Visitor
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2 Messages
Modem logging constant T3 timeouts
Sporadic drops, buffering, and general slowness for over a week. Happens on both wired and wireless clients, so it's not a Wi-Fi issue.
Had a tech out (9/26). He confirmed the coax from the outside box to my modem was undamaged, no degradation, no filters or splitters, and he found no errors. He concluded my UniFi UCI modem was the issue.
What I've done since:
- Swapped the UCI for an Arris G36 in bridge mode. Different modem, different vendor, exact same problem.
- Replaced the Ethernet cable between modem and gateway.
- Confirmed the drops on my own network monitoring, independent of the modem.
Pulled the Arris event log. Last night (9/27), 8:39–8:41 PM: 21 T3 timeouts and 11 loss-of-sync errors in two minutes, plus lock failures on downstream channels 4, 5, 6 and OFDM channel 193.
Checked signal levels 48 minutes later and everything was clean — downstream +1 to +5 dBmV, SNR 37–39, upstream high 30s, all locked. So it's intermittent, which is likely why the tech found nothing while he was here.
At this point I've replaced every piece of customer equipment in the path. The modem, the cable between modem and gateway, and the client type are all ruled out.
Questions:
- Who do I talk to about T3 timeouts and line errors?
- Who can check my modem against the CMTS flap list?
- Who can look at upstream ingress on my node?
Full event log available, MACs scrubbed.
user_i5otpf
Visitor
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2 Messages
2 days ago
Happened again this morning (9/28), 8:29–8:31 AM: 21 T3 timeouts and 13 loss-of-sync errors in 85 seconds, with downstream lock failures now on channels 4, 5, 6, and 7. Same signature as the night before. The log shows a clean hour and a half leading up to it, then total collapse, then recovery — so this is a repeating, self-clearing fault, not a one-time event.
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XfinityRay
Official Employee
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4.3K Messages
9 hours ago
Hi there, @user_i5otpf! Thanks for taking the time out of your day to reach out about your service. We always want that to be fast and reliable. I am sorry to hear it has been acting up and am glad to further help. We can check the area and the signals to the modem for any concerns. We may need to have a repeat visit depending on our findings.
Please send us a direct message with your full name and complete service address to “Xfinity Support”. To do so, click on the direct messaging icon located at the top right of this forums page.
Here's the detailed steps to direct message us:
1. Click "Sign In" if necessary.
2. Click the "Direct Messaging" icon.
3. Click the "Start new conversation" (pencil and paper) icon.
4. In the "To:" line, type "Xfinity Support".
5. As you type, a drop-down list will appear. Select "Xfinity Support" from that list.
6. An "Xfinity Support" graphic will replace the "To:" line.
7. Type your message in the text area near the bottom of the window.
8. Press Enter to send it.
You can see how to send us a direct message here, https://forums.xfinity.com/conversations/guidelines/how-to-direct-messaging-within-the-forum/697ba1e570934d009185c514.
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