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Spotty intermittent connection - Critical "SYNC Timing Synchronization failure"
I have been trying to debug why my connection has been so spotty lately. There were many instances in which I have lost connection entirely, and dropped out of important meetings due to this. After checking my modem's Event Log, I've found many instances of a Critical error described as "SYNC Timing Synchronization failure - Loss of Sync" followed by a MAC address. After doing some research online and in this forum, most people recommended checking coax cables integrity, etc., but with no single resolution to the issue. I am posting this message in hopes that someone from Xfinity responds, so we can dive deeper into my particular case.
I've had several episodes of package loss in this same address a year ago, requiring several visits from Xfinity technicians. But since Xfinity upgraded their infrastructure around the area, I haven't had any more issues.
Here are some more specific info and details:
Modem: Motorola MB8611
Router: ASUS RT-AX92U
Hired Internet speed: 1.2 Gbps
Observed speed on wifi: ~600 Gbps
Observed speed on ethernet: ~100 Gbps (??? - another issue I haven't been able to figure out, prob with my router)
Sample Event Log from Modem:
| Time | Priority | Description |
| 23:43:09 Wed Mar 15 2023 |
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; |
| 23:43:30 Wed Mar 15 2023 |
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; |
| 23:43:30 Wed Mar 15 2023 |
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; |
| 23:43:49 Wed Mar 15 2023 |
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; |
| 23:43:50 Wed Mar 15 2023 |
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; |
| 23:44:09 Wed Mar 15 2023 |
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; |
| 23:44:09 Wed Mar 15 2023 |
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; |
| 23:44:15 Wed Mar 15 2023 |
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; |
| 23:45:13 Wed Mar 15 2023 |
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; |
| 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; |
| Time Not Established | Notice (6) | Honoring MDD; IP provisioning mode = IPv6 |
| 11:58:21 Sun Mar 26 2023 |
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; |
| 11:58:26 Sun Mar 26 2023 |
Warning (5) | REG-RSP-MP Mismatch Between Calculated Value for P1.6hi Compared to CCAP Provided Value;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 11:58:26 Sun Mar 26 2023 |
Warning (5) | RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 11:58:26 Sun Mar 26 2023 |
Warning (5) | Dynamic Range Window violation |
| 12:10:31 Sun Mar 26 2023 |
Critical (3) | SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 12:10:33 Sun Mar 26 2023 |
Warning (5) | DBC-REQ Mismatch Between Calculated Value for P1.6hi Compared to CCAP Provided Value;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 18:35:28 Sun Mar 26 2023 |
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; |
| 18:35:28 Sun Mar 26 2023 |
Warning (5) | MDD message timeout;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 18:35:33 Sun Mar 26 2023 |
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; |
| 18:35:34 Sun Mar 26 2023 |
Warning (5) | MDD message timeout;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 18:36:28 Sun Mar 26 2023 |
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; |
| 18:36:28 Sun Mar 26 2023 |
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; |
| 18:36:36 Sun Mar 26 2023 |
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; |
| 18:36:37 Sun Mar 26 2023 |
Critical (3) | SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 18:36:38 Sun Mar 26 2023 |
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; |
| 18:36:48 Sun Mar 26 2023 |
Warning (5) | DBC-REQ Mismatch Between Calculated Value for P1.6hi Compared to CCAP Provided Value;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 18:37:05 Sun Mar 26 2023 |
Notice (6) | Honoring MDD; IP provisioning mode = IPv6 |
| 18:37:16 Sun Mar 26 2023 |
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; |
| 18:37:22 Sun Mar 26 2023 |
Warning (5) | REG-RSP-MP Mismatch Between Calculated Value for P1.6hi Compared to CCAP Provided Value;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 18:49:29 Sun Mar 26 2023 |
Critical (3) | SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
| 18:49:31 Sun Mar 26 2023 |
Warning (5) | DBC-REQ Mismatch Between Calculated Value for P1.6hi Compared to CCAP Provided Value;CM-MAC=[Edited: "Personal Information"];CMTS-MAC=[Edited: "Personal Information"];CM-QOS=1.1;CM-VER=3.1; |
BruceW
Gold Problem Solver
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26.4K Messages
2 years ago
If you want to troubleshoot this yourself, please see Internet Troubleshooting Tips. If you still need help, please post the following information from your modem (from http://192.168.100.1):
If you can't find the problem you'll need to have Comcast 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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