ISP sees modem offline, but connection works

[Brk]

Might anyone have an idea as to why my cable ISP tells me they see my modem as being offline even though my connection works? They've told me this twice now when I've called in for tech support since getting this modem (which is on the ISP's approved modem list) back in January. I recall that even when I was getting it provisioned, the tech said they couldn't see it online even though the connection was live.

We've been having low downstream speeds for months now (can't get higher than ~35 Mbps on an "up to" 200 Mbps plan, both on speed tests and in real-world downloads), so I was thinking perhaps this "offline modem" issue might be the culprit? They assure me we are not being throttled, but connecting through a VPN gets us 100 Mbps+ down, and I'm told that's a sign that throttling IS happening.

[Philip]

Hi, it's been a while, good to see you around!

You may be correct about the throttling, if the headend doesn't see your modem it may be defaulting to a lower tier? Just a wild guess, you may want to verify it with a tech.

I would still look into the cable modem settings, the system page is usually at 192.168.1.100. You can look at the signal levels, and the log of events while it is trying to sync (even though the DOCSIS logs can be kind of cryptic). For the signal levels, here is a list of what's considered good: https://www.speedguide.net/faq/what-...idered-good-78

[Brk]

Looks like our signal levels are pretty poor on some channels with lots of errors. This screenshot was taken right after powercycling the modem. I assume it's a line problem, either coming into the house, or the house's coax itself. I've removed every splitter I can get to, replaced all the ethernet cables with new CAT6, done firmware updates, different modems, routers, etc. -- so probably the latter.

[Philip]

You are right, there seems to be an issue with the line/coax. I would get the Cable modem on a straight run of RJ6 coax from outside the house. I would also call a tech to fix the line, those power levels (PWR column) should be close to zero, anything lower than -10 dBmV means the signal from the headend is just too low and you will be experiencing issues. There is also some noise/errors in the 600-650MHz range, but a tech should be able to look into all that. The upstream power seems a bit low.

Because there is a big difference in the downstream Power levels on the different channels, this could point to water in the line/tap, damage/cracks in the outside coax cable insulation, or an issue with a cable amplifier near your location. I would definitely call a tech to look at those signal levels.

[Brk]

Guy came out and replaced the coax from the tap to the house. Ran a speed test and got over 100 Mbps, first time in a long time. Here's what it looks like now. Not sure what can be done about all those errors, though. This house is probably 45+ years old, and wouldn't be surprised if it didn't have the original, or at least very old, coax in the walls! Thanks for the insight, Philip.

[Philip]

Signal looks much better now, notice the downstream power is close to zero!

Some errors are unavoidable with cable technology, correction is built into the system. The errors are only concentrated in 625-645 MHz it seems. If this is at your house at all, this could be some interference from TV channels, cell phone signals, etc. I wouldn't worry about it too much, but if you feel like it you can try to cap any unused/unterminated coax outlets to possibly reduce it a bit... https://www.amazon.com/Terminator-10.../dp/B07VWHX2FS

Here is what operates in that band generally: https://fccid.io/frequency-explorer....=630&upper=660