Use an Optical Time Domain Reflectometer (OTDR) to identify where the signal loss occurs. Check for visible bends or damage in the fiber, as this can cause light to leak out. Fiber optic networks are generally reliable, but like any technology, they can experience problems that affect performance. Below are some of the most common fiber optic issues and how to diagnose and fix them. A practical step-by-step guide to diagnosing and fixing common fiber optic network problems. From signal loss to ONT registration failures, learn what to check first. Tip #1: How can we distinguish between the SFP module's RX and TX ports? The triangle indicates the Tx (transmit) port with the pole facing outward on the SFP module, whereas the. Problems within a fiber link can occur due to a wide variety of reasons. A very common problem is that a connector is not fully engaged - often hard to notice in a crowded patch panel. Or it could be caused by the quality of the connector itself, such as poor end-face geometry that doesn't pass the.