In reply to a post by flipdee:

By that reckoning, would going up by 0.3mm nearly double the distance?

The ratio of resistance for copper wire of 0.4mm, 0.5mm, 0.7mm and 0.9mm is

150:100:50:30

That gives you a rough idea of how the distances would factor too, though obviously inversely to that ratio

Obviously capacitance and inductance play a part too, but in more complicated ways. I can only cope with ohm's law!

What would the largest cross sectional area of twisted pair cable be feasible?

Take a look in this (large) PDF, pages 90-92. That suggests 1.1mm for BT drop wire, to a variety of "CWxxx" standards.

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.

ADSL from the exchange is often described as an "alien disturber" which can't be cancelled. That means that vectoring won't be useful at those frequencies, though the actual frequencies will vary from cabinet to cabinet depending on the distance to the exchange. I suspect that one of the things the trials are meant to show BT is how they have to configure vectoring at each cabinet so it doesn't bother trying to work on the frequencies where ADSL is still active.

In reply to a post by Chrysalis:

I believe it wont fix crosstalk caused by things such as split and damaged pairs. In other words it doesnt fix a physically broken network.

It ought to be able to fix any crosstalk (ie signal from other lines) that behave in a predictable, constant manner. But it can't fix noise from any other source (arc'ing, intermittent contact or RFI), whether that is "normal" noise, or noise from a fault.

So if the failure makes a line susceptible to crosstalk in general, vectoring will work. If this additional impact varies over time (such as when the wind blows), then vectoring can't have much effect.

If the failure makes the line susceptible to other forms of noise, with sources other than crosstalk, then vectoring isn't in a position to help at all. That still has to be left to the existing forms of DLM.

So, does a line fault tend to generate its own noise, or magnify crosstalk specifically? I don't know the answer, but I suspect it is the former.

In reply to a post by Chrysalis:

if its too young how have others had it deployed already?

The technical leader in vectoring is Alcatel-Lucent, and they do have some equipment deployed, particularly in Belgium. But it isn't really in full-blown use yet - with the first area going live 2 weeks ago.

The Belgians aren't going to tax it too strongly at first - with "up to 70Mbps" their first aim.

Swisscom should be going live around now, with Germany later this year.

Other vendors are behind the curve on this one - Huawei a little behind and ECI further behind. This impacts the operators they have sold to, such as BT.

It is unfortunate, for us, that BT have chosen suppliers who aren't quite up to speed.

there is commercial products on the market both dslams and modems that have the technology, its not something thats still in the labs only.

Both are out there for sale, so it is definitely past the "lab-only" stage.

But, while the plugfests started up 18 months ago, and the vendors were added into the schedule a year ago, they are still going on (next one in April).

Presumably, the vendors such as Alcatel are taking a punt that their hardware is up to scratch, and any fixes can be handled with firmware changes alone.

Simply its BT just been slow again and trying to rollout FTTC on the cheap.

Well, BT started to plan the FTTC rollout in 2008, and actually had equipment out in 2009. The main project was running in 2010, with 1.5m premises passed in the summer. By the end of 2011, they'd passed 7m premises, with around 19,000 cabinets.

Meanwhile, vectoring was approved by the ITU in April 2010, when BT were already in flow.

By the end of 2011 (when BT had 19k cabinets rolled out), the chipset manufacturers had just held their second plugfest, but the system vendors hadn't had any inter-operability tests at all.

Could they deploy faster? Certainly... they could have deployed untested equipment which had no certainty of working in the field. However, BT are certainly too conservative on that front. But I don't think that has held anything up so far.

Of course, they might yet choose to delay things *after* the vendors are ready.

I suppose they could have held back, and not deployed any cabinets at all.

I think they skipped over it because originally they were expect a decent FTTP rollout to go along with it and perhaps planning to migrate FTTC to FTTP as well, but their FTTP problems probably means FTTC is more long term than originally planned and now because of that they started looking into vectoring

I suspect that is a conspiracy theory too far.

Certainly, BT were touting vectoring as the way to get >50% of premises to 100Mbps in Jan 2012... and in the same meeting, were still talking about FTTP as being the "large-scale" deployment. The cutback hadn't happened at that point

In reply to a post by Ignitionnet:

I took those stats the day after the install, I'm pretty sure FEC was in use at that time and was activated overnight.

I guess it is hard to tell, because this upstream usage of FEC doesn't appear to be triggered by DLM.