Connectivity
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westptx
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Significant number of connection drops last 2 days + reduced speed

I've been on and off the phone with Comcast "technical" support for the better part of two days trying to understand a mutlitude of issues that started Thursday.

 

The first:  my connection drops consistently every ~30 seconds

The second:  I'm maxing out at 10MBps down despite paying for 50MBps

 

Any person that I've been able to get on the phone has been completely unhelpful (try as they might) and throws my equipment back in my face (because it must be my equipment and must have no idea what I'm doing).

 

From the top...I use my own modem (SB 6121) and router.  I've been using the same combination for the better part of 3 years without issue.  On Thursday, the connection started dropping consistently.  Looking at the modem signal:

 

Downstream Bonding Channel Value
Channel ID83 81 82 84 
Frequency615000000 Hz 603000000 Hz 609000000 Hz 621000000 Hz 
Signal to Noise Ratio37 dB 38 dB 37 dB 37 dB 
Downstream ModulationQAM256 QAM256 QAM256 QAM256 
Power Level2 dBmV  3 dBmV  3 dBmV  2 dBmV  

 

Upstream Bonding Channel Value
Channel ID
Frequency30100000 Hz 36500000 Hz 18900000 Hz 23700000 Hz 
Ranging Service ID
Symbol Rate5.120 Msym/sec 5.120 Msym/sec 2.560 Msym/sec 5.120 Msym/sec 
Power Level42 dBmV 42 dBmV 42 dBmV 42 dBmV 
Upstream Modulation[3] QPSK
[3] 64QAM
 
[3] QPSK
[3] 64QAM
 
[3] QPSK
[3] 64QAM
 
[3] QPSK
[3] 64QAM
 
Ranging StatusContinue Success Success Success 

 

Signal Stats (Codewords) Bonding Channel Value
Channel ID83 81 82 84 
Total Unerrored Codewords368782 368785 368787 368788 
Total Correctable Codewords12 48 12 23 
Total Uncorrectable Codewords734 698 733 722 

 

Everything looks fairly legitimate here.  Downstream SNR is within the normal range.  Downstream power looks good.  Upstream power looks normal.  

 

Despite this, I went out and bought a brand spaking new SB6121 and it showed results near identical to what I pasted above.

 

Looking at the modem logs, I do see some T3 timeouts:

Time Priority Code Message

Dec 20 2014 13:19:015-WarningZ00.0MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1;CM-MAC=7c:bf:b1:61:c9:54;CMTS-MAC=68:ef:bd:86:16:74;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:146-NoticeN/ACable Modem Reboot due to power reset ;CM-MAC=7c:bf:b1:61:c9:54;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;
Dec 19 2014 22:20:085-WarningZ00.0MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1;CM-MAC=7c:bf:b1:61:c9:54;CMTS-MAC=68:ef:bd:86:16:74;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:233-CriticalR02.0No Ranging Response received - T3 time-out;CM-MAC=7c:bf:b1:61:c9:54;CMTS-MAC=68:ef:bd:86:16:74;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:136-NoticeN/ACable Modem Reboot due to power reset ;CM-MAC=7c:bf:b1:61:c9:54;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;
Dec 19 2014 21:28:055-WarningZ00.0MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1;CM-MAC=7c:bf:b1:61:c9:54;CMTS-MAC=68:ef:bd:86:16:74;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:283-CriticalR02.0No Ranging Response received - T3 time-out;CM-MAC=7c:bf:b1:61:c9:54;CMTS-MAC=68:ef:bd:86:16:74;CM-QOS=1.1;CM-VER=3.0;
Jan 01 1970 00:00:146-NoticeN/ACable Modem Reboot from GUI/Configuration page ;CM-MAC=7c:bf:b1:61:c9:54;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.0;

 

...though I'm not sure what would cause that or if it's a benign issue/red herring.

 

Here is the firmware info from the cable modem itself:

 

Model Name: SB6121
Vendor Name: Motorola
Firmware Name: SB_KOMODO-1.0.6.14-SCM01-NOSH
Boot Version: PSPU-Boot(25CLK) 1.0.12.18m3
Hardware Version: 5.0
Serial Number: XXXXXXXXXXXXXXXXXXXXXXXX
Firmware Build Time: Mar 6 2014 15:23:55

 

I've checked/replaced every single cable that I can find.  We have quad-shield RG6 that was installed in 2011 from outside directly to our panel (seen in the fairly strong signals from the modem output).  We've tried 2 different SB 6121s with 2 different routers and the problem is consistent across both.  

 

I initially thought it was our routers since one was fairly old (DGL-4500 from 2009) and underpowered (DIR-615) but neither of them have ever had issues, both of them work just fine with our home internet connection, so I'm having a hard time believing that it's my equipment.

 

One thing that did help (to some degree) was moving off of the Comcast DNS servers (75.75.75.75 and 75.75.76.76) to Google's Public DNS (8.8.8.8 and 8.8.4.4) but, again, that isn't really the problem.

 

I, fortuitiously, have an Archer C7 router arriving at some point today, so we'll see how that one fairs (I don't expect a different result).  I do have a tech coming out tomorrow under the threat of a $100 service charge (which is BS based upon all of the investigation that I've done), but I'd like to avoid wasting their time for an issue that I think is related to Comcast's own network and not the line itself.

 

To sum up, I think Comcast's technical support is absolutely awful.  I'm tired of having my time wasted by scripted steps (unplug the modem for 30 seconds, check the connections, etc).  Give me someone who knows WTF a DNS server does, what SNR means, and why -1db isn't the end of the world.

 

If any network engineers happen to read this, let me know if there is anything else that I can do/try on my end.

 

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Trusted Forum Contributor

Re: Significant number of connection drops last 2 days + reduced speed

Hello westptx and welcome,

 

Yes your downstream power levels being @ 2-3 dBmV, QAM=256 and your upstream power levels being 42dBmV, QAM64 do look primo. This does not look like any signaling issue UNLESS you are having fluctuation. So make sure the Tech meansures your 30 day period of your power levels because if you have a constant fluctuation, then this could be caused by one of your splitters intermitently breaking down, cabling interconnection issues, etc. Another thing you might want the Tech to check is what the Comcast boot file is that your modem is receiving.  If you have a SB6121, then that is what it should be receiving and if it is not, then you could have some intermittent interconnect issues due to this, too. Lastly, there is a great youtube flick  you might be interested in checking out for grins. It goes over some Motorola active return filter that some folks have been using mainly to avoid intermittent modem restarts when the upstream power level get up beyond the 54 dBmV level and it seems to do the trick.

 

Hope this helps you out.

 

 

 

 

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