Line noise, plant problems, or a failing node upstream

I'm going to keep this brief, as I am absolutely done with Xfinity's abysmal support system.

I'm experiencing frequent brief outages, high latency, and half my subscribed download speed.

I am using a Netgear CM2000 modem, that I own, purchased in January 2025.

Long story short: The issue is not with my hardware.

According to the modem's logs, there are persistent T3 timeouts, UCD channel unusable errors, and symbol timing sync failures on my DOCSIS 3.1 modem. These logs show critical issues going back months. This strongly suggests line noise, plant problems, or a failing node upstream of my address.

Xfinity's automated troubleshooting system is pleb-tier trash. It tells me my connection is fine. Yeah, if all you're looking at is "is link up or down?" then it is "working", but not as advertised.

Responses

EG

Expert

•

110.7K Messages

2 days ago

Please post those error log entries in their entirety (copy and paste them, don't post a screenshot) but redact any CM MAC and the CMTS MAC addresses for your privacy. They are considered to be personal information. The posting of personally identifying information is a violation of their forum guidelines. The forum bot will not allow your post to be seen publicly.

And what do the modem's signal status values look like ? Please also copy all of the text in its entirety of the *Downstream Power Levels*, the *SNR's* (Signal to Noise Ratios), and the *Upstream Power Level* numbers and paste them into your next post.

user_ssdut4

Visitor

•

3 Messages

1 day ago

Hello EG, thank you for the prompt reply.

Here's my Cable Diagnostics:

Status: Good

Action:

Your setup looks fine. If you can't access the internet, make sure you properly activated the modem. If modem has been activated and you still can't access the internet, contact your service provider for troubleshooting help.

If you can access the internet but has other internet issue, the Netgear Cable Knowledge Base can provide additional troubleshooting info.

CM Status: Good

Downstream Status: Good

Downstream Power Level: Good

Downstream SNR Level: Good

Upstream Status: Good

Upstream Power Level: Good

Current Time: Fri May 30 22:21:26 2025

Startup Procedure

Acquire Downstream Channel: 453000000 Hz Locked

Connectivity State: OK Operational

Boot State: OK Operational

Security: Enabled BPI+

IP Provisioning Mode: Honor MDD IPv6 only

Downstream Bonded Channels

Channel LockedStatus Modulation ChannelID Frequency Power SNR Correctables Uncorrectables

1 Locked QAM256 12 453000000 Hz 7.7 44.7 23 0

2 Locked QAM256 1 387000000 Hz 8.1 44.8 18 0

3 Locked QAM256 2 393000000 Hz 8.1 44.8 16 0

4 Locked QAM256 3 399000000 Hz 7.9 44.8 15 0

5 Locked QAM256 4 405000000 Hz 7.7 44.6 29 0

6 Locked QAM256 5 411000000 Hz 7.6 44.5 40 0

7 Locked QAM256 6 417000000 Hz 7.7 44.6 37 0

8 Locked QAM256 7 423000000 Hz 7.8 44.7 26 0

9 Locked QAM256 8 429000000 Hz 7.6 44.7 24 0

10 Locked QAM256 9 435000000 Hz 7.5 44.6 32 0

11 Locked QAM256 10 441000000 Hz 7.4 44.6 30 0

12 Locked QAM256 11 447000000 Hz 7.5 44.7 28 0

13 Locked QAM256 13 459000000 Hz 7.7 44.7 15 0

14 Locked QAM256 14 465000000 Hz 7.7 44.7 7 0

15 Locked QAM256 15 471000000 Hz 7.8 44.7 6 0

16 Locked QAM256 16 477000000 Hz 7.8 44.7 6 0

17 Locked QAM256 17 483000000 Hz 7.8 44.7 6 0

18 Locked QAM256 18 489000000 Hz 7.8 44.7 5 0

19 Locked QAM256 19 495000000 Hz 7.9 44.8 7 0

20 Locked QAM256 20 501000000 Hz 7.8 44.7 8 0

21 Locked QAM256 21 507000000 Hz 7.7 44.6 19 0

22 Locked QAM256 22 513000000 Hz 7.6 44.6 19 0

23 Locked QAM256 23 519000000 Hz 7.6 44.6 15 0

24 Locked QAM256 24 525000000 Hz 7.4 44.5 9 0

25 Locked QAM256 25 531000000 Hz 7.2 44.4 2 0

26 Locked QAM256 26 537000000 Hz 7.3 44.4 2 0

27 Locked QAM256 27 543000000 Hz 7.4 44.4 2 0

28 Locked QAM256 28 549000000 Hz 7.1 44.2 5 0

29 Locked QAM256 29 555000000 Hz 6.8 44.1 7 0

30 Locked QAM256 30 561000000 Hz 7 44.1 8 0

31 Locked QAM256 31 567000000 Hz 7.1 44.1 7 0

32 Locked QAM256 32 573000000 Hz 6.8 44 6 0

Upstream Bonded Channels

Channel LockedStatus ChannelType ChannelID SymbolRate Frequency Power

1 Locked ATDMA 19 5120 Ksym/sec 29200000 Hz 37.0 dBmV

2 Locked ATDMA 18 5120 Ksym/sec 22800000 Hz 36.8 dBmV

3 Locked ATDMA 17 5120 Ksym/sec 16400000 Hz 36.5 dBmV

4 Locked ATDMA 20 5120 Ksym/sec 35600000 Hz 37.3 dBmV

5 Not Locked Unknown 0 0 0 0.0

6 Not Locked Unknown 0 0 0 0.0

7 Not Locked Unknown 0 0 0 0.0

8 Not Locked Unknown 0 0 0 0.0

Downstream OFDM Channels

Channel LockedStatus ProfileID ChannelID Frequency Power SNR/MER ActiveSubcarrier Unerror Correctable Uncorrectable

1 Locked 0 ,1 ,2 ,3 193 722000000 Hz 7.28 dBmV 43.1 dB 448 ~ 3647 9806261932 6470645498 0

2 Locked 0 ,1 ,2 ,3 194 957000000 Hz 2.38 dBmV 40.9 dB 148 ~ 3947 9983105084 5763581899 1

Upstream OFDMA Channels

Channel LockedStatus ProfileID ChannelID Frequency Power

1 Not Locked 0 0 0 Hz 0 dBmV

2 Not Locked 0 0 0 Hz 0 dBmV

Event Log

Time Priority Description

Fri May 30 09:49:11 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Mon May 26 22:26:43 2025 Notice (6) CM-STATUS message sent. Event Type Code: 23; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Mon May 26 22:26:42 2025 Notice (6) CM-STATUS message sent. Event Type Code: 22; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Mon May 26 22:24:24 2025 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0 1 2 3.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Mon May 26 22:23:19 2025 Notice (6) CM-STATUS message sent. Event Type Code: 4; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Mon May 26 22:22:59 2025 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0 1 2 3.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Mon May 26 22:22:25 2025 Notice (6) CM-STATUS message sent. Event Type Code: 1; Chan ID: 194; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Mon May 26 22:22:03 2025 Warning (5) MDD message timeout;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Sun May 25 10:52:40 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Thu May 22 17:09:50 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Thu May 22 17:09:44 2025 Notice (6) DS profile assignment change. DS Chan ID: 33; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Thu May 22 17:09:42 2025 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Thu May 22 17:09:36 2025 Notice (6) TLV-11 - unrecognized OID;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Thu May 22 17:09:27 2025 Notice (6) Honoring MDD; IP provisioning mode = IPv6

Thu May 22 17:09:23 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Thu May 22 17:09:18 2025 Warning (5) ToD request sent - No Response received;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Time Not Established Notice (6) Honoring MDD; IP provisioning mode = IPv6

Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

Fri May 09 16:58:30 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Fri May 09 16:58:04 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

Sat Mar 29 00:47:52 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Sat Mar 29 00:47:25 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

Sat Mar 29 00:46:02 2025 Critical (3) Resetting the cable modem due to docsDevResetNow

Mon Mar 24 10:36:31 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Sun Mar 23 18:32:01 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Thu Mar 20 00:40:07 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Thu Mar 20 00:19:05 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Tue Mar 11 18:18:34 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Tue Mar 11 17:53:34 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Thu Mar 06 23:43:23 2025 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Wed Feb 26 14:04:43 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Wed Feb 26 14:04:15 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

Fri Feb 21 12:52:38 2025 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Fri Feb 21 12:52:38 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Tue Feb 18 00:29:35 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Tue Feb 18 00:29:16 2025 Critical (3) UCD invalid or channel unusable;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=yy:yy:yy:yy:yy:yy;CM-QOS=1.1;CM-VER=3.1;

Tue Feb 18 00:28:51 2025 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;

�

train_wreck

Contributor

•

53 Messages

1 day ago

Line noise can absolutely be coming from the lines in your own house/apartment, as well as from the pole to the premises. I would recommend letting them take a look. One of the mods will likely ask you to message them directly soon.

EG

Expert

•

110.7K Messages

23 hours ago

The signal status values at that snapshot in time were OK but the error log entries indicate that something is going on. Perhaps there is noise ingress into the line(s) / an upstream channel / return path impairment somewhere.

There are other signal stat values 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 (The Digital Care Team) who are available to these boards. They will be able to poll the CMTS (Cable Modem Termination System) to check 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 those upstream receive signal stats.

You should get a reply here in your topic. Good luck !

user_ssdut4

Visitor

•

3 Messages

Many thanks, EG and train_wreck. I sincerely appreciate the help!

I’ll report back with any amazing and/or mundane discoveries, and hopefully a resolution!

21 hours ago

EG

Expert

•

110.7K Messages

👍

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.

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20 hours ago

Your Home Network

user_ssdut4

Line noise, plant problems, or a failing node upstream

EG

user_ssdut4

train_wreck

EG

user_ssdut4

EG

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