An Optical Time Domain Reflectometer (OTDR) is the most powerful tool for characterizing fiber optic networks. It works like "radar for fiber optics," sending light pulses down the fiber and analyzing the reflected light to measure loss, locate faults, and verify installations. OTDR testing analyzes fiber optic cable performance from end to end by testing components along the cable, including connection points, bends, and splices. For total end-to-end insertion loss certification, use an OLTS or light source and power meter as well. For municipal utilities, which are increasingly building and operating their own fiber optic infrastructures, the professional implementation of OTDR measurements is becoming a decisive success. An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber.