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Internet suddenly slow, T3 errors, low and 0 SNR values

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Frequent Visitor

Internet suddenly slow, T3 errors, low and 0 SNR values

About a month ago my MBPS went from mid 80's to in the 30's (the slowness started very suddenly) and the last few days it's in the teens. I upgraded my package to 200 mbps thinking it would fix it but it did not. Looking in the logs I'm seeing several T3 Timeout and Sync Timing Synchronizations errors and T4 errors. 

 

All my downstream levels look good expect for 11, 12 and 13. I've connected directly into the drop coming in from outside and I'm still having issues. Several calls to comcast and Arris and modem resets later I'm still having issues. Comcast wouldn't send a tech out as they said their signal looks fine. Is there anyone that can help?

Modem: Arris Sb6183

Router - Google Wifi

 

Downstream:

Channel Lock Status Modulation Channel ID Frequency Power SNR Corrected Uncorrectables
1 Locked QAM256 5 483000000 Hz -2.8 dBmV 41.4 dB 0 0
2 Locked QAM256 1 459000000 Hz -3.0 dBmV 41.4 dB 0 0
3 Locked QAM256 2 465000000 Hz -3.0 dBmV 41.4 dB 0 0
4 Locked QAM256 3 471000000 Hz -3.0 dBmV 41.3 dB 0 0
5 Locked QAM256 4 477000000 Hz -2.9 dBmV 41.4 dB 0 0
6 Locked QAM256 6 489000000 Hz -3.0 dBmV 41.3 dB 0 0
7 Locked QAM256 7 495000000 Hz -3.0 dBmV 41.3 dB 0 0
8 Locked QAM256 8 507000000 Hz -3.1 dBmV 40.2 dB 0 0
9 Locked QAM256 9 513000000 Hz -3.1 dBmV 40.2 dB 0 0
10 Locked QAM256 10 519000000 Hz -3.2 dBmV 40.6 dB 0 0
11 Locked QAM256 11 525000000 Hz -3.3 dBmV 28.3 dB 3428519 958
12 Locked QAM256 12 531000000 Hz -3.1 dBmV 0.0 dB 0 0
13 Locked QAM256 13 543000000 Hz -3.7 dBmV 33.7 dB 0 0
14 Locked QAM256 14 549000000 Hz -3.9 dBmV 40.4 dB 0 0
15 Locked QAM256 15 555000000 Hz -4.1 dBmV 40.3 dB 0 0
16 Locked QAM256 16 561000000 Hz -4.1 dBmV 40.3 dB 0 0

 

Upstream: 

Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 6 5120 Ksym/sec 36500000 Hz 47.8 dBmV
2 Locked ATDMA 5 5120 Ksym/sec 30100000 Hz 47.8 dBmV
3 Locked ATDMA 7 5120 Ksym/sec 17300000 Hz 49.8 dBmV
4 Locked ATDMA 8 5120 Ksym/sec 23700000 Hz 47.8 dBmV

 

Event Log

Time Priority Description
Time Not Established Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
Time Not Established Critical (3) No Ranging Response received - T3 time-out
Wed Jun 03 18:02:20 2020 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 18:02:59 2020 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 18:03:01 2020 Critical (3) SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 18:03:05 2020 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 18:04:25 2020 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 19:31:13 2020 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 19:32:01 2020 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 19:32:01 2020 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 19:32:20 2020 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 19:32:20 2020 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 19:32:41 2020 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 19:32:41 2020 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 19:33:01 2020 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
Wed Jun 03 19:33:01 2020 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=74:ea:e8:ee:53:94;CMTS-MAC=dc:eb:94:b5:cc:e9;CM-QOS=1.1;CM-VER=3.0;
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Expert

Re: Internet suddenly slow, T3 errors, low and 0 SNR values

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.



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Frequent Visitor

Re: Internet suddenly slow, T3 errors, low and 0 SNR values

Thank you for the reply - I've tested this by plugging my modem directly from the drop from the outside as it comes into my house before any splitters or anything and I'm still seeing this issue and these numbers.

 

I've tried 4 times to get a tech to come out to my house but each time the agent on the phone says there's nothing wrong on their end so they can't send a tech. Clearly there is something wrong with the signal. I'm desperate at this point. Trying to get a hold of someone at Comcast is incredibly frustrating as the automated phone system says "the first step in troubleshooting is to restart your modem, if that doesn't work call us back" so I tell the bot to restart my modem. When that predictibly doesn't work I call back and the first thing I get is "the first step in troubleshooting is to restart your model, if that doesn't work call us back". It's incredibly frustrating. 

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Expert

Re: Internet suddenly slow, T3 errors, low and 0 SNR values

Perhaps there is noise ingress into the line(s) somewhere.

 

There are other signal stat figures 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 that are available to these boards. They will be able to poll the CMTS to see whether or not everything is in the green zone, see your node / cable plant and modem health, and also see a history plot for the modem. You should get a reply here in your topic. Good luck !



I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
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Official Employee

Re: Internet suddenly slow, T3 errors, low and 0 SNR values

Hi Ztjohnson. Thanks for visiting and posting on our Forum. We appreciate you doing the testing and posting of your findings. I can assist with further troubleshooting your internet issues. Please reach out to me via private message and include your full name so I can assist you. 


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Official Employees are from multiple teams within Comcast: CARE, Product, Leadership. We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
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Frequent Visitor

Re: Internet suddenly slow, T3 errors, low and 0 SNR values

Thank you! 🙂