This is a long and complicated question, mostly because it has been going on for 2.5 years without a solution in sight. It also is only one-third computer related, the other two-thirds are cable TV and cable-phone related.


I have COX Communications for a cable provider, and we get Internet, digital cable TV, and digital phone service through them. The Internet is a SB5101 right now, and has been a DPC2100 and SB5120 in the past. Same results. The phone service is provided through a telephone interface mounted on the outside of the house (not classic VoIP) and the CATV is through a Scientific Atlanta receiver without DVR. I do have a TiVo connected to the CATV box.


  • The CATV shows "blocking" -- sometimes very very short duration where a few blocks appear on the screen. Sometimes it lasts long enough that the video "pauses" for 2-5 seconds, and rarely but not unseen the audio also fails.
  • The CATV decoder box shows no correctable (FEC) or uncorrectable errors. That is, all BER counters are zero for the video stream.
  • The Internet shows "micro-outages" where it appears that sent packets are not making it out, but I continue to receive packets from local modems. That is, pings stop coming back, but I continue to see modems broadcast for DHCP, and sometimes they ask more than once.
  • The cable modem shows no errors during this time, but cable modems lie like you would not believe. It is actually possible to unplug the coax from the modem for 20 seconds and it reports NO ERRORS to the provider's tools.
  • The phone service cuts out for 1-3 seconds, infrequently. When this happens, I hear NOTHING (not even comfort noise) and the remote side hears a "click" as if I were getting a call waiting message. However, there is no call incoming, other than the one I'm currently on of course.
  • Things SEEM to happen more frequently when the temperature outside swings from cold to warm, so fall/spring seems worse than summer/winter.
  • All micro-outages occur between once or twice a day (which I could ignore) to 10 times per hour.
  • All SNR, signal levels, noise levels, etc. show very close to optimal when measured.

COX's diagnosis

This is a continual pain for me. Over the last 2.5 years, they have opened, "fixed" something, and closed the tickets. They close it without confirming that it is indeed better, and when I reopen they cannot do that, but instead they open a new ticket and send yet another low-level tech out to do the same signal tests and report that all is OK.

I've finally gotten a line tech who has a clue and is motivated enough to pursue this with me. We have tried things like switching the local nodes over to UPS and generator power, but this does not trigger the noise. We have tried replacing all cabling, the tap outside my house, the modem, the CATV decoder -- all without resolution.

Recently they have decided it is both my computer or switch, my TiVo, and my phone that are all broken and causing this issue.

My debugging steps

I spent the worse day of my TV-watching life yesterday and part of today. I watched live TV without the TiVo. I witnessed blocking, but it did "feel different." and was actually more severe. Some days it is better, some days it is worse, so perhaps this was just a very bad day.

Today, I connected the TiVo to my DVD player, and ran two very long movies through it. I saw no blocking at all during nearly 6 hours of video.


Does anyone have any suggestions on what to do next?

I understand perhaps only the IP side can be addressed here, but it is one of the more limiting debugging options.


What kind of experience are your neighbors having? If any of them are using the same cable company and live close enough that the likelihood of them using the same underlying infrastructure is high, could it be that they're all having the same issues as you?

Otherwise, cable companies can be a royal pain to deal with. Call them and threaten to switch to another carrier if they don't make a good faith effort to improve your service. The technical issues are IMHO irrelevant. The larger issue you're faced with is crappy customer service.

  • 1
    My equipment shows no outages in their 2-hour polling intervals, the signals are good, etc. My neighbors also show the same signal quality levels. However, the biggest problem here is that Windows has taught people that computers are unreliable, and little issues like CATV blocking and such are just something to ignore. They won't bother reporting a 2-3 second blocking issue even if it happens 10 times/hour. They might report an outage lasting minutes, but that's not what I'm having -- unfortunately.
    – Michael Graff
    Dec 1 '09 at 21:18
  • BTW, I've sat with the line tech (David) and walked through other modems and CATV boxes which share my line. Instantaneous signal level checks are always perfect, and no BER counters change when there is a micro-outage. From what I understand, there is a fiber -> coax conversion, and this is where the FEC bits are added for the RF side. I wonder if this is part of the issue -- garbage in == garbage-out with FEC added.
    – Michael Graff
    Dec 1 '09 at 21:24
  • 1
    Here's another alternative. Depending on where you live, a site such as dslreports.com can have a significant number of users from your area that may or may not be having the same issues. I've had success in the past in debugging issues with DSL and cable ISPs here in Brooklyn using information from dslreports.com. At the very least you may be able to either correlate what you're seeing on your end with wider outages, or (at the other extreme) determine that your local equipment is solely at fault.
    – Max A.
    Dec 1 '09 at 21:24
  • I still can't fathom the answer from your response here. Are your neighbors experiencing the same symptoms, or not? If you establish that they are seeing the same issue, you can rule out your home equipment. If they're not having it, then it's definitely something to do with your setup individually, and not part of a wider exchange/trunk problem.
    – Chris Thorpe
    Dec 1 '09 at 21:25
  • The neighbors are probably seeing the issues, but they do not bother reporting short outages. I've asked a few, and yes, they see them -- but they also will not call in, and COX will ignore any proxy reports.
    – Michael Graff
    Dec 1 '09 at 21:37

Are any WiFi connections involved here, or is it all wired connections?

Also, you can see my similar quest to get my cable performance fixed here:


and see if that gives you any ideas.

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