LOS stands for Loss of Signal, and it is an indicator on a networking device that shows that a network signal or connection has been lost. When you see the LOS light blinking or steady on your modem or router, it usually indicates that there is a problem with the signal reaching your device. This means that your modem/router may be able to establish a local network connection for your personal devices, but it itself cannot communicate with your ISP because of signal loss. There could be numerous reasons behind the loss of signal, such as loose or damaged patch cords, extreme fiber cable bends, unpaid bills, maintenance issues, or a power outage on the ISPs side. To fix the LOS problem, you can try power cycling your modem/router, checking for loose cables, checking if your ISP has a firmware update, or contacting your Internet Service Provider.