We use Optical Time Domain Reflectometer (OTDR) for testing the integrity of long fibre optic cables or cables plants with splices. It verifies splice loss, measures length and finds a fault.
OTDR produces data that is used to create trace to be stored for later reference or to check against the blueprint in the case of a network fault.
Thus, OTDR simply shows where cables are terminated and confirms the quality of the fibres, connectors and splices. OTDR traces also show where breaks are in the fibre cable, so in a troubleshoot case the OTDR traces are being compared with the installation documentation.