Understanding and optimising transceiver efficiency using internal metrics for improved power savings#

Dr. Gerhard Stein (FLEXOPTIX Research)

• Why: Power consumption of optics is a first-order DC design constraint. This is one of the few talks with actual measured VDM data across multiple transceiver types and switch platforms — directly relevant to the PM's optics and power-efficiency interests.
• What: An empirical study of transceiver power behavior using Versatile Diagnostics Monitoring (VDM, the CMIS successor to DDM) metrics — particularly TEC current, laser temperature, and optical power. Key findings: laser and TEC power draw is negligible at any temperature; the real energy consumers are the MCU/DSP; and shutting a port forces low-power mode consuming 7–20× less energy.
• How: VDM exposes per-transceiver laser temperature, TEC current, and related telemetry via CMIS memory pages 20h–2Fh. The team built software prototypes to collect, evaluate, and visualize transceiver efficiency in Watts across DUTs including 100G QSFP28, 400G QSFP-DD Coherent ZR (120km), and 800G QSFP-DD modules, tested on Cisco Nexus 93600CD-GX, Cisco C9500, and Juniper QFX5120. An experiment with frozen transceivers showed ~200mW average increase per 20°C temperature differential. Notably, VDM support is spotty across platforms — Juniper QFX5120 and Cisco C9500 don't expose it; the Nexus does.
• Where applicable: Any operator deploying 100G+ optics who wants to measure per-port power in production. VDM availability depends on switch platform and CMIS version. FLEXOPTIX-affiliated but the methodology and data are vendor-agnostic in applicability.