Regular Visitor
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11 Messages
Noise/interference on cable system affecting speeds
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:
EG
Expert
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111.5K Messages
5 years ago
Can't see your pic. Since you are a new poster, it needs to be approved by a Forum Admin. That could take some time. In the interim, you could try hosting it at one of those free third-party pic hosting sites like Imgur or Photobucket and post the link to it here.
Or copy all of the text of the status page and paste it into the body of your next post here.
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NJ_nondo
Regular Visitor
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11 Messages
5 years ago
Here is the image showing all signal levels. Note the modem uptime was only 12 hours in this particular instance but typically the uncorrectables would be much higher in a typical 24-hr period.
https://imgur.com/sxtKYnJ
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EG
Expert
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111.5K Messages
5 years ago
The stats are o/k. Please also post the modem's error / event log entries.
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NJ_nondo
Regular Visitor
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11 Messages
5 years ago
Sure, here is the most recent event log. Looks like there are multiple scattered T3 timeouts, among other things.
https://imgur.com/Wk8PvEy
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EG
Expert
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111.5K Messages
5 years ago
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 !
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XfinityMichaelC
Administrator
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4.4K Messages
5 years ago
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.
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