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Author Topic: Free speed upgrade for BT Infinity 1 customers to 80/20  (Read 16609 times)

gt94sss2

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #60 on: October 04, 2017, 06:07:49 PM »

Of course,

VDSL gets BT Infinity 1
g.Fast gets BT Infinity 2, BT Infinity 3 and BT Infinity 4
FTTP gets BT Infinity 1, BT Infinity 2, BT Infinity 3 and BT Infinity 4

looks more elegant

I thought that there were only 2 g.fast speed tiers?

If so, that would be:

VDSL gets BT Infinity 1 and lets not forget about Unlimited Faster Broadband
g.Fast gets BT Infinity 2 and BT Infinity 3
FTTP gets BT Infinity 1, BT Infinity 2 and  BT Infinity 3

On a more serious note, BT have been saying for several years that they want to differentiate BT Broadband on service and quality rather than cost (for which they have Plusnet) - and its not the first time that BT Retail have upgraded the speed of their customers.
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Ronski

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #61 on: October 04, 2017, 08:30:24 PM »

I've just spotted a comment on ISP Review dated 1 September, which seems to make a lot of sense why they'd change Infinity 2 to G.Fast

https://www.ispreview.co.uk/index.php/2017/09/330mbps-g-fast-pods-appearing-broadband-delivery-uk-areas.html#comment-181122

OK it's only someone's opinion but it does make sense from a marketing perspective.

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WWWombat

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #62 on: October 05, 2017, 11:31:59 AM »

I guess there's a temporary limit as to how much they want to promote G.Fast too - with the pods only capable of supporting 48 subscribers instead of the ultimate 96.
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kitz

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #63 on: October 06, 2017, 01:53:36 AM »

That section suggests that the best way to set access rules (ie in the ANFP) is by specifying spectral limits rather than explicit modem settings. ie by PSD masks. It further says that the UK & Dutch rules are set using PSD masks, and then explains that the UK rules are based on line length from the cabinet.

So I went back to the ANFP, to find there is a "Part C" that describes the PSD mask for CPE placed at the NTE. Within a single graph, it seems to include PSD restrictions that apply simultaneously for exchange-based ADSL (with 5 named configurations, dependent on line length: "ushort", "eshort", "short", "medium", "long") and for cabinet-based VDSL2 (with variations based on "kl0").

Ahhh  thank you for that -  So I was on the right track & my memory wasnt that bad then when I said. 


I could be wrong, but I just assumed this was something to do with line length in a similar way that differing spectral masks are used for some of the tones in D1 shared with adsl which are based on cab location from exchange.  From memory theres several (5?) different masks in use based on line length from cab.
If so then neighbouring lines of similar length should have little impact because they should have a similar [upstream] PSD mask.


Its just that there are more available U1 masks than there are for D1.   Perhaps I could have worded it better,  but if you re-read, you can see I was aware of the 5 D1 masks based on cab location, and was assuming that another (5?) applied for UPBO based on loop line length between the cab and NTE.

Quote
The ANFP Part C suggests that the upstream PSD mask varies for kl0 values between 0 and 24, suggesting that UPBO has an effect for cables up to 1.2km.


Nice find...  and even better detective work on putting together some kl0 values.  :thumbs:

I'm trying to put together all that info along with that in the white paper. 
So in summary have I got this right

  • D1 has 5 available PSD masks based on cab location from the exchange.
  • U1 has 10 available PSD masks up to 1200m based on line length
    (The white paper gives an example for 7 different lengths up to 1500m).
  • U2 has 4 or is that 5 available PSD masks up to 400m based on line length.

[edited in an attempt to clarify]
« Last Edit: October 06, 2017, 02:19:21 AM by kitz »
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kitz

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #64 on: October 06, 2017, 01:56:41 AM »

PS
I also noticed this in section 3 of the white paper
Quote
UPBO is only meaningful for upstream frequencies that are strictly separated from downstream frequencies, in
combination with topologies where nearby and distant customers served via the same cable are very different in
distance [7].

I guess that then covers my earlier doubts about any differing lengths perhaps occurring in the same bundle.  What's your take on the tie pair at the cab?
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WWWombat

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #65 on: October 06, 2017, 05:36:10 PM »

Yes, it does come back to you being right about how it works. I'm happy to think I've got a good handle on how UPBO gets configured now.

However, I still think there are ~25 masks downstream, and an infinite number upstream. More than are shown in the graphs, at any rate.

Let me think about your questions & get back later...
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WWWombat

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #66 on: October 08, 2017, 06:53:28 PM »

I just tried putting the ANFP upstream formulae into a spreadsheet, to come up with my own example graphs. Here are a few, which I think shows that the graphs can vary as much as kl0 can vary.

If kl0 is restricted to integers, then there are 25 masks. If kl0 can hold any real value, then the number of possible graphs goes up.

Here are some examples...
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WWWombat

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #67 on: October 08, 2017, 07:06:41 PM »

This graph shows that the mask in U1 maxs out around kl0=23.5.

My conclusion is that the ANFP really specifies modem behaviour in the formulae in the table; the graphs are just a few examples made using those formulae.

For upstream, I don't (yet) know how many decimal places kl0 can be calculated to (the formulae in the table runs to 5 significant figures). But we do know that the table copes as it varies between 0 and (just under) 24.

Individually, and slightly more accurately, it looks like U1 changes as kl0 varies over a range of 0-23.6, whereas u2 changes as kl0 varies over a range of 0-8.5.

For downstream, we know that CAL can vary from 0 to 52, but only in integer steps of 2, so we know there are exactly 27 graphs there.
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WWWombat

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #68 on: October 08, 2017, 07:15:28 PM »

PS
I also noticed this in section 3 of the white paper
Quote
UPBO is only meaningful for upstream frequencies that are strictly separated from downstream frequencies, in
combination with topologies where nearby and distant customers served via the same cable are very different in
distance [7].
I guess that then covers my earlier doubts about any differing lengths perhaps occurring in the same bundle.  What's your take on the tie pair at the cab?

The first restriction seems strange. Surely VDSL2 only works where upstream and downstream bands are separated anyway, never mind the UPBO tweaks? However, if you did allow overlap, then the ensuing NEXT would be made even worse if you tried to reduce upstream power via UPBO.

The second part is a condition that we obviously meet through the tie pair, if no other part.

I tend to think that most crosstalk happens where power is the highest, and so the electrical field is at its greatest. That would mean FEXT is induced most at the DSLAM (and thus in the tie pairs), and least in the drop wires.

It also means that you'd expect less crosstalk where the tie pairs are shortest.
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ejs

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #69 on: October 08, 2017, 08:12:35 PM »

For downstream, we know that CAL can vary from 0 to 52, but only in integer steps of 2, so we know there are exactly 27 graphs there.

I don't think what it says in the ANFP document means that those are the only values of CAL.

The range and precision of kl0 is defined in ITU-T G.997.1, "The value ranges from 0 to 128 dB in steps of 0.1 dB".
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WWWombat

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #70 on: October 08, 2017, 10:53:30 PM »

I don't think what it says in the ANFP document means that those are the only values of CAL.

So there could be more than that? By being outside the range 0-52, or by taking values that aren't in 2dB steps?

For a normative section, part B of the ANFP is pretty vague about the range. It clearly mentions the 0-52dB in 2dB steps, but it only actually specifies that range as important for the "critical intersection points" on the graphs, not as a definitive statement of the complete range.

The range and precision of kl0 is defined in ITU-T G.997.1, "The value ranges from 0 to 128 dB in steps of 0.1 dB".

Thanks. I guess, then:
- That limits the worthwhile upstream PSD graphs (max 24dB) to be approx 240 in number.
- A maximum of 128dB will be roughly equivalent to 6.4km of 0.5mm copper.
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Chrysalis

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #71 on: October 09, 2017, 02:57:42 AM »

I guess that then covers my earlier doubts about any differing lengths perhaps occurring in the same bundle.  What's your take on the tie pair at the cab?


The first restriction seems strange. Surely VDSL2 only works where upstream and downstream bands are separated anyway, never mind the UPBO tweaks? However, if you did allow overlap, then the ensuing NEXT would be made even worse if you tried to reduce upstream power via UPBO.

The second part is a condition that we obviously meet through the tie pair, if no other part.

I tend to think that most crosstalk happens where power is the highest, and so the electrical field is at its greatest. That would mean FEXT is induced most at the DSLAM (and thus in the tie pairs), and least in the drop wires.

It also means that you'd expect less crosstalk where the tie pairs are shortest.


yep and remember what happened to my line when they reordered my tie pairs.  Massive change in crosstalk levels.
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GigabitEthernet

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #72 on: October 09, 2017, 03:49:30 PM »

I sync at 54997, will I get this? I won't get much more than that.
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WWWombat

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #73 on: October 09, 2017, 10:52:23 PM »

I'm happy to think I've got a good handle on how UPBO gets configured now.

Famous last words, eh?

It seems that UPBO can take two forms, and the one we've been discussing here (and, it appears, that BT uses) is a static model.

There is also a dynamic mode, where the DSLAM can make adjustments to subscribers on the fly. I haven't assimilated the details as yet - there doesn't seem to be much point if BT aren't using it!

Source? There is an interesting document, "Guidelines on the Use of DSL Transmission Systems in the BT Access Network", ND1405 rev 4.1.1.

As a whole, the document covers how different DSL systems meet (or don't meet) the ANFP. Section 6.11 is for VDSL2, and includes information about DPBO, static UPBO and dynamic UPBO.

yep and remember what happened to my line when they reordered my tie pairs.  Massive change in crosstalk levels.

I don't recall that, but it doesn't surprise me.
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Chrysalis

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Re: Free speed upgrade for BT Infinity 1 customers to 80/20
« Reply #74 on: October 10, 2017, 12:36:49 AM »

Check my saga here.

http://forum.kitz.co.uk/index.php/topic,20191.0.html

Sorry for the delay got distracted after starting the reply.

The short story if you dont want to read the thread is that a car flattened my cab, openreach had to redo all the tie pairs and feed new power, after work was done my stats were much more favourable. 10-30mbit increase on attainable for DS.

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