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Trends in next-generation data center interconnects (DCI)
ECOC 2022, 8th International Symposium for Optical Interconnects in Data Centers
Jörg-Peter Elbers, SVP, advanced technology, standards & IPR, ADVA

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© 2022 ADVA. All rights reserved.
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Need to explore all dimensions to scale up network capacity in a sustainable way
The capacity crunch continues
Claude Shannon by Konrad Jacobs,
CC BY-SA 2.0 de
C = P × M × B ×
log2 (1+ SNR)
The optimization is different for intra- and inter-DCI – the knobs are the same
Traffic growth
25% CAGR (global IP traffic):
~10x growth in 10 years
50% CAGR (hyperscalers):
~60x growth in 10 years

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Want to minimize electronic processing between ASIC and optical engine
Switch silicon is in the driving seat - optics need to follow
CMOS roadmap creates technology push
2018 2020 2022 2025* 2028*
CMOS node (nm) 16.0 7.0 5.0 3.0 2.1
ToR switch ASIC (Tb/s) 12.8 25.6 51.2 102.4 204.8
Packet fabric ASIC (Tb/s) 9.6 --- 19.2 --- 38.4
Packet processor ASIC (Tb/s) 4.8 7.2 14.4 28.8 57.6
Coherent DSP (GBd) 60 90 120 180 240
Electrical SerDes (Gb/s)** 25/50 50/100 50/100 100/200 100/200
*Predictions **NRZ up to 25G, PAM4 for 50G+

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Interface standards facilitate interoperability
Intra-DCI (SR to FR) Inter-DCI (from LR to ZR+)
Simplest solution if number of optical and electrical lanes match
OIF OIF

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Ultimately, a trade-off between flexibility, scalability and power consumption
Pluggable transceivers vs. co-packaged optics (CPO)
https://docs.broadcom.com/doc/cpo-switch-deployment
800G-DR8 OSFP module
5W coherent 100G-ZR QSFP-28 module

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Coherent interfaces have replaced direct detect in inter-DC applications
Really a discussion of intra- vs inter-DC interconnects today
Direct detect vs. coherent interfaces
QSFP28 100G-ZR “lite“
Gen 1 DCI-OLS (direct detect)
up to 100km, 4.8Tbit/s
QSFP-DD 400G-ZR
Gen2 DCI-OLS (coherent)
up to 120km, 25.6Tbit/s
Open line system (OLS):
• Twin-amp & mux/demux
• Automatic power &
dispersion* equalization
• OCM & OTDR option
*direct detect only
Terminals:
• Pluggable interfaces in
switches & routers
Control & management:
• Device APIs, optional
domain controller

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There is value in an optical bypass of packet switches/routers
Replacement of electrical packet switches by optical circuit switches (OCS)
Electrical vs. optical switching
AB: Aggregation block (leaf)
SP: Spine block
Jupiter evolving | Proceedings of ACM SIGCOMM 2022
Apollo architecture
Jupiter architecture

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Thank you
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