intermittent cable modem resets caused by signal drop

intermittent cable modem resets caused by signal drop

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Hello all

Here's the lengthy status of my current problems with cox cable modem dropping.

Cable modem SB6121 will lose connectivity and reset, going down to one light, then rebuilding the connection after about a one minute outage.  Happens regularly and randomly.

Here's an example of the logs found in the motorola cable modem.  If you haven't checked your own cable modem logs and you're having this problem, here's the link to prove you're having the same problem as me: http://192.168.100.1/cmLogs.htm .  I xxx'd out my MAC addresses in the logs.

Jun 20 2012 01:57:47 6-Notice I401.0 TLV-11 - unrecognized OID;CM-MAC=xxxx;CMTS-MAC=xxxx;CM-QOS=1.1;CM-VER=3.0;
Jun 20 2012 01:57:46 5-Warning D04.1 ToD request sent - No Response received;CM-MAC=xxxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Jun 20 2012 01:57:34 3-Critical R02.0 No Ranging Response received - T3 time-out;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Jun 20 2012 01:57:30 4-Error T201.0 Missing Mandatory MDD TLV on primary DS Channel;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;

When it comes to signal strength, this is apparently not the problem.  

Here's what motorola says should be fine, according to Motorola Tech Support:

Downstream Signal to Noise Ratio (SNR): 25 dB or greater
Downstream Power Level: +15 to -15dBmV
Upstream Transmit Power Level: less than 58dBmV

My values, pasted from http://192.168.100.1/cmSignal.htm.  I've sampled these values over time and they have never strayed much from these numbers.

downstream Signal to Noise Ratio 38 dB  38 dB  38 dB  38 dB 
downstream Power Level 1 dBmV   0 dBmV   0 dBmV   0 dBmV
upstream Power Level 44 dBmV

After multiple lengthy calls with Motorola Tech Support, who are surprisingly helpful, they told me that this problem is definitely at the service provider end (Cox), with the signal dropping out on the modem.  They offered for free to replace my old Motorola SB6120 with a  new SB6121, saying they're only doing this to prove that the cable modem isn't the problem, and to aide my case for Cox to fix it.

Now, I've been receiving these random restarts (which sometimes occur in bursts of 3-4 per hour) since I lived at my prior residence, three blocks away from my new place in the same neighborhood.

So, in summary.

Cable modem random restarts resulting in 1 minute outages.

Two different cable modems.

Two different HOUSES in the same neighborhood.

Signal strength to the cable modem is NOT a problem.

What does Cox do?

Schedule another technician to come out.  The last scheduled appointment on Thursday from 5-7pm didn't call, didn't show.  Got another one scheduled on Monday.  We'll see.

I'm posting this because if anyone else has the same problems, they should check their Motorola cable modem logs and signal strengths and post here.

All Replies
  • Posted by dubyada
    23 Jun 2012 5:59 PM

    FYI I am in Baton Rouge, Louisiana.

  • Posted by Greg
    23 Jun 2012 8:37 PM

    i had the exact same issue... had 7 cox techs come out... none could find issue... bought a brand new motorola 6121 and had the same issue...  finally I tried Cox's new Cisco DPC3010 (I think it was $70 or $80 and it fixed the problem entirely... cox and motorola aren't getting along and they will not acknowledge that fact... you can get one of the cox techs to loan you the modem to try it for a few days pretty easily... if you talk to cust. service you can probably get them to GIVE you the modem as compensation for your downtime...

  • Posted by T123
    25 Jun 2012 5:41 PM

    Have the same issues but I have the SB6120. Will post my logs here shortly.

  • Posted by dubyada
    25 Jun 2012 5:56 PM

    That is very interesting and explains why multiple houses and multiple cable modems keep having the same problems.  I can only assume that Cox's problems with Motorola are Cox's fault, otherwise there would be more of a public "stay away" message.  Cox phone support people recommend the Motorola 6121 first and foremost, so I have trouble thinking that is the problem.  

    What this does NOT explain is why the 6120 and 6121 work fine MOST of the time, for long stretches even.  

    My guess would be that Cox experiences this issue when localized demand has outgrown capacity, but I suppose we'll never know.

  • Posted by dubyada
    25 Jun 2012 9:20 PM

    Cox technician came today and said that he sees this problem once a week - the new Docsis 3.0 modems "range" to different frequencies when more bandwidth is detected on another frequencies.  During this "ranging" the signal drops.  He said it happens with all brands of cable modems.

    The technician said that the "engineers" back at the office can "fix" this.  He said he didn't really know how.  I asked if it was essentially locking the modem into one frequency, and he said yes.  He checked the signal, as he had to do at every visit, and said I had a good signal.  He took my information, said he'd be glad to call me back and let me know when "she" back at the office "fixes it". I appreciated that gesture at least.  

    I'm not sure what/if anything to believe from Cox, other than they seem incapable of delivering clear information to the general public regarding their troublesome service.  Instead of treating cable signals like "magic" it would make more sense to deliver clearer information, so as to remove superstition and prevent silly things like me buying a new cable modem and spending hours on the phone with Motorola to fix mysterious problems.

  • Posted by pac522
    10 Jul 2012 10:59 PM

    Having the same problem with the Motorola 6580, it Docsis3 modem also. Live in Kenner, LA. Had an old Docsis 1.1 Motorola modem before this new one and never had a problem with disconnects. If it keeps up I'm going to take your advice. Thanks.

  • Posted by redmeansgo
    13 Jul 2012 6:10 PM

    Okay, my SB6120 (which I bought last year when I started my Cox service) has been doing exactly the same thing. I'm in Northern Virginia, and we hadn't had a single problem until last weekend. With all the derecho cleanup in this area we first thought maybe it was out because of repairs on the lines or something, but then we checked the cable and saw that wasn't the case. I'm a little naïve here, so bear with me. Does this mean I need to buy yet another modem? Do I need to miss a day of work so a technician can come out and perform some magic? Do I need to talk to Verizon about getting FiOS? Someone please guide me in the right direction. Tongue Tied

  • Posted by ChrisL
    14 Jul 2012 6:46 AM

    I'd say it's too early to tell if the modem needs to be replaced.  A good start might be to check your signal levels as reported by the modem.  Go to http://192.168.100.1. in your browser to access this information.

    -Chris

    Cox Support Forums Moderator

  • Posted by redmeansgo
    14 Jul 2012 6:45 PM

    Chris- Is there a way I can send you an email with a screenshot of the log and signal levels? I have to send over my 4g data plan since we can't get the modem to connect at all now. Pretty unhappy considering I can't telecommute without web access. 

  • Posted by ChrisL
    17 Jul 2012 7:09 AM

    Sure, you can email me at coxhelp@cox.com.

    -Chris

    Cox Support Forums Moderator

  • Posted by paula
    21 Jul 2012 6:29 PM

    Dropping connection every 3 minutes on the hour. I work from home so could possible lose my job.Tech coming out. I have latest Cox NetGear router/modem less than 1yr. I am at zip code 22130. The Tech came by replaced the modem and issue has been resolved.

    Fri Jul 20 15:03:59 2012    Critical (3)   Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=e0:46:9a:21:ce:c0;CMTS-MAC=00:1f:ca:20:2e:69;CM-QOS=1.1;CM-VER=3.0; 
     Fri Jul 20 15:02:51 2012    Critical (3)   Resetting the cable modem due to docsDevResetNow 
     Fri Jul 20 14:02:52 2012    Critical (3)   Resetting the cable modem due to docsDevResetNow 
     Time Not Established   Warning (5)   DHCP WARNING - Non-critical field invalid in response ;CM-MAC=e0:46:9a:21:ce:c0;CMTS-MAC=00:1f:ca:20:2e:69;CM-QOS=1.0;CM-VER=3.0; 

    Sat Jul 21 20:05:00 2012    Warning (5)   Admin login authentication fail 
     Sat Jul 21 20:03:44 2012    Notice (6)   TLV-11 - unrecognized OID;CM-MAC=e0:46:9a:21:ce:c0;CMTS-MAC=00:1f:ca:20:2e:69;CM-QOS=1.1;CM-VER=3.0; 
     Sat Jul 21 20:02:45 2012    Critical (3)   Resetting the cable modem due to docsDevResetNow 
     Time Not Established   Warning (5)   DHCP WARNING - Non-critical field invalid in response ;CM-MAC=e0:46:9a:21:ce:c0;CMTS-MAC=00:1f:ca:20:2e:69;CM-QOS=1.0;CM-VER=3.0; 
  • Posted by Jlm1228
    21 Jul 2012 8:28 PM

    I am also seeing dropped connections here on my SB6120 (area code 85024). This SB6120 was purchased and installed three months ago. It was very reliable until the beginning of July. I see similar log errors reported by others.

    JLM

  • Posted by Jlm1228
    21 Jul 2012 8:30 PM

    One correction.... I have a SB6121

  • Posted by paula
    24 Jul 2012 6:54 PM

    Tech  changes my modem and i am working nicely again. So that error means the modem is bad if the signal strength tested good. i had test with speedtest.net and signal was good when it  wasn't working well.

  • Posted by ptupper
    25 Jul 2012 9:21 PM

    Interesting conversation... I have a SB6120 and I see the same problem with another service provider.  Lately, so bad, that I struggle to maintain a connection for any length of time. From what I can see, my stats are fine, so I can already predict the answer I'll get.

    Downstream

     

    Bonding Channel Value

     

     

     

    Channel ID

    26 

    25 

    27 

    28 

    Frequency

    621000000 Hz 

    615000000 Hz 

    627000000 Hz 

    633000000 Hz 

    Signal to Noise Ratio

    37 dB 

    37 dB 

    38 dB 

    38 dB 

    Downstream Modulation

    QAM256 

    QAM256 

    QAM256 

    QAM256 

    Power Level

    0 dBmV  

    0 dBmV  

    0 dBmV  

    0 dBmV  

     

    Upstream

    Bonding Channel Value

     

    Channel ID

    Frequency

    36800000 Hz 

    30200000 Hz 

    Ranging Service ID

    39 

    39 

    Symbol Rate

    5.120 Msym/sec 

    5.120 Msym/sec 

    Power Level

    48 dBmV 

    48 dBmV 

    Upstream Modulation

    [3] QPSK

    [3] 64QAM

    [3] QPSK

    [3] 64QAM

    Ranging Status

    Success 

    Success