What's going on with the red light on the light signal?

The reasons why the optical signal lights up in red are: 1. The optical fiber is broken; 2. The optical fiber pigtail is not inserted into the optical cat; 3. The optical cat is faulty; 4. The uplink optical splitter is faulty. The solution: 1. Check whether the fiber optic cable behind the fiber optic modem is folded or squeezed; 2. Refresh or restart the broadband port; 3. Ask staff to come to repair.