Use an optical power meter to measure receiving-end optical power; high attenuation may indicate a fault. Substitute the switch connected to the transceiver to isolate the issue. For network engineers working with fiber optics (SFP, SFP+, QSFP), understanding TX (Transmit) and RX (Receive) signal strength is critical. Measured in decibels (dB), it's the logarithmic ratio of the output power to the input power. 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. Understanding attenuation is critical in fiber optic testing. It tells us how much signal is lost as it travels through the fiber. This guide will help you do just that.