Question Internet download speed slows down over time in just one device

Jul 24, 2019
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I am at my wits end over this issue.

I'm using windows 10 (updated to 1903) and I'm hardwired to my router. When I turn the computer on, I do get close to 1 gigabit of speed as intended for my download and 40 Mbps upload.

As time goes on, the download speed starts degrading and in less than 24 hours it gets to a point that the download speed goes lower than 100Mbps while the upload speed remains constant.

Here are some of the things I have already checked / tried:

  1. Made sure it wasn't a NIC issue (swapped NIC cards and had the same result).
  2. Made sure it was not a router issue (swapped between two routers, and got the same result)
  3. Updated my NIC drivers, with no luck there.
  4. Made sure QoS was disabled on the router.
  5. tried turning Autotunninglevel off in the TCP Global Parameters (didn't work... it actually capped my connectivity down to 500 Mbps when I did, had more success putting it at experimental level).
  6. Disabled the NIC and tried using wifi, but the speeds remained the same.
  7. Checked other devices in my household, both wired and on wi-fi, and their speeds are as advertised, so it seems it may not be an issue with my ISP.
  8. Changed ethernet cables.
Anyone has any clue what may be causing this? I'm completely stumped.
 
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Ralston18

Titan
Moderator
When the computer is first turned on open either Task Manager or Resource Monitor.

Check what is being launched at Startup (tab in Task Manager) and what all is running.

Keep the window open and slide to one side. Keep watching what is happening and over time (hopefully less than 24 hours) you will note some bottleneck occurring or some app, service, process, gradually hogging a resource.

If nothing is apparent in Task Manager then go to Resource Monitor.

What make and model routers?

I had a problem a few weeks ago where upload speed became faster than download speed on my Linksys WRT1900ac router.

Ended the problem by resetting Media Prioritization on the router.

Reference link FYI:

https://www.linksys.com/us/support-article?articleNum=138353

But look first (i.e., Task Manager and Resource Monitor) and see what you find before doing anything to the router.
 
Jul 24, 2019
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Thank you Ralston. I was originally using an GT AC-5300 and now I'm using the ISP's Askey Router. I may have found the problem, but I won't declare victory just yet, as I have rebooted the computer several times over thinking I was now in the clear, only to see degradation a few hours later.

The solution: New drivers for the NIC from Intel appeared yesterday (dated March of 2019). I also saw that my new Gigabyte motherboard (yes, I changed motherboards as well, as I was already intending to buy one but this issue had me accelerate the process) included a Fospeed software, that may have modeled the speed a bit too much.

I'll keep people posted, in case anyone has a similar issue.
 
Jul 24, 2019
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Talked too soon. I was able to stabilize it a bit, when it won't drop to less than 100 mpbs, but it does drop over time to about 400mbps. It seems the issue partially gets worse after downloading big files.
 
Jul 24, 2019
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It seems the two drivers that light up the most when I try to do a speed test are ndis.sys and tcpip.sys whenever I try to download something large. I'm not sure if this is related to the issue, but I found it odd, nonetheless.

Using latencymon, the dpc routine execution jumps to a very crimson red (very bad) and I start getting latency and page faults as a result... which I find super odd as I have 64gb of ram and I don't even get 40% utilization of it at any point in time, so there should be no issue for the system to revert to hard drive page files due to RAM saturation.

Any ideas?
 
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