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October 22, 2018

400G-SR8 Broad Applications for Datacenters

Features:

  • Low cost: SR8 is the cost optimized 400G end to end solution for greenfield new install/ brownfield upgrade for <50m reach.
  • Flexibility: 400G-SR8 offers flexibility of fiber shuffling with 50G/100G/200G configurations. It also supports breakout at different speeds for various applications: compute, storage, flash, GPU, and TPU.
  • High density: 400G-SR8 OSFP/QSFP DD transceiver can be used as 400GBASE-SR8, 2x200GBASE-SR4, 4x100GBASE-SR2, 8x50GBASE-SR
  • Backward compatibility: Compatible optical specifications (850nm wavelength, receiver sensitivity, etc) with 100GBASE-SR4 and 40GBASE-SR4. Compatible with existing MPO-12 fiber plant through use of break-out cable.
  • Reach: Same reach as 100GBASE-SR4: 70m OM3, 100m OM4.
  • Fast time to market: All components (850nm 50G PAM4 VCSEL, MPO16)are ready.

 

ToR to Leaf: Flexible BW with Better Fault Tolerance
8-lane MMF enables flexible BW between switches in green field (new install)

Per port in TOR Per port in Leaf switch Cable Implementation Example
1x400GbE 1x400GbE MPO16 at switch <-> MPO16 at patch panel
2x200GbE 2x200GbE Shuffle cable: MPO16 at switch port, MPO16/MPO32 at patch panel
4x100GbE 4x100GbE Shuffle cable: MPO16 at switch port, MPO16/MPO32 at patch panel
2x200GbE 200GbE MPO-16 break-out to two MPO-12 cables (octopus)

8-lane MMF design allows maximum port density and maximum efficiency in brown field upgrade.

Per port in TOR Per port in Leaf switch Cable Implementation Example
2x100GbE (8x25G NRZ) 1x100GbE (4x25G NRZ) Breakout cable: MPO16 at TOR <-> 2xMPO8 at patch panel
2x40GbE (8x10G NRZ) 1x40GbE (4x10G NRZ) Breakout cable: MPO16 at TOR <-> 2xMPO8 at patch panel

ToR/Switch to Server Breakout Topology

  • Optical connection between TOR/S1 switch and servers provides flexible bandwidth to server and solve the mismatch between network ports and server ports.
  • Different application required different server BW, from 50GbE to 200GbE/400GbE
  • 8-lane MMF applications: break out to IEEE lower speed interfaces:
    • 8x 50GBASE-SR: MPO16 to 8xLC
    • 4x 100GBASE-SR2 (2×50): MPO 16 to 2xMPO8
    • 2x 200GBASE-SR4 (4×50): MPO 16 to 2xMPO8
    • 2x 100GBASE-SR4 (4×25): MPO 16 to 2xMPO8
  • AOC could be an option, but deployment is difficult especially when one server connects to multiple switches.

Technical feasibility

  • 100m OM3 reach with KP4 FEC (2e-4) has been demonstrated with PAM4 VCSEL and 25G NRZ VCSEL.
  • Leverage 50GbE Electrical I/O specification.
  • Define optical specification for 400G-SR8

Summary

  • 400GBASE-SR8 has distinct identity from SR16 and supports applications not supported by SR4.2
  • For 400GbE switch to switch connections, SR8 operates over a lower cost and more user-friendly MMF cable than SR16. It offers better network port utilization
  • 400GBASE-SR8 specification would permit implementers to design one module offering breakout capability to support 50G/100G/200G connections
  • This is no different than 40GBASE-SR4, and 100GBASE-SR4 which were all used for break-out and shuffle, with IEEE standard only specifying point to point link. These were very successful IEEE MMF standards.
  • Technical feasibility has been demonstrated.
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