This document discusses testing and loss measurement techniques in optical fiber communication systems. It describes how optical time domain reflectometry (OTDR) is commonly used to characterize optical fibers and locate faults by measuring backscattered light. OTDR can measure splice and connector losses, fiber quality, and reflectance. Other techniques mentioned include using a light source and power meter to check continuity and measure insertion loss. The document provides a table comparing the capabilities of different fiber testing equipment and concludes that both OTDR and optical loss test sets provide important loss measurement information to ensure healthy optical fiber communication.