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Author Topic: BT LR-VDSL trial in Isle of Lewis  (Read 11728 times)

Weaver

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j0hn

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #1 on: August 20, 2016, 11:57:16 AM »

What's your current situation? I've picked up that you have 3 very long ADSL lines. Are you connected to an FTTC enabled cabinet that could benefit from this trial or just thinking ahead?
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Weaver

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #2 on: August 20, 2016, 05:41:26 PM »

Just thinking ahead. I have three 4.6 mile long EO lines. (EO for the moment, they will be putting in cabs in Broadford fairly soon, so I believe because FTTC is promised for the Broadford residents.

In Lewis, the tiny village of Tolastadh bho Thuath is very remote, at the end of a long string of townships stretching north up the east coast of the island from Steòrnabhagh, the capital. So it's a bit like Heasta where I live, but Heasta is much more remote, one of the most remote villages in Skye, because there's nothing at all, not even one house, along the four mile road from Broadford to me. So there must already be a green cab in Tolastadh, yet there's none right here, so they would have to get on and do that.

Anyway, here, we are permanently screwed unless someone runs five miles of fibre to Heasta from Broadford. (And there's no line of sight either, would need one or two intermediate nodes.) There's a horrible local long-range wireless ISP in the village, which is slow, unpredictably so, and I'm told by neighbours that it's hopelessly unreliable because there is no maintenance contract so faults go unfixed, violent storms just wreck the kit and it stays down.

There's an earlier thread in which Burakkucat, BlackSheep and I discussed the road to Heasta, complete with pics, map and details about the Broadford exchange.
    http://forum.kitz.co.uk/index.php?topic=16585.90
Unfortunately it's rather long and rambling, but skim through and there are some pics and geographic details. The post code is IV49 9BN which gives you number six in the village, a third of a mile south of me. I'm the first, northernmost house in the village.
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Weaver

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #3 on: August 20, 2016, 11:01:21 PM »

this is the road from my house to civilisation, DSL lines run alongside the desolate road for four miles, without even a tree, wall or house.
  https://www.facebook.com/SkyeShepherdHuts/photos/a.142739519215436.30671.142459132576808/687901248032591/?type=3&theater&notif_t=like&notif_id=1471709301616166
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Weaver

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #4 on: August 30, 2016, 03:47:15 PM »

I just read BT SIN 522 concerning LR-VDSL in the trial
     http://www.btplc.com/sinet/sins/pdf/STIN522v1p0.pdf

It seems very conservative, if I'm reading it right. Physical retransmission turned on in both directions, vectoring in downstream, altered power spectrum and SRA (hurrah)! It seems like just a load of modest, but welcome tweaks, rather than anything very new and space-age.

To qualify, you have to have better than 40 dB loop loss at 300 kHz. I'm not sure how the single 300 kHz frequency technique relates to my own “67 dB” at who-knows-what (weighted?) wide range of frequencies but being 37 dB shy of that figure doesn't sound like there's any hope at all for the likes of me.
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burakkucat

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #5 on: August 30, 2016, 04:09:41 PM »

Quote from: STIN 522 Issue 1 (c) British Telecommunications plc
2.2 LR-VDSL Line Selection

In order for a line to be selected for uplifting to LR-VDSL, the following criteria must be
met:

1) The D-side insertion loss (measured at 300kHz) of the line shall be greater than
12.5dB and less than 40 dB (both measured at 300kHz). Lines with a loss lower than
this will not benefit from LR-VDSL and will remain as a 17MHz vectored VDSL2
line.

2) The CP shall have confirmed to Openreach Product Line that they are prepared to
participate in the trial activity.

3) The CP provided CPE shall support Profile 8b operation and vectoring as defined in
G.993.2 [2] and G.993.5 [3].

A frequency of 300 kHz is equates to sub-carrier number 69 or 70.

300 kHz / 4.3125 kHz per sub-carrier ~= 69.6
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Weaver

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #6 on: August 30, 2016, 04:14:50 PM »

Apol., I meant that I wonder how the frequency-dependant attenuation summed over my whole frequency-range equates to the 300 kHz figure, ie the ratio of the attenuation figures obtained by the two methods. 
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burakkucat

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #7 on: August 30, 2016, 04:41:48 PM »

I sense that I have been somewhat opaque with my choice of words . . .

Please don't try to deduce the insertion loss at a particular frequency by performing a mathematical operation on the overall (summed) attenuation but consider how to measure that loss at the relevant sub-carrier(s).

I wonder how good an approximation for that value could be obtained by connecting, say, a Huawei HG612 to one of your three circuits and then harvesting the Hlog values --

xdslcmd info --Hlog

Then just look up the value for sub-carriers 69 & 70.

It's been a long time since I last used a 2Wire 2700HGV but I have a vague memory that they actually report the insertion loss at 300 kHz on their MDC page.  :-\
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Weaver

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #8 on: August 30, 2016, 05:12:45 PM »

Understood. I used to get some nice, per-bin numbers from my old Netgear DG834v3.

Btw, how is the overall attenuation reported by typical xDSL modems derived mathematically, that was the other half of my question? A straight summation, or weighted in any way?
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Weaver

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #9 on: August 30, 2016, 05:15:15 PM »

We are about the same size as Tolastadh bho Thuath in Lewis, where the LR-VDSL trial is going on. If we aren't, then we soon will be, at the rate of new house building. Actually, I wonder what happens if we outgrow the bundle? Something good, or something bad?

Hope they give us no less than the current lovely fat (0.9 mm² ?) copper which BlackSheep kindly looked up, iirc.
« Last Edit: August 30, 2016, 05:18:48 PM by Weaver »
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burakkucat

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #10 on: August 30, 2016, 09:11:45 PM »

Btw, how is the overall attenuation reported by typical xDSL modems derived mathematically, that was the other half of my question? A straight summation, or weighted in any way?

It is very much a mystery, one that we would very much like to know the answer thereto.
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niemand

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #11 on: August 31, 2016, 12:08:25 AM »

It's vendor specific I believe.  :)
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WWWombat

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #12 on: August 31, 2016, 12:25:54 AM »

It is very much a mystery, one that we would very much like to know the answer thereto.

Normally, I'd take that as a challenge, but I'm somewhat busy at the mo. I think @Ignition might be right - especially as we jump into VDSL2

To qualify, you have to have better than 40 dB loop loss at 300 kHz.
...
but being 37 dB shy of that figure doesn't sound like there's any hope at all for the likes of me.

We discussed the actual effect of the "insertion loss" requirements over on this thread.

The end result was that it ran at 10dB per km. So BT are aiming at this applying to lines of 1.25km - 4km of 0.5mm copper on the D-side.

I might be wrong, but I thought that original ADSL modems, when reporting "attenuation" usually gave the figure as measured at 300kHz. Not true, though, for ADSL2 or ADSL2+.
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Weaver

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #13 on: August 31, 2016, 12:31:27 AM »

@WWombat assuming that's true (good point btw) my reported attenuation didn't change by much when I went from ADSL1 to ADSL2. (No “+”.)
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niemand

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Re: BT LR-VDSL trial in Isle of Lewis
« Reply #14 on: August 31, 2016, 12:36:25 AM »

Both would be measuring attenuation in the same band so not surprising. Both ADSL 2 and ADSL 1 use the band up to 1.1 MHz.
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