In this detailed guide, we explore the process and significance of Optical Time-Domain Reflectometer (OTDR) testing for a 20.3km optical fiber link. OTDR testing is crucial for assessing the integrity and performance of fiber optic networks, providing precise measurements of fiber length, loss, and any potential faults or splices along the link. This document covers the principles of OTDR operation, step-by-step testing procedures, interpretation of OTDR traces, and best practices for ensuring accurate results in long-distance fiber optic installations. Whether you are a seasoned technician or a novice in fiber optics, this guide will enhance your understanding and application of OTDR testing for optimal network performance.