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New docsis 3.1 gateway and 1 downstream channel problem

Contributor

New docsis 3.1 gateway and 1 downstream channel problem

So I have been using a new Technicolor XB6 gateway for a couple days. In the admin 10.0.0.1 page I saw I have 1 downstream channel out of 29 channels that the SNR is only 15 on that 1 channel. All others are minimum 40.4 - 41.7. Also, on this channel 25 the QAM instead of showing 256 like the other channels it says "other". <br>I have had a tech out to my house just last month who said everything is perfect when I complained about tv pixelation few times a week which, after he replaced connection terminal at pole, went away. He shook the wire going to my house afterwards HARD and zero issues with any of my services(triple play). He said That he never sees stronger or clearer signals as mine using his signal reader at house. Other techs have said same. I have had everything checked and replaced from pole connection in my yard to house and every splitter and cables inside. Why this channel 25 showing so low a SNR with QAM as "other" now? After a reset, immediate corrected codewords of over 8K instantly. I checked these readings to make sure I had no uncorrected codewords and I don't.<br>But, my previous Arris TG1682G gateway had great SNR and power levels but always developed multiple corrected and uncorrected codewords in 3-4 days.<br>Any Comcast employee that can help me here? I'd greatly appreciate help with this channel 25, out of now showing 29 locked downstream channels, and low SNR and QAM of "other".<br>Thanks.

Accepted Solutions
Expert

Re: New docsis 3.1 gateway and 1 downstream channel problem

@Neverendingmods,

I conversed with a Comcast engineer who reports that your weird SNR value is an anomaly. "If it’s in the OFDM carrier, it’s a reporting issue, not an actual issue." He analyzed your modem signals and its communication with the CMTS:

 

neverendingmods1.pngneverendingmods2.png

 

The conclusion is that your modem is reporting weird stuff, but it all looks fine on the back end, which is what really matters. 

 


All Replies
Expert

Re: New docsis 3.1 gateway and 1 downstream channel problem

DOCSIS 3.1 modems utilize a channel known as the OFDM channel. The easiest way to identify this channel is that the modulation type will be displayed as “other”. It’s normal for the OFDM channel to have correctables and uncorrectables, it is not a cause for concern. 

Expert

Re: New docsis 3.1 gateway and 1 downstream channel problem

FWIW, no downstream channel should ever have an SNR that is only 15 dB.
Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

Thanks so much.
Expert

Re: New docsis 3.1 gateway and 1 downstream channel problem

FWIW, if that channel is still showing a low SNR, there is a problem with noise ingress on it..

Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

What could be the cause? I have had techs out and I am told everything is perfect. That they never see better signal quality as mine going in and out of my house.
Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

2 replies and they contradict each other. Is it ok or not?
Expert

Re: New docsis 3.1 gateway and 1 downstream channel problem

@Neverendingmods

Can you post a screenshot of your levels, please? Also, pls check your PMs.

 

Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

Let me try to take a screenshot. I never did it before,lol.
Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

Here it is.
Screenshot_2018-04-10-11-59-58.png
Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

Try this.
Screenshot_2018-04-10-12-05-09.png
Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

Now my primary and secondary IPV6 DNS addresses are completely blank. I did a Comcast speed test and IPV6 passed with average speed this time of day.
Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

Getting uncorrected error codes now on the mid channels.
Screenshot_2018-04-10-12-15-24.png
Expert

Re: New docsis 3.1 gateway and 1 downstream channel problem

Screenshot.png

 

FWIW, that 14.9 SNR is not normal.

Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

I wish a Comcast employee would step up and resolve this. I just had a tech out 4-5 weeks ago who checked everything inside and out, even replaced the terminal at pole my cable connects to. Said my levels are "perfect". He called someone on phone and complained how he sees nothing wrong at my house, his supervisor I guess, and told me I was SOL as if he sees nothing wrong at my house he won't escalate the situation further. I asked "even if I keep calling?. And he said "doesn't matter" I see nothing wrong to have any further assistance granted. He was a jerk.
Expert

Re: New docsis 3.1 gateway and 1 downstream channel problem

@Neverendingmods,

I conversed with a Comcast engineer who reports that your weird SNR value is an anomaly. "If it’s in the OFDM carrier, it’s a reporting issue, not an actual issue." He analyzed your modem signals and its communication with the CMTS:

 

neverendingmods1.pngneverendingmods2.png

 

The conclusion is that your modem is reporting weird stuff, but it all looks fine on the back end, which is what really matters. 

 

Expert

Re: New docsis 3.1 gateway and 1 downstream channel problem

FWIW, If that is supposed to be their modem's readout, that 693 MHz channel is not even listed there.

Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

Thanks man. I guess I need to chalk it up to a new to the public gateway that needs some firmware updates to correct the odd readings. Because no one who looks into my signals can ever find a problem. And I'm not having reboots yet with this new gateway or wifi drops that would indicate a problem with service at this point.
Thanks for having this checked out for me.
Contributor

Re: New docsis 3.1 gateway and 1 downstream channel problem

EG, that channel 25 not showing up on that readout would back up nerd's statement that ....
DOCSIS 3.1 modems utilize a channel known as the OFDM channel. The easiest way to identify this channel is that the modulation type will be displayed as “other”. It’s normal for the OFDM channel to have correctables and uncorrectables, it is not a cause for concern.
Expert

Re: New docsis 3.1 gateway and 1 downstream channel problem

I know all of that about DOCSIS, it's not my first rodeo. I don't see how it not being listed "backs anything up". Whatever. As long as you're happy that's all that matters !!