Visitor
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2 Messages
Unstable Home Cable Internet, Blinking Uplink Light
Hello all. I have been struggling with an unstable home internet connection. I have Xfinity Cable Internet, a Netgear CM400 Modem, and a TP-Link AC1200 router that I primarily connect to via Ethernet.
Since moving into a new home, my internet has been somewhat functioning but very unstable. The uplink light on my modem blinks about 50% of the time, whereas the downlink light is steady green. While browsing, I get frequent 5-10 second periods when the internet is unresponsive, and I get 2-3 full disconnects per day requiring me to restart my modem. Here are the channel statistics from my modem:
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Here is my modem's event log, covering just two hours:
| Time | Priority | Description |
| May 4 19:13:35 2022 | Critical (3) | No Ranging Response received - T3 time-out |
| May 4 19:15:08 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 19:15:09 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 2 |
| May 4 19:15:09 2022 | Warning (5) | TCS Partial Service |
| May 4 19:15:11 2022 | Error (4) | DBC-ACK not received |
| May 4 19:15:38 2022 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out |
| May 4 19:32:24 2022 | Critical (3) | No Ranging Response received - T3 time-out |
| May 4 19:37:40 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 19:37:40 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 2 |
| May 4 19:37:47 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 19:37:47 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 4 |
| May 4 19:37:52 2022 | Critical (3) | No Ranging Response received - T3 time-out |
| May 4 19:38:07 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 19:38:07 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 3 |
| May 4 19:38:07 2022 | Warning (5) | TCS Partial Service |
| May 4 19:38:09 2022 | Error (4) | DBC-ACK not received |
| May 4 19:38:37 2022 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out |
| May 4 19:57:36 2022 | Critical (3) | No Ranging Response received - T3 time-out |
| May 4 20:01:50 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 20:01:51 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 3 |
| May 4 20:01:54 2022 | Critical (3) | No Ranging Response received - T3 time-out |
| May 4 20:02:20 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 20:02:20 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 2 |
| May 4 20:02:39 2022 | Critical (3) | No Ranging Response received - T3 time-out |
| May 4 20:04:38 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 20:04:38 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 4 |
| May 4 20:04:38 2022 | Warning (5) | TCS Partial Service |
| May 4 20:04:40 2022 | Error (4) | DBC-ACK not received |
| May 4 20:05:08 2022 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out |
| May 4 20:22:48 2022 | Critical (3) | No Ranging Response received - T3 time-out |
| May 4 20:28:16 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 20:28:17 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 2 |
| May 4 20:28:33 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 20:28:33 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 3 |
| May 4 20:28:49 2022 | Critical (3) | No Ranging Response received - T3 time-out |
| May 4 20:29:01 2022 | Critical (3) | Ranging Request Retries exhausted |
| May 4 20:29:01 2022 | Critical (3) | 16 consecutive T3 timeouts while trying to range on upstream channel 4 |
| May 4 20:29:01 2022 | Warning (5) | TCS Partial Service |
| May 4 20:29:03 2022 | Error (4) | DBC-ACK not received |
| May 4 20:29:31 2022 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out |
There is one Commscope brand 'subscriber amplifier' splitter, model CSMAPDU9VP, between the incoming cable and the wall cable ports around the unit. I have tried plugging the modem directly into the splitter on an unused port, and also disconnecting the splitter entirely and plugging the input line directly into the modem. In both cases, I get exactly the same behavior as before -- somewhat working connection, but blinking green uplink light and disconnects at regular intervals. There are no other splitters than I am aware of.
It has been frustrating to deal with the unstable internet. I would greatly appreciate any help with getting to a more consistent connection.
Accepted Solution
BruceW
Gold Problem Solver
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26.3K Messages
3 years ago
Perhaps not the primary problem, but you should be aware that https://www.xfinity.com/support/devices says the CM400 is no longer supported. You didn't mention your Internet plan speed, but when the CM400 was supported, it was only approved for use with plan speeds "Up to 287 Mbps".
In the stats you posted only one upstream channel is locked. There should be at least three. Network connection problems like this are often due to poor coax connections or damaged coax cable, usually in or near your home.
If you want to troubleshoot this yourself, please see Internet Troubleshooting Tips. If you can't find the problem or you'd rather have Comcast take care of it, call them at the phone number on your bill or 1-800-Comcast, or use one of the options on https://www.xfinity.com/support/contact-us/. It's not likely they can fix the problem remotely. If not, insist they send a tech out to identify the cause and correct it.
If the tech finds bad coax, splitters, amplifiers, or connections in your home (even if Comcast originally supplied them) you'll probably have to pay for the visit ($70-$100) unless you have their Service Protection Plan ( https://www.xfinity.com/support/articles/service-protection-plan, closed to customers that don't already have it). If the trouble is due to a faulty Comcast rental device or anything outside your home you shouldn't be charged.
Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.
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EG
Expert
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110K Messages
3 years ago
I will add that the SNR's are marginal. There may be some spurious noise leaking into the line(s) somewhere. Good luck with it !
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user_b1c1ce
Visitor
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2 Messages
3 years ago
Thanks for the help. My plan is 100 Mbps down, so my modem should be sufficient. I'll try to get a tech to look at it.
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