Slow single-threaded upload speeds

(forgot to attach screenshots)

I contacted Support a couple of days ago and got a tech scheduled to come out yesterday afternoon. I explained the situation to him, but he basically said that there's nothing he can do for me if the Cox speed test and the speedtest.net results look good. He said that he would try to escalate this but wasn't confident that it would go anywhere. Unfortunately, he was a contractor and did not really understand the specifics of my problem, though he was very polite about it. Supposedly I should expect a call back in a few days.

I just did some more file transfer tests between two Linux boxes, one at my house and the other at my sister's house 2 miles away (also on Cox). Uploading a file to her house, I got the usual 600 KBps whereas uploading a file from her house to mine, I got 1200 KBps (which is way higher than the 5 Mbps of her Preferred tier!) I'm also trying to contact my neighbors who are Cox customers to see if they are experiencing the same behavior.

My problem has been resolved! For anyone interested, here's an update: A Cox rep called me to follow up on the survey I filled out after the contractor came (and did nothing) last week. The rep was very apologetic, and although not technical, took down the details I gave her and said she'd try to get an employee scheduled. On Saturday, David, a Cox employee came out and immediately went to the box at the street to test the line after I described my problem. He spent almost an hour there on the phone with back-end support, and he checked the line from the street to my house. He came back saying that there were some issues he saw at the box on the street, as well as on the line to my house. He put in ticket for the problem at the street and another one to replace the line to my house. I asked if I'd be notified about these, and he said there wasn't a good mechanism for this but that he'd call or text me with an update.

Tuesday morning I noticed that speed tests on testmy.net and speedof.me were showing uploads of 15-22 Mbps, which were 2-3x faster than I'd ever gotten before! It was not consistent though, as later that day the topped out much lower. My modem signals were unchanged though, and I could tell the line to my house hadn't been touched. That afternoon David called me saying that they did something on the back-end, which I'm attributing to the improved uploads I was seeing. He asked if the cable to my house was replaced yet, and when I told him no, he guessed that it would be done very soon. Sure enough, they came the next day and after 30 minutes had the cable replaced. My modem now reports downstream signals between 7.0 - 5.5 dBmV, SNR between 41-43, and 0 errors so far. Upstream power is 38-40 dBmV (compared to 44-49 before).

I'm a happy camper, and all in all, it wasn't that much hassle. Much kudos to David for his great work and excellent customer service, as well as the CSR that called me because of the survey. It's disappointing to have multiple Cox representatives say that they can't do anything about this even though that is clearly false. To others struggling with similar issues, keep pushing Cox to investigate your problem, and good luck!

Another update to this ongoing saga... earlier this week I noticed uploads were slow again despite really good power levels. I contacted support on chat asking about SNR on the upstream channels and they remarked that the "returns were red indicating a power problem". Another tech (contractor) came out yesterday. He checked the signal at my line and the drop, tried swapping out the modem, ran a temporary RG6 from the drop to the modem, but with no improvement. He said that the backline folks were able to run a speed test from their end to my modem and got 300/30--is that even a thing? Interestingly, even the Cox speed test was only showing 11-13 up, which was unusual. Finally I asked him to check signals at the tap, which looked fine. After this he left, basically saying that there's nothing else he could do and that the slow speed tests were likely due to congestion with the servers.

About 30 minutes after he left, the speed tests starting showing 25-32, and not just some of them, but ALL of them! This included switching various servers to test against. The bandwidth graph on my router showed I was getting short spikes of 40-50 Mbps, which I'm guessing was probably Powerboost. I tested streaming a 10 Mbps video off my network from a cell phone and it worked perfectly. Clearly something changed, and I even called the tech and asked what he did, but he had no clue. However, this lasted for about 90 minutes, and then things went back to the usual slow and inconsistent uploads. At least now I know that everything with my connection is capable of 30 up on single thread.

I posted this to another forum and got a suggestion this could be due to a bad ground that's causing ingress on the upstream. When they replaced my drop last week, it appears they bonded the grounding block to my electrical panel, so perhaps the bad ground is at the tap. I have another tech (hopefully a Cox employee this time) scheduled to come out tomorrow morning and I'll press him to check the grounding throughout.

Here's some testmy.net data showing upload results over the past 10 days or so. The 90 minute period yesterday when uploads were full speed is obvious in the graph. Note that power levels were more or less the same before, during, and after that period.

Poor grounding/bonding will not effect packetloss in anyway. All it does is provide a path for foreign voltage to ground out if something happens to the electrical wiring in your house such as a bad neutral and your equipment decides to use the coax shielding as a path to ground.

Your issue here is likely upstream noise on the node, which won't be noticed in your RF stats

Another update: after continuing to contact Support, I had another Cox employee come out 2 weeks ago who was very receptive to my concerns and spent a lot of time on the phone with back end support. With their help, he confirmed there was significant ingress at the node on the 17Mhz upstream channel, and a small amount on the 32Mhz channel. Not enough to raise alarms, but likely enough to cause my slow uploads. He put in a ticket to investigate this. Unfortunately, that ticket was closed with the resolution "schedule tech vist with customer".  I convinced them to create another ticket for the upstream ingress at the node, and suddenly 2 days later things starting running really well. All upload speed tests were consistently in the 20s! I used to get a consistent ~1% packet loss on a Smokeping to the CMTS, but now it's gone. The ticket is still pending with no update a week later, so I will continue to check in with Support to find out for sure what was done to address this in case it happens again.