Kitz Forum

Broadband Related => Broadband Technology => Topic started by: Westie on March 05, 2018, 02:38:28 PM

Title: SNR/Tone
Post by: Westie on March 05, 2018, 02:38:28 PM

For some time I have noticed a sawtooth pattern on my SNR/Tone graph. At first I thought it might be due to interference from a DECT phone, but unplugging the phone and connecting the modem/router to the master socket eliminated that as a source.

Then I compared the results with others on MDWS (which is now in its final few days), and it seems to me that everyone reporting from the UK that is on Vectored VDSL shows a similar pattern above a SNR of 40-45dB.

It would appear that Vectoring introduces the phenomenon. I have no idea why or how it happens, and I only mention it now out of interest.

Title: Re: SNR/Tone
Post by: konrado5 on March 05, 2018, 02:44:36 PM

Could you attach your SNR/tone ?

Title: Re: SNR/Tone
Post by: Westie on March 05, 2018, 03:55:01 PM

Quote from: konrado5 on March 05, 2018, 02:44:36 PM

Could you attach your SNR/tone ?

I think it's attached! :fingers:

Edit: changed attachment to more recent & better formatted version

Title: Re: SNR/Tone
Post by: konrado5 on March 06, 2018, 11:41:00 PM

Have you got vectoring on upstream? On upstream I don't notice sawtoogh pattern.

Title: Re: SNR/Tone
Post by: Westie on March 07, 2018, 12:29:11 AM

Line stats Report Vectoring status as '1 (VECT_FULL)', or as '3 (VECT_RUNNING)', and seems to toggle between the two every few minutes.
It's not clear if it is applied only on the downstream or on both, but since the SNR on the upstream is below 40dB I wouldn't expect to see the pattern there anyway.

Title: Re: SNR/Tone
Post by: burakkucat on March 07, 2018, 12:58:34 AM

Quote from: Westie on March 07, 2018, 12:29:11 AM

. . . but since the SNR on the upstream is below 40dB I wouldn't expect to see the pattern there anyway.

I am intrigued. What is so "magical" about 40 dB that it is the level where "things happen"?  ???

Title: Re: SNR/Tone
Post by: Westie on March 07, 2018, 01:32:00 AM

I don't know! I'm only going by my observations of others' stats.  :puzzled:
I haven't a clue what causes it in the first place :no:

Does any else? :shrug2:

Title: Re: SNR/Tone
Post by: burakkucat on March 07, 2018, 07:28:33 PM

Quote from: Westie on March 07, 2018, 01:32:00 AM

I don't know! I'm only going by my observations of others' stats.  :puzzled:

Ah, so just an observation.

Quote

I haven't a clue what causes it in the first place :no:

Does any else? :shrug2:

I don't think so. Certainly I have no idea.

Title: Re: SNR/Tone
Post by: ejs on March 07, 2018, 07:37:47 PM

This is purely speculation, but I guess it's either that the vectoring isn't quite cancelling out all the crosstalk noise and leaving some residual noise making that shape on the graph, and/or something to do with some modems connected to the cabinet not supporting vectoring or not doing vectoring very well.