BT FTTC Estimates vs Reality

About to get install of VDSL next Tuesday. BT Are quoting Range A 33.2 - 24.1 Range B 26.2 - 13.3 . My home wiring is fine. What are people normally seeing as the reality the Low or High end? I notice that the ISP's all quote "Up to 24.1" as my estimated speed, is this being cautious too?

It varies is the best (but not most useful answer).

I am currently in the middle of my quoted A range; at 65 in a range 56-74. When I first connected a couple of years ago (after a slight hiccup due to internal wiring) I was above the top of the A range, at around 70 for a quoted A range max of 58. My speed went up at one point, and the estimate at another; and until a few days ago I was at 72 in the range 65-74 for quite a long time. I think from reading other posts on various forums that it is fairly typical to be in the upper half of the A range. However, there is a very significant proportion who fall well into the B range, or even below it; of course these people are much more motivated to post on forums. (basically, just a long-winded way of saying what MrSaffron said)

Quoted speeds are line speeds. Profile will be a fraction below line speed, and on a good day, downloads a fraction below that.

Edited by StephenTodd (Wed 24-Sep-14 14:25:01)

Reality ... anywhere from 13 up to 35! There is no way to tell until it is actually installed and tested. Some customers are unlucky and get a line that is prone to noise and others get a nice clean signal.

In reply to a post by plankton:

About to get install of VDSL next Tuesday. BT Are quoting Range A 33.2 - 24.1 Range B 26.2 - 13.3 . My home wiring is fine. What are people normally seeing as the reality the Low or High end? I notice that the ISP's all quote "Up to 24.1" as my estimated speed, is this being cautious too?

I think you're failing to understand what an estimate is

No, I understand the concept of estimate, but curious to understand the reality of distribution with in the estimate.

In my case the download speed estimate is 36-51mbps and the upload 8-13mbps.

The thinkbroadband speed test results are (avg) 52.97 down and 8.86 up (line sync speed are, of course, about 5% higher). I should note that download had dropped to abut 35mbps and upload 5mbps until I reported a fault which was apparently due to an imbalance. (Nothing to do with the internal wiring I should add - that's pretty well optimal).

I suspect that for the vast majority speed estimates are accurate, but only where there isn't a line fault. I'd also add that I think upload speeds seem to deteriorate more than download as cabinets become more utilised, probably because of increased cross-talk at the DSLAM end (which makes sense as that's where the signal is weakest and there are the largest number of cables in close proximity (in contrast, the download signal is strongest at the DSLAM send it's less vulnerable to cross-talk. I saw this in that my original upload speed was over 12mbps (losing almost 30%) whilst the download has deteriorated by only about 5% since the cabinet was enabled. There seems to be less sign of deterioration of throughput due to cross-talk now.

nb. I've no idea what the original estimate was. It's very likely Openreach tweaks estimates according to real results on the cabinet.

In my case, the estimate is 60/19-79/20 clean and 44/14-71/20 impacted.

The line is clean, and gives a nice smooth Hlog graph.

We've had 80/20 line speeds for the best part of 3 years. Crosstalk has been increasing gradually, so the best we can do now is 79/20 (matching the top of the clean), but we are close to DLM intervention on the current error rates. When DLM intervenes, we end up at 72/20.

My estimate was 63 Mbps and initially I got 74 Mbps but now it's down to 55 Mbps which, according to the engineer that last visited, is down to deteriorating joints between aluminium and copper cable. Unfortunately where the cables join was sealed in some sort of epoxy compound which he hadn't seen before. He also said there didn't appear to be any crosstalk issues.

He tried another pair but could only get the line to sync at 38 Mbps.

AIUI the "Impacted" (B) range is allowing for imperfect home wiring. In the days of "engineer install only" that line didn't exist, and when it came in the A range was the same as the previous only range.

If you are an early adopter on your cabinet you are likely to be somewhere around the top of the range. As the cabinet becomes more and more populated it is probable the real speed and the estimate will decrease, due to new crosstalk. If you are not an early adopter, you will just slot into the range somewhere, depending on the take-up there.

Unfortunately the crosstalk isn't simply dependent on the number on the cabinet. It is very dependent on the proximity of in-use pairs. You could see many join and have no effect, then one more really hits you. Alternatively, that one is the first after you and you get hit immediately but then stay stable. Or, it's your joining that hits that one and you start off affected! Plus any permutation you care to think about wrt such factors.

What is guaranteed is that unless what you get is clearly a fault, (and that can take a long time to prove), you get what you get and Openreach don't give a damn. As a result, your ISP can do (many censored words) very little.

A final factor is Interleaving. If that kicks in the normal (lowest) hit is about 10Mbps with a latency increase of 8ms. Unlike the old ADSLx DLM interleaving however, this one does revert to Fast Path if it proves over a couple of weeks or so to have been an isolated burst of errors/noise.

Are there any Ofcom guidelines as to what rights the customer has to cancel a broadband (and phone) contract if the service provided falls short of the estimate speed, or estimated speed range?

In reply to a post by RobertoS:

AIUI the "Impacted" (B) range is allowing for imperfect home wiring. In the days of "engineer install only" that line didn't exist, and when it came in the A range was the same as the previous only range.

Um, no. Maybe that is "how you understand it" but it's not how BT ever explained it, nor how it works. The "B" range estimates allow for common types of problem with the physical infrastructure on BT's side such as, (as the site says right there for you to read) Bridge Taps.

You can't cure high frequency "echo" from a Bridge Tap by having an engineer install a new faceplate and eat your biscuits. BT doesn't factor in twenty metres of 1980s B&Q own brand phone extension wire running along next to the power lines to your back bedroom, because it's well within your power to rip that out and just plug the VDSL modem into the master socket like it says in the instructions. If they did want to factor in such sub-optimal installs they wouldn't need to do it on a per-line basis as they do with the checker's B estimates.

in my view downstream deteriorates way more than upstream. But i am mostly analysing those people on short D sides, maybe its different for those on longer D sides.

On my first pair my upstream attainable went from 36 to 24. Which is a smack bam on 33.3% drop. This includes power cutback applied so it wasnt all crosstalk.
The downstream went from 110 all the way down to 50. Which is over 50%. Much scarier. None of that loss was down to DLM, it was still fast path at 50mbit. When the engineer came who swapped the pair he could only manage 45 at my socket and only 50mbit at 120m from cabinet.

My clean estimate is 69.5 to 80. (was 73 when I signed up to plusnet). GEA test results report the low end of live clean range which mine was 69500 at time of GEA test.

On my new pair I had 73 down and 30 up. The up is still 30 and also with extremely low error count's (single digit per day), my down I am still synced at 73 but the snrm dropped a couple of nights ago and the attainable is now reported as 71.9. The error rate started out at just 1 10th of my old pair but now over the 13 days sync its averaged about 850 a day which is about 60% of my old pair, however the ES is still way lower I am just getting occasional bursts of errors, the frequency of ES or the MTBE is still way better.

Edited by Chrysalis (Thu 25-Sep-14 01:51:17)

Bridge taps are one of the main home wiring problems we see on these forums, particularly on FTTC after Kelly/Quinn's installations.

Openreach side should not have bridge taps. That part refers to in house, but impacted is a cover all manor of sins line

Plankton - my advice is to ignore the BT figures (they put a caveat on them, after all) Performance at your router will all depend on the state of the line to you from the cabinet. Results on our exchange range from as good as estimate to diabolical, especially on longer lines with 'intermediate' cabinets.

A few to start with:

• Aluminium or Copper
• Old wiring or new - basically the gauge of copper used
• Twisted or non-twisted pairs
• Damp cabinet or dry cabinet
• Damp or dry junction boxes
• Joints on line
• Worn through insulation
• Line under tension (causing thinning)
• Localised noise sources - inside or outside the property
• Actual physical length of cable

They can all cause a reduction in the "perfect" performance of the line. The chance of one or two factors affecting the line is reasonably high, the chance of all occurring is quite small but could happen. The line figures are a combination of calculation and experience of other local lines and probably includes a factor to allow for a real worst case scenario. One problem is that BT do not know which of those may affect a line and by how much.

I have come across people who have exceeded the top of the estimate and others sitting close to the lowest impacted figure.

No hard and fast and usual 'give reasonable chance to resolve issue' rules apply and the CISAS/OTELO schemes.

Is a "manor of sins" a large, old house of ill repute?

In reply to a post by RobertoS:

Bridge taps are one of the main home wiring problems we see on these forums, particularly on FTTC after Kelly/Quinn's installations.

Could you explain what a 'Bridge tap' is please?
Surely if the engineer fits a new faceplate filter to the NTE5 then the home wiring should all be fine?

A Bridge Tap is a length of phone cable, normally unterminated or badly terminated that is connected to your line - could be due to maintenance, previous routing, bad installation or configuration.. It will alter the line characteristics - the impedance of the line will change, there can be reflections of the signal both of which adversely affect the quality of the ADSL/VDSL signal. The length of a bridge tap will determine frequencies and tones it will affect.

edit to add:

In some countries (not-UK) the Telco will run one or more high capacity cables, maybe 50 pair from pole to pole along a road. When service is required they will just tap into the cable and connect the customer to an unused pair. However, the pair is still there and continues on to the end of the road or cable meaning that the customer has a length of unterminated cable on the line.

Edited by MHC (Fri 26-Sep-14 12:38:52)

In reply to a post by b4dger:

Surely if the engineer fits a new faceplate filter to the NTE5 then the home wiring should all be fine?

Sometimes an old extension will have been taken off the incoming pair earlier than the joint box in the hall or living room ... then later disconnected at the extension, but not on the incoming cable. Over time, it gets forgotten.

Perhaps it remained forgotten when old GPO joint boxes were converted into modern master sockets.

An extra bit of wire dangling on the side isn't detrimental to a voice call, and may not even have caused problems on ADSL. But it does on VDSL2.

MHC has given a technical description. This post is about the result.

The (most) common form of bridge tap in UK home wiring is star wiring of extensions.

That arises in older installations where star wiring didn't matter. The line comes in to the premises to a junction box, and some or all extensions are wired from that, including the one that has the master socket on the end. Extensions do not need to be wired from the master for pure phone functions.

In the past the replacement of an old style master by an NTE5 would not normally have resulted in an alteration to that setup. An engineer installation of FTTC should include removal in one way or another of such bridge taps.

A self-install is highly unlikely to include that.

In reply to a post by WWWombat:

An extra bit of wire dangling on the side isn't detrimental to a voice call, and may not even have caused problems on ADSL. But it does on VDSL2.

Normally the length is fairly short, and they tend to affect the higher frequencies which is why VDSL is affected and not ADSL (as much). I have seen Dial-Up affected by very, very long BTs.

With ADSL2+ being up to 2.2MHz, the BT would need to be greater than 35metres in length to have an effect, whereas with VDSL's 17 MHz BTs down to 4m long can have an effect. A long BT will not just affect a single frequency either, there can be a pirmary reflection at 1/4 wave, then further ones at 3/4, 5/4, 7/4 ...

Thanks for replies.
Just checking it was as I thought.

i.e. A correctly installed NTE5 with faceplate filter avoids the 'bridge tap' in a home's wiring you mentioned.

That isn't what I said.

Also, we have had several reports of bridge taps still existing following a Kelly's or Quinn's FTTC installation. Not following an Openreach one.

Edited by RobertoS (Fri 26-Sep-14 16:41:31)

Huh?

I've read the replies (re Bridge taps and home wiring) and understood that if the Master Socket (NTE5) is 'correctly' installed (i.e. direct to incoming phone line with no hidden extensions etc. etc) along with an Openreach supplied faceplate filter then 'bridge taps' isn't an issue with home wiring.

Have I got it wrong?

Just re-read my post, as to how they can arise.

The VDSL2 faceplate filter is irrelevant to the bridge tap question.

Edit - typo.

Edited by RobertoS (Fri 26-Sep-14 17:02:10)

The problem tends to arise when the installer (which could, of course, be a builder or householder) *thinks* he has fitted the NTE5 to the end of the line, but it turns out there is an earlier junction.

The installer will therefore swear blind that the master has been installed correctly, but in reality this is not true.

The trick, of course, is to identify the cases where a master exists and looks to have been installed correctly, but a can of worms lurks somewhere behind the scenes.

Sorry - I'm still not clear then...

I've read the replies (re Bridge taps and home wiring) and understood that if the Master Socket (NTE5) is 'correctly' installed (i.e. direct to incoming phone line with no hidden extensions etc. etc) along with an Openreach supplied faceplate filter then 'bridge taps' isn't an issue with home wiring.

i.e. DSL and voice correctly separated at the faceplate.

Am I wrong in thinking the above?

Thanks, that's how I'm reading things.

So my understanding here http://forums.thinkbroadband.com/fibre/t/4360053-bt-... is correct?

So far as I know, yes, you are correct there.

Phew - got there in the end - I thought these 'bridge taps' were something new, basically dodgy wiring/setup.

Thought it was worth checking to make sure my FTTC setup is as it should be.

I was estimated between 70.5 and Full whack. Now getting 53 @ around 200m from the Cabinet.

BT will over estimate to get the sale. I've learned that when you get an estimate, ALWAYS expect it to be lower. That way you won't be disappointed if it actually does go lower.

We had a resident here (he contributes here) who's estimate was 'reasonable' but turned out to be VASTLY over-optimistic. The reaction from BT? They simply reduced the BT wholesale checker estimates (after the contract was signed...) to what he was actually getting. Hence my warning - ignore them - they lie sometimes. You will get what you will get.