Question Internet DL speeds are extremely low (<5 Mbps; subbed to Gigabit) - Not entirely sure if it's the modem

shyam09

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Oct 22, 2014
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I am with Cox Communications, and have a Voice and Internet (Gigabit) plan with them. I have their Arris TM3402a modem, but I was interested in getting a non-PUMA chipset. The contenders were Netgear CM1000-1200 or Arris SB8200.

Before that, let me explain my prior setup. I had a 200 Mbps plan with Cox with their DOCSIS 2.0 modem. They had attached a 6 dB attenuator to the coax cable that attached to the modem [coax -> attenuator -> modem]. Here are the modem Downstream/Upstream info: View: https://imgur.com/a/GkgbZul


I ended up getting the Netgear CM1200 from Amazon Warehouse Deals (it was marked "acceptable", but looked brand new). I used a 2-way splitter and attached one end to the Arris TM3402 which connected to my phone, and the Netgear CM1200 which connected to my router.

The initial experience was great and I achieved greater speeds than the Arris TM and the webpages were much more snappier.

This morning was horrible. My router decided to lose its life somehow, and I tried to figure out the issues. I ended up grabbing a Linksys Velop MX10 (I was curious to see what Wifi 6 would be like - tbh, I'll probably stick with a Wifi 5 router) and the first couple of minutes were great. Internet speeds were high, webpages loaded snappier, everything was great.

And then it just came to a crash.

Here are screenshots of the modem page and the speed tests. View: https://imgur.com/a/kXzZb83


This was with the splitter + new router. There are uncorrectables across all channels. When I had this set up with the old router, the uncorrectables were in the 200s in the bottom chunk.
The speeds were similar. Low download, mid-upload.

I ended up removing the splitter and connected using coax + 6 dB attenuator.
Uncorrectables and correctables were 0 across the board about 30 minutes in. The Power range was 3-6 dBmv, and the SNR was low-mid 40s. Speed was low DL, expected UL.
View: https://imgur.com/a/LcTvvjl
[forgot to take screen caps with of modem page]


I also decided to remove the attenuator and connected the coax directly to internet modem. Rebooted router too.
See screenshots. View: https://imgur.com/a/ULgPahg

Uncorrectables and correctable were 0 across the board 10 minutes in. The power range was higher in the 9-11 range. Speed test yielded was low DL, expected UL.

Right now, I had Cox revert to using the Arris TM3402 as my internet/voice modem. I placed an order for an Arris 8200, but I'm curious to know what suggestions you all have in regards to set up?

My inclination is the modem itself may be bad because I did not see a change between the three tests [w/ splitter; w/ attenuator; direct; I did wait five minutes before testing something new].

Should I be looking at a 2-way splitter or a four-way splitter with coax terminator caps (x2) to get as close to the 6dB attenuator?
 
I am surprised that you got 2 different cable modems to work at the same time unless you were calling the ISP up every time you move the internet back and forth.

I would not be concerned about the puma chipset issues. Like most things the news services hype up the problem but think it is boring when the vendor puts out a patch to fix it so they don't report it much. The puma bug is fixed for actual user data. The guys that wrote the test tools redid it so they can still show a problem but pretty much only if you run some very special case will you see it the problems with games and other actual traffic was resolved by the patch. But you know a tool that does not show a problem is pretty worthless and they don't want to feel worthless.

You best test is with a cable connected directly to the modem with no router. This eliminates the router as the issues. You will likely have to reboot the router every time you swap between your pc and the router it locks the first mac address it sees.

I suspect you are getting errors especially when the download is so much lower than the upload. It is strange that you do not see uncorrectable errors. Maybe a ping command would show packet loss. Best to test to the ISP router so they don't blame google or some other ISP.

Check the log page also. You will have to look the messages up many mean nothing.

I would try different ethernet cables just in case that is the problem.

The ISP is pretty good about knowing when and how much you need things like attenuators They generally test the line with their meters rather than depend on the modem. If this keeps happening especially plugged direclty into a modem I would have them come out and check the line.
 
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shyam09

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Oct 22, 2014
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I am surprised that you got 2 different cable modems to work at the same time unless you were calling the ISP up every time you move the internet back and forth.

I would not be concerned about the puma chipset issues. Like most things the news services hype up the problem but think it is boring when the vendor puts out a patch to fix it so they don't report it much. The puma bug is fixed for actual user data. The guys that wrote the test tools redid it so they can still show a problem but pretty much only if you run some very special case will you see it the problems with games and other actual traffic was resolved by the patch. But you know a tool that does not show a problem is pretty worthless and they don't want to feel worthless.

You best test is with a cable connected directly to the modem with no router. This eliminates the router as the issues. You will likely have to reboot the router every time you swap between your pc and the router it locks the first mac address it sees.

I suspect you are getting errors especially when the download is so much lower than the upload. It is strange that you do not see uncorrectable errors. Maybe a ping command would show packet loss. Best to test to the ISP router so they don't blame google or some other ISP.

Check the log page also. You will have to look the messages up many mean nothing.

I would try different ethernet cables just in case that is the problem.

The ISP is pretty good about knowing when and how much you need things like attenuators They generally test the line with their meters rather than depend on the modem. If this keeps happening especially plugged direclty into a modem I would have them come out and check the line.
The two modems were for different purposes.

The Cox provided Arris was initially used for Voice and Internet. I called to have the Netgear activated for just the Internet.

I currently have the Cox provided Arris activated for Internet and Voice. So I’m back to the original high speeds.

From what I recall (first image set, image 4/4), the log showed notices, and a warning everyone now and then. I never saw errors.

Out of curiosity, I got a DOCSIS 2.0 modem when I initially subbed to Cox. Would DOCSIS 3.1 change the required attenuation? My guess is it wouldn’t,
 
It all depends what the ISP is running. It to a point has to match. The newer 3.1 will drop to 2.0 if that is all the ISP supports. The reverse it not true if the ISP only uses 3.1. I don't think 2.0 can run gigabit speeds. Part of the reason they use stuff like 3.1 is even though it runs at 10g that just means they can share the bandwidth with more customers.

The attenuation might be different because they are using many more channels. The attenuation needed varies by the frequencies but there is not much they can do except put something in that is average.
 

dengamle

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Apr 18, 2007
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CM1200 doesn't lock onto the OFDM channel, so that is a sign of something wrong going on.

A positive thing: the diplexer is set to 85 MHz. That is Cox getting ready for 3.1 in the upstream. :)
 

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