Visitor
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2 Messages
SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing
We've been having intermittent internet outages for years and tried several modems. We managed when we worked in offices, but now that my wife and I do not, the internet outages have gone from "well, I guess we can't play video games online for a while while this happens" to "oh no, we're missing or dropping out of important meetings or interviews."
The modem seems to reboot anywhere from 1-3x in a row, sometimes with multiple groups of failures in an hour. On average, we have outages at least once per day, usually more. Techs have been out here, have replaced the line leading from the end of our driveway to the outside of our house, and have verified that there are no splitters anywhere. They also note that we have good internet speed test results when they are here.
The only lead I have is the error logs on our current modem, which show a lot of recurring errors after a 12:30-ish PM crash (I think that my router is on EST, so 15:30ish for the router timestamps):
| Time | Priority | Description | |||
| 15:11:07 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:11:09 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:12:05 Wed May 10 2023 |
Critical (3) | No Ranging Response received - T3 time-out;CM-MAC=;CMTS-MAC=;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=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| Time Not Established | Critical (3) | No Ranging Response received - T3 time-out;CM-MAC=;CMTS-MAC=;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=;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1; | |||
| Time Not Established | Critical (3) | No Ranging Response received - T3 time-out;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:31:34 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:31:40 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:15 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:16 Wed May 10 2023 |
Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:21 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:21 Wed May 10 2023 |
Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:21 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:22 Wed May 10 2023 |
Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:22 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:22 Wed May 10 2023 |
Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:23 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:35:23 Wed May 10 2023 |
Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:39:22 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:39:27 Wed May 10 2023 |
Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=;CMTS-MAC=;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=;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1; | |||
| Time Not Established | Critical (3) | No Ranging Response received - T3 time-out;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:45:37 Wed May 10 2023 |
Critical (3) | SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 15:45:46 Wed May 10 2023 |
Critical (3) | No Ranging Response received - T3 time-out;CM-MAC=;CMTS-MAC=;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=;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1; | |||
| Time Not Established | Critical (3) | No Ranging Response received - T3 time-out;CM-MAC=;CMTS-MAC=;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=;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1; | |||
| Time Not Established | Critical (3) | No Ranging Response received - T3 time-out;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| Time Not Established | Notice (6) | Honoring MDD; IP provisioning mode = IPv6 | |||
| 11:30:55 Thu May 11 2023 |
Notice (6) | DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; | |||
| 11:31:12 Thu May 11 2023 |
Notice (6) | CM-STATUS message sent. Event Type Code: 24; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0.;CM-MAC=;CMTS-MAC=;CM-QOS=1.1;CM-VER=3.1; |
I've seen this problem a lot on the forums, and it seems like signal info is also requested for those, so here is my signal info as of right now:
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Please help us!
EG
Expert
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110K Messages
2 years 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 poll the CMTS for those upstream receive signal stats.
You should get a reply here in your topic. Good luck !
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CCYvonne
Contributor
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340 Messages
2 years ago
Hello @user_py I am sorry to hear you have been experiencing issues for years! We appreciate you reaching out to bring this to our attention, so that we can resolve this as soon as possible. I'd like to start off by checking your signals.
Please send our team a direct message with your full name and full address?
To send a "Direct Message" to Xfinity Support:
Click "Sign In" if necessary
Click the "Direct Messaging" icon
Click the "New message" (pencil and paper) icon
The "To:" line prompts you to "Type the name of a person". Instead, type "Xfinity Support" there
- As you are typing a drop-down list appears. Select "Xfinity Support" from that list
- An "Xfinity Support" graphic replaces the "To:" line
Type your message in the text area near the bottom of the window
Press Enter to send it
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user_py
Visitor
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2 Messages
2 years ago
Sharing an update to keep the thread open - I've talked to support via messaging. We're trying another gateway and plan to ask a 3 tech to come out the next time there is an outage.
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