/drop sources
Less scalable
– Eats up WSS ports more quickly
Increased WSS cost?
Requires more expensive
high port count WSS for DWDM Line
Cost Effective CDC for the Metro Tellabs Metro CDC Study
LPC MCS is more cost-effective than HPC MCS unless # of wavelengths
increases dramatically
– 100G and 400G are likely to depress the number of wavelengths
CDC with LPC MCS can even be lower cost than CD only (with R&S)
Scale of demands (1=current wavelengths)
Evolving the Metro to 400G Summary
Hub Office
Metro / Regional
• Stick with 10G friendly solution
• Stick with B&S
• Focus on low cost
Traditional Metro Consumer/Enterprise Delivery
• Deploy Overlay 100G/400G friendly
optical Layer
• All Coherent
• Choose between B&S for cost
effectiveness and R&S for flexibility
• LPC MCS is likely to be the most cost-
effective option for CDC – could even be
less expensive than CD only
New Metro Data Centre to Data Centre
Cloud & Virtualization have resulted in an explosion of horizontal
traffic between data centres, creating two completely separate
traffic profiles in metro networks
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