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3 Messages
Increasing internet connection issues/timeouts
Over the past couple of months, I've noticed an increasing number of times that the internet has dropped or timed out. When browsing, pages stop loading. Upon looking at my modem logs, I noticed a lot of critical errors. The upstream and downstream levels all seem within range. I'll post the Cable Diagnostic info (with all of the personal info removed) as well as the modem info below to see if anyone can help. I'm thinking this may be the incoming cable from the street as the problems began after some severe icing a couple of months ago.
Modem: Netgear Nighthawk CM2000
Hardware Version: 1.01
Cable Firmware Version: V8.01.02
Diagnostics:
Cable Diagnostic
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: Mon Mar 23 06:13:18 2026
Startup Procedure
Acquire Downstream Channel: 483000000 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 17 483000000 Hz -2.6 41.5 142 3
2 Locked QAM256 1 387000000 Hz -5 41.1 182 28
3 Locked QAM256 2 393000000 Hz -4.8 41.1 281 559
4 Locked QAM256 3 399000000 Hz -4.7 41.1 270 588
5 Locked QAM256 4 405000000 Hz -4.4 41.3 286 524
6 Locked QAM256 5 411000000 Hz -4.1 41.4 234 526
7 Locked QAM256 6 417000000 Hz -3.9 41.4 227 535
8 Locked QAM256 7 423000000 Hz -3.8 41.5 104 25
9 Locked QAM256 8 429000000 Hz -3.7 41.5 231 524
10 Locked QAM256 9 435000000 Hz -3.6 41.5 237 521
11 Locked QAM256 10 441000000 Hz -3.5 41.6 215 518
12 Locked QAM256 11 447000000 Hz -3.3 41.6 205 529
13 Locked QAM256 12 453000000 Hz -3.3 41.5 233 499
14 Locked QAM256 13 459000000 Hz -3 41.2 212 503
15 Locked QAM256 14 465000000 Hz -3 41.6 201 525
16 Locked QAM256 15 471000000 Hz -2.8 41.6 202 511
17 Locked QAM256 16 477000000 Hz -2.6 41.7 183 518
18 Locked QAM256 18 489000000 Hz -2.5 41.5 225 472
19 Locked QAM256 19 495000000 Hz -2.2 40.9 187 520
20 Locked QAM256 20 507000000 Hz -2.2 41.6 192 485
21 Locked QAM256 21 513000000 Hz -2.1 41.7 171 505
22 Locked QAM256 22 519000000 Hz -2.1 41.6 173 507
23 Locked QAM256 23 525000000 Hz -2.1 41.6 213 479
24 Locked QAM256 24 531000000 Hz -1.9 41.7 191 490
25 Locked QAM256 25 537000000 Hz -2 41.6 144 537
26 Locked QAM256 26 543000000 Hz -1.8 41.7 148 521
27 Locked QAM256 27 555000000 Hz -1.7 41.8 182 488
28 Locked QAM256 28 561000000 Hz -1.6 41.7 164 482
29 Locked QAM256 29 567000000 Hz -1.6 41.3 169 482
30 Locked QAM256 30 573000000 Hz -1.6 41.5 146 510
31 Locked QAM256 31 579000000 Hz -1.6 41.5 159 486
32 Not Locked Unknown 0 0 Hz 0.0 0.0 0 0
Upstream Bonded Channels
Channel LockedStatus ChannelType ChannelID SymbolRate Frequency Power
1 Locked ATDMA 7 5120 Ksym/sec 22800000 Hz 39.5 dBmV
2 Locked ATDMA 6 5120 Ksym/sec 16300000 Hz 38.5 dBmV
3 Locked ATDMA 8 5120 Ksym/sec 29200000 Hz 39.8 dBmV
4 Locked ATDMA 11 5120 Ksym/sec 35600000 Hz 40.3 dBmV
5 Locked ATDMA 12 2560 Ksym/sec 40400000 Hz 40.5 dBmV
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 37 690000000 Hz -0.12 dBmV 41.5 dB 1108 ~ 2987 13772943 11817762 49
2 Not Locked 0 0 0 Hz 0 dBmV 0 dB 0 ~ 4095 0 0 0
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
Mon Mar 23 06:02:24 2026 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;
Mon Mar 23 06:02:17 2026 Notice (6) TLV-11 - unrecognized OID;
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;
Mon Mar 23 06:00:45 2026 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;
Sun Mar 22 07:06:19 2026 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 3;
Sun Mar 22 07:06:19 2026 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted;
Sun Mar 22 07:06:19 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sun Mar 22 07:05:55 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sun Mar 22 07:05:43 2026 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 4;
Sun Mar 22 07:05:43 2026 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted;
Sun Mar 22 07:05:43 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sun Mar 22 07:05:30 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sun Mar 22 07:04:54 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sun Mar 22 07:04:40 2026 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 2;
Sun Mar 22 07:04:40 2026 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted;
Sun Mar 22 07:04:40 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sun Mar 22 07:04:40 2026 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 1;
Sun Mar 22 07:04:40 2026 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted;
Sun Mar 22 07:04:40 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sun Mar 22 07:04:39 2026 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 0;
Sun Mar 22 07:04:39 2026 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted;
Sun Mar 22 07:04:39 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sat Mar 21 20:49:04 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sat Mar 21 20:49:01 2026 Critical (3) No Ranging Response received - T3 time-out;
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;
Sat Mar 21 09:01:22 2026 Critical (3) SYNC Timing Synchronization failure - Loss of Sync;
Sat Mar 21 08:21:03 2026 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 2;
Sat Mar 21 08:21:03 2026 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted;
Sat Mar 21 08:21:03 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sat Mar 21 08:20:55 2026 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 0;
Sat Mar 21 08:20:55 2026 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted;
Sat Mar 21 08:20:55 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sat Mar 21 08:19:54 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sat Mar 21 08:19:04 2026 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 4;
Sat Mar 21 08:19:04 2026 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted;
Sat Mar 21 08:19:04 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
Sat Mar 21 08:18:58 2026 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 3;
Sat Mar 21 08:18:58 2026 Critical (3) Unicast Maintenance Ranging attempted - No response - Retries exhausted;
Sat Mar 21 08:18:58 2026 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;
EG
Expert
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116.8K Messages
17 minutes ago
Even though the signal status values looked OK at that snapshot in time, the error log entries confirm that something is going on. Perhaps there is intermittent 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 check those upstream receive signal stats.
You should get a reply here in your topic. Good luck !
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XfinityAngie
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