Most often, there are two indicators per port: one indicating link status (also lighting up briefly when an inserted module is activated) and the other indicating activity - either direction. This document describes how to troubleshoot fiber optic interfaces by addressing some of the fiber optic module and cabling specifications. There are no specific requirements for this document. Sometimes, the LEDs flash. When optical modules operate on a switch, it is usually necessary to read the module's internal information to understand its working status—such as connection status and real-time metrics like optical power and temperature. Additionally, identifying module information helps detect coding. Before you blame the switch or replace the cable, you need to look at the invisible data: the light levels.