U

Visitor

 • 

8 Messages

Wed, Dec 1, 2021 7:41 PM

Closed

Internet connection is unstable since September

Hi there,

Our interent connection is unstable since September when an comcast network outage affected our area. We observed that during video conference or online gaming, the screen freezed for a few seconds sometimes. It looks like the ping became very high suddenly. It happens frequently, nearly once per hour. I think it's not a wireless network issue, since we saw the same issue on mobile phones and our destktop that connects to the router via cable. Just wondering what we can do to fix the network issue?

EG

Expert

 • 

91.5K Messages

2 m ago

Start with the modem's signal stats. Perhaps they already are, or they are close to being out of spec and intermittently they go completely of spec. Try getting them here http://192.168.100.1 or here http://10.0.0.1 


Please copy all of the text of the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers and paste them into your next post.


What is the exact make and model number of the modem ?

Visitor

 • 

8 Messages

Sure, copied all the stats here. The make and model number of the modem is Motorola, SB6121. We have used it for a few years.

https://www.amazon.com/Motorola-Surfboard-SB6121-Cable-Modem/dp/B075LGS8HX

Downstream Bonding Channel Value
Channel ID 28  29  30  31 
Frequency 555000000 Hz  561000000 Hz  567000000 Hz  573000000 Hz 
Signal to Noise Ratio 36 dB  35 dB  36 dB  36 dB 
Downstream Modulation QAM256  QAM256  QAM256  QAM256 
Power Level
The Downstream Power Level reading is a snapshot taken at the time this page was requested. Please Reload/Refresh this Page for a new reading
-2 dBmV   -1 dBmV   -1 dBmV   -1 dBmV  

Upstream Bonding Channel Value
Channel ID
Frequency 16400000 Hz  35600000 Hz  29200000 Hz  22800000 Hz 
Ranging Service ID 11480  11480  11480  11480 
Symbol Rate 5.120 Msym/sec  5.120 Msym/sec  5.120 Msym/sec  5.120 Msym/sec 
Power Level 44 dBmV  44 dBmV  44 dBmV  44 dBmV 
Upstream Modulation [2] QPSK
[1] 32QAM
[3] 64QAM
 
[2] QPSK
[1] 32QAM
[3] 64QAM
 
[2] QPSK
[1] 32QAM
[3] 64QAM
 
[2] QPSK
[1] 32QAM
[3] 64QAM
 
Ranging Status Success  Success  Success  Success 

Signal Status (Codewords) Bonding Channel Value
Channel ID 28  29  30  31 
Total Unerrored Codewords 15702859283  15701937261  15701937109  15701937658 
Total Correctable Codewords 5544  5345  5059  4919 
Total Uncorrectable Codewords 635  521  526  660 

(edited)

EG

Expert

 • 

91.5K Messages

2 m ago

FWIW, that modem is no longer supported by them. It may be time to update it. Just sayin'.

The stats that you posted so far are good / in spec. Are there four more downstream channels being shown ? If so, are the stats similar ?

Visitor

 • 

8 Messages

I don't see more downstream channels. 

EG

Expert

 • 

91.5K Messages

2 m ago

Hmmm. They may be being disabled due to it being unsupported. The lack of channels may be contributing to the instability. I would definitely update it to a more modern one that has more channels capability before proceeding with any more troubleshooting.

Look here at their compatible modems list: https://www.xfinity.com/support/devices#auth 

Enter your speed tier info.

Good luck !

Visitor

 • 

8 Messages

Thanks! We will replace it first.

Visitor

 • 

8 Messages

We replaced the old modem with Motorola MB8611, which is supported, but it does not fix the issue. Copied all the stats of the new modem here:

Connection
   Startup Sequence    
   Startup Step Status Comment

  
   Acquire Downstream Channel 651000000 Hz Locked
  
   Upstream Connection OK Operational
  
   Boot State OK Operational

  
   Configuration File OK
  
   Security Enabled BPI+
  


   Connection Status    
   System Up Time 1 days 03h:48m:33s  
  
   Network Access Allowed  
  


   Downstream Bonded Channels  
  
   Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected
   1 Locked QAM256 44 651.0 0.4 42.3 0 0
   2 Locked QAM256 4 405.0 1.2 43.3 26 0
   3 Locked QAM256 5 411.0 1.0 43.2 14 0
   4 Locked QAM256 6 417.0 1.4 43.3 13 0
   5 Locked QAM256 7 423.0 0.9 43.1 9 0
   6 Locked QAM256 8 429.0 1.4 43.3 15 0
   7 Locked QAM256 9 435.0 1.0 43.2 4618 11344
   8 Locked QAM256 10 441.0 1.2 43.1 8 0
   9 Locked QAM256 11 447.0 1.4 43.3 10 0
   10 Locked QAM256 12 453.0 1.1 43.2 25 0
   11 Locked QAM256 13 459.0 1.5 43.4 65 0
   12 Locked QAM256 14 465.0 0.7 43.0 62 0
   13 Locked QAM256 15 471.0 1.3 43.3 46 0
   14 Locked QAM256 16 477.0 1.2 43.3 51 0
   15 Locked QAM256 17 483.0 1.2 43.2 68 0
   16 Locked QAM256 18 489.0 1.6 43.3 74 0
   17 Locked QAM256 19 495.0 0.5 42.9 86 0
   18 Locked QAM256 20 507.0 0.9 34.7 16 0
   19 Locked QAM256 21 513.0 0.5 41.9 12 0
   20 Locked QAM256 22 519.0 0.9 42.9 1 0
   21 Locked QAM256 23 525.0 0.4 42.9 0 0
   22 Locked QAM256 24 531.0 1.1 43.1 2 0
   23 Locked QAM256 28 555.0 0.4 42.5 13 0
   24 Locked QAM256 30 567.0 0.7 42.8 6 0
   25 Locked QAM256 32 579.0 1.0 42.5 2 0
   26 Locked QAM256 33 585.0 1.3 42.8 1 0
   27 Locked QAM256 34 591.0 1.8 42.9 0 0
   28 Locked QAM256 35 597.0 1.1 42.6 1 0
   29 Locked QAM256 36 603.0 1.4 34.9 8 0
   30 Locked QAM256 37 609.0 0.9 38.1 4 0
   31 Locked QAM256 38 615.0 1.6 42.9 12 0
   32 Locked QAM256 39 621.0 1.6 42.8 0 0


   Upstream Bonded Channels  
  
   Channel Lock Status Channel Type Channel ID Symb. Rate (Ksym/sec) Freq. (MHz) Pwr (dBmV)
   1 Locked SC-QAM 1 5120 16.4 43.5
   2 Locked SC-QAM 2 5120 22.8 43.8
   3 Locked SC-QAM 3 5120 29.2 44.0
   4 Locked SC-QAM 4 5120 35.6 44.3


   Downstream Frequency Setting    
   Downstream Frequency Select   
  
EG

Expert

 • 

91.5K Messages

1 m ago

Well all of the channels are locked in now and all of the signal stats are very good !

Are there any modem error log entries being shown ? If so, please post them as well in their entirety (copy and paste them, don't post a screenshot) but redact the CM MAC and the CMTS MAC addresses for your privacy. They are considered to be personal information. Personally identifying information is a violation of their forum guidelines. The forum bot will not allow your post to be seen publically.

Also. For a test, does a computer / device that is hardwired directly to the MB8611 (remove the router from the mix) have the same problem ? 

(edited)

Visitor

 • 

8 Messages

This is the log. Our desktop is connected to the modem via a router. 

Event Log  
  
    Time    Priority    Description 
    Time Not Established   Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;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=xxx;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=xxx;CMTS-MAC=xxx;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=xxx;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=00:40:36:85:77:e6;CMTS-MAC=xxx;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=xxx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
    16:11:17
Tue Dec 14 2021
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    16:11:17
Tue Dec 14 2021
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    16:11:18
Tue Dec 14 2021
  Critical (3)   Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    16:11:23
Tue Dec 14 2021
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    16:15:06
Tue Dec 14 2021
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    16:15:07
Tue Dec 14 2021
  Critical (3)   Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    16:15:11
Tue Dec 14 2021
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    16:15:11
Tue Dec 14 2021
  Critical (3)   Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    16:15:11
Tue Dec 14 2021
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    16:15:11
Tue Dec 14 2021
  Critical (3)   Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=xxx;CMTS-MAC=xxxCM-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=xxx;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=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.1;
    Time Not Established   Notice (6)   Honoring MDD; IP provisioning mode = IPv6
EG

Expert

 • 

91.5K Messages

@user_8b18a3 wrote;

This is the log.

Thanks for the log entries !

Our desktop is connected to the modem via a router. 

I understand that but it doesn't answer my question. Did you try that test that I suggested ?

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

Visitor

 • 

8 Messages

I will try it later since others still need to use the wireless network. 

Visitor

 • 

8 Messages

We found the issue was the router. It's hard to reproduce the issue if the computer is directly connected to the modem, so we tried to replace the router, and the lagging issue disappeared afterwards. Thank you for the help!

EG

Expert

 • 

91.5K Messages

Glad you got it figured out ! Now closing your toplc.

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

New to the Community?

Start Here