2.5km line

Does anyone have actual experience of a 2.5km line? What speeds are actually achieved?

About to do an upgrade on a friends line - currently around 1Mb ADSL with around 9km to the exchange - which suggests reasonable quality .

The cabinet is 2.5km and the fibre cabinet right next to it. Estimates are: 7.9 to 4.5 Clean and 5.9 to 3 Impacted. So, I am wondering how realistic those actually are especially as most of the run is overhead and on shared power/BT poles.

No actual experience to add, but...

IIRC, the model that BT uses for the access network means that no line is longer than 6.5km of cable equivalent to 0.5mm copper.

What this means in reality is that the resistance of the cable actually used must be no higher than the resistance of 6.5km of 0.5mm copper (1km of a pair would be 180 ohms). The same stands for attenuation values.

If a cable is actually physically longer than that, then it must be formed of thicker copper, at least partially.

IIRC correctly again, 0.7mm copper is half the resistance of 0.5mm copper, while 0.9mm copper is around one third.

We know the total line length here is 9km, so some of it must be thick ... but which bit? Somewhere in the D-side or the E-side?

That means there is most certainly a chance that the estimate is plausible, but the issue with thickness is that almost no-one knows it - so you cannot make any reasonable comparisons with other 2.5km lines.

I'm pretty sure the only way to find out is to order it...

I would have thought the E side would be fibre.

Exactly ... that is why I said "reasonable quality".

I also know several hundred metres were replaced recently - cable theft! on the E-side.


The real pain, is that the house is around 1km straight line, and under 2km by road from the exchange!

In reply to a post by BatBoy:

I would have thought the E side would be fibre.

Not yet! He is talking about the current line and gauge of copper in use in the various parts.

I would imagine that heavier poundage cables are towards the end of a run on local main cables. Duct space at the exchange is at a premium.

I doubt you would find a 0.7mm cable anywhere in the UK.

The only thing leaving the exchange at 0.9mm is likely to be a junction which may drop off and feed punters in remote areas but is highly likely to have loading pots on.

Edited by deleted (Mon 01-Dec-14 21:36:43)

Some time in January I might be able to order FTTC on my mum's line which is 2.57KM from the cabinet by road so could easily be 3KM long! Really doesn't sound promising for FTTC

So I'm very interested to hear what your experience is like.

Shame her property doesn't connect to the same cabinet as all other properties in the post code, which is just 800 meters in the other direction.

I'll likely try and order a BT line for the field next to the BT pole that delivers the overhead line to the neighbours that connect to the nearer cabinet and then run Ethernet back to the house ~85 meters away. Might be an opportunity to connect other neighbours via a little wireless network also...

I live in a tiny village in rural Suffolk. According to the BT Openreach engineer, I am 2.9km from the cabinet (which is in the next village) with a 'near perfect line' (engineer's own words)

I have had Fibre installed for just over 3 weeks and I've gone from 1.9Mbps down 0.25 up on DSL to 2.9Mbps down 0.6up on FTTC... not much of an improvement... my ping is around 30-40ms

When the engineer came out following my complaint to ISP (I use Timico and have done for many years as they always gave me the best speed locally) he was unable to even get his test kit to sync although my modem connects pretty quickly)

My next door neighbour just had FTTC installed yesterday. He is less than 100m closer to the cabinet. He used to get 0.9 down and 0.4 up (suggesting that his line was not as good as mine?) but he is now getting 7Mbps down and 0.4up with a ping of about 75ms.

I thought that the line speed would drop off in a near linear manner at this sort of range so I have a couple of questions...

1. Is it possible that the bit of line that comes after his house has a problem (although the BT engineer seemed to think not)?
2. He is with BT - is it possible that BT prioritises speed for their own customers?

Any thoughts would be welcome.

Even 2.9Mbps is faster than almost everyone else in the village but as I'm paying for a service which promised 4.5 - 8Mbps it would be good to get it!

This is what I was hoping to hear - that people are getting service at over 2.5km - albeit with variable speeds and that the higher clean figures are attainable.

In reply to a post by RuralFibre14:

I thought that the line speed would drop off in a near linear manner at this sort of range so I have a couple of questions...

1. Is it possible that the bit of line that comes after his house has a problem (although the BT engineer seemed to think not)?
2. He is with BT - is it possible that BT prioritises speed for their own customers?

What you might be finding is that a large number of tones or bins are using just one or two bits rather than the maximum so any small change in noise or attenuation of those could result in the loss of the remaining ones and what looks to be a disproportionate effect.

The latency figures do suggest he has a greater level of interleaving on.

You could have localised noise in your house, or the modem has slightly different termination characteristics resulting which can effect the sync speed - even on a good line.

And NO, BT would not be prioritising speed for their own customers.

Make sure your modem is located at the master socket and there is a minimal amount of electrical or electronic equipment close by. Does the cable enter the house and immediately terminated in teh master or is there a large amount of internal wiring?

Promised? Or estimated? If it was a promise then feel free to complain but given broadband is not a guaranteed service their remedy may be a choice of cancelling and just going back to ADSL. The 2 Mbps USC seems to be being met which is a big tick for the politicians involved.

Beyond 1.5km the variables around individuals situations are such that you cannot accurately predict the speed and the drop off is a long way from linear.

In reply to a post by partial:

I would imagine that heavier poundage cables are towards the end of a run on local main cables. Duct space at the exchange is at a premium.

I kinda agree here, at least in the general case.

However, this cabinet is already 6.5km from the exchange, leaving no allowance (in resistance/attenuation terms) left for the D-sides. At least some of the E-side must be thicker than 0.5mm.

Of course it could still be only in a part towards the end of the E-side, as the available duct space is likely to come under less pressure there.

However, aren't the E-side cables pressurised? If so, how does that system cope with joints within the E-side?

I doubt you would find a 0.7mm cable anywhere in the UK.

I could have sworn I had seen plenty of UK-spec cable at 0.7mm, but it appears otherwise. I wonder what made me think 0.7mm was in the inventory?

The only thing leaving the exchange at 0.9mm is likely to be a junction which may drop off and feed punters in remote areas but is highly likely to have loading pots on.

I'm not sure what you mean by "a junction which may drop off", but a 9km line certainly suggests a remote feed.

It is good to see someone getting a service at a distance.

I think the longest I have ever heard of is reportedly 4.2km: see this plusnet thread.

One extra word: It used to be the case that long lines would be limited by the upstream availability first. I'm not sure if BT have since altered settings which allows the distant modems more of a fighting chance; for example with different UPBO settings, or different bitloading algorithms.

Distance of the cabinet from the exchange is also a factor, as different power masks are used to avoid destroying ADSL/ADSL2+, which may explain the variation in what are thankfully a small sample size of very long lines to cabinets.

Useful information would be your IP Profile. (I think Timico use BT Wholesale so there will be one). Multiplying the IP Profile by 1.033 gives the sync speed within a few kbps.

Comparing that with your estimates and actual throughput speed would be interesting.

BTW Performance Test. For now, ignore the red instructions and just say you've followed them. At the bottom of the initial results page click the Further diagnostics button.

Please copy and paste the full contents of the two text boxes of results. We don't need to see the graphics.

A word of caution based on the experience of a neighbour who is a few hundred metres closer to the cabinet...

After getting an initial speed of 7Mbps down and 0.5Mbps up with a ping of nearly 100ms, my neighbours service failed within the day and despite Openreach spending several days working on this, he was eventually told that BT couldn't support FTTC for his house (too far away from cabinet and on the worst of the 2 bundles of cables that come to our village) so he would have to go back to ADSL...

Meantime my service seems quite stable at what I suspect may be one of the slowest 'Superfast Broadband' FTTC speeds in the country... 3.1Mbps down and 0.9Mbps up - but this is the maximum that the line will support.

I think the thing that I learnt from this is that if your ADSL was 'ok' before (I had 1.9Mbps down / 0.3Mbps up) then you 'might' see an improvement - otherwise don't bother and look for a non BT based alternative.

Perhaps the most useful change seems to be the one yet to be announced - the possibility of ADSL2+ from the cabinet.

I have read this thread in the past when I was thinking of ordering FTTC as my line is approx 6km long, the cabinet reduces my line length by about 3km.

Had BTO install FTTC yesterday, it connected at between 4Mb and 8Mb but it would not stay connected, the BTO person suggest this implies a line fault and after trying to swap pairs and rule out other obvious things, he has put me back to ADSL and raised this as a fault. The JDSU showed my line to the cabinet is now a 36dB attenuation and claims the line length is now 1.9km.

Waiting to hear what BTO and PlusNet say are the next steps.

But ... what happened to the people in the thread on long lines, did they ever get resolved?

In reply to a post by WWWombat:

... ADSL2+ from the cabinet.

OK so if ADSL2+ from the Cabinet is available at the same cost as Standard Broadband that would be great.

But everything I have read states that at long distances VDSL2 and ADSL2+ have the same performance. So if VDSL2+ has problems working on these long lines then so should ADSL2+.

Vdsl2 can work great on short loop lengths but rapidly runs out steam from about 400m onwards, where as ADSLx will work for several km, even from the cabinet it should have considerably more range than VDSL 2, otherwise there will be no point.

In theory, VDSL2 can extend reach in the same way as ADSL2+, when unhampered.

In practice, VDSL2 runs out long before ADSL2+ would - and it seems to be the upstream side that is lost first.

I suspect the reasons come down to something related to power - either:

a) The extra PSD mask that restricts transmit power at the cabinet. Which, for the lowest frequencies with the potential longest range, causes the FTTC cabinet to transmit at a reduced power level. In the end, the signal will be received at the same power level as though it came from the exchange, not the cabinet!

b) The fact that VDSL2 has upstream bands above U0 that most subscribers rely on, means that U0 can be transmitted at lower power ... helping to make sure it doesn't crowd out ADSL2+ upstream. I don't know whether that affects the longest lines or not, but it could...

The need to work in a network that also has to support exchange-based ADSL is what hampers VDSL2 in practice.

Im 3.5km line length from the exchange and when i was on ADSL it was 2Mbit faster than ADSL2+, for long lines i wouldn't even bother with ADSL2+

Actually, ADSL2 sometimes gives better behaviour on long lines compared with either ADSL2+ or ADSL.

ADSL2 brings better modulation and line coding, so can make more efficient use of the same frequencies available to ADSL. But without the extra frequencies opened up by ADSL2+.

Weird, but sometimes true...

cant see that one coming any time soor if ever