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Frequent, but intermittent internet disconnects.

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Regular Visitor

Frequent, but intermittent internet disconnects.

I have been enjoying my -new- Comcast-recommended Motorola MB8600 modem for >several weeks without issue<.  It has suddenly started dropping its connection, which seems to be a very common theme.  Indeed, I have checked and tightened connections.  The events are random, and seemingly at the most inopportune moments - as I (like many) am working from home and conduct business over the various video and screen-sharing connections available.  I have a very small, but "enterprise class" network - so changing service providers is a simple swap-out at the closet ahead of my firewall.

 

The modem dropped again this morning, so I restarted it, and then captured the information shown below.

 

Any help interpreting these logs would be appreciated.

 

Time    Priority    Description 
    11:55:49
Fri Jun 12 2020
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;CM-QOS=1.1;CM-VER=3.1;
    11:56:02
Fri Jun 12 2020
  Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;CM-QOS=1.1;CM-VER=3.1;
    14:52:02
Mon Jun 15 2020
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;CM-QOS=1.1;CM-VER=3.1;
    14:52:03
Mon Jun 15 2020
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;CM-QOS=1.1;CM-VER=3.1;
    14:52:26
Mon Jun 15 2020
  Critical (3)   SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
    14:52:36
Mon Jun 15 2020
  Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
    15:20:28
Mon Jun 15 2020
  Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;CM-QOS=1.1;CM-VER=3.1;
    15:20:29
Mon Jun 15 2020
  Critical (3)   Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;CM-QOS=1.1;CM-VER=3.1;
    15:20:29
Mon Jun 15 2020
  Critical (3)   No Ranging Response received - T3 time-out;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;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=00:40:36:61:71:03;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=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;CM-QOS=1.1;CM-VER=3.1;
    Time Not Established   Notice (6)   Honoring MDD; IP provisioning mode = IPv6
    06:47:09
Fri Jun 26 2020
  Notice (6)   DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=00:40:36:61:71:03;CMTS-MAC=00:01:5c:7f:84:4b;CM-QOS=1.1;CM-VER=3.1;
Device Information
 

 

   
   Cable Specification Version DOCSIS 3.1
 

 


  
   Hardware Version V1.0
 

 


  
   Software Version 8600-18.2.17
 

 


  
   Cable Modem MAC Address (hidden)
 

 


  
   Cable Modem Serial Number 0980-MB8600-1639
 

 


  
   CM Certificate Installed
 

 


  
    Prod_18.2_d31
 

 

 
Connection
   Startup Sequence
 

 

   
   Startup Step Status Comment
 

 



  
   Acquire Downstream Channel 387000000 Hz Locked
 

 


  
   Upstream Connection OK Operational
 

 


  
   Boot State OK Operational
 

 



  
   Configuration File OK  
 

 


  
   Security Enabled BPI+
 

 


  


   Connection Status
 

 

   
   System Up Time 0 days 00h:50m:54s  
 

 


  
   Network Access Allowed  
 

 


  


   Downstream Bonded Channels
 

 

 
 

 


  
   Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected
   1 Locked QAM256 5 387.0 5.9 40.9 0 0
   2 Locked QAM256 1 363.0 6.2 41.2 0 0
   3 Locked QAM256 2 369.0 6.1 41.0 0 0
   4 Locked QAM256 3 375.0 6.0 41.2 0 0
   5 Locked QAM256 4 381.0 6.1 41.1 0 0
   6 Locked QAM256 6 393.0 5.8 40.8 0 0
   7 Locked QAM256 7 399.0 5.6 40.7 0 0
   8 Locked QAM256 8 405.0 5.5 40.4 0 0
   9 Locked QAM256 9 411.0 4.9 40.3 0 0
   10 Locked QAM256 10 417.0 4.5 40.3 0 0
   11 Locked QAM256 11 423.0 3.9 40.2 0 0
   12 Locked QAM256 12 429.0 3.7 40.3 0 0
   13 Locked QAM256 13 435.0 3.3 40.3 0 0
   14 Locked QAM256 14 441.0 3.6 40.4 0 0
   15 Locked QAM256 15 447.0 3.7 40.5 0 0
   16 Locked QAM256 16 453.0 3.7 40.4 0 0
   17 Locked QAM256 17 459.0 3.1 40.2 0 0
   18 Locked QAM256 18 465.0 3.1 40.2 0 0
   19 Locked QAM256 19 471.0 3.0 40.1 0 0
   20 Locked QAM256 20 477.0 2.7 40.2 0 0
   21 Locked QAM256 21 483.0 1.9 40.0 0 0
   22 Locked QAM256 22 489.0 2.0 40.0 0 0
   23 Locked QAM256 23 495.0 1.7 39.9 0 0
   24 Locked QAM256 24 507.0 0.1 39.2 0 0
   25 Locked QAM256 25 513.0 -0.7 39.0 0 0
   26 Locked QAM256 26 519.0 -1.6 38.6 0 0
   27 Locked QAM256 27 525.0 0.4 39.4 0 0
   28 Locked QAM256 33 339.0 6.7 40.8 0 0
   29 Locked QAM256 34 345.0 6.6 41.4 0 0
   30 Locked QAM256 35 351.0 6.6 41.4 0 0
   31 Locked QAM256 36 357.0 6.5 41.3 0 0
   32 Locked OFDM PLC 37 589.0 1.5 38.2 22094 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 35.8 46.0
   2 Locked SC-QAM 2 5120 29.4 46.5
   3 Locked SC-QAM 3 5120 23.0 46.5
   4 Locked SC-QAM 4 5120 16.6 46.0


   Downstream Frequency Setting
 

 

   
   Downstream Frequency Select   
 

 


  


   LAG Enable/Disable
 

 

   
   LAG(Link Aggregation Group, or Ethernet Port Bonding)        
 

 



  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Highlighted
Expert

Re: Frequent, but intermittent internet disconnects.

The signal stats are o/k but the error log entries indicate that something is going on. 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.
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Highlighted
Official Employee

Re: Frequent, but intermittent internet disconnects.

Hi DangerClose3. We appreciate you visiting and posting on the Xfinity Forums. I can assist with troubleshooting your internet connectivity issues. Please reach out to me via private message and include your full name and service address so I can access your account. To send a private message: click my name (ComcastJoeTru) to view my profile. Then click the link that says "Send a message" and there you can private message me. 


I am an Official Comcast Employee.
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!