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Hello.  I am using an SBG8300 to connect to Xfinity.  Most of the time it works just fine, but several times lately the download speed has dropped from 45-50 Mbps to under 5Mbps.  If I unplug the modem, wait a couple of minutes, and plug it back in, everything returns to normal.

The Xfinity service doesn’t appear to be the issue.

Any idea what this could be.  I purchased the modem less and a year ago, so it’s still under warranty.

The last time I’m aware of it happening was last Wednesday and Thursday, but I was away over the weekend.  It hasn’t happened today, as far as I can tell.

I’ve downloaded the logs from the model administrator panel.

How do I proceed from here getting technical/warranty support?

Thanks.

In this case we would suggest you to help us with few more details to isolate the issue and work on this issue,

Are you facing this slow speed issue on wifi or even with direct connection?

What is your current speed plan?

Have you performed hard reset on modem?

 

Thanks for replying.  I have done a live chat with support and they determined the problem is somewhere in the coax cable.  They had me look at the WAN data on the admin panel and found that the upstream power levels are too low.  Since the problem is intermittent, getting Xfinity to investigate it properly may be a challenge, but I have an appointment with a tech to come check everything and I can show him the conversation transcript.

For the benefit of anyone reading this later:

  1.  I had rebooted the modem every time this happened.  That corrected the problem for a while, then it would happen again.
  2. I had experienced the problem over wifi.  I have one computer connected via ethernet, but didn’t think to check it.  The Xfinity speed test shows that my typical speed over wifi is between 45 and 50 Mbps, over ethernet it’s closer to 100 Mbps.  When experiencing the problem, the wifi speed is 5 Mbps or less.
  3. Having read other posts, I started downloading logs from the modem, but we didn’t look at them during the live chat.
  4. The tech had me log on to the modem, go to Connections then WAN.
  5. Under Downstream QAM, she asked for the highest and lowest Power Levels and the highest and lowest SNR values.
  6. Under Upstream QAM, she asked for the highest and lowest Power Levels. 

The Upstream QAM power level appears to be where the problem lies.  My highest value was less than 43.  She told me the value should be between 45 and 51 for the device to work properly.  There may be a faulty cable splitter or a coax cable in need of maintenance. 

As a side note, this started around the time there was an upgrade performed in my neighborhood.  However, I installed this modem at about the same time, making it difficult to know which was the problem.  Looks like it’s the service itself, but we’ll see.

Usually, the upstream bonded channel power level should be between 45 dBmv and 51 dBmv to avoid slow/intermittent internet connection. If it's not within a range, you have to contact the internet service provider to adjust the signals within a range or to reprovision the modem.

http://arris.force.com/consumers/articles/General_FAQs/SBG8300-Cable-Signal-Levels

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