DIN EN 61280-4-2 is the definitive standard for OTDR measurements on single-mode optical fibers. ”The Optical Time Domain Reflectometer (OTDR) is useful for testing the integrity of fiber optic cables. Later, comparisons can be made. It is required for fiber testing per industry standards. An OTDR characterizes the loss of the link for individual splices and connectors by transmitting light pulses into a fiber and measuring the amount of light. OTDR settings are a balance between dynamic range, acquisition time, spatial resolution and accuracy. It helps find breaks, shows cable length, and checks connection quality. Using an OTDR often stops network problems.