Fault-finding
The fiber box is showing a red LOS light
Loss of signal — no light is arriving from the ISP. Check the fiber connector is fully seated and the cable is not sharply bent or crushed, then report it. This is an ISP-side fault in the large majority of cases, and restarting the router will not change it.
Written and reviewed by our networks and fiber bench · Last reviewed
What LOS actually reports
The ONT is telling you that no optical signal is reaching it. That is a different statement from 'no internet' — it means the light itself is absent, so nothing downstream can possibly work. Restarting the router does nothing for it, and repeated restarts are the most common wasted response to this light.
The two things worth checking yourself
First, that the fiber connector is fully seated in the ONT — they work loose, and reseating it is occasionally the whole fix. Second, that the cable is not kinked, crushed under furniture, or bent tightly around a corner. Fiber tolerates far less bending than copper and a sharp bend genuinely stops light.
Then it belongs with the ISP
Beyond the connector and the drop cable inside your premises, the fault is on their side: a cut in the street, damage at a splice enclosure, or a problem at their equipment. Report it with the word LOS, because it tells their support desk immediately that this is an optical fault rather than a configuration one.
Where we come in
If the break is in cabling inside or around your premises, that is a splice — located with an OTDR to within a couple of metres, fused, and tested bidirectionally with a printed trace. For a break in the ISP's own network, it is their repair and no third party can shorten it.
What does the red LOS light on my fiber ONT mean?
Can I fix a red LOS light myself?
Only by reseating the fiber connector and checking the cable is not kinked or crushed. Beyond that, no — there is no configuration change that produces light where none is arriving. Anyone suggesting a router reset for an LOS condition has not understood what the light means.
How long does an ISP take to fix a fiber cut?
It depends entirely on where the break is and how accessible it is, and no honest answer exists before they locate it. What speeds things up is reporting it as an LOS fault rather than as 'internet not working', because that routes it to the right team immediately instead of through a scripted reboot sequence.
Is a red light always a cut cable?
Not always — it can also be a fault at the ISP's equipment, a dirty or damaged connector, or an ONT whose optical receiver has failed. The connector is the only one you can address. The rest is diagnosed at their end, usually with an OTDR from the exchange side.
Rather have it done?
Fusion splicing joins fiber cores permanently, and an OTDR trace proves the join is good rather than merely passing light. Splicing with a printed OTDR result starts at PKR 3,500 per splice with a callout, and the trace is what turns a repair into something you can hold someone to.
Fiber splicing and OTDR testing in Islamabad — prices and scope