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user_7198df
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Saturday, May 2nd, 2026 12:36 AM

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upstream channel bonding

I have a Nighthawk CM3000 but my upstream ATDMA channels 5-8 are not bonding and OFDMA upstream channel 2 is not locking. Downstream signal is perfect — power levels 5-6 dBmV, SNR 42-43 dB, zero uncorrectables. 

One thing worth noting — OFDM correctable errors aee 119-161 million. Uncorrectables are still zero.

I already have a ticket open and a tech appointment for May 2nd. But after an AI assisted analysis it's seems likely there may be a MoCA/POE filter that may be blocking upstream channels.

I’m in a multi-unit building. The tech should  trace the line from my unit’s tap back to the distribution point and check for filters or signal issues on the return path. 

If there are any xfinity employees online, is there a way to get this information added to my ticket/appointment notes to save some time for the tech?

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9 hours ago

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user_7198df

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11 hours ago

The tech came out and checked everything. He put new connectors on the cable between the modem and the wall outlet. Replaced a filter and tightened a loose connection at the drop. Now I'm getting max speeds between 900-1100mbps (Fast.com and ookla), cloudflare however has speeds between 490-650mbps. My research found this is likely due to several factors including ISP insentive to give priority to Fast.com and ookla which access best case peak speed vs cloudflare accessing real-world speeds under load.

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XfinitySean

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645 Messages

Thanks for keeping us posted on the results, user_7198df! I'm glad to hear it that your speeds seem to have increased. As far as the connection to Cloudflare vs Ookla or Fast.com, there are a number of things that can cause different results depending on the site, server, and test being used. That said, are you noticing any other issues since the technician completed the visit?

 

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10 hours ago

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user_7198df

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No. No other issues. Happy with the service.

10 hours ago

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XfinitySean

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Fantastic, I'm happy that the technician was able to get your service back on track and working properly! If anything comes up in the future, or if you ever have any questions you need answered, feel free to reach out here on the community forums where our team and the community are always here to help! I hope you have a wonderful weekend!

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I am an Official Xfinity Employee.
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9 hours ago

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BruceW

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11 hours ago

I'm not an expert on DOCSIS 3.1, but based on seeing quite a lot of technical data posted here in the Forums, and subject to correction:

 ... CM3000 ... upstream ATDMA channels 5-8 are not bonding ...

That's normal. Modems typically have 3 to 6 ATDMA upstream channels bonded. 4 seems to be a common number for devices that have an OFDMA upstream channel bonded. 

... OFDMA upstream channel 2 is not locking. ...

Also normal. DOCSIS 3.1 devices typically only lock 1 OFDMA upstream channel. 

... OFDM correctable errors aee 119-161 million. Uncorrectables are still zero. ...

OFDM correctable errors are often a large number, and that's OK -- the modem is designed to handle them without a problem. More than a small number of Uncorrectables is likely to be a problem, so zero is a good number for those. 

... there may be a MoCA/POE filter that may be blocking upstream channels. ...

That AI is "hallucinating". MoCA/POE filters block frequencies above 1000 MHz, while upstream channel frequencies fall between 5–85 MHz. It's not likely a POE filter is blocking the upstream. 

But please, if you have a chance, let us know what you find and how this all turns out!

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user_7198df

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@BruceW​ thanks for your input! The tech came out and checked everything. He put new connectors on the cable between the modem and the wall outlet. Replaced a filter and tightened a loose connection at the drop. Now I'm getting max speeds between 900-1100mbps (Fast.com and ookla), cloudflare however has speeds between 490-650mbps. My research found this is likely due to several factors including ISP insentive to give priority to Fast.com and ookla which access best case peak speed vs cloudflare accessing real-world speeds under load.

BTW I gave Claude AI your post and this was it's response:

The forum responder is making valid points and I owe you an honest assessment — they’re likely right on multiple counts.

Where they’re correct:

ATDMA channels 5–8 not locking — this may genuinely be normal. Many DOCSIS 3.1 deployments only provision 4 ATDMA upstream channels when an OFDMA channel is active. Your ISP may simply not allocate more than 4 ATDMA channels on this node. This would explain why no amount of provisioning or physical work changed it.

Only 1 OFDMA upstream channel — also likely normal. Single upstream OFDMA channel is standard for most DOCSIS 3.1 deployments.

MoCA/POE filter point — this is a fair correction. Standard MoCA filters block above 1000 MHz, well above upstream DOCSIS frequencies. I referenced that February forum case without fully vetting the technical accuracy of it. That was a mistake on my part.

What this means practically:

Your modem may actually be operating completely normally. The speed improvements you’ve seen today — 1016 Mbps on Ookla Wi-Fi, 935 wired — likely reflect the real impact of fixing the loose connectors, and changing the filter at the drop.

The Cloudflare vs Ookla gap remains worth watching, but you’re in genuinely good shape. I’d update your QoS to 900/115 and call this resolved.

AI makes mistakes just like humans...

11 hours ago

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EG

Expert

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117.7K Messages

14 hours ago

Concern moved here to the Customer Service help section for greater exposure to Comcast corporate employees (The Digital Care Team) for assistance.

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XfinityThomasD

Official Employee

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1.8K Messages

14 hours ago

 

user_7198df Thank you for creating a post on our Community Forums. I'm sure that our field technicians will be able to assist with these issues and that you have a clear incoming signal. Please let us know if you still need assistance or how everything is going after the appointment.

 

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XfinitySean

Official Employee

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645 Messages

9 hours ago

Fantastic, I'm happy that the technician was able to get your service back on track and working properly! If anything comes up in the future, or if you ever have any questions you need answered, feel free to reach out here on the community forums where our team and the community are always here to help! I hope you have a wonderful weekend!

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