N

Visitor

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4 Messages

Fri, Jan 14, 2022 7:19 PM

Closed

Intermittent T3/T4 Timeouts, 90-99% speed throttle, 2-10% packet loss

For the past few weeks I've been getting intermittent connectivity issues.  Speed tests when good are 360Mbps/12Mbps, always tested via LAN.  When the issue occurs its absolutely anywhere from 1.5 to 300Mbps, but usually low enough to interrupt VoIP or Netflix.  Packet loss up to 10%, average is 4-5%..significant enough to make gaming impossible.   But more importantly my wife and I work from home so this needs a resolution.

I've done endless reading/troubleshooting & factory resets on the modem (Motorola MB7621) and router (Asus AC1900).  Modem always points to upstream issues via T3/T4 ranging timeouts, from what I read here.  I've removed all unnecessary connections from the house entry to the modem (entry -> adapter -> coax direct to modem), but still get timeouts, which leads me to suspect out-of-home issues. 

It would be fantastic if someone from support can provide direction or information before I call a tech, especially with how intermittent it is - comes and goes out of nowhere.  

 Downstream Bonded Channels  
  
   Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected
1 Locked QAM256 25 627.0 4.9 37.0 1125874 1523150
2 Locked QAM256 9 531.0 5.9 40.2 0 0
3 Locked QAM256 10 537.0 5.8 40.1 0 0
4 Locked QAM256 11 543.0 5.7 40.0 0 0
5 Locked QAM256 12 549.0 5.7 40.0 0 0
6 Locked QAM256 13 555.0 6.1 40.0 0 0
7 Locked QAM256 14 561.0 6.0 40.0 0 0
8 Locked QAM256 15 567.0 5.9 39.8 0 0
9 Locked QAM256 16 573.0 5.9 39.8 0 0
10 Locked QAM256 17 579.0 5.7 39.8 0 0
11 Locked QAM256 18 585.0 5.6 39.9 0 0
12 Locked QAM256 19 591.0 5.8 40.0 0 0
13 Locked QAM256 20 597.0 5.6 40.0 0 0
14 Locked QAM256 21 603.0 5.4 39.9 1 0
15 Locked QAM256 22 609.0 5.3 39.9 1 0
16 Locked QAM256 23 615.0 5.2 39.8 0 0
17 Locked QAM256 24 621.0 4.5 40.5 77778 4365
18 Locked QAM256 26 633.0 4.4 40.2 27961239 22822163
19 Locked QAM256 27 639.0 4.1 40.5 7129 0
20 Locked QAM256 28 645.0 3.8 31.7 3847610 3436688
21 Locked QAM256 29 651.0 3.9 40.5 1 0
22 Locked QAM256 30 657.0 3.9 40.6 1 0
23 Locked QAM256 31 663.0 4.0 40.4 0 0
24 Locked QAM256 33 669.0 4.4 40.5 0 0
Total             33019634 27786366

Upstream Bonded Channels  
  
   Channel Lock Status Channel Type Channel ID Symb. Rate (Ksym/sec) Freq. (MHz) Pwr (dBmV)
1 Locked ATDMA 1 5120 35.6 41.0
2 Locked ATDMA 4 5120 16.4 40.2
3 Locked ATDMA 2 5120 29.2 40.2
4 Locked ATDMA 3 5120 22.8 40.2
5 Locked ATDMA 5 1280 39.6 39.8
6 Not Locked Unknown 0 0 0 0.0
7 Not Locked Unknown 0 0 0 0.0
8 Not Locked Unknown 0 0 0 0.0

Log  
  
 Time   Priority   Description 
 Fri Jan 14 13:52:43 2022    Critical (3)   Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=...
 Fri Jan 14 13:52:58 2022    Critical (3)   Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=...
 Fri Jan 14 13:53:07 2022    Critical (3)   Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=...
 Fri Jan 14 13:53:22 2022    Critical (3)   Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-...
 Fri Jan 14 13:53:39 2022    Critical (3)   SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=...

Error text varies a bit but always specifies timeout.  Also goes on infinitely but I didn't want to redact that many MAC addresses.

Thanks in advance,

NNN 

EG

Expert

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93.7K Messages

4 m ago

Even though the signal stats looked o/k at that snapshot in time, the error log entries and a few downstream channels with a large number of uncorrectable bit errors confirm that something is going on. Perhaps there is noise ingress into the line(s) / an impairment 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 can check the CMTS (Cable Modem Termination System) 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 for those upstream receive signal stats.

You should get a reply here in your topic. Good luck !

Visitor

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4 Messages

@EG
Thank you very much, I appreciate your help!
 

EG

Expert

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93.7K Messages

@NoNeckNunzio

Quite welcome ! It's why I lurk ! 😊 

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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.

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Official Employee

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161 Messages

4 m ago

Hi, @NoNeckNunzio, I'd really like to take a closer look into the signal levels here on our side. Could you please send over a private message with your first and last name, and address for further assistance?

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Visitor

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4 Messages

@XfinityLayla
Sent! Thanks!
 

Visitor

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4 Messages

4 m ago

Hi all, 

Just coming back to close the loop for those who might wonder what the outcome was - 

The technician confirmed signal lock was slow and investigated outside the house.  He told me he found a filter on the incoming coax line that was likely the culprit so he replaced it and confirmed proper signal behavior/timing was restored.  While my tests (speed, packets) can be intermittent in behavior they did show 0% packet loss and 360/12mbps on LAN.  So I trust the change in his readings confirmed this was the issue, since I can't be absolutely sure.  Nonetheless I think this is closed for now, unless Xfinity sees something in their readings that I can't. 

@EG thanks for the escalation & time to explain the background, and @XfinityLayla for the quick responses!

Best,

NNN

EG

Expert

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93.7K Messages

@NoNeckNunzio

My pleasure ! Thanks for circling back ! Hope things hold up for you ! 

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? Please mark an Accepted Answer!tick

Official Employee

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171 Messages

@NoNeckNunzio Thank you for letting us know, and for reaching out so we could help through Xfinity Forums! If you do need any further assistance, please feel free to create a new post at any time. We're always here to help!

I am an Official Xfinity Employee.
Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Please, mark a reply as the Accepted Answer.tick
EG

Expert

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93.7K Messages

4 m ago

Now closing this topic...

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