I recently upgraded to the 600/15 tier with a D3.1 modem, and I never get anywhere close to the advertised 600 Mbps. I've even tried bypassing all my networking gear to rule out any issues, going directly from a windows PC to the modem over 1gig ethernet, and the highest I'll ever hit is ~390 Mbps.
Upon further investigation of the modem logs, there is a large number of uncorrectables on all 32 channels. What's funny, though, is that the uncorrectables show up in large numbers randomly; they don't build up consistently over time. For example, I'll reset the FEC counter in the morning, go the whole day without any uncorrectables, then all of a sudden, get a million across all channels in a span of a few minutes late at night.
This leads me to believe there is some device on the cable system that is introducing noise or interference when it's being turned on. It just doesn't make any sense that there should be such a high number of uncorrectables in spurts.
Screenshot of modem levels for reference:
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The stats are o/k. Please also post the modem's error / event log entries.
Even though the signal stats looked o/k at that snapshot in time, the error log entries confirm that something is going on. Perhaps there is noise ingress into the line(s) somewhere.
There are other signal stat figures that can't be read by the modem. They are the "Upstream Rx Power" (Upstream Receive Power Level), the "Upstream SNR Ch." (Upstream Signal To Noise Ratio), and the "Upstream ICFR" (In Channel Frequency Response). These are as equally important in diagnosing connectivity issues as are the modem's stats.
I'm going to escalate your issue to the Comcast corporate employees that are available to these boards. They can check the CMTS (Cable Modem Termination System) for any real time degradation and / or error reports, see your node / cable plant and modem health, and see whether or not everything is in the green zone. They can also see a history plot for the modem and poll for those upstream receive signal stats.
You should get a reply here in your topic. Good luck !
Greetings, @NJ_nondo! I appreciate you taking the time to reach out to us here on the forums. I hope you are having an amazing day. I apologize to hear of the issues you are running into with you internet speeds. I know it can be frustrating to have them fluctuate when gaming or even working. I would like to have a further look into this and see what could be going on. Can you please send me a PM with your first and last name so I may further assist you?
To send a private message, please click my name "ComcastMichael" then select "Send a Message" on the right side.