Highly variable internet speed - logs show uncorrectable code words on Downstream OFDM Channel 1

For months now, we've been seeing intermittent internet and highly variable speeds - multiple technicians have been out and unable to solve the issue. To be sure it wasn't too many devices on the XB8 Xfinity gateway, I purchased a NightHawk CM2050V modem along with a NightHawk BE12000 (RS500) WiFi7 router. The problem has persisted.

After figuring out how to view the cable connection statistics through the modem, I'm seeing that most of the channels look good, but one stands out as possibly the problem:

Downstream OFDM Channels
Channel LockedStatus ProfileID ChannelID Frequency Power SNR/MER ActiveSubcarrier Unerror Correctable Uncorrectable
1 Locked 0 ,1 ,2 ,3 48 850000000 Hz -5.32 dBmV 37.6 dB 1108 ~ 2987 7929666275 7459832055 1567819
2 Not Locked 0 0 0 Hz 0 dBmV 0 dB 0 ~ 4095 0 0 0

This along with a pretty consistent "notice (6)" and "critical (3)" error messages in the modem log:

Tue Apr 15 19:15:25 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 48;

Mon Apr 14 16:33:37 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;

These appear to coincide with the points at which my internet runs either incredibly slowly or loses connection entirely.

While it's possible there could be a problem (damage) in my cable line running through the roof, I see the same issues when I plug directly into the line on the first floor that shows no sign of damage or kinking.

I have the incoming cable line, with a single splitter (1 to 3, 1 is open and unterminated) - one line goes to the cable on the first floor, the second line runs under the roof to the second floor bedroom where the modem resides.

Any ideas how to get this fixed? Do the readings show there's a problem?

Thanks

user_te

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U

User_te

12 Messages

11 days ago

I'm new to posting new topics on the board, do new topic posts always start listed as "private" in the upper right?

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Aceq2jot

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112 Messages

10 days ago

I think you will find this is all part of the back-end upgrades. The OFDM channel is one that I believe from what I have read will change over to OFDMA when they enable X-Class in your area. Honestly the correctable codewords are fine it is more a very high number of uncorrectable you need to look for on the primary channel. My primary channel is 20 and when I have had high uncorrectable code words, I unplug my gateway for a few minutes to reboot and apply any software changes that may have been pushed.

Sadly, due to Xfinity doing a lot of network upgrades to get us to 2gig and above through fiber over coax and occasionally part of the process is slower speeds which are teething problems and clear up on their own. Yes, a slowdown is a bummer but in the long run it will be worth it, and it seems for you like it is for me it is only occasional. For the most part i have found the slow speeds fix themselves after a reboot.

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EG

Expert

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110K Messages

@Aceq2jot wrote;

The OFDM channel is one that I believe from what I have read will change over to OFDMA when they enable X-Class in your area.

Actually, the OFDM modulation scheme is used for the downstream/forward path channels, and the OFDMA scheme is used for the upstream/return path.

(edited)

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10 days ago

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U

User_te

12 Messages

@Aceq2jot

Yeah, it was the huge number of uncorrectable code words (1567819) that was the concern. And the problem is that it's consistent enough that I can't actually expect it to work for more than an hour at a time. I've never been able to resolve the problem with a router reboot - it's just another 10 minutes I'm sitting around waiting for the router to boot up to find that it hasn't helped.

I can't finish a round of Call of Duty multiplayer without spending at least a minute teleporting around the map because latency jumps to 15000 for minutes at a time.

It's great that they're trying to upgrade, but they have to provide consistent connection in the meantime. Given we have no viable alternatives in my area, we're stuck with an internet connection that may or may not work at any given minute. This seems to be worst in the evening, what used to be 8-10PM now seems to be more like 7-11PM, but I'm now dropping WebEx calls for work in both the morning and afternoon. It's unsustainable.

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10 days ago

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Aceq2jot

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112 Messages

@User_te I would send the message to XfinityVianney who posted after me as they can put a ticket in for an Engineer. I feel you as I had the same prob in the fall until an engineer fixed the problem on the rear end. Hopefully soon you can reboot and enjoy X2 speeds. One of the best ways to see what is happening in your area is to log into your comcast account and click on billing and see if you get a pop up about planned outages. I know it is not a fix and from what I remember reading the OFDM is not really used it is reserved for the High Speed and will change to OFDMA when you get X2 and then you will have two channels of OFDMA.

EDIT: You can also check here for work on your network Comcast Customer Service - Xfinity Technical Support I have had two already this week and a third tonight.

(edited)

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10 days ago

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EG

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110K Messages

@Aceq2jot wrote;

and from what I remember reading the OFDM is not really used it is reserved for the High Speed and will change to OFDMA when you get X2

Again. That's not how it works.

(edited)

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10 days ago

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XfinityVianney

Official Employee

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2.1K Messages

10 days ago

Hi @User_te,

Thank you for reaching out. I hope you are doing well today. I see you've had techs out already, but you haven't seen any changes on your end yet. I'm sorry to hear about that, however, I'll be glad to help. I would like to review the notes from the previous visits, so we can determine the next best steps. When you have a moment, please send me a direct message with your full name and address to get started.

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

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U

User_te

12 Messages

Information sent, thank you!

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10 days ago

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XfinityAlfonso

Official Employee

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1.6K Messages

Great! We look forward to working with you! We will be with you shortly on that 1-1 thread.

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10 days ago

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User_te

Highly variable internet speed - logs show uncorrectable code words on Downstream OFDM Channel 1

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Aceq2jot

EG

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Aceq2jot

EG

XfinityVianney

User_te

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