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

Gerhard Stein, Flexoptix GmbH

• Why: Transceiver power is becoming a first-order DC design constraint; this is one of the few talks showing how to actually measure and optimize it from data already readable off modern optics.
• What: How to use Versatile Diagnostics Monitoring (VDM, available on >100G optics) — especially Thermoelectric Cooler (TEC) current — alongside temperature and cable length to find the efficient operating point per transceiver, in Watts, on real hardware.
• How: TEC power is computed as V_trc × I_TEC from VDM (vs DDM which only exposes laser current); tested across 100G QSFP28, 400G coherent ZR, and 800G QSFP-DD transceivers on Cisco Nexus 93600CD-GX, Catalyst 9500, and Juniper QFX5120. Support is patchy: QFX5120 and IOS XE expose DDM only; NX-OS reads CMIS VDM but assumes a 50°C laser target. Includes power-trend data (400G FR4: 12W→9W; 800G OSFP: 16.5→15.5W; 1.6T: 30→26W as DSP nodes shrink) and an entertaining frozen-transceiver experiment showing the laser re-warms within seconds.
• Where applicable: Broadly applicable to optics power budgeting; requires CMIS/VDM-capable transceivers and switch support, so check your NOS before counting on it. Vendor talk, but methodology is transferable.