Direct answer
DOM/DDM provides module diagnostic telemetry, not a substitute for an external power measurement or a documented link-loss test. Compare location, wavelength, channel definition and stated uncertainty before treating different readings as a cable failure.
Definition and applications
DOM and DDM describe module monitoring or diagnostic information. Cisco documents transmit and receive power telemetry on its ASR 900 platform; availability depends on the actual module, platform and software. An external meter reads power at the connected measurement point. Neither is automatically a substitute for the other.
Use this review for commissioning, receiver alarms and investigations after optics replacement. The comparison below is a procurement checklist, not a universal accuracy specification.
Basis：Cisco DOM guide。
Reading comparison checklist
| Field | Record | Avoid assuming |
|---|---|---|
| Location | Receiver or external test point | Different locations measure identical power |
| Wavelength | Optics wavelength and meter setting | One calibration setting fits every signal |
| Channel definition | Per-lane or aggregate; power definition | Port readings are directly comparable |
| Timing | Configuration, time and operating state | Changes always originate in the cable |
| Uncertainty | Both instrument and module statements | Every external meter is more accurate |
Turning an alarm into evidence
Save module identity, software, diagnostics and meter configuration before changing the path. Plan any disconnected measurement under the approved isolation and laser-safety procedure. Inspect and clean interfaces, then record wavelength, adapters and readings.
Where passive-link loss is the acceptance requirement, perform the agreed source/meter or OLTS procedure with a documented reference. dBm describes power; dB describes a ratio or loss. Do not subtract unrelated telemetry readings and call that a certified cable result. Retain original readings and the acceptance basis, and investigate configuration differences before rejecting an assembly.
Procurement FAQ
- Does normal DOM certify cabling? No; use the agreed link-acceptance method.
- Does a mismatch prove cable failure? First reconcile location and definitions.
- Is a meter always more accurate? Review stated uncertainty and conditions.
- Can total power be compared for 800G? Confirm the actual channel definitions.
- What should an RFQ include? Optics IDs, interfaces, readings and acceptance method.
Related guides and products
Link loss budget · OLTS vs OTDR acceptance。
Related product configuration · Contact an engineer。The product link supports configuration review, not an unverified performance or availability claim.
Sources and review date
Sources reviewed: 2026-10-07. Checklists and process recommendations are general procurement guidance, not complete standard clauses or verified ARRANEX product claims.
Sources checked: 2026-10-07