Cabling_
Fiber Certification Workflow: From Splice to Signed Acceptance Report
This article specifies the sequential MPO trunk certification workflow for scale-out InfiniBand or Ethernet fabrics in NVL72-class GPU racks, from incoming inspection through OTDR traces and signed acceptance documentation that satisfies OEM warranty and operator handover requirements.
Key facts
- MPO trunk cables for scale-out networks are factory-terminated; field work consists of routing, cleaning, inspection per IEC 61300-3-35, and testing only.
- TIA-568.3-D defines polarity Types A, B, and C for MPO links and requires documentation of each link's polarity before testing.
- An OTDR with launch and receive fibers is required for backbone links longer than 100 m to locate events to within the instrument's dead-zone specification.
- Power-meter and light-source Tier-1 testing per ANSI/TIA-526-14-B must be performed after OTDR Tier-2 traces when both are specified in the project test plan.
- End-face inspection must pass IEC 61300-3-35 Zone A and Zone B criteria before any insertion-loss measurement is recorded.
- All test results must be stored in native format plus PDF with cable IDs, test dates, operator names, and instrument serial numbers for traceability.
- NVLink connectivity inside NVL72 racks uses copper backplanes; MPO fiber certification applies exclusively to the separate scale-out network.
Incoming inspection of factory-terminated MPO trunks
Verify reel or box labels against the bill of materials and confirm length, fiber count, polarity type, and connector gender before any cable leaves the staging area. Perform a visual check of both MPO connectors for shipping damage and run a quick continuity test with a calibrated MPO continuity tester to confirm all fibers are present and in the expected order.
Record the factory test report serial numbers and compare them to the measured length using an OTDR set to the correct index of refraction for the cable type. Any discrepancy outside the OEM tolerance requires the cable to be quarantined and the supplier contacted before installation proceeds.
Routing MPO trunks through pathways and racks
Pull trunks using the manufacturer's recommended grip or pulling eye and maintain the minimum bend radius at all times, especially at the transition from vertical managers into the rack. Dress cables so that MPO connectors reach the patch panels without tension and with slack loops sized to allow future moves, adds, and changes.
Separate MPO trunks from power cables by the distances required in the project specification and secure them with hook-and-loop fasteners only. Label both ends of every trunk with the permanent cable ID before the cable is fully seated in the pathway.
Cleaning and end-face inspection before mating
Clean every MPO connector with the OEM-approved dry or wet-dry method immediately before insertion into an adapter or transceiver. Inspect the end face with a microscope that meets the magnification and field-of-view requirements of IEC 61300-3-35 and record a passing image for each fiber in Zones A and B.
Any connector that fails inspection must be recleaned and reinspected; repeated failures require replacement of the trunk segment. Never mate a connector that has not passed inspection, because contamination is the dominant cause of high insertion loss and reflectance in MPO links.
Tier-1 and Tier-2 certification testing sequence
Execute Tier-1 insertion-loss testing with a calibrated power meter and light source after all connectors have passed inspection. Use the one-jumper reference method for each MPO polarity type and record loss values for every fiber against the project loss budget.
Follow with Tier-2 OTDR traces from both directions on links exceeding the length threshold stated in the test plan. Compare bidirectional event tables, confirm that splice or connector events fall within acceptable reflectance and loss limits, and store the native trace files with the corresponding power-meter results.
Common field failure modes and detection points
The most frequent cause of failed certification is end-face contamination that survives initial cleaning; it appears as high loss or reflectance on the first power-meter reading and is caught by mandatory pre-test inspection. Incorrect polarity produces failing continuity or swapped fiber results and must be verified with the continuity tester before any loss measurement.
Bend-radius violations during routing create macrobend events visible on the OTDR trace but invisible to a simple power meter; these are caught only when the full Tier-2 test sequence is executed. Damaged factory terminations from excessive pulling tension show elevated loss at the near-end connector and are identified by comparing incoming reel tests to post-installation results.
Documentation package and signed acceptance
Compile the acceptance package with cable schedules, as-built pathway drawings, native OTDR traces, power-meter results, end-face images, and calibration certificates for all test instruments. Include operator names, dates, and instrument serial numbers so that every result is traceable to the technician who performed the work.
Submit the package for review against the project test plan; once accepted, obtain the operator signature on the formal acceptance report. Retain the complete digital archive for the warranty period specified by the cable manufacturer and the operator's records-retention policy.
Standards referenced: TIA-568.3-D · ANSI/TIA-526-14-B · IEC 61300-3-35
Frequently asked_
Do MPO trunks require field termination or splicing on site?
No. MPO trunks for scale-out fabrics arrive factory-terminated and polished. Field work is limited to routing, cleaning, inspection, and testing. Any requirement for field splicing or termination indicates a non-standard cable type that should be clarified with the design engineer before procurement.
When is an OTDR required versus a power meter alone?
Project test plans for links longer than 100 m normally require both Tier-1 power-meter measurements and Tier-2 OTDR traces. The OTDR locates and quantifies individual events; the power meter confirms total link loss. Both data sets are needed for warranty submission on most hyperscale deployments.
How is polarity verified and documented?
Use an MPO continuity tester to confirm the mapping of fiber positions at both ends against the specified Type A, B, or C configuration. Record the polarity type and the continuity test result for each trunk in the test report before insertion-loss measurements begin.
What happens if an end face fails inspection after cleaning?
Reclean and reinspect. Persistent failure requires replacement of the affected trunk. Mating a failing connector risks damaging the mated connector or transceiver and will produce failing loss or reflectance values that prevent certification sign-off.
Who typically signs the final acceptance report?
The operator's representative or commissioning authority signs after the full documentation package passes review. Leviathan Systems supplies the complete test archive and assists with any clarifications required during that review.