Community Forum

Intermittent connection drops/ T3 timeouts

TWright1
Regular Visitor

Intermittent connection drops/ T3 timeouts

Hi Everyone,

 

I have an issue similiar to some others posted here but I think perhaps a little different.  For the past week or more, I have been having occaisonal connection drops.   Usually they are only for 1 minute or less, but this is enough to interrupt my work, or streaming video etc.    

 

As I am well versed in networking, I have troubleshooted the issue back to my combination cable modem/ router.   I have  a script running checking the connectivty against OpenDNS and generally record something around 20 minutes of total outage per day, in <60 second increments.  It seems very variable.  

 

I have a Motorola MG7750 that has been more or less trouble free for the past 3 years until now.  I checked the status log and found a fairly large number of errors,   which per the other posts are indiciative of connection issues.  I also checked the connection SNR and power levels against the guides available here, and they look normal, (at least when connected). 

 

Based on all of this, I believe the issue is either with the modem or connection.  However, this modem is the only device connected in the house, as I don't have TV service.  I checked the connections that I can find, and no obvious faults.  

 

What I am looking for is clues to if this this might be a noise issue on the line, or perhaps my modem is going bad.   Below are samples of the error logs, and connection data.  In particular, are the large number of corrected packets a sign of a noisy line, a bad modem, or something else?

 

If it's the modem I can just replace it and move on, what I am looking for is if that is likely before I go and take the time and money to do so.  Hope  one of you can help.  

 

Sample of the T3 errors, (not all of them by any means)

 

Fri Jun 26 02:15:36 2020   Critical (3)  Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=00:40:36:47:df:04;CMTS-MAC=00:01:5c:ae:00:85;CM-QOS=1.1;CM-VER=3.0; 
Fri Jun 26 02:15:36 2020   Critical (3)  Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=00:40:36:47:df:04;CMTS-MAC=00:01:5c:ae:00:85;CM-QOS=1.1;CM-VER=3.0; 
Fri Jun 26 02:15:36 2020   Critical (3)  16 consecutive T3 timeouts while trying to range on upstream channel 3;CM-MAC=00:40:36:47:df:04;CMTS-MAC=00:01:5c:ae:00:85;CM-QOS=1.1;CM-VER=3.0; 
Fri Jun 26 02:17:12 2020   Critical (3)  Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=00:40:36:47:df:04;CMTS-MAC=00:01:5c:ae:00:85;CM-QOS=1.1;CM-VER=3.0; 
Fri Jun 26 02:17:12 2020   Critical (3)  Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=00:40:36:47:df:04;CMTS-MAC=00:01:5c:ae:00:85;CM-QOS=1.1;CM-VER=3.0; 
Fri Jun 26 02:17:12 2020   Critical (3)  16 consecutive T3 timeouts while trying to range on upstream channel 2;CM-MAC=00:40:36:47:df:04;CMTS-MAC=00:01:5c:ae:00:85;CM-QOS=1.1;CM-VER=3.0; 
Fri Jun 26 02:21:26 2020   Critical (3)  Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=00:40:36:47:df:04;CMTS-MAC=00:01:5c:ae:00:85;CM-QOS=1.1;CM-VER=3.0; 
Fri Jun 26 02:21:26 2020   Critical (3)  Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=00:40:36:47:df:04;CMTS-MAC=00:01:5c:ae:00:85;CM-QOS=1.1;CM-VER=3.0; 
Fri Jun 26 02:21:26 2020   Critical (3)  16 consecutive T3 timeouts while trying to range on upstream channel 3;CM-MAC=00:40:36:47:df:04;CMTS-MAC=00:01:5c:ae:00:85;CM-QOS=1.1;CM-VER=3.0; 

 

Connection data as of this writing

  Downstream Bonded Channels
 

 

 
 

 


  
   Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected
1 Locked QAM256 17 621.0 -1.1 38.6 7954 5674
2 Locked QAM256 18 627.0 -0.7 38.7 7736 5869
3 Locked QAM256 19 633.0 -0.4 38.8 7514 6155
4 Locked QAM256 20 639.0 -0.2 38.4 7256 5744
5 Locked QAM256 21 645.0 -0.1 38.8 7193 6091
6 Locked QAM256 22 651.0 -0.2 38.8 6994 6051
7 Locked QAM256 23 657.0 -0.2 38.9 7075 5948
8 Locked QAM256 24 663.0 -0.2 38.7 6673 5717
9 Locked QAM256 25 669.0 -0.2 38.7 6583 5455
10 Locked QAM256 26 675.0 -0.4 38.5 7044 5238
11 Locked QAM256 27 681.0 -0.3 38.8 6786 5031
12 Locked QAM256 28 687.0 -0.1 39.0 8852 8023
13 Locked QAM256 29 693.0 -0.1 39.0 6970 5802
14 Locked QAM256 30 699.0 -0.3 38.9 6528 5220
15 Locked QAM256 32 705.0 -0.7 38.8 6155 5366
16 Locked QAM256 36 711.0 -0.8 38.7 6182 4986
Total             113495 92370



   Upstream Bonded Channels
 

 

 
 

 


  
   Channel Lock Status Channel Type Channel ID Symb. Rate (Ksym/sec) Freq. (MHz) Pwr (dBmV)
1 Locked ATDMA 2 5120 29.4 45.8
2 Locked ATDMA 1 5120 35.8 45.5
3 Locked ATDMA 3 5120 23.0 45.2
4 Locked ATDMA 4 5120 16.6 44.0

 

 

EG
Expert

Re: Intermittent connection drops/ T3 timeouts

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 !



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ComcastJoeTru
Official Employee

Re: Intermittent connection drops/ T3 timeouts

Hello TWright1. Thank you for creating a post on our Forum. I can help troubleshoot your intermittent connectivity issues. To get started, please send me a private message and include your full name sand service address so I can access your equipment. Click my name (ComcastJoeTru) to view my profile, then click the link that says "Send a message". There you can private message me. 


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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!
LTCreations
Frequent Visitor

Re: Intermittent connection drops/ T3 timeouts

The number of people who have the exact same issue would love to have help. Why was 1 person signeld out to get help?!!