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Author Topic: Ultra long VDSL2 link ?  (Read 644 times)

Weaver

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Ultra long VDSL2 link ?
« on: October 20, 2020, 11:40:47 PM »

My ~7.3 km line #2 is, so we worked out, supplied from a cab, and is not an EO line, unlike my other lines. Given that there is an FTTC cab right across the road, is there any reason why I could not have had FTTC VDSL2 ?

Is VDSL2 worse than ADSL2/ADSL2+ at ultra long distances?

I realise the sync speed might have been horrendous in terms of FTTC expectations but even if it was only 5 Mbps downstream plus whatever upstream that would have been a huge improvement. That cuts off 900 m or so worth of copper from the exchange along the main road to the green cabs at Harapul near the Claymore restaurant so it shortens the line if nothing else.
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burakkucat

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Re: Ultra long VDSL2 link ?
« Reply #1 on: October 20, 2020, 11:46:15 PM »

Is VDSL2 worse than ADSL2/ADSL2+ at ultra long distances?

Unfortunately, yes.

At first thoughts it's a good idea but, in practice, it will be a big failure.
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Weaver

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Re: Ultra long VDSL2 link ?
« Reply #2 on: October 20, 2020, 11:53:14 PM »

Why is that ? A quirk of the design of VDSL2 tuning it for the realistic use-case that it will be used in?

I would need to butcher a cab and put an ordinary ADSL2 DSLAM in it :-)
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burakkucat

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Re: Ultra long VDSL2 link ?
« Reply #3 on: October 20, 2020, 11:59:26 PM »

Attenuation is proportional to the frequency at which it is measured.

In the U.K., a VDSL2 circuit is configured with Profile 17a. I.e. the upper bound of the bandwidth is 17 MHz.
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Weaver

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Re: Ultra long VDSL2 link ?
« Reply #4 on: October 21, 2020, 12:16:48 AM »

So the higher tones wouldnít be used, but isnít that just equally true for ADSL2 ? Sorry if Iím being a bit dim here  :)
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burakkucat

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Re: Ultra long VDSL2 link ?
« Reply #5 on: October 21, 2020, 12:52:54 AM »

Sorry, I failed to mention the power cut-back that is applied to all VDSL2 circuits.

There is a unique CAL (cabinet assigned loss) calculated for and assigned to each & every PCP - fibre cabinet pair. The purpose is to protect all exchange originating ADSL2(+) signals from being swamped out by all the signals originating from the VDSL2 DSLAM.

The power of the VDSL2 signals, across the frequencies in common with the ADSL2(+) bandwidth, are reduced, i.e. "cut back", proportional to the CAL. Hence that at the point where the D-side cables exit the PCP, all ADSL2(+) and VDSL2 signals are at an equal power level.
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Weaver

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Re: Ultra long VDSL2 link ?
« Reply #6 on: October 21, 2020, 01:10:11 PM »

Ah. Iíve seen the power cut-back in graphs of VDSL2. So that would ruin the lower tones in an ultra-long vdsl used without sanity adjustment setup. The VDSL2 long-range thing used at in the trial at Tolastadh fo Thuath in the Isle of Lewis had no competing ADSL - it was a case of no ADSL and everyone on the new trial system, iirc.

So am I correct in thinking that VDSL2 is not inherently inferior, itís just the way it is set up in practice with the ADSL coexistence requirements?
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burakkucat

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Re: Ultra long VDSL2 link ?
« Reply #7 on: October 21, 2020, 03:05:45 PM »

So am I correct in thinking that VDSL2 is not inherently inferior, itís just the way it is set up in practice with the ADSL coexistence requirements?

Yes, that is correct.

Although approximately 900 m of the physical metallic pathway is taken out of the equation, the logical effect is re-instated by the power cut-back on the US0 and DS1 bands.
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Chrysalis

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Re: Ultra long VDSL2 link ?
« Reply #8 on: October 21, 2020, 04:20:39 PM »

There is a long reach variant BT trailed, I dont think they use it anymore though, that variant had no power cutback on the ADSL frequencies, and there may have been other bits of fine tuning as well.

But I think at extreme distances ADSL 1/2 are likely the best.
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burakkucat

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Re: Ultra long VDSL2 link ?
« Reply #9 on: October 21, 2020, 05:02:08 PM »

There is a long reach variant BT trailed, I dont think they use it anymore though, that variant had no power cutback on the ADSL frequencies, and there may have been other bits of fine tuning as well.

Yes, I remember that trial. (But not from personal experience.) I have a vague memory that a different profile was used (i.e. not 17a).
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j0hn

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Re: Ultra long VDSL2 link ?
« Reply #10 on: October 21, 2020, 05:40:15 PM »

Entering the telephone number of the line connected to the PCP in to the Broadband Availability Checker will give any VDSL estimates the line is capable of.

Any line that is too long to receive a viable service will have no estimates.

Given that there is an FTTC cab right across the road, is there any reason why I could not have had FTTC VDSL2 ?

How far is the FTTC cabinet in question from you?
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Black Sheep

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Re: Ultra long VDSL2 link ?
« Reply #11 on: October 21, 2020, 07:16:49 PM »

Entering the telephone number of the line connected to the PCP in to the Broadband Availability Checker will give any VDSL estimates the line is capable of.

Any line that is too long to receive a viable service will have no estimates.

How far is the FTTC cabinet in question from you?

Normally correct, but there are the odd occasions whereby the customers serving DP can be a few miles away from the actual premises, (obviously this will be in rural areas) and the checker will produce an estimated speed that will never, ever be attainable. 
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burakkucat

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Re: Ultra long VDSL2 link ?
« Reply #12 on: October 21, 2020, 07:29:18 PM »

How far is the FTTC cabinet in question from you?

Answering on behalf of Weaver . . .

The distance is that of a rambling and picturesque journey from the northern edge of Heasta all the way to Harrapul.
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Alex Atkin UK

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Re: Ultra long VDSL2 link ?
« Reply #13 on: October 21, 2020, 07:30:54 PM »

Answering on behalf of Weaver . . .

The distance is that of a rambling and picturesque journey from the northern edge of Heasta all the way to Harrapul.

Same distance as mentioned in first post I believe?  As in the cabinet is across from the one hosting his ADSL line?  We know its not across from the house!
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burakkucat

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Re: Ultra long VDSL2 link ?
« Reply #14 on: October 21, 2020, 07:45:00 PM »

Same distance as mentioned in first post I believe?

I've just checked with Google Maps and it declares a distance of 4.1 miles.
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