US Cable Support > Comcast HSI > Modem developing an affinity for 1 of 4 downstream channels

Modem developing an affinity for 1 of 4 downstream channels

I also have the first channel bearing the higher amount of usage, and my SB6121 has been working without problems for the last 3 months. I get the provisioned speeds when I speed test. Perhaps the modem uses the first channel as the default channel and if a small file is being downloaded, the modem doesn't have a chance to send much on the other channels.

reply to dorkino
Not seeing this on my SB6120.

reply to dorkino
If you look at the Configuration tab in the modem admin pages, you will see a category called "Favorite Frequency", and most likely that "Favorite Frequency" will be the one that you see being given preference.

My 6120 is evenly split between the channels. I think that 'favorite frequency' just means the first one it tries on a reboot. Just like a non-D3 modem, it just remember that last one used. Once it makes the connection, it is then assigned the other channels.

I wonder if the 6121 is counting ARP traffic or whatever that may only travel over the primary channel, but the 6120 isn't.

FWIW, the UCD (Upstream Channel Descriptor) information that the modem needs to know in order to establish the frequency of the return / upstream channel to talk back to the CMTS on is contained on that favorite channel. It is my understanding the the UCD data is not present on all the forward / downstream channels on a system, just certain ones.

reply to dorkino
What's also strange is that, while the Total Unerrored Codewords shown for that one channel is over 50 times greater than the others, the Correctable and Uncorrectable codeword counts are not that much different from the other channels.

That would indicate that the error rate is therefore about 50 times less than the other 3 channels, yet the estimated SNR (which, I believe, is calculated from the error rate) for that channel is shown as being the same (37 dB) as the others.

To me, it seems that there is some problem with the display of the Total Unerrored Codewords count for that first channel/column.

Well the errored codeword count happened directly after reboot. I don't think they've increased at all in the 13 days the modem's been online.

Favorite frequency is, in fact, 669000000Hz.

Yeah, with the Motorola SB61XX modems, it's typical that they display about several hundred to a thousand Uncorrectable Codewords for each channel right after it boots up. After that, the Correctable and Uncorrectable errored codeword counts will normally slowly increment if you're getting good downstream signals.

On my SB6121 modem, the Total Unerrored Codewords counts are roughly the same, as well as for many of the SB61XX signal page screenshoots I've seen posted in this forum, though a few of them have shown one channel having a count of up to twice as much as the others.

As the errored codeword counts for your modem look good, and you say it's operating OK, I wouldn't worry about that anomaly.

Come to think of it, I don't recall ever seeing this happen prior to the most recent firmware push that I received a few months ago. Maybe it's related; maybe not.

Model Name: SB6121
Vendor Name: Motorola
Firmware Name: SB_KOMODO-1.0.6.8-SCM01-NOSH
Boot Version: PSPU-Boot(25CLK) 1.0.12.18m3
Hardware Version: 5.0
Serial Number: (redacted)
Firmware Build Time: Aug 30 2012 15:35:46

But, yeah, you're right. I'm not really concerned about this... just curious is all. Thanks everyone for your input.

FWIW, for about the past week, my SB6121 has been showing a preference for the highest frequency channel (not the "Favorite Frequency"). I suspect that it is just random chance based on how busy each channel is.
         

reply to dorkino
My current SB6121 is even on all four channels, but I frequently noticed one being higher than the rest on my previous SB6120.
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KI6RIT

reply to dorkino

reply to dorkino

reply to plencnerb
It's not unique to a specific modem brand; I have a different ARRIS cable modem (WBM-760A) than plencnerb and it has a similar-though-different affinity; if anything, I suspect CMTS differences AND modem chipset differences are in play.