Pluggable DWDM: Considerations For Campus and Metro … · Pluggable DWDM: Considerations For...
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Pluggable DWDM: Considerations For
Campus and Metro DCI Applications
XiangZhouandHongLiu
Pla0ormDatacenterOp9cs
ECOC 2016 WS 3 Short range optical transmission for emerging 5G, DCI and Metro Networks
With input from Vijay, Tad and Vinayak from NetArch group
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Distance
Google DC Interconnection Network
Cluster
Intra-DC (Clusters)
Inter-DC (Campus)
DC to Backbone (Metro)
Global Inter-DC (Backbone, LH)
500m-1kmm
2km 80km 1000s km
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Google Datacenter Traffic Growth
● Datacentertraffichasincreased50xfrom2008to2014● Roughlydoublingeveryyear.
○ FasterthanInternetgrowth
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Datacenter Campus Network (today)
● Interconnec9ngmul9pleDCswithgeographicproximity(~2km)
● Oneormul9plewarehousecomputers(Clusters)withineachDC○ GoogleJupiterclusterprovides1.3
Petabitsbisec9onbandwidth
● Interconnec9ontechnique○ Pluggablegrayop9cs(typical)○ Singlemodefiber
Google Oklahoma data center campus
Google’sPerspec9ve
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Edge access (Metro) network (today)
Clientgrayop9cs
Datacenter router
Backbone router DWDM
Transport
Transport based DWDM Transport
LinesideDWDM
● Interconnec9ngdatacenter/POPandbackbone(~40-80km)● Tradi9onalDWDMtransporttechnique
○ GreyOp9csforclientside,coloredDWDMop9csforlineside○ Clientsidespeedtypicallysmallerthanlinesidespeed
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Challenges Facing Current Solutions
q Bandwidth scaling challenge for DCI campus o Fiberexhaus9onproblem
§ Pullingnewfiberisexpensive§ Pullingnewfiberalsoconstrainedbyphysicalcondi9ons
q Cost scaling challenges for DCI Metro (edge access)o MuxponderbasedDWDMop9mizedfortradi9onaltelecomMetro,where
§ reachupto300-600km§ clientspeedsignificantlyslowerthanlinesidespeed
o Notop9malforDCImetro,where§ reachonly~40-80km§ clientspeedequal(orclose)tothelinesidespeed
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Emerging Technical Trend
DWDM directly on Linecard
● DWDM directly on router and switch card (pluggable DWDM) ○ Elimina9ngclientinterconnec9onandterminalchassis(reducecost,power)○ Allowingsimplermanagementandcontrol○ Poten9aluseforbothcampusandMetro
Datacenter router/Switch
Backbone router
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Pluggable DWDM: Performance Metrics
q Cost
q Power, Size and Density o DC grey optics form factor
q Wavelength Tunability
q Link performance (OSNR, dispersion tolerance etc)
q Spectral Efficiency (less important than LH)
Google’sPerspec9ve
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q Serial 100Gb/s direct modulation with 16nm CMOS
o 50-Gbaud PAM4 [1]
o 50-Gbaud (equivalent) DMT
q Lower power and small footprint tunable lase
o Withrelaxedpower,wavelengthstabilityandphasenoiserequirements
q FBG based full C-band tunable DCM (in line systems)
[1] over 80km performance demonstrated: D. Sadot et al, OE 2015
100G Tunable QSFP28: Enabling Technologies
PAM4
DMT (courtesy to Socionext)
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Revisit Optical Dispersion Compensation
q Multi-span DWDM systems o Require optical DCM every span
o Additional tunable DCM
o Cost is high compared to electrical dispersion compensator
q Single-span DCI Metro
o Single broadband tunable DCM (FBG based technology)
o Cost and power shared by 40-80 channels
§ Likely lower than electrical dispersion compensator
o Reduce transceiver power
§ Help meet stringent power density requirement of pluggable optics
Broadband TDCM
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Beyond 100G: Coherent or Direct Detection ?
q Direct detection o Require multiple tunable lasers (four for 400G ! )
§ Cost and power likely high o Spectral efficiency (SE) difficult to scale
§ Single sideband modulation could double SE but complex Tx design
q Coherent detection o Single tunable laser for 400G (shared by both the signal and the LO !)
§ More stringent laser performance o Higher spectral efficiency (2-4 times higher) o Support greater link loss (better OSNR sensitivity) o High DSP power: extra power for pol. and phase recovery
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Ultra-Low Power Coherent DSP q 7nm CMOS node
q Baud-rate or minimum over-sampling DSP
o Baud-rateDSPachievesthelowestpowerconsump9onbuthaslimiteddispersion
compensa9oncapability
q Minimal MIMO EQ tap length
q Less powerful FEC
q 2/3-bit DAC for 16/64-QAM
q Remove OTN framer Residual CD (ps/nm)
With Baud-rate DSP
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Conclusions
q Greyop9csDCcampusinterconnec9onfacesbandwidthscalingchallenges
q Pluggable(andtunable)DWDMisapromisingsolu9onforbothcampusand
Metrowithoutsacrificeofrouterandswitchportdensity
q PAM4/DMTbasedserial100Gcouldenable100GtunableQSFP28
q 7nmultra-lowpowercoherentDSPlikelyenables400GpluggableDWDM