Testing, Measurement, and Troubleshooting
Tier 1 and Tier 2
Tier 1 testing uses an optical loss test set (OLTS) - a light source and power meter - to measure insertion loss and length at the operating wavelength(s). Tier 2 adds an OTDR trace for event-level detail (splice loss, connector loss, reflectance, distance to an event). Basic link/channel testing per TIA-568 usually requires Tier 1; OTDR is used for troubleshooting, acceptance of OSP spans, and documenting splices.
Referencing and method
Set the reference (zero) properly before testing. The two-jumper (Method B) reference is common for MM per TIA-526-14; SM per TIA-526-7. Using the wrong reference method, or forgetting to re-set the reference after swapping test jumpers, is the classic source of a false pass/fail. Always test with clean, inspected end faces.
OTDR essentials
An OTDR needs a launch (and ideally receive) cable to move the first and last connectors out of the dead zone; the dead zone is the distance after a reflective event where the OTDR cannot resolve another event. Ghosts are reflections from high-reflectance events that appear at multiples of a distance - they are not real. Test from both directions and average when the spec requires it, because splice loss measured from one side can be misleading.
Troubleshooting tools
A VFL (visual fault locator, red laser) finds breaks, bad connectors, and tight bends glowing through the jacket. A power meter alone can confirm a transmitter's output; comparing dBm readings at each end localizes loss.
Rule of thumb
If a link fails at 850 nm and passes at 1300 nm, suspect a macrobend or a multimode launch-condition problem; if it fails only at 1550 nm on SM, suspect a tight bend. Always record wavelength, direction, reference method, and instrument serial number in the report.