What is DDM/DOM in optical modules and why is it important?
82
✓
✓ Best Answer
DDM (Digital Diagnostic Monitoring), also called DOM (Digital Optical Monitoring), is a feature defined in SFF-8472 that provides real-time monitoring of optical transceiver parameters.
Parameters Monitored
- Module temperature: -40°C to +85°C typical range
- Supply voltage: 3.3V ±5%
- Laser bias current: mA
- Transmit optical power: dBm
- Receive optical power: dBm
Why It Matters
- Proactive fault detection before hard failure
- Identify degrading modules (declining Tx power)
- Diagnose link issues without physical access
- Verify installation quality
- Monitor thermal environment
Typical Values (10G LR module)
| Parameter | Normal Range | Alert If |
|---|---|---|
| Temperature | 0-70°C | >80°C |
| Tx Power | -5 to +0.5 dBm | <-8 dBm |
| Rx Power | -14 to -1 dBm | <-14 or >+1 dBm |
| Bias Current | 10-80 mA | >90 mA (aging laser) |
Reading DDM Values
- CLI command:
show interface transceiver - SNMP: DDM MIB variables
- Web UI: Interface diagnostics page
Best Practices
- Baseline DDM values at installation
- Poll via SNMP every 5-15 minutes
- Alert on trend degradation, not just thresholds
- Compare Tx power on both ends of same link
- Track laser bias — climbing bias = failing laser
Interpreting Anomalies
- Low Rx power: Dirty connector, cable damage, distance too long
- Low Tx power: Failing module, replace
- High bias current: Laser degrading, plan replacement
- High temperature: Cooling issue or ambient too hot
2 Other Answers
25
DDM monitoring detected a failing SFP 2 weeks before failure. Saved a critical link.
16
Establish baseline DDM at install time — it's your reference for years to come.
Your Answer
You must be signed in to post an answer.