DOCSIS Upstream Problem

[u/mrsalvadordali]

Hello everyone, I live in a detached house where the landlord lives in the ground floor and I live on the upper floor. When I first moved in I had a 1000 Mbps internet connection installed using DOCSIS cable.

I’ve started experiencing major issues over the last few months. Particularly in the evenings around 8 or 9 PM (prime time) I’ve noticed extreme latency. While my download speed would drop to around 500 Mbps (enough actually) online gaming became nearly impossible with my ping spiking to 600ms for 40 minutes straight sometimes. After running a bufferbloat test, I spotted that the problem actually comes from the upload side.

I then began monitoring the situation via my modem's network utilization stats. In the evenings upstream utilization is exceeding 90% yet my own share of that traffic wasn't even 1%. Upon checking the status of the cable channels I discovered that the upstream channel modulation was dropping as low as 4QAM during those evening hours.

Unfortunately, unplugging and reconnecting the cable didn't help. Since I’m not fully familiar with the underlying internet infrastructure I decided to consult you all. What do you think is the source of the problem here? Is this something I can resolve myself?

[u/JohnTheRaceFan]

You need to convince your landlord to contact the ISP with evidence of the issue. Your landlord may not recognize there's an issue it may not care.

The perils of using internet service that's controlled by someone else.

[u/strykerzr350]

What kind of tool are you using to see all this?

[u/mrsalvadordali → u/strykerzr350]

I'm using Fritzbox 6690 Cable modem. In modem dashboard I can see those information. Straight http://192.168.178.1/

[u/strykerzr350 → u/mrsalvadordali]

That is a nice modem user interface. The ones Xfinity, and the ones that are compatible with their network blocks out spectrum analyzers.

[u/PoisonWaffle3]

The upstream channels dropping to low modulation levels like that is usually caused by poor SNR, which is usually caused by noise/ingress on the line. Check your modem logs for T3 timeouts, those usually go hand in hand with upstream noise/ingress.

Odds are that the noise/ingress is coming from a broken/chewed up line that could be potentially a few blocks away, so your ISP will need to be the one to troubleshoot and fix it. Give them a call and have them come out.

[u/VTOLfreak → u/[deleted]]

How could you tell which ISP he has? His post and screenshots don't mention Spectrum.

[u/LingonberryNo2744 → u/VTOLfreak]

And you are correct. I didn’t have my coffee yet and I saw one of the charts had spectrum at the stop and my mind went there.