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user_anick916
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Wednesday, July 9th, 2025

Upstream OFDMA Causing T3/T4 Timeouts – Need CMTS Provisioning Fix (Netgear CM3000, 2 Gbps Plan)

After countless hours today with several virtual chats, live on the phone support, and “Tier 2” transfers i’m trying this as a last hopeful resort.

Hi Xfinity Support,

I'm having persistent internet drops that appear directly tied to upstream OFDMA instability. I’ve already had a technician visit, and phone support has stated OFDMA was disabled — but my modem logs and status page show otherwise.

📦 Setup:

  • Modem: Netgear CM3000 (DOCSIS 3.1, Xfinity-approved)

  • Plan: 2 Gbps

  • Connection: Wired and wireless drops

  • Symptoms:

    • Frequent disconnections

    • Event logs full of T3 timeouts, T4 timeouts, and no unicast ranging opportunities

    • Drops correlate with OFDMA Channel locking or flapping

Key Log Indicators:

  • Started Unicast Maintenance Ranging - No Response received - T3 time-out

  • 16 consecutive T3 timeouts

  • Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out

  • OFDMA Channel 1 = Locked

  • OFDMA Channel 2 = Not Locked

  • Profile IDs: 12, 13

  • Power levels around 37.3 dBmV

What I've Tried:

  • Power-cycled modem

  • Factory reset modem

  • Tech visit (confirmed signals look clean)

  • Xfinity phone support says they "disabled OFDMA", but modem is still receiving OFDMA provisioning from CMTS

Request:

I’m requesting that upstream OFDMA be fully disabled at the CMTS level:

  • A new provisioning config file pushed to my modem that excludes OFDMA upstream channels

  • Verification that Profiles 12/13 are no longer being assigned

  • Confirmation from engineering that the CMTS override is in place

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16 days ago

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user_anick916

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20 days ago

Hi all, just wanted to follow up with today’s logs — unfortunately, the issue with upstream OFDMA is still ongoing.

I’m continuing to see repeated T3 and T4 timeouts, and my modem log confirms that Channel ID 41 (OFDMA) is still active:

CM-STATUS message sent. Event Type Code: 8; Chan ID: 41

These errors continue to appear:

  • 16 consecutive T3 timeouts while trying to range on upstream channel 8

  • Unicast Maintenance Ranging attempted – No response – Retries exhausted

  • Started Unicast Maintenance Ranging – No Response received – T3 time-out

  • Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received – T4 time-out

All of these point to upstream OFDMA remaining enabled and unstable.

To Xfinity reps or engineers monitoring this thread — could you please verify that the CMTS config for my modem has actually been updated to remove OFDMA (Channel ID 41) from the upstream bonding group?

I’m on a Netgear CM3000 modem with a 2 Gbps plan, and based on everything I’ve researched (and others have confirmed), this model often needs OFDMA disabled to maintain a stable upstream connection.

Really hoping this can be escalated to Tier 3 or engineering if it hasn’t already. Happy to provide any more logs or details you need.

Thanks again for your time and help.

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XfinityShawn

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1.7K Messages

 

user_amantenick916 My team can further help you with your timeout concerns today.  To send a direct message, please click on the chat icon in the top-right corner of the screen, and select "Xfinity Support" to initiate a Direct Message. 
Click "Sign In" if necessary
Click the "direct messaging" icon or https://forums.xfinity.com/direct-messaging
Click the "New message" (pencil and paper) icon
Type "Xfinity Support" in the "To:" line and select "Xfinity Support" from the drop-down list which appears. The "Xfinity Support" graphic replaces the "To:" line
Type your message in the text area near the bottom of the window
Press Enter to send it

 

I am an Official Xfinity Employee.
Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
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19 days ago

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user_anick916

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This got totally buried with the other responses below and I sincerely apologize.  I will proceed as directed.  Thank you!

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17 days ago

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EG

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@user_amantenick916 @XfinityShawn 

Please circle back here and post any possible solutions for the issue here in these open public forums so that all readers here may benefit from the exchange / info. This is in keeping with the spirit for which these public help forums were originally intended. Thank you.

I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.

Was your question answered? Please mark an Accepted Answer!tick

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16 days ago

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EG

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18 days ago

@user_amantenick916 

As an FYI, in case you are not aware, you won't be able to get your 2 gig download speeds if there is no OFDM channel.

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user_anick916

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Thanks for the input — that’s a helpful clarification. Just to be clear, I’m not asking to disable downstream OFDM, which I know is essential for my 2 Gbps download speeds. My downstream OFDM channels (193 and 194) are locked, healthy, and delivering high throughput.

The issue is with upstream OFDMA, specifically Channel ID 41, which is triggering T3 and T4 timeouts and causing connectivity drops. This has been reported across various DOCSIS 3.1 modems, including the Netgear CM3000, when OFDMA upstream is provisioned but unstable due to CMTS-side config or signal compatibility.

Others have had success by requesting their ISP (in this case, Xfinity) disable upstream OFDMA via CMTS provisioning — which does not affect downstream OFDM or download speeds, but often stabilizes the connection.

So just to reiterate: this is about upstream OFDMA only, not disabling any part of the download path.

Thanks again for the discussion — hoping Tier 3 or engineering can take a deeper look soon.

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18 days ago

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EG

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18 days ago

Ok, sorry for the confusion. So likewise, without an upstream OFDMA channel, you won't get your rated upload speed.

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user_anick916

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Not a problem at all!  At this point I’m so frustrated with the overall instability that I’ll take a reduction of upload speed.  It’s been extremely frustrating as a remote worker from home.

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18 days ago

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EG

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18 days ago

Be advised that you may get slower default upload and download speeds (typically 30-5) if they can't push the correct config file to the modem. The root cause of the problem should be addressed (typically noise ingress somewhere) rather than resorting to a workaround. Good luck !

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