US Cable Support > Comcast HSI > (Un)correctable codeword count high

reply to dorkino

Re: (Un)correctable codeword count high

reply to nerdburg
I think you're right about the problem being in the neighborhood. I received the Zoom 5341J modem and hooked it up. It seems to tolerate the RF issues better than the Motorola did. The problem isn't fixed, as I do still sometimes see T3 errors in the Zoom log, and the errored codeword count increases periodically. However, the frequency of the T3 timeouts seems to have decreased.

I'm considering calling out a tech to check for line noise or other issues. As I mentioned in my previous post, when I moved it to a different drop in the house that had approx 45' less coax and one less barrel connector, the problem actually became worse. I don't understand why this is, but I theorize it's either because my downstream level increased to around 6dBmV from 0-1, and if there is noise on the line then maybe this exacerbated the problem. Or, perhaps the modem locked onto different frequencies that are experiencing more noise issues than where it was previously hooked up.

reply to dorkino
Codewords have to do with forward error correction (FEC). Cable uses what is known as a Reed-Solomon (RS) encoder or interleaver to inject codewords or blocks of RS data which allow malformed packets to self-correct.

Your modem looks at every packet on its segment to see what packets/codewords are addressed to it. This is expressed by "Total Unerrored Codewords". For our purposes, it's pretty meaningless.

"Total Correctable Codewords" are the codewords that were addressed to your modem that were corrected.

And you guessed it -- "Total Uncorrectable Codewords" are the number of codewords that your modem couldn't correct.

The numbers are cumulative, so in order to use this as a diagnostic tool, you would first rest your modem, then watch for new errors.

I wouldn't think that the problem isn't related to your modem, most likely something flaky was going on with the local cable plant.

reply to dorkino
Cable modems do not read the downstream SNR, nor do CMTS read the upstream SNR. They estimate it based upon the current ration of correctable code words to total codewords. If the modem is reporting a good (high) SNR, then the number of bad codewords is not a problem.

reply to dorkino
Thanks. I'll try getting that info.

I've also tried moving the modem to a different drop, but the T3 errors keep occuring, and the uncorrectable/correctable codewords keep increasing periodically. The upstream power level remains around 44dBmV.

There are not any splitters on the way to the modem either. Only a barrel connector that Comcast installed in the outside demarc box on the side of the house. It's a connector that has a ground wire attached to it. Other than that, it's a straight run from the outside box to a bedroom wall jack, which adds one more connector, then to the modem via a roughly 6 foot cable. Previously, I had this thing hooked up through a different jack in the master bedroom; it was spliced onto that wire coming from the outside to a 50ft wire going thru the attic that terminates in the laundry room where I have all my wiring run. I've since moved it to this other bedroom in an effort to simplify things in the hopes that I can clear this up myself.

Edit: Since I've moved it, the problem remains. It may even be worse, because the modem rebooted from a T4 timeout just a little while ago.

I found a thread on Comcast's forums started by Nerdburg a couple of months ago that indicates suspicion of a possible problem with the 1.0.6.6 firmware and this SB 6121 modem. Supposedly the Zoom 5341J behaves well on Comcast's network, so I'm going to try one of those out. Although, can a firmware issue be to blame for the errored codeword bursts? Isn't that more likely some source of noise entering into the network?

Edit #2: I polled the neighborhood on FB, and many other folks are having similar issues. What would be the best way to have the problem investigated considering this is likely not a problem just at my house?

reply to dorkino
I'd call in and ask what your upstream SNR is.
--
»www.VAJeeps.com

reply to ExoticFish
It's a little lower - 44dBmV. I'm not certain if that's changing at the time of error, or if that's just what it would have been at that time anyway.

reply to dorkino
Is your upstream power level changing at all during this time ?
--
»www.VAJeeps.com

reply to dorkino
Gotcha. Well, I've kept an eye on the count, and normally it doesn't move. However, I just noticed a lag spike while gaming that resolved itself after about 10-20 seconds. The log showed a T3 timeout at this time, and both the correctable and uncorrectable codewords were increasing in realtime. Then another T3 timeout occured, according to the log. After a couple of minutes of this, the "storm" stopped. The correctable and uncorrectable codewords stopped increasing. The increase was about 25% during this period.

So it appears that my unusually high # of errors are occuring in short bursts that are spread out quite a bit apart. The numbers went from a couple hundred (which was received at startup), to over 100,000 correctable and over 1,000,000 uncorrectable overnight last night. It's now 12:30AM EDT here - the problem occured just 10 minutes ago at 12:20AM.

I wonder what it could be?

reply to dorkino
The error counts mean nothing. All that matters is the PERCENTAGE of total codewords that are uncorrectable. Before you were getting about 1 out of 20,000. The numbers are better now but still around 1 in 35,000, so I wouldn't assume that everything is okay. Mine are closer to 1 in 5,000,000.

reply to dorkino
Great.

reply to dorkino

reply to dorkino
Yes, those are very high. Signal levels are fine though. Try a "reset all defaults" then "restart" and see what happens.
--
»www.VAJeeps.com