Digital Optical Monitoring (DOM), also known as Digital Diagnostic Monitoring (DDM), is a standardized capability in modern optical transceivers that provides real-time measurement of key operating parameters — enabling proactive maintenance and faster fault diagnosis.
Monitored Parameters
- Temperature: Internal transceiver case temperature (°C), ±3°C accuracy
- Supply Voltage (Vcc): Module supply voltage; variations can indicate line card power issues
- Tx Bias Current: Laser diode bias current (mA); increasing bias at constant power indicates laser aging
- Tx Output Power: Optical transmit power (dBm); deviations indicate laser or driver degradation
- Rx Input Power: Received optical power (dBm); low values indicate fiber loss or far-end failure
Alarm and Warning Thresholds
Each parameter has four thresholds stored in EEPROM: high alarm, high warning, low warning, low alarm. Monitor warning thresholds — they trigger before the link fails, giving you time to investigate.
How to Access DOM Data
-
Arista EOS:
show interfaces transceiver detail -
Cisco NX-OS:
show interface ethernet X/Y transceiver detail -
Juniper Junos:
show interfaces diagnostics optics et-X/Y/Z -
Linux host:
ethtool -m ethX
Practical Diagnostics
Rx power below threshold, link up: Dirty fiber connector or excessive bend radius — clean and check cable routing.
Tx bias significantly higher than baseline: Laser approaching end of life — plan proactive replacement.
Temperature above warning threshold: Insufficient airflow — check fan health and cable management.
ATL Optics transceivers include fully populated, calibrated DOM registers on all product lines.