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user_x5y7z0
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Thursday, March 20th, 2025 7:24 PM

netgear docsis 3.1 mdem cm1000v2

Hi, I am now experiencing random (and often daily or 2-5x/day) frequent disconnects after several years of stable service with my Netgear DOCSIS 3.1 modem CM1000v2.

Sometimes, the modem reconnects itself, in a few minutes to a few hours.  When the system is not reconnecting, removing power to the modem and then booting usually connects successfully on the first attempt.

My modem hardware version is 2.02, and the firmware version is V10.01.07 (which Comcast indicates as the most recent update).  When connecting CAT 5 cable to my LAN on my PFSense router, I get up to 1.0GBPS max.  Using wifi, I get up to ~400 MBPS (max).

The event log for the Modem shows typical recurring errors:

1. UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
Another critical error: SYNC Timing Synchronization failure:
2. Failed to acquire QAM/QPSK symbol timing;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
Any suggestions, or is it time to replace the modem?
Thanks, William

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1 month ago

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EG

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110K Messages

1 month ago

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.

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user_x5y7z0

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@EG​ 

Thank you very much for your suggestions. In the last 24 hours, I haven't experienced any outage of the router.  Even when I am offline, the router signal status lights are all lit and not red or otherewise indicative of a problem. 

I am not sure how to get the SNR's and the upstream/power level numbers, can you give me a suggestion where to find them when I am logged into the cable modem?

Today, not only was the modem working without failure, it showed 1.7 GBPS speed (on fast.com) through my gateway/firewall.  Levels I have never seen, i.e.  >1 GBPS before...

Below, I pasted the printouts from 3/20 when there were multiple failures.  

2025-03-20, 13:28:18 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 2 3.;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-03-20, 12:41:32 Notice (6) CM-STATUS message sent. Event Type Code: 16; Chan ID: 193; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-03-20, 12:41:15 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-03-20, 12:41:15 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-03-20, 12:41:01 Notice (6) Honoring MDD; IP provisioning mode = IPv6
2025-03-20, 12:40:56 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];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=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
2025-03-14, 21:11:24 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-03-14, 21:11:06 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];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=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
2025-03-01, 19:41:34 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-03-01, 19:41:15 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];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=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
2025-02-18, 06:44:27 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-02-18, 06:44:13 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-02-18, 06:44:04 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
2025-02-18, 06:39:57 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
2025-02-18, 06:39:52 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-02-18, 06:39:45 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-02-18, 06:39:44 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-02-18, 06:39:03 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-02-18, 06:39:01 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-02-17, 21:40:30 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
2025-02-17, 21:40:12 Critical (3) UCD invalid or channel unusable;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1;
Time Not Established Critical (3) SYNC Timing Synchronization failure - Faile

(edited)

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1 month ago

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XfinityAirelle

Official Employee

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2.5K Messages

 

 

Thanks so much for sharing all those details, William—you’ve clearly put a lot of time and effort into tracking this, and I know how frustrating it is to go from years of stable service to multiple daily disconnects with no clear cause. You're doing everything right on your end, so let's talk through what's happening.

Based on the logs and symptoms you’ve described, it looks like your Netgear CM1000v2 is having intermittent signal and sync issues, which is leading to those unexpected disconnects. Errors like:

  • "SYNC Timing Synchronization failure"

  • "UCD invalid or channel unusable"

  • "T4 time out"

…are strong indicators that your modem is struggling to maintain a consistent connection with the network—likely due to line noise, signal fluctuations, or a problem further up the line (sometimes outside the home). Our team would like to take a look at your account to confirm. Can you initiate a direct message and start with your full name and address? To start a direct message, you must be signed in. Please click the "Direct Messaging" icon in the top right of the page next to the bell, and send your message to "Xfinity Support". Talk to you there!

I am an Official Xfinity Employee.
Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Please, mark a reply as the Accepted Answer.tick

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1 month ago

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user_x5y7z0

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@XfinityAirelle 

Thank you for your reply, which I very much appreciated, with yourrequest to look into my account. Unfortunately, I have three separate xfinity/comcast cable accounts, one in Baltimore (the one I was having dropouts) and two in California. Originally, when I registered the accounts some years ago, I had three different phone numbers: one cell, one Google Voice, and my office number, one for each distinct account. Comcast wouldn't let me register without a phone number linked to only one account (i.e.,  couldn't use the same phone number for two separately billed accounts).  Now, I am retired and have only one working iPhone, and there is no working phone number linked to the Baltimore account (I am not sure I even have the missing phone numbers), so I have no way of authenticating using your link with a phone.

It's just one of the many long standing frustrations I have had with Comcast/Xfinity over the years. Communication with customers who have meaningful requests and some technical background get unhelpfully told: "unplug your modem and wait 60 seconds", etc.

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1 month ago

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user_x5y7z0

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Forgot to mention - I have not experienced any outages since 3/20 and my internet download speed through the modem and the firewall/router LAN on Cat5e is 1.1GBPS this evening.

Perhaps Xfinity upgraded to provide faster internet over the last month or two, and that is completed now, so the signal strength is steady. Our download speed is definitely up from about 700-800 max on Cat5.

LMK if you have any knowledge of what might have been happening please let me know.  I am glad we are not dropping the link because each time it occurs, I incur screams from my spouse or whomever of our relatives happen to be on their laptops at our home, and I have to reset the modem and then go scratching my head looking for a problem. Sometimes, I am out of town and have to try to instruct someone at our house to go through the steps, starting with turning the router off and restarting it. One time, my brother-in-law decided to shut the entire system down by turning off the breaker panel that shut my entire system down, and it put the router/gateway unable to restart by itself. 

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1 month ago

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EG

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110K Messages

1 month ago

@user_x5y7z0 

Try the Cable Connection button / tab.

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EG

Expert

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110K Messages

1 month ago

@user_x5y7z0 

Did you have a chance to try to obtain those signal values via that method ? Please respond right here in your topic on these public help forums. Thank you. 

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user_x5y7z0

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@EG​ 

Sorry to be slow...overloaded with other issues not related to networking, et al.

Here is the printout from the Cable Connection button and advanced tab:

Cable Connection
 
Frequency start Value
This field below allows you to modify the frequency the cable modem start with its scan during initialization and registration. Enter the new start frequency and restart the cable modem for it to take effect.
Starting Frequency
<tabindex=-1>Startup Procedure</tabindex=-1>
Procedure Status Comment
Acquire Downstream Channel 469750000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Security Enable BPI+
IP Provisioning Mode Honor MDD IPv6 only
<tabindex=-1>Downstream Bonded Channels</tabindex=-1>
Channel Lock Status Modulation Channel ID Frequency Power SNR / MER Unerrored Codewords Correctable Codewords Uncorrectable Codewords
1 Locked QAM256 4 469750000 Hz -0.8 dBmV 44.0 dB 775964593 15 0
2 Locked QAM256 1 451750000 Hz 0.8 dBmV 44.9 dB 775076233 18 0
3 Locked QAM256 2 457750000 Hz -0.4 dBmV 44.2 dB 775078653 22 0
4 Locked QAM256 3 463750000 Hz -0.6 dBmV 44.0 dB 775070937 9 0
5 Locked QAM256 5 475750000 Hz -2.2 dBmV 42.9 dB 775085756 9 0
6 Locked QAM256 6 481750000 Hz -4.7 dBmV 41.2 dB 775089483 19 0
7 Locked QAM256 7 487750000 Hz -5.1 dBmV 40.9 dB 775094740 16 0
8 Locked QAM256 8 493750000 Hz -3.2 dBmV 42.1 dB 775098381 27 0
9 Locked QAM256 9 499750000 Hz 0.5 dBmV 44.7 dB 775100864 12 0
10 Locked QAM256 10 505750000 Hz 1.1 dBmV 45.1 dB 775106282 10 0
11 Locked QAM256 11 511750000 Hz -1.2 dBmV 43.6 dB 775111139 10 0
12 Locked QAM256 12 517750000 Hz -5.5 dBmV 40.4 dB 775115477 8 0
13 Locked QAM256 13 523750000 Hz -6.8 dBmV 39.5 dB 775118587 19 0
14 Locked QAM256 14 529750000 Hz -5.6 dBmV 40.5 dB 775113337 17 0
15 Locked QAM256 15 535750000 Hz -4.7 dBmV 40.6 dB 775125115 18 0
16 Locked QAM256 16 541750000 Hz -7.1 dBmV 37.0 dB 775128312 25 0
17 Locked QAM256 17 547750000 Hz -7.6 dBmV 38.1 dB 775131861 12 0
18 Locked QAM256 18 553750000 Hz -4.0 dBmV 41.5 dB 775136174 11 0
19 Locked QAM256 19 559750000 Hz -2.0 dBmV 43.2 dB 775138332 5 0
20 Locked QAM256 20 565750000 Hz -2.4 dBmV 42.9 dB 775142979 6 0
21 Locked QAM256 21 571750000 Hz -0.6 dBmV 44.1 dB 775146872 8 0
22 Locked QAM256 22 577750000 Hz -0.4 dBmV 44.1 dB 775152778 8 0
23 Locked QAM256 23 583750000 Hz -0.4 dBmV 44.1 dB 775153348 13 0
24 Locked QAM256 24 589750000 Hz 1.1 dBmV 45.0 dB 775159203 10 0
25 Locked QAM256 25 595750000 Hz -2.1 dBmV 43.0 dB 775163850 14 0
26 Locked QAM256 26 601750000 Hz -2.2 dBmV 42.7 dB 775168389 12 0
27 Locked QAM256 27 607750000 Hz 0.7 dBmV 44.6 dB 775163011 3 0
28 Locked QAM256 28 613750000 Hz -0.1 dBmV 44.2 dB 775173473 5 0
29 Locked QAM256 29 619750000 Hz -0.6 dBmV 43.8 dB 775177368 3 0
30 Locked QAM256 30 625750000 Hz 1.1 dBmV 43.7 dB 775181059 5 0
31 Locked QAM256 31 631750000 Hz 1.8 dBmV 45.1 dB 775198548 3 0
32 Locked QAM256 32 637750000 Hz 1.2 dBmV 43.7 dB 775187979 10 0
<tabindex=-1>Upstream Bonded Channels</tabindex=-1>
Channel Lock Status Modulation Channel ID Frequency Power
1 Locked ATDMA 17 16400000 Hz 37.3 dBmV
2 Locked ATDMA 18 22800000 Hz 37.3 dBmV
3 Locked ATDMA 19 29200000 Hz 36.8 dBmV
4 Locked ATDMA 20 35600000 Hz 37.5 dBmV
5 Not Locked Unknown 0 0 Hz 0.0 dBmV
6 Not Locked Unknown 0 0 Hz 0.0 dBmV
7 Not Locked Unknown 0 0 Hz 0.0 dBmV
8 Not Locked Unknown 0 0 Hz 0.0 dBmV
<tabindex=-1>Downstream OFDM Channels</tabindex=-1>
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power SNR / MER Active Subcarrier Number Range Unerrored Codewords Correctable Codewords Uncorrectable Codewords
1 Locked 0, 1, 2, 3 193 957000000 Hz -16.2 dBmV 27.3 dB 148 ~ 3947 742129441 265839500 470514054
2 Not Locked 0 0 0 Hz -0.2 dBmV 0.0 dB 0 ~ 4095 0 0 0
<tabindex=-1>Upstream OFDMA Channels</tabindex=-1>
Channel Lock Status Modulation / Profile ID Channel ID Frequency Power
1 Not Locked Unknown 0 0 Hz 0 dBmV
2 Not Locked Unknown 0 0 Hz 0 dBmV
Current System Time: Sat Mar 22 16:56:26 2025
System Up Time: 57:16:05
Help Center Show/Hide Help Center
I have not experienced any dropouts since 3/22 and the log is also free from any critical alerts that were seen on 3/20.

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1 month ago

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