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400G PAM4 FEC Forward Error Correction KP4 Pre-FEC BER Network Monitoring Signal Integrity Lane Diagnostics Data Center Networking NRZ Optical Networking oFEC RS544 MPO Connector Chromatic Dispersion OSNR

400G Does Not Fail — It Degrades

An interface can be up while the link is already operating outside a stable margin. At 400G, a link being 'up' is not a useful indicator of health.

Rene Fichtmueller / 2026-04-15 / ~3 min read min read