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Internet problems - router or modem?
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Laminar
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Apr 19, 2020, 03:30 PM
 
I have cable internet from a local provider that rhymes with "Shmediacom." I've had random problems with them on and off - for a while, I could track my download speeds degrading over the course of several days from 150Mb down to 5Mb or less, but as soon as I reset the modem, they'd be back up to full speed.

Last year, it got to the point where I was resetting the modem and router at least twice a day to get internet to work. I flashed my router with an OpenWRT BIOS and it was great, for a few months, then it was back to frequent resets. What I found was that if I just reset the router, I wouldn't regain connectivity until I reset the modem too. But if I plugged the modem directly into my computer, all of a sudden it'd nab an IP address and start working with a reset.

I broke down and bought a new router (Netgear AC1750). Since then, perfect, no problems! Until the last few weeks, obviously, when it's crucial for our livelihood that we have consistent, functioning internet. Connectivity would randomly go away and require a reset of the router and modem before it'd come back. Wife was getting kicked out of meetings/off calls.

I don't think my new router is somehow bad after just a few months.

I bought a new Docsis 3.1 modem and it arrived, but then the internet problems went away, so I set it on the shelf.

But problems are back, so I'm back to deciding whether or not the modem is actually the problem. If it can be fixed another way, it'd be nice to return it and get the $150 back. But if this will legit fix my problem that's fine.

I'm semi-afraid to call my ISP. I'm on a weird plan where I'm getting 200+Mb down for much cheaper than their current 60Mb plan, and I'm afraid if I call in asking too many questions, I'll get "upgraded" to a newer plan.

I'm also jaded about calling basic tech support that's used to dealing with dumb, easy issues. I'm assuming they'll remotely reset my modem and tell me it's fixed and to go away and stop bothering them.

Any thoughts on whether the modem could be the culprit?
     
reader50
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Apr 19, 2020, 03:58 PM
 
You've tried three routers. Old with original firmware, old with OpenWRT, new router. Can't be the router, though resetting it does pull a new IP. The delay in getting an IP may be because the routers' MAC has tried for an IP too many times recently. ISP sees a different MAC (your computer) and issues an IP right away.

You haven't tried replacing the modem yet. I'd say go for it. If only to eliminate the modem as the problem. As your connection is work-critical, having a backup modem should be more important than getting $150 back.

A dodgy cable connector. Either your incoming cable, or farther back in the cable system. But calling tech support may mean letting someone into your home. Someone who's been in other homes, and contacted a lot of people. That would be my last choice.

Many modems will let you in: http://192.168.100.1 and let you see cumulative channel errors. Look for low signal-to-noise ratios, and high error counts since a recent reset. You can also see logs of general connection errors. But many ISPs block user access to these pages on some modems, probably so regular Joes won't nag them about noncritical line noise. If the login page loads, google your modem model for the default login. Often 'admin', with blank pass, 'admin' again for pass, or 'password'. Also try checking bottom/back of modem for login info.

Many modems will also let you see a spectrum analyzer, with no login needed. Exact port varies by manufacturer. Try these three:
Arris: http://192.168.100.1:8080
Netgear: http://192.168.100.1:49200
Zoom: http://192.168.100.1:22267
     
Laminar  (op)
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Apr 20, 2020, 08:39 AM
 
Thanks for the input! I have been able to get into the modem and look through the error logs before, but I don't remember what they said. I do know it offers a "health" readout with signal levels, but I don't know what a "high" or "low" signal is.
     
reader50
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Apr 20, 2020, 12:00 PM
 
Downstream:
SNR (signal to noise ratio) in the 30s is OK. 40s is great. 50+ dB means you are right beside the node.
Power (dBmV) should be in the range of -15 to +15. Probably best if it didn't hug the edges, so you have some margin left.
Correctables = advisory. OK to be in hundreds if modem has been up for a day. Thousands or even 10s of thousands ok if it's been up for weeks.
Uncorrectables = packets had to be resent. Not desirable, but still ok if "low". Same count guidelines as above.
All supplied channels should be locked - usually 16, 24, or 32 for Docsis 3.0. For 3.1, usually 1 or 2 channels + the 3.0 channels for backup.
A problem channel or two indicates an outside signal (like a radio station) is getting in. Bad connection somewhere, or cable damage.
Tilt - channels getting worse as frequency going up (or down) probably indicates cable going bad, or a bad amp.

Upstream:
Power (dBmV) - I think this goes up to 55 max. So long as it isn't at the max, has some wiggle room left, you're good.
All supplied channels should be locked. Usually 4-8 for Docsis 3.0. For 3.1, usually 1 but potentially 2. Plus D3.0 channels for backup.

All the noise and power figures supplied are for Docsis 3.0 channels. I don't have a D3.1 modem, so am not sure if those numbers are valid for 3.1 channels.
     
Laminar  (op)
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Apr 21, 2020, 08:08 AM
 
Awesome. I'll screenshot it today and see what we have.
     
Laminar  (op)
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Apr 22, 2020, 09:16 AM
 
Here is right after reset:



Here's my error log:



A minute later:



After about 7 minutes:



Overnight:



Looks like SNR is ok-to-great. Power is fine. Correctables are fine, uncorrectables are a little high? Not sure how to see what's locked. What do you think?
     
reader50
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Apr 22, 2020, 09:45 AM
 
If a channel doesn't lock, the channel number would remain blank. Along with the specs for that channel.

Uncorrected doesn't change after the first minute, suggesting stable operation after startup.

What modem is this? Assuming it's a D3.0 modem, then 8 down channels is not adequate for most speeds today. D3.0-8 can theoretically go to 320 Mbps, but that assumes no one else is sharing those channels. Under normal conditions I'd expect 100 Mbps to be reliable. With most people home and online today, you're likely to see congestion most of the time.

Also, what model is your replacement new modem? And what speed tier are you on with your ISP?
     
Laminar  (op)
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Apr 22, 2020, 01:19 PM
 
Current modem is a Surfboard SB6141. New one is an SB8200. I generally see 170-220Mb when I check with Speakeasy. When doing sustained large downloads I see 16-19MB/s, which is around 125-150Mb.

No clue what speed I'm supposed to be at with my ISP, their system in convoluted and a pain. My bill lists a name for the tier like "Ultra" or something, but it doesn't align with any of their current tiers.
     
reader50
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Apr 22, 2020, 04:18 PM
 
An SB6141 is an old modem today, an 8 down x 4 up. Retire it to emergency spare. The SB8200 is a gigabit modem, with 32x8 backup D3.0 mode.

Your speed tier is probably in the 200-400 range, which is way too high for an 8x4. If you're super lucky, they made a mistake and left your speed uncapped.

You are probably suffering from heavy congestion, due to everyone sheltering at home. With not enough channels to get your fair share of node bandwidth. If the system is saturated, whoever has the least channels will get the short end of the stick.
     
Laminar  (op)
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Apr 23, 2020, 07:27 AM
 
That's good info, thank you. I'll see if I can get the new modem all set up and ready to party, it'll probably have to be on a weekend when I can afford the downtime.
     
ghporter
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Apr 23, 2020, 12:19 PM
 
You can probably find out what the local network load is through DSL Reports

My “up to 40Mbps” down connection was pushing 50 most of the time until around mid-March. Since then it’s slowed, sometimes a lot.

Glenn -----OTR/L, MOT, Tx
     
Laminar  (op)
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Apr 26, 2020, 10:44 AM
 
Installed the modem today, had to call the ISP so they could activate it. Looks like it may have unlocked a little extra speed.

Previously:


Now:


Downloading a game from Steam, Steam reported 33.6MB sustained download speed, which checks out. Here's hoping reliability is up as well! Thank you!
     
Laminar  (op)
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May 5, 2020, 10:01 AM
 
Once late last week the connection slowed and slowed until it stopped working, had to reset everything.

Again today (I'm gone) the same thing happened, wife got kicked out of a meeting.

What do I need to look for to troubleshoot this. Will there be anything in the modem's logs that will tell me what's going on?

The modem has dual ethernet ports, as does my Mac Pro. I'm thinking of connecting the second MP ethernet port straight to the modem so when I have problems I can activate that port and see if the router is causing me issues.
     
reader50
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May 5, 2020, 12:22 PM
 
2nd port on modem will try to pull a 2nd IP address.

Log into the modem and check corrected/uncorrected totals. See if they've gone up rapidly on one or more channels. Logs can show if the modem had to reconnect. Either case is likely to require a service tech to come and check lines. But if it's working good again when the tech arrives, you have only so-so chances they'll find the problem.

Assuming at least one comp is connected to router via ethernet, you can eliminate a congested WiFi channel.
     
   
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