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Topic # 159903 16-Dec-2014 18:38
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I was looking for info / calculations on the possibility of a VDSL connection for a client. I had been told no by an ISP but wanted to know how bad  / good the signal was.

I found this link:

Given the downstream Attenuation it gives you a rough estimate of distance to cabinet, ADSL, ADSL 2 and VDSL speeds possible.

Being a newbie to figuring out VDSL signals I'll also put what else I think I've discovered here:

Attenuation is the reduction in signal strength on your line, sometimes also refered to as "loop loss". - Lower is good. Should be ideally under 20dB

SNR - signal To Noise Ratio - Higher is good.

A good graph to get a guide on attenuation vs distance vs speed / dsl type is found here:

A good explanation of how it hangs together is found here:

Chorus capability map found here:

and of course steves info on fixing line issues.



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'That VDSL Cat'
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  Reply # 1198580 16-Dec-2014 18:42
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Things to be aware of, all of these links are based off dsl networks in other countries Where they would operate with different line profiles and such.

While its good for a rough estimation, ild be careful about taking it for anything more than that..

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  Reply # 1198593 16-Dec-2014 19:21
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SNR - signal To Noise Ratio - Higher is good.

Modems typically don't report SNR, even if they label it SNR. What most modems report is noise margin which in layman's terms is the difference between the wanted signal and the background noise.

xDSL equipment sets a noise margin and the negotiates the maximum line speed possible while maintaining that margin. Chorus gear on a normal profile is set to 12dB, so if you see a slightly lower value reported (say 11dB) it means the background noise on the line has increased slightly since the line speed was negotiated - opposite is also true.

A lot of ULL gear uses a 6dB margin - basically sacrificing a little robustness for increased line speed.

So with reported noise margin (often labelled SNR), it's not a case of higher is better, but a tradeoff between reliability and speed - some modems will let you force the SNR way down, increasing your speed, but also increasing reliability problems.

The closer your reported noise margin is to the target the better - it means the line is stable.

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