In reply to a post by Brookzy:

So essentially a 25% loss in attainable downstream. Staggering.

Even more of a loss up. Good isn't it?

Hopefully Openreach will lay down the law service agreement and ensure only approved modems are used!

In reply to a post by Brookzy:

So essentially a 25% loss in attainable downstream. Staggering.

Yup.

I wonder how effective vectoring is? Does it wipe out the crosstalk or only mitigate it?

The Broadband Forum (industry group) has this description of vectoring. Figure 6 shows their figures for the difference between vectoring (red circles) and non-vectoring (blue crosses and, worst case, blue triangles).

Note for those blue crosses: My current BT estimate gives two speed ranges for my 350m line. The best estimate is 60-80 - which maps to the region covered by the bottom 50% of the blue crosses, while the lower estimate is 41-70 - which is from the lowest blue triangle to the lowest blue cross.

Vectoring, in theory and in limited practice, can make a huge difference. Whether it will work well live in BT's network depends on both BT's network, Huawei's (and ECI's) implementation, and the other interference left after crosstalk is removed.

In reply to a post by R0NSKI:

Didn't Plusnet say is wasn't as effective as they had hoped, I'm sure there is a thread about the trials on their forums.

There was indeed a thread, and the quote gave numbers lower than we would have liked (of the order of 10 Mbps IIRC), but the author seemed quite happy with the effect and the quote itself was (it seems) fairly rough-and-ready. On going away for more details, I imagine the author was told not to reveal anything more until BT were ready.

It could have been that Huawei's implementation isn't ready for the limelight yet, and it could have been that the chosen sites were a particular problem (chosen, IIRC, for the expected impact of external RFI).

BT have been very quiet on the results of the trial. I wonder when we'll hear?

BTW, I've seen that a BT engineer is due to talk about the results of their G.fast trial in April in Paris. Surely we'll hear about vectoring before that one!

Interesting report. Added to the reading list.

Figure 6 - DS Rates Profile 17a, 26 AWG, -136 dBm/Hz noise, 80 users, and 47 cancelled

So crosstalk will still exist among the other 33 then? Makes the improvement even more impressive.

Judging by their data my current 58 Mbps sync could be increased to beyond 70 Mbps with vectoring.

Without wanting to be Captain Hindsight, BT's omission of vectoring from the outset seems a bit myopic!

In reply to a post by Ignitionnet:

Even more of a loss up. Good isn't it?

Were the "before" figures using FEC? Both the "after" figures are using 6% of the bandwidth for error correction, even though no interleaving is in use.

(R=16/N=254)

Vectoring is too young to have been deployed before now.

VDSL2 was standardised in 2006, while vectoring was only approved in 2010. The chipset manufacturers are still ironing out interworking problems at plugfests.

As for the 80 users vs 47 cancelled, I agree... but it is probably more complicated than that. Often a cable has its pairs broken down into groups, known as binders. The 47 that are cancelled are probably within the same binder as "ours" (total 48), which is the same set of wires that twist around each other. The other 32 will be in different binder(s) in the cable.

Pairs in the same binders are the ones that are likely to have the biggest impact.

Note too that the graph is for 26AWG cable, which is 0.4mm. Our D-side is more likely to be 0.5mm. Adtran reckon that the extra 0.1mm improves range by a factor of 1.3

This Adtran presentation shows more. Page 35 has something on binders, while page 42 shows the importance of cancelling every other line.

Excellent post WWWombat,
By that reckoning, would going up by 0.3mm nearly double the distance?
What would the largest cross sectional area of twisted pair cable be feasible?
There doesn't seem to be a huge selection of heavy gauge twisted pair cable.
The other thing I don't see much mention of is how adsl on adjoining cables effects vectoring?
Obviously the adsl signal will have a degree of separation.
Cheers,
Flipdee

Edited by deleted (Wed 05-Mar-14 06:25:48)

some other news?

earlier this week openreach and plusnet decided to fix my issue by reducing my speed estimate, brilliant.

Openreach acknowledged that in multiple engineer visits engineer's ignoring failing HR tests and failing to even swap out faceplate/NTE5 was a fail, but they otherwise insist a 40+% loss of dsl signal is perfectly within parameters.

Basically senior openreach management have now admitted to me as long as the remote tester unit tests ok there is 'zero' justification for doing any manual physical checks on 'any' part of the line. Quality control and pride doesnt mean anything in that corporation.

Im not convinced my speed loss is all down to crosstalk its much more than what most people report.

to rub salt into wounds my neighbour was activated also within the past week and he has a decent margin on a full 80mbit sync, is in same building as me.

I'd get a new line provision with fttc, wait till full 80Mbps on it, then tell them to stick their original line and fttc connection up their proverbial.