When this light appears on your fiber router or ONU (Optical Network Unit), it indicates that the device has lost its connection to the fiber network — even though your router may still be powered on and Wi-Fi may appear active. When it's green and steady, everything is fine. However, when it blinks red or stays solid red, it signifies a Loss of Signal, a problem preventing your router from communicating. A LOS red light in your router or modem means that there is a disruption in the fiber optic connection from your Internet service provider (ISP), hence a “loss of signal” (LOS). In most cases, a loss of signal indicates a technical issue with the ISP, but it could also be a problem with your. If the LOS light on your fiber router or ONT is blinking red, it usually means Loss Of Signal. This guide explains the likely causes, the checks you can do at home, and when the issue needs technician support. This can happen due to various reasons, such as a. LOS means loss of signal.
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