A pluggable optical module is not commissioned simply because the link LED turns green. A controlled handover should confirm the exact host and software combination, port mode, module identity, fiber path, received power, alarms, error counters and traffic behavior. Recording that baseline makes later faults faster to isolate and prevents a marginal link from being accepted as healthy.

Freeze the approved link design before installation

Start with the design that was actually approved, not a generic module description. The installation record should identify both endpoint devices, cards or adapters, software releases, port identifiers, required data rate, port mode, forward error correction (FEC) setting where applicable, optical interface, connector path and expected route loss.

For bidirectional (BiDi) optics, record the complementary transmit and receive wavelengths at both ends. For parallel optics, record the lane mapping, MPO gender and polarity. For wavelength-division multiplexing links, record the assigned channel or wavelength and the passive path.

Confirm that the module is supported by the host platform and software release. Recognition of an EEPROM is not proof that the port supports the intended speed, FEC, breakout or monitoring behavior. The 100G QSFP28 selection guide explains why interface and lane architecture must be matched before deployment.

Inspect the module and cable path

Keep dust plugs in place until the connection is ready. Use electrostatic-discharge controls when handling modules and follow the equipment vendor's installation procedure. Check the module label, latch and connector for damage before insertion.

Inspect and clean optical connector end faces using the site's approved process. Do not assume that a factory-sealed cable is clean. Contamination can be moved from one interface to another and can create loss or reflection without producing an obvious physical defect.

Before mating the link, confirm:

• Correct fiber type and connector polish.
• Correct duplex polarity or multi-fiber lane mapping.
• No unapproved adapters, bends or temporary jumpers in the path.
• Patch-panel and cassette records match the physical route.
• Test leads and cleaning tools fit the deployed connector types.

Install one controlled link first

Use a representative link before installing a complete batch. Insert the modules fully, confirm that latches are engaged and allow the host to complete recognition. Save the device output before changing configuration.

Record whether the module appears in inventory and whether the host reports the expected identifier, data rate and monitoring capability. If the host rejects or disables the module, preserve the exact warning, platform model and software release. Do not apply an unsupported command copied from another platform.

If the module is detected but the link remains down, use the structured checks in SFP detected but link down. Separate host acceptance from port configuration, remote-end matching and fiber-path faults.

Verify port mode, FEC and remote-end agreement

Both endpoints must implement the same intended Ethernet optical application. A matching form factor does not guarantee interoperability.

Check, where applicable:

• Administrative state and configured speed.
• Native or breakout port mode.
• Lane allocation and breakout mapping.
• FEC mode and whether it is required, optional or unsupported for the selected interface.
• Auto-negotiation settings for interfaces that use it.
• Remote-end optical application and connector path.
• Vendor-specific restrictions documented for the exact platform and software.

Change one variable at a time. When a configuration change is necessary, record the previous value, the approved new value and the rollback step.

Capture an optical and thermal baseline

Digital optical monitoring (DOM), also called digital diagnostics monitoring (DDM), can report module temperature, supply voltage, laser bias current and transmit and receive optical power when supported. Save the values from both endpoints after the link stabilizes.

Compare readings with the thresholds and specifications for the exact module and host. Do not use one universal receive-power target for every optic. A value inside a reported alarm range is useful evidence, but it does not replace the module data sheet, route-loss calculation or independent power measurement when the project requires one.

Look for asymmetry between the two directions, unexpected lane differences and readings close to a warning threshold. Also confirm that a short link does not overload a sensitive receiver. A link can be up while operating with little margin.

Test errors and real traffic

Clear relevant counters only after saving the initial state. Run the approved traffic or service test for long enough to expose intermittent behavior. Monitor physical-layer alarms, symbol or code errors, FEC counters, interface discards, link flaps and temperature.

Acceptance should be based on the service requirement. A management ping proves reachability, not capacity or stability. For a critical link, include the organization's required throughput, loss, latency, failover or bit-error testing.

When testing a batch, use a defined sample plan and keep the host, software, cable path and configuration controlled. A module that passes in a coding board or another switch is not automatically validated for the production endpoint.

Complete the handover record

The final record should make the link reproducible. Include:

1. Endpoint devices, cards, ports and software releases.
2. Module models, coding profile, serial or lot information where required.
3. Optical interface, wavelengths, fiber, connectors and route identification.
4. Port mode, FEC and breakout settings.
5. Initial DOM or DDM values and relevant thresholds.
6. Error-counter and traffic-test results.
7. Exceptions, approved changes and rollback information.
8. Spare-module location and the replacement procedure.

This information is more valuable than a photograph of a green LED. It establishes what normal looked like when the link entered service.

Frequently asked questions

Is a green link LED enough to accept a new optic?

No. Confirm host acceptance, intended speed and port mode, FEC where applicable, optical levels, alarms, error counters and real traffic behavior.

Should connectors be cleaned even when they are new?

They should be inspected according to the approved procedure and cleaned when required before mating. Packaging does not prove that an end face is free of contamination.

What DOM values should be recorded?

When supported, record temperature, voltage, laser bias, transmit power and receive power for both ends or each lane. Interpret them against the exact module and host documentation.

Why can a detected module still have no link?

Detection only shows that the host can read some module information. Port mode, speed, FEC, remote interface, polarity, wavelengths or the fiber path may still be wrong.

How long should a commissioning test run?

Use the duration required by the service acceptance plan and link risk. A short functional check may be insufficient for intermittent faults or thermally sensitive links.

What should be saved before troubleshooting?

Save module inventory, exact alarms, interface state, software release, configuration, DOM or DDM readings and error counters before changing hardware or settings.

Confirm the link before a batch rollout

Share both host platforms, software releases, port mode, FEC, module type, wavelengths, fiber path, connectors, route loss, quantities and acceptance requirements. Axonode can help coordinate compatible optics, coding and a project-specific validation plan with vetted OEM manufacturing and testing partners.

Contact Axonode for optics compatibility and commissioning support. You can also review the optical transceiver portfolio and the network-service-provider upgrade checklist.