What should you do if the telecom optical modem has a major degradation? Check the backend for speed fluctuations; after -28, don't mess around with it
last winter, my broadband caught a strange problem: during the day, 940 Mbps was fine, but by 8 or 9 PM it dropped to about 100 Mbps, video buffering was reversed, and game latency could jump to triple digits. The router restarted eight times, and the optical modem also lost power, but none worked. The technician came to the door to test the optical power meter; upon entering the house, the light power received was -29. The root cause was an aging cold connector in the hallway. Later, I found out that the numbers had been openly written in the optical modem backend, and I had wasted several days of effort. This article will straighten out the path I've traveled: where to look at light decay, how much is considered significant, which ones can be saved yourself, and which ones must be called 10,000.
light decay is just a piece of light lost on the road; backend can directly count
light comes out of the community data center, passes through the optical splitter, passes through each fusion joint, and finally passes through your yellow leather wire. By the time you reach the optical modem, it's already much weaker. The optical modem records the received light intensity as a number, called received optical power , unit: dBm. This number is negative; the more negative it is, the more severe the loss of light—this part is commonly known as light decay.
look at this number, you don't need a super password; just the regular account on the sticker on the back of the modem is enough. Open 192.168.2.1 in your browser, log in with an account like useradmin, and go to the 'Status' → 'Device Info' some models call it 'Network Side Info.' Scroll down and you'll see a 'Receiving Optical Power' section, usually accompanied by a 'Transmitting Optical Power' section. My ZTE F7015T can be seen on the first screen of the status page. Huawei HS8145V5 need to flip through half a page, and TEWA-based ones are in 'System Info.' Just look at the numbers without changing any settings; regular permissions are more than enough. Don't be scared off by super password .
If you can't even open 192.168.2.1, go through the section on 'Can't Open Troubleshooting ' first; If you're not sure if this address is actually your optical modem, check out this comparison of the three models .
value tiers: Use anywhere within -27, after -28 it starts to cause problems
by the way, transmit optical power. That section is usually between positive and zero-point range. The light intensity from the data center is basically constant, and there are rarely any issues. what really determines your network's fate is the reception . The technician mentioned "light decay -29" also refers to this one — don't look at the two columns in the list.
after getting the numbers, check this table. For gear settings, I used the alarm threshold of a GPON-like optical modem. The XG-PON gigabit modem threshold is slightly different, but it's enough for trend reading.
| receive light power | status | what you need to do |
| -8 ~ -27 dBm | health | don't need to worry , use the numbers as a base |
| -27 ~ -28 dBm | the edge | look again every few days and watch to see if it will move down |
| -28 ~ -30 dBm | low light | high frequency of error and disconnections—it's time to take action. |
| -30 dBm | most cats immediately flash a red light and request repair |
three real sensations. If it's below -27, if your speed is off, don't blame light degradation—go the article the four-layer checks for speed failing standards. The -28 to -30 range is the most unsettling: it runs full during the day, but at night when the temperature drops or the connection shakes slightly, the bits get lost and errors spike. This shows up like my 'sometimes fast, sometimes slow' mode. There's also a constant lag at night, and many people suspect it's the router's firmware all the way. Outside -30 hot, the optical modem basically drops off, LOS lights flash red, and the network is intermittent or completely disconnected.
check these three spots before requesting repairs; all are free
number is over -28, don't rush to call—just list your own plot of land. All three locations cost nothing, and everything was done in ten minutes.
the first spot, follow the line. ran along the yellow leather wire behind the optical modem all the way to the entryway, checking for any tight bends, door gaps, or sofas or cabinets pinned down. The bending radius of the fiber should not be less than 5 centimeters; it's better to coil it around and hang it than to bend it at a right angle. During a colleague's home renovation, workers bent the leather wire at the corner of the wall at nearly a right angle. Light decay was usually just over -30, but after straightening it went back to -24, and nothing happened. is simple: if you see a crease or a white mark on the thread, that's it.
second place: wiping the head. carefully unplug the fiber optic connector (the green or blue block head) on the back of the optical modem and check the end face for dust and oil stains under the light. If so, gently wipe with anhydrous alcohol and a dust-free stick, let it cool for a few seconds before inserting it back. You'll feel a slight clicking sensation when inserted. Two taboos: Do not touch the end face directly with your fingers, and do not rub it with tissues—once the face is scratched, it can't be fixed by wiping.
the third place, reinsert. connectors aren't inserted properly, the flange is loose, and poor contact can still reduce power. Unplug it and reinsert it tightly, then refresh the backend page to see if the numbers return.
also took a look at the place where the Light Cat lived. many optical modems are packed into weak current boxes, and during assembly, technicians wrap the extra leather wire into a lump and tuck it to the side. If it's too tight or too small, it still consumes power. Pull out the wire and loosely coil it into a big circle, making sure the box door doesn't press the wire. I've seen this move save two dB once. Also, the weak current box is hot, and the optical modem and router are stacked for baking. Over time, the optical module itself ages, and when the transmitter weakens, the receiver suffers—you can't fix this yourself, but you can explain that "the cable hasn't been touched, but the light degradation gets worse year by year."
three moves are completed, the number drops back to -27, and the case is closed. If it's still outside -28 hot, then it's not a family matter. Read on.
these three types can't handle them yourself, just report them as 'dim light'
the area at home is cleaned up, the remaining lesions are all outside the wall, and all need to be installed and brought by the technician with the machines:
cold joints age. early days to build quickly, some sections used cold splicers (mechanical splicing) instead of fusion fiber, which naturally caused more wear than fusion splicing. As the years grew and the equipment grew gray and aged, the losses grew larger and larger. That was the case I solved. Replacing cold splicers or remelting fibers requires a fusion splice machine; buying one for yourself is not worth it. about moving the machine, the technician came to collect the melted fibers and also had to test the light decay for acceptance. The same repair process also applies.
the route from the corridor splitter to the entrance. leather wires in hallways are chewed by rats or scraped off by debris, and the splitter port malfunctions—these are things you can't see or touch.
inherently long distance and many fusion joints. some community data centers are far away or clustered along the road, light degradation is naturally high. The only option is to have technicians adjust the splitting ratio or replace ports, which cannot be completely cured but can be alleviated.
repair claims have some tricks: don't just say "slow internet speed"—slow speeds will be treated as ordinary faults and slowly scheduled; If you simply say, "My optical modem receives negative XX optical power, high light decay, weak light," the technician will bring a power meter to your home for segmented measurements, measuring each segment from the hallway to the entrance, positioning everything in one go. Call 10000 or report the issue in the Xiaoyi Butler App. For line maintenance and fiber refusion, there is no extra charge. Don't be scared off by the 'on-site fee' claim—it's mostly just a nonsense.
light decay and LOS red light are related to chronic diseases and emergencies
many people treat LOS red lights and light decay as two separate things. -28 to -30 is a chronic condition: the light is still blue (or normal green), the internet is open, but there are misprints and disconnections, sometimes fast, sometimes slow, you can just keep watching. If it goes beyond -30, it's an emergency. The optical modem just gives up, the LOS red light flashes, and you can skip a self-check—the red light means the light hasn't reached much, and you can't save it at home, so just call for repair.
what each light actually means, how to distinguish LOS and PON, the article on indicator lights has a complete comparison table, so I won't repeat it here. By the way, a somewhat confusing note: LOS flashing is a light issue, PON flashing is a registration issue. The latter is mostly a problem with ITMS, two different matters, so don't report them together.
Ending: Complete Order and Two Habits
go through the whole thing in order; following it won't take any detours:
| steps | actions | determine that the |
| 1 | speed test is abnormal, do not restart the router yet | fast, sometimes slow, fixed at night, most likely |
| 2 | 192.168.2.1 to check the receiving optical power within | -27 to check other |
| 3 | -28 margins, self-check the line alignment/wipe/reinsertion | and once the numbers return, the case is closed |
| 4 | still not working, 10000 reported 'low light' | technician brought an optical power meter for segment positioning |
| 5 | After the repair, I asked | the technician to record the values after repair and compare them before repair |
two habits of ending things are both the result of suffering losses. First, record the numbers on the day of installation: when the installer finishes adjusting and asks you to sign for acceptance, you can go backend and record the received optical power in a notebook. Light decay is slow—-25 this year, -26.5 next year, -28 the year after. Only with a baseline can you know if it's getting worse. When you request a repair, you can easily say, '-25 when installing, -29 now.' Second, the repair is completed and retested: The technician said not to just check Netcom after repairing it, to have him report the amount, or to check the backend himself. Only if it is below -27 is it considered truly finished, otherwise you have to come back again in two months.
in the end, it comes down to one thing: when your internet speed is running low, check the light degradation first. If it's below -27, don't worry; if it's below -28, check three points yourself. If it can't be saved, report 'weak light'—it's more effective than anything else.
