In rural areas it's more likely than not cabinets are connected to a different exchange. For instance, in Charlbury (Oxfordshire) where I've moved to and there is a local exchange (with LLU), the fibre cabinets are connected back to Witney. Almost certainly that is the case with most of the half dozen or more smaller exchanges in the area.

I only know as there's an OR jointer in the local pub. He gives quite an interesting, if colourful, insight into what's involved. It appears a jointer is a few stages up the ladder from the customer engineers that visit houses to fix problems (or maybe that's just an impression he's giving me).

It appears a jointer is a few stages up the ladder from the customer engineers that visit houses to fix problems (or maybe that's just an impression he's giving me).

Buy him another pint and leave him mumbling his rubbish in the corner

It's because VDSL2 uses higher frequencies (so it doesn't overlap with those used by ADSL which would cause interference). Unfortunately, whilst those higher frequencies can carry more data (as there's more bandwidth), they don't travel as far before the signal is so attenuated as to be useless.

There is a slight proviso on that. If a cabinet is a long way from the exchange, some of the ADSL frequencies are so attenuated as to be useless, and the cabinet an reuses some of those lower frequency (and hence more usable at distance) frequencies. Unfortunately this means if you are a long way from you exhange and the cabinet is next to the exchange, you get the worst of all worlds. In that case VDSL will very likely be worse than ADSL as the latter has all the useful "long distance" low frequencies.

The power profile that can be used by a cabinet across the frequency range is called the PSD and it does vary according to the cabinet-to-exchange distance.

Edited by deleted (Mon 09-May-16 09:58:32)

There is an important but subtle point here regarding the ANFP (and which will impact directly on speed calculations). It also means this scenario (cabinet close to the exchange with the customer 2-3km away by "wire distance") will have considerably worse outcome than if you 2-3km from a cabinet which is, itself, perhaps 3km from the exchange.

That point is that the Power Spectrum Density (PSD) mask alters according to the distance from the exchange (in electrical terms - broadly wire length, but subtly altered by wire gauge and other factors). What happens is that the further from the exchange the more of the ADSL frequency range becomes reusable by VDSL (as the higher frequency ADSL bands drop out of usability as the distance from the exchange increases).

What this means is that a VDSL speed assessment based solely on the distance to cabinet and ignoring the cabinet to exchange distance is misleading. The OR systems ought to take account of this in their estimate.

So, the bad news is that if you are on a modest length EO line (say 1.5-2km) and there's been a new cabinet put in next to the exchange then your VDSL service could well be worse than your ADSL speeds.

It's more common in rural areas yes, but I don't live in a rural area. Not remotely.

It seems maybe they've done it so that in future they at least have the option to close down some of the smaller exchanges. We have exchanges here with over 9000 lines (not small then), but they aren't fibre headends.

In reply to a post by BatBoy:

I didn't know it was common, in fact I didn't know it was possible until this thread, as you may be able to see from my earlier replies.

No I didn't interperate your reply like that at all. I would have just assumed you'd know anyway.

Edited by deleted (Mon 09-May-16 10:13:03)

I'm sure it's more widespread than just rural areas, just that is the most obvious situation and one which I'd garnered some knowledge about. Obviously in larger towns with more than one exchange it also makes sense.

I can see the logic of being about to retire many local exchanges by fibre hosting from fewer, large ones. But I also think that the problem of retiring all the E-side copper are enormous. It means everybody will have to be on some form of BB or cabinet-based voice service. We are surely a long, long way from that. There's all those LLU MSANs which require copper, and the future of those is beyond BT's powers to decide. Then there is the reliability/resilience issue. Given the inherent complexity of broadband, the number of elements (and parties) involved, getting PSTN-level availability of voice is extremely difficult (although if Ofcom were to recognise that fixed & mobile voice provide a resilient solution together that could surely be relaxed).

So I think this is a distant twinkle, and if significant E-side copper was to be retired by (say) tend years' time, there would have to be regulatory approval now along with detailed technical solutions. However, I can imagine OR trialling the concept in some areas where LLU isn't a complicating factor. It doesn't even need to be a whole exchange.

In reply to a post by TheEulerID:

It's because VDSL2 uses higher frequencies (so it doesn't overlap with those used by ADSL which would cause interference).

That statement is wrong.

VDSL tends to start at Tone7 on the upstream (0) which is 30.1875 kHz with downstream starting at tone 33, 142.3125 kHz.

ADSL2+ Uses up to about 140KHz for upstream with downstream immediately above that.

The Up0/Down1 changeover point was obviously chosen to match that used on an ADSL2 service.

When my contract with BT ends I was thinking of switching back to ADSL. Currently I am on a good discount as a new customer but do not really want to pay the full rate.

I was getting 15 to 18 Mbps before switching to fibre, so not bad for what I need.

I take on board the comments about cockups if trying this but as BT cocked up my switch to fibre, leaving me with no BB for three days nothing new there then.

So as I understand it there is no reason why this is not possible?

For you there shouldn't be.

The OP is in a position where the FTTC provider isn't present in their actual exchange where the ADSL is served from and cannot provide an alternative service.

Matt

Thank you for that, may not do it, but nice to know there should not be a problem.