7 Messages
SYNC Timing Synchronization failure error in modem log
I have random disconnects and I noticed SYNC Timing Synchronization failures in cable modem logs and need some assistance in resolving this issue. I recently had an Xfinity tech visit my house and put a filter on my tap due to back interference. I had to schedule another tech to come out and review the situation inside the house. The second tech noticed one possible connector issue and re-terminated it. Also I only have the coax going into the house and straight to the cable modem. I don't have any splitters in the line and I don't have the coax being used for TV services or anything else. The second tech removed the tap and said all the levels look good from the modem to the box outside. After all that I thought my connection would be more stable. But I continue to have random disconnects. Below is what I need help with. This morning about 7:43am my internet was unavailable. I captured the log below. You can see the SYNC Timing Synchronization failure near the end of this log. It's not timestamped because the time can't be synced!!! But you see it recover at 7:43am (the times are before the event in the log).
Can someone help me troubleshoot this?
Start of redacted (removed MAC addresses) log:
Event LogTime Priority Description14:31:54Fri Dec 27 2024 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;Time Not EstablishedCritical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;14:37:05Fri Dec 27 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;14:37:11Fri Dec 27 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;14:38:00Fri Dec 27 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;14:39:14Fri Dec 27 2024 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;15:09:50Fri Dec 27 2024 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:15:43Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:15:49Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:15:58Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:16:42Sat Dec 28 2024 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:17:09Sat Dec 28 2024 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:23:43Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:23:49Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:25:43Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:25:43Sat Dec 28 2024 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:26:21Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:26:21Sat Dec 28 2024 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:26:26Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:26:26Sat Dec 28 2024 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:26:31Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:26:32Sat Dec 28 2024 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:26:32Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:26:33Sat Dec 28 2024 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:28:23Sat Dec 28 2024 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;11:28:29Sat Dec 28 2024 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;11:28:56Sat Dec 28 2024 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;Time Not EstablishedCritical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;Time Not EstablishedCritical (3) No Ranging Response received - T3 time-out;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;Time Not EstablishedNotice (6) Honoring MDD; IP provisioning mode = IPv607:43:11Thu Jan 2 2025 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;07:43:26Thu Jan 2 2025 Notice (6) CM-STATUS message sent. Event Type Code: 24; Chan ID: 32; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0.;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;
EG
Expert
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109.9K Messages
4 months ago
What do the modem's signal status values look like ? Try getting them here; http://192.168.100.1 or here http://10.0.0.1
Please copy all of the text in its entirety of the *Downstream Power Levels*, the *SNR's* (Signal to Noise Ratios), and the *Upstream Power Level* numbers and paste them into your next post.
What is the exact make and model number of the modem / gateway device ?
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EG
Expert
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109.9K Messages
4 months ago
This may or may not be the root cause of the problem (YMMV) but it should be addressed regardless.
The downstream power is high / strong. It may be over-driving the front-end receiver circuit of the modem. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels.
Is there a drop amplifier on the coax cable line leading to the modem ? If so, try removing / bypassing it and see. If not, you can try installing a -6 dB forward path-only attenuator pad such as this one on the coax port on the rear of the modem to knock that power level down and see;
https://www.amazon.com/line-Signal-Forward-Attenuator-FPA6-54/dp/B07882H96R
For areas that have been upgraded to the new Next Gen (mid-split) upload speeds;
https://www.multicominc.com/product/multicom-mul-fpa85-forward-path-attenuator
These won't affect the upload power which is within specs.
(edited)
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EG
Expert
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109.9K Messages
4 months ago
Quite welcome ! So, -7 dB to +7 dB is the desired range. If your area has been upgraded for the Next Gen speeds, you should have received an E-mail stating so.
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user_g3qiy7
7 Messages
4 months ago
@EG I installed the splitter today and my power levels range from 2 - 5.5. I'll keep an eye on it and let you know what happens. If this ends up being the smoking gun. I may suggest this to my neighbor. What's your formula for determining which attenuator drop to recommend?
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XfinityMarcos
Official Employee
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2.3K Messages
4 months ago
Hi user_g3qiy7, thank you for coming to our Forum for help with those dropped signals, those would get old pretty fast, so I get it. How has your connection been since that recently installed splitter? I'm also happy to see our awesome community has been able to help you as well, thanks @EG!
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user_g3qiy7
7 Messages
3 months ago
I've still got the same issue. I can see the power levels are still 2 - 5.5 range. But I've had more events occur.
High latency
1/8/2025, 1:59 PM
1/7/2025, 12:01 PM
1/6/2025, 12:00 PM
1/4/2025, 11:00 PM
Packet loss
1/8/2025, 3:26 AM
1/5/2025, 7:24 AM
Disconnect
1/5/2025, 7:26 AM (which I can see in the cable modem logs below - still likes the same as before adding the attenuator)
Time Not Established
Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=<REDACTED>;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=<REDACTED>;CMTS-MAC=<REDACTED>;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=<REDACTED>;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=<REDACTED>;CMTS-MAC=<REDACTED>;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=<REDACTED>;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=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;
Time Not Established
Notice (6) Honoring MDD; IP provisioning mode = IPv6
07:25:32
Sun Jan 5 2025 Notice (6) DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=<REDACTED>;CMTS-MAC=<REDACTED>;CM-QOS=1.1;CM-VER=3.1;
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EG
Expert
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109.9K Messages
3 months ago
@user_g3qiy7
OK so even though the signal status values look good now, the error log entries confirm 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 check those upstream receive signal stats.
You should get a reply here in your topic. Good luck !
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