There are several common methods used to assess various aspects of fiber optic performance, including continuity testing, insertion loss testing, return loss testing, and Optical Time Domain Reflectometer (OTDR) testing. Fiber optic cabling is the high-performance core of today's datacom networks. What do fiber testers do? Which fiber tester is right for you? In. This Applications Engineering Note (AEN 135) explains and recommends standard measurement methods for characterizing optical fiber system performance. A typical fiber optic communication system consists of three primary components: a transmitter, a fiber optic cable (the transmission medium), and a receiver.